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  • Optimum Power Analysis of a Self-Reactive Wave Energy Point Absorber with Mechanically-driven Power Take-Offs
    Energy (IF 5.537) Pub Date : 2020-01-17
    Xiaofan Li; Changwei Liang; Chien-An Chen; Qiuchi Xiong; Robert.G. Parker; Lei Zuo

    This paper studies a self-reactive ocean wave energy converter (WEC) where energy is absorbed through the relative motion between a floating buoy on the ocean surface and a submerged body. Two types of direct-drive power take off (PTO) systems are examined. One adopts a ball screw system in inverse driving mode with mechanical motion rectifier (MMR) that converts the oscillating bi-directional input heave motion into unidirectional rotation to drive an electromagnetic generator, and another one uses a ball screw system to directly drive the generator (called non-MMR). Dynamic models for both types of PTOs are established and integrated with the overall WEC system model in both the time and frequency domains. Numerical simulation is used to investigate the dynamic performance of both PTOs. The influences of the PTO inerter, which is from the rotational inertia of the flywheel and generator, and the WEC drag damping coefficient are discussed and explored. The analytical closed-form solution for the optimum condition of the non-MMR system is derived based on the criterion of maximum power absorption, and numerical simulation yields the optimum condition for the MMR system. The results under regular and irregular waves show that the PTO inerter in the MMR system can improve the power absorption for small wave periods and maintain the same performance for large wave periods. The PTO inerter in the non-MMR system shifts the peak frequency. The WEC drag damping negatively influences the power absorption in both PTO systems, especially at large wave periods.

    更新日期:2020-01-17
  • Analysis of China's oil and gas consumption under different scenarios toward 2050: An integrated modeling
    Energy (IF 5.537) Pub Date : 2020-01-17
    Xunzhang Pan; Lining Wang; Jiaquan Dai; Qi Zhang; Tianduo Peng; Wenying Chen

    China's oil and gas consumption, which is not only significant to the industry but also related with national energy security, faces uncertainties in the future. This paper analyzes China's oil and gas consumption under five representative scenarios toward 2050 using an integrated modeling. In the Nationally Determined Contribution (NDC) scenario, China's oil consumption peaks at 705 million tons by 2035, and gas consumption ramps steadily up to reach 780 billion cubic meters by 2050. Oil provides 18% of China's primary energy by 2030 and 15% by 2050, and gas 14% by 2030 and 17% by 2050. The 2 °C and the 1.5 °C scenarios control China's 2050 oil consumption to 10% and 45% below the NDC level, respectively. Interestingly, more stringent mitigation tends to upscale China's gas consumption before 2040. Compared with the NDC scenario, the oil-price scenarios present limited influences on China's total energy consumption and end-use electrification but mainly feature a substitution between oil, gas and coal, non-fossil energy. Particularly, across our scenarios, China's oil import dependence is projected to largely fluctuate around 70% toward 2050, and gas import dependence to reach 50–60% beyond 2030, implying a continuously high risk of energy resource supply and national energy security.

    更新日期:2020-01-17
  • Effect of dilute sulfuric acid pretreatment on the physicochemical properties and enzymatic hydrolysis of Coffee cut-stems.
    Energy (IF 5.537) Pub Date : 2020-01-17
    Juan Camilo Solarte-Toro; Yessica Chacón-Pérez; Sara Piedrahita-Rodríguez; Jhonny Alejandro Poveda-Giraldo; José António Teixeira; Konstantinos Moustakas; Carlos Ariel Cardona Alzate
    更新日期:2020-01-17
  • New insights into the technical challenges of the Mauritius Long Term Energy Strategy
    Energy (IF 5.537) Pub Date : 2020-01-16
    M.N. Edoo; Robert T.F. Ah King

    The Mauritius Long Term Energy Strategy targets 35% of electricity generation from renewables by 2025. This work presents the modeling of the Mauritian energy system in the EnergyPLAN software to identify and gain insights into the major technical challenges involved to achieve that target. Based on simulation of alternative scenarios, it is shown that if solar PV is to be the main source of renewable energy by 2025, operation of the conventional generation fleet at very low levels (20 - 30% of instantaneous demand) and high ramping requirements become indispensable to avoid significant curtailment and meet the net load. Alternatively, the use of AC-coupled battery energy storage for curtailment reduction was found to be economically unviable due to low utilization. Curtailment to increase solar PV penetration was found to be effective as allowing a modest curtailment rate increased penetration significantly. Consequently, new policy implications are derived. First, it is vital that the generation expansion planning methodology prioritize generation flexibility requirements. Second, the techno-economic feasibility of using DC-coupled Solar plus storage should be investigated as it circumvents the grid stability problem. Third, an effective curtailment policy should be formulated to optimize the contribution of solar PV in the national electricity mix.

    更新日期:2020-01-16
  • Experimental study of the influence of thermal mass on thermal comfort and cooling energy demand in residential buildings
    Energy (IF 5.537) Pub Date : 2020-01-16
    T. Kuczyński; A. Staszczuk

    The article presents the results of experimental research carried out in two real-scale detached energy-efficient single-family buildings designed to be almost identical with exempt to the construction of their external and internal walls; lightweight skeletal versus traditional masonry construction. The reduction of the average indoor temperature during the August heat wave obtained by increasing the thermal mass of the building was 2.8 ± 0.34oC, with the maximum value at the hottest part of the day being 3.4oC. Replacing the lightweight frame structure of the walls with cellular concrete, in an exceptionally warm August, with an average outside temperature of 22.5°C, shortened the total time of occurrence of indoor temperature higher than 28oC from 18.6 days to only 8 hours. The cooling effect of building thermal mass remained stable during all 14 days of heat wave with only slight diurnal variations. The total reduction in the cooling energy demand achieved was 67% at 25oC set point temperature and 75% at set point temperature 26oC respectively.

    更新日期:2020-01-16
  • Optimization of the thermodynamic configurations of a thermoacoustic engine auxiliary power unit for range extended hybrid electric vehicles
    Energy (IF 5.537) Pub Date : 2020-01-16
    Wissam Bou Nader; Joy Chamoun; Clément Dumand

    Significant research efforts are considered in the automotive industry on the use of low carbon alternative fuels in order to reduce carbon emissions of future vehicles, some of which are only compatible with external combustion machines. These machines are only suitable for electrified powertrains relying on electric propulsion, particularly in range extenders, where the energy converter operates steadily at a constant power at its optimal efficiency. The fuel consumption of these powertrains strongly relies on the performance of the energy converter in terms of efficiency, as well as on the deployed energy management strategy. This paper investigates the potential of fuel savings of a Extended Range hybrid Electric Vehicle (EREV) using a Thermoacoustic Engine (TAE) system as energy converter substitute to the conventional Internal Combustion Engine (ICE). An exergo-technological explicit analysis is conducted to identify the different TAE-system thermodynamic configurations. The Regenerative Reheat two-stage thermoacoustic engine is selected among numerous identified thermodynamic configurations, offering high efficiency and net specific work compared to other configurations. An EREV model is developed and the presented RRe-n2-TAE configuration is integrated. Fuel consumption simulations are performed on the Worldwide-harmonized Light Vehicles Test Cycle (WLTC). Results are compared to the reference ICE-APU. Results show more than 20% of fuel savings with the RRe-n2-TAE as Auxiliary Power Unit (APU) compared to the basic TAE configuration and comparable fuel consumption with the ICE. Consequently, the studied RRe-n2-TEG-APU presents a potential for the implementation in EREVs with zero carbon alternative fuels.

    更新日期:2020-01-16
  • Techno-economic and life-cycle assessment of integrated Fischer-Tropsch process in ethanol industry for bio-diesel and bio-gasoline production
    Energy (IF 5.537) Pub Date : 2020-01-16
    Venu Babu Borugadda; Girish Kamath; Ajay K. Dalai

    The Fischer-Tropsch process is less complex and more environmentally friendly alternative to petroleum-based fuels. With growing interest in biomass-to-fuel conversion like the production of bioethanol, there is a steady supply of unfermentable biomass from bioethanol industries, which can be gasified and converted to Fischer-Tropsch syncrude. In this work, the economic and ecological feasibility of integrating a Fischer-Tropsch process using syngas obtained from the gasification of dry distillers’ grain is explored. Data from a lab-scale experiment using pelletized promoted iron supported on Carbon Nano Tubes (Fe/CNT) is used to simulate a plant for the production of 1000 kg of syncrude/h. The techno-economic feasibility of setting up a Fischer-Tropsch process is explored based on chemical engineering plant cost index of 628.2. An internal rate of return of 107.9% was obtained with a net annual profit of 5.2 MUSD/year which is higher than those reported for other Fischer-Tropsch plants due to the readily availability of the feedstock without any associated transportation costs. The potential environmental impact of the Fischer-Tropsch fuels was evaluated by the Waste Reduction (WAR) algorithm and suggested that the integration of the Fischer-Tropsch process into the bio-ethanol production plant is environmentally benign.

    更新日期:2020-01-16
  • The energy-saving mechanism of coal-fired power plant with S-CO2 cycle compared to steam-Rankine cycle
    Energy (IF 5.537) Pub Date : 2020-01-15
    Zhewen Chen; Yanjuan Wang; Xiaosong Zhang; Jinliang Xu

    S-CO2 (Supercritical-CO2) coal-fired power plant is a promising technology for efficient and clean utilization of coal for power generation. The comparative study between the S-CO2 coal-fired power plant and the power plant with steam Rankine cycle from aspects of energy and exergy balances is conducted. The conversion and transfer of the energy and exergy in the power plants are revealed. With the main gas parameters of 32MPa/620°C and double-reheat process, the power generation efficiencies of the S-CO2 coal-fired power plant and the power plant with steam Rankine cycle are 49.06% and 48.12%, respectively. The corresponding exergy efficiencies are 48.02% and 47.10%, respectively. The energy-saving mechanism of the S-CO2 coal-fired power plant is revealed: the smaller boiler efficiency and larger exergy efficiency of the boiler system in the S-CO2 coal-fired power plant make the energy level of the energy being transferred to the S-CO2 cycle is higher than that of the energy being transported to the Rankine cycle. The CO2 absorbs the high-level energy and produces more mechanical power through the S-CO2 cycle to obtain higher power efficiency.

    更新日期:2020-01-15
  • Self-healing Oriented Supply Restoration Method Based on the Coordination of Multiple SOPs in Active Distribution Networks
    Energy (IF 5.537) Pub Date : 2020-01-14
    Peng Li; Jie Ji; Haoran Ji; Guanyu Song; Chengshan Wang; Jianzhong Wu

    Supply restoration from outages is essential for improving the self-healing ability of active distribution networks (ADNs). Soft open point (SOP) refers to a novel power electronic device installed to replace the traditional tie switch. Under fault situation, the coordination of multiple SOPs can provide voltage support and effectively expand the range of supply restoration. In this paper, a supply restoration method based on the coordination of multiple SOPs is proposed to improve the self-healing ability of ADNs. First, the coordinated service restoration strategy of multiple SOPs is proposed. Then, a self-healing oriented supply restoration method is proposed to restore loads from outages based on multiple SOPs. The contingency set is also established for practical application. Finally, the effectiveness of the proposed supply restoration method is validated on the IEEE 33-node distribution system. It shows that the proposed method can exploit the potential benefits of multiple SOPs and effectively improve the load recovery level of ADNs.

    更新日期:2020-01-15
  • Fuel reactivity controlled self-starting and propulsion performance of a scramjet: A model investigation
    Energy (IF 5.537) Pub Date : 2020-01-14
    Xiaojie Li; Xiaobin Huang; Hong Liu; Jianke Du

    The performance of a scramjet engine relies heavily on the combustion characteristics of fuel. This work aims to propose a concept of controlling the self-starting characteristics and propulsion performance of a scramjet via fuel reactivity modification. The fuel reactivity was modified by adjusting the activation energy of each elementary reaction. The thermodynamic analysis was then systemically performed to evaluate the effects of fuel reactivity on the lowest flight Mach number required for self-starting and the specific thrust. The results indicate that the lowest flight Mach number for self-starting of a hydrogen-fueled scramjet reduces from 6.1 to 5.1 when the activation energy is decreased by 50%. Under a given flight condition, fuel reactivity has a remarkable influence on the characteristic ignition length, which affects the specific thrust, especially at low flight Mach numbers. It is demonstrated that there exists an optimal reaction rate to achieve the maximum specific thrust, rather than increase the reaction rate infinitely. The optimal reaction rate relates to the supersonic flow condition, the exothermic heat of fuel, and the wall friction. The results obtained in this investigation provide a theoretical basis for the design of high-reactivity supersonic combustion fuel and further research of advanced scramjet engine operation.

    更新日期:2020-01-15
  • Energy consumption of rainfed durum wheat cultivation in a Mediterranean area using three different soil management systems
    Energy (IF 5.537) Pub Date : 2020-01-14
    Sabina Failla; Carlo Ingrao; Claudia Arcidiacono

    An energy analysis comparing three different soil management systems was carried out in Southern Italy using data collected in a five-year field experiment, with the aim of identifying the most energy efficient system. On average, because of a little more energy is demanded (13.3 GJ ha-1) and a higher grain yield is obtained (2.20 t ha-1) in the Intensive case than the other two practices, the total Energy Input required to produce 1kg durum wheat was higher in the No tillage-based system (11.05 MJ kg-1) than in the Intensive (6.80 MJ kg-1) and the Minimum one (6.78 MJ kg-1). The highest contribution to Energy Input derived from nitrogen fertiliser followed by diesel fuel. In this regard, No-tillage allowed for reduction of diesel energy consumption by about 70% and 60% compared with Intensive tillage and Minimum tillage, respectively. The Minimum tillage practice showed the best energy performance, because it determined the following results on an average base: the highest energy ratio (4.69) and the highest energy profitability (3.69); the lowest energy intensity (5.86 MJ kg-1). Therefore, MT may be considered as the practice exhibiting the best energy performance and representing the viable trade-off between IT and NT.

    更新日期:2020-01-15
  • Study on pyrolysis products characteristics of medical waste and fractional condensation of the pyrolysis oil
    Energy (IF 5.537) Pub Date : 2020-01-14
    Shuqi Fang; Luyao Jiang; Pan Li; Jing Bai; Chun Chang

    The dried and pulverized medical solid waste was pyrolyzed at 500°C, and the components and characteristics were analyzed after the solid, liquid and gas products were collected respectively. Experimental results showed that the combustible component in the obtained gas product accounted for 83.22% and the heat value was 10995.02kcal/Nm3. The liquid product obtained was black viscous tar with a heat value of 8972.82kcal/kg, GC/MS analysis indicated that hydrocarbons and lipids accounted for about 60% of liquid product, and the carbon chain length of the products is C6-C28. The carbon content of solid product after purification was up to 63.13%, and the heat value was 5454.54kcal/kg. Furthermore, in order to make the most of the pyrolysis oil, the liquid product was separated and purified by fractional condensation under the condition of decompression. The effect of process parameters such as vacuum degree and condensing temperature was emphasized, and the optimum technological condition was obtained as follows: vacuum degree 0.04 MPa, heating temperature 140°C and the first stage condensing temperature was 70°C. Finally, the viscosity measurement of the residual high-viscosity components was intended to provide data support for the solution of tar plugging equipment and piping problems in practical applications.

    更新日期:2020-01-15
  • Experimental investigation on the performance of direct-expansion roof-PV/T heat pump system
    Energy (IF 5.537) Pub Date : 2020-01-14
    Nina Shao; Liangdong Ma; Jili Zhang

    Although the integration of photovoltaic-thermal (PV/T) heat pump systems on buildings can assist in reducing the electricity demand of high-energy consuming buildings, the large occupation area of PV/T modules hinders its popularization. To overcome this problem, a novel PV/T evaporation roof coupled with a heat pump system composed of electronic expansion valves, a condenser and a compressor is proposed, which serves as an electric generator, evaporator for the heat pump system and the external surface of a building roof. This paper investigates the actual operating performance of the direct-expansion roof-PV/T heat pump system under different seasonal conditions. The structure and design of PV/T evaporation roof and the whole system are first presented, followed by the construction of an experimental platform and finally the operation of the system is analyzed through performance evaluation indices and field-testing. The experimental results indicated that the system performed better in the summer than in the winter, with the electrical efficiency, thermal efficiency and overall efficiency averaging at 11.23%, 64.25% and 83.32%, respectively. The average COP was 5.9, with a maximum value of 8.9. Additionally, it took two hours to heat the water within a 1.5 m3 heat storage tank from 25°C to 60°C, which was twice as fast as under winter conditions. Meanwhile, a significant decrease in system performance resulting from changes in environmental parameters in the winter was observed. The average electrical efficiency, thermal efficiency, and overall efficiency were 11.67%, 60.17% and 78.84%, respectively, while the average and maximum COP were 3.7 and 5.24 respectively.

    更新日期:2020-01-15
  • A multi-criteria decision method for performance evaluation of public charging service quality
    Energy (IF 5.537) Pub Date : 2020-01-14
    Lihui Zhang; Zhenli Zhao; Meng Yang; Songrui Li

    Public electric vehicle charging infrastructure provides an essential support for sustainable electric transportation systems. However, the current development model for such infrastructure tends to emphasize quantity over quality and cannot meet the charging needs of electric vehicle users. Addressing this situation requires further guidance from governments, which should be based on performance evaluation systems. This study therefore developed a multi-criteria evaluation framework to assess the performance of public charging infrastructure in terms of planning rationality, operational efficiency, service capacity, charging safety, and sustainable development. After defining individual charging station attributes through numerical data and user/expert input, a modified Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) model was used, with vague sets to standardize, weight, and process the data. The assessed stations were subsequently ranked. The model was applied to three public charging stations in Beijing, China to verify its effectiveness and robustness. The resulting rankings can facilitate regulatory assessment of these stations’ performance and guide improvements in the quality of their charging services. The results further indicated that the sustainable development value of charging facilities is often undervalued, and relevant incentive strategies should thus be implemented by policymakers.

    更新日期:2020-01-15
  • Uncertainty quantification based optimization of centrifugal compressor impeller for aerodynamic robustness under stochastic operational conditions
    Energy (IF 5.537) Pub Date : 2020-01-14
    Xinzi Tang; Zhe Wang; Peng Xiao; Ruitao Peng; Xiongwei Liu

    Centrifugal compressor impeller operates at stochastic boundary conditions. The operational uncertainties cause performance deviation from design value and consequently affect the reliability of the compressor. Considering the stochastic operational uncertainties in the early design stage, this paper presents an uncertainty quantification based optimization of centrifugal compressor impeller with splitter blades for aerodynamic robustness. The nonlinear response relation between the design variables, the aerodynamic boundary uncertainties and the impeller performance is modelled by a combination of the Latin Hypercube Sampling, the three dimensional CFD, the Kriging surrogate model and the Non-intrusive Probability Collocation method. A sensitivity analysis with single and multiple random geometry variations is carried out to identify the most sensitive parameters. The effects of rotor speed uncertainty on pressure ratio and efficiency are quantified. A case study is conducted to search for optimal impellers with higher performance and lower sensitivity to boundary uncertainty using NSGA-II. The optimization is verified by the Monte Carlo method. The results demonstrate that the aerodynamic robustness of the compress impeller with splitter blades is enhanced by the proposed approach, which provides references for compressors, turbines and other turbo machinery.

    更新日期:2020-01-14
  • Multi-energy load forecasting for regional integrated energy systems considering temporal dynamic and coupling characteristics
    Energy (IF 5.537) Pub Date : 2020-01-13
    Shaomin Wang; Shouxiang Wang; Haiwen Chen; Qiang Gu

    —Accurate multi-energy load forecasting (MELF) is the key to realize the balance between supply and demand in regional integrated energy systems (RIES). To this end, a hybrid MELF method for RIES considering temporal dynamic and coupling characteristics (MELF_TDCC) is proposed. The novelty of MELF_TDCC lies in the following three aspects: 1) considering the high-dimensional temporal dynamic characteristic, an encoder-decoder model based on long-short term memory network (LSTMED) is proposed, which can extract the high dimensional potential feature, and reflect the temporal dynamic characteristics of historical load sequence effectively; 2) considering the cross-coupling characteristic, a coupling feature matrix of multi-energy load is constructed, which reflects the cross-influence of electricity, cooling and heating loads; 3) with the feature fusion layer of the hybrid model being built by gradient boosting decision tree (GBDT), the extended feature matrix for each class of load is constructed considering the intra-class inherent characteristics and inter-class coupling characteristic of loads, and the GBDT model is trained on the extended feature matrix, which provides multi-dimensional perspective for researching load essential characteristics. MELF_TDCC is verified on the ultra-short-term and short-term MELF scenarios based on an actual dataset. The simulation result shows that the proposed MELF_TDCC outperforms the current advanced methods.

    更新日期:2020-01-13
  • Comparative analysis of different valve timing control methods for single-piston free piston expander-linear generator via an orthogonal experimental design
    Energy (IF 5.537) Pub Date : 2020-01-13
    Jian Li; Fubin Yang; Hongguang Zhang; Zhong Wu; Yaming Tian; Xiaochen Hou; Yonghong Xu; Jing Ren

    This paper presents a single-piston free piston expander-linear generator for small-scale organic Rankine cycle. In order to achieve stable operation, two types of valve timing control methods are developed: time control method (TCM) and position control method (PCM). The orthogonal experimental design is adopted to evaluate the influence degree and significance level of different factors on the prototype performance. Results show that the symmetry motion characteristics are worse when the TCM is used than those of the PCM. Furthermore, such characteristics could be improved by appropriately increasing expansion duration and intake duration tBT. For the PCM, operating frequency gradually increases as external resistance, intake pressure, and intake duration but significantly decreases as theoretical stroke. For the TCM, operating frequency is only related with intake and expansion durations. Intake pressure has the greatest influence on the peak power output, peak velocity, and actual stroke length, followed by intake duration. Theoretical stroke is the dominant factor affecting operating frequency, followed by intake pressure, and then by intake duration and external resistance. Thermal-work, work-electric, and thermal-electric conversion efficiencies can achieve a maximum of 5.4%, 28.8%, 1.4%, respectively.

    更新日期:2020-01-13
  • Modeling microalgae growth in continuous culture: Parameters analysis and temperature dependence
    Energy (IF 5.537) Pub Date : 2020-01-13
    Shuo Yuan; Jinrun Hu; Zhiyuan Liu; Yuanzhuo Hong; Xianyong Wang

    Microalgae are considered to be a promising biofuel resource for carbon dioxide fixation in the future. Modeling the growth of microalgae is an effective method to study the growth performance of microalgae, which is also helpful to control the cultivation of microalgae in artificial bioreactor. In continuous culture, dilution rate and influent inorganic nitrogen concentration have shown significant effects on the growth of microalgae. In this paper, the common and overall influences of dilution rate and influent inorganic nitrogen concentration on the microalgae growth have been investigated. Based on numerical simulation, this paper plots the results of total and unit time particulate carbon concentration in 3D figures to expose the varied tendency. It is found that the value of points on the ridge line increases with the dilution rate decreasing and influent inorganic nitrogen concentration increasing for both the total particulate carbon concentration and the particulate carbon concentration per day. The influence of several typical temperatures has been modeled and calculated. The value of biomass productivity will be further increased when the dilution rate is getting closer to 0. This paper will go a step further for the parameters design of continuous culture photo-bioreactor (PBR) for later study.

    更新日期:2020-01-13
  • Numerical investigation on flow and heat transfer processes of novel methanol cracking device for internal combustion engine exhaust heat recovery
    Energy (IF 5.537) Pub Date : 2020-01-13
    Jun Shu; Jianqin Fu; Chengqin Ren; Jingping Liu; Shuqian Wang; Sha Feng

    In this research, a novel structure of methanol cracking device was designed for methanol decomposition by using internal combustion (IC) engine exhaust heat. To evaluate and optimize its performance, the flow and heat transfer processes in methanol cracking device were investigated by computational fluid dynamics (CFD) simulation. The results show that methanol flow rate has important effects on the pressure loss, temperature distribution and heat flux. In general, the flow velocity and pressure in methanol cracking device are not well-proportioned and it results in the asymmetrical distributions of temperature and heat transfer coefficient. The maximum heat transfer coefficient is close to 100 W/(m2·K) while the minimum almost equals to zero because of flow stagnant zone. The average heat transfer coefficient increases as methanol flow rate rises, and it reaches to 51.63 W/(m2·K) at the methanol flow rate of 0.06 kg/s. When methanol flow rate increases from 0.03 kg/s to 0.06 kg/s, the average outlet temperature decreases from 615K to 560K and meets the requirements for methanol cracking reaction. All these indicate that the designed methanol cracking device can be used for IC engine exhaust heat cracking methanol, and also provide theoretical guidance for further optimizing the geometry structure.

    更新日期:2020-01-13
  • Comparative analysis of energy costs on farms in the European Union: A nonparametric approach
    Energy (IF 5.537) Pub Date : 2020-01-13
    Vítor João Pereira Domingues Martinho

    A rational and efficient use of the various sources of energy available to farms allows, not only for cost cutting, but also, a reduction in the environmental impacts bringing positive externalities and contributions toward sustainability. Of course, this efficiency depends on several factors that may influence the dynamics and performance of the farms in question which may also change spatially between countries and regions. These questions related to the great diversity of realities in the agricultural sector are especially relevant within the European Union (EU) context. In this framework, the main objective of the research presented here is to make an efficiency analysis of energy costs in farms across EU countries and regions, stressing possibilities of savings and taking into account the several realities. For this purpose, data at farm level from the Farm Accountancy Data Network (FADN) was considered for the period 2014-2016 which were then explored through the nonparametric approach Data Envelopment Analysis (DEA). For the nonparametric analysis the Cobb-Douglas model was considered as a base. In this way, the total production (euros) was considered as output. Paid labour (hours), the total fixed assets (euros) and the energy costs (euros) were considered as inputs. In an alternative attempt to take into account the different realities across the EU countries the statistical information in monetary units was corrected by the Price Level Indices and was deflated by the Harmonised Indices of Consumer Prices. Furthermore, to alternatively consider the diversity of contexts of the farms from the EU, the several regions and countries here were clustered through cluster analysis, after factor analysis so as to avoid problems of collinearity. As main insights, it is worthy of stressing the possibilities of significantly reducing the costs of energy consumption in farms from many EU regions. For example, it is possible to reduce the costs of energy use by about 55% in Pohjanmaa (Finland), 53% in Cyprus, 56% in Makedonia-Thraki (Greece), 52% in Thessalia (Greece), 56% in Puglia (Italy) and 53% in Basilicata (Italy). In these contexts the Common Agricultural Policy (CAP) should play a determinant role.

    更新日期:2020-01-13
  • Energy and exergy analyses of a novel hybrid system consisting of a phosphoric acid fuel cell and a triple-effect compression–absorption refrigerator with [mmim]DMP/CH3OH as working fluid
    Energy (IF 5.537) Pub Date : 2020-01-13
    Wei Chen; Chenbin Xu; Haibo Wu; Yang Bai; Zoulu Li; Bin Zhang

    Energy and exergy analyses were conducted on a proposed hybrid system consisting of a phosphoric acid fuel cell (PAFC) and a triple-effect compression–absorption refrigerator with [mmim]DMP/CH3OH as working fluid (HFCAR). The HFCAR system was modeled and simulated based on the current density model of PAFC, isentropic efficiency model of assisted compressor, and mass and energy conservation model of the compression–absorption refrigerator. For the basic design condition, the detailed operating parameters of each status point, energy conservation, temperature difference, and total thermal conductance of each component were simulated and discussed. For the variable conditions, the effects of electrical current density, PAFC temperature, and compression ratios on 16 key operating parameters were simulated and analyzed. A critical electrical current density was proposed. Under condition of critical current density, HFCAR system works as a cooling system with the largest cooling capacity. The variation characteristics of the critical electrical current density were studied. The exergy losses of each component were simulated and analyzed. The PAFC efficiency and heat transfer characteristic of certain components should be optimized to improve the thermal performance of the HFCAR system.

    更新日期:2020-01-13
  • Developing innovative business models for reducing return temperatures in district heating systems: approach and first results
    Energy (IF 5.537) Pub Date : 2020-01-13
    Paolo Leoni; Roman Geyer; Ralf-Roman Schmidt

    Temperature reduction plays a key-role in increasing the energy efficiency of existing European district heating systems and, most important, in allowing a higher and more cost-efficient integration of sustainable low-temperature sources. However, technical, economical and legal barriers hamper the necessary investments. Purpose of this study is the elaboration of business models encouraging a substantial temperature reduction in existing DH systems and enabling the transition towards the 4GDH. Particular focus has been paid on solutions incentivizing the deep implementation of measures on the demand side to reduce the network return temperatures. The information collected through the review of international success stories and through interviews with stakeholders are used to derive recommendations for business models and propose new ideas for Austrian DH utilities, though the replicability in other countries is not excluded. The elaborated solutions are intended to overcome the main barriers acting in synergy on three levels: 1) customers’ engagement in fault detection and in temperature reduction; 2) financing of fault detection and optimization measures through strategic partnerships and crowdfunding platforms; 3) Energy Saving Contracting, especially (but not only) to solve the split incentive issue in rental homes.

    更新日期:2020-01-13
  • A novel thermophotovoltaic optical cavity for improved irradiance uniformity and system performance
    Energy (IF 5.537) Pub Date : 2020-01-13
    Chao Zhang; Liangliang Tang; Yan Liu; Zhuming Liu; Wei Liu; Kuanrong Qiu

    It has been demonstrated that a single thermophotovoltaic (TPV) cell can produce a high-output power density. In practical applications, many such cells are arrayed to obtain a high level of output. However, the irradiance on the surface of each cell of an array may be different. This nonuniformity causes mismatch loss in the array and reduces the reliability of the cells. To address these problems, a novel TPV optical cavity with reflectors was proposed to improve the irradiance uniformity of the cell array. A model TPV system using the proposed cavity was built and evaluated for comparison with traditional systems. TracePro and MATLAB software were used to examine the irradiance uniformity of cell arrays and the electrical performance of TPV systems that incorporate these arrays. Besides system efficiency ηsystem and maximum output power Pmax, several critical parameters degree of uniformity N, network efficiency ηnet, and average cell electric power density Wave, were used to evaluate the performance of the TPV systems. The results indicate that the proposed cavity improved the irradiance uniformity of the TPV cell array, thereby reducing mismatch loss and enhancing system performance, and it did so with a reduced number of cells.

    更新日期:2020-01-13
  • Process Simulation of Chemical Looping Combustion using ASPEN Plus for a Mixture of Biomass and Coal with Various Oxygen Carriers
    Energy (IF 5.537) Pub Date : 2020-01-13
    Ling Zhou; Kartik Deshpande; Xiao Zhang; Ramesh K. Agarwal

    Chemical Looping Combustion (CLC) is an emerging technology that has shown great promise for capture of almost pure CO2 in combustion of fossil fuels in power plants. In this paper, the CLC process is modeled in ASPEN Plus and then validated using experimental data from combustion of three types of biomass as fuel, and Hematite (Fe2O3) as an oxygen carrier (OC). Three types of biomass used in the simulation are pine sawdust, almond shells, and olive stones. The effect of the fuel reactor temperature on gas concentrations (namely CO2, CO, H2, and CH4) in the fuel reactor, and the carbon capture efficiency are examined. It is found that all three biomass types have very high carbon capture efficiencies, with pine sawdust and almond shell reaching nearly 100% capture efficiency when temperatures are greater than or equal to 950°C, while olive stones reach a capture efficiency of nearly 100% at temperatures greater than 980°C. It is also found that the CO2 concentrations in the fuel reactor vary across the three biomass types. The effect of using Mn2O3 as OC in place of Fe2O3 was also investigated. It was found that switching the oxygen carrier to Mn2O3 caused the concentrations of CO and H2 in the fuel reactor to decrease slightly, while the concentration of CO2 increased slightly. Additionally, a mixture of coal and biomass at 895°C was used with each of the two oxygen carriers. The results show that the system using Fe2O3 had a greater power output than the one using Mn2O3, and that power output increased as the fraction of coal in the coal-biomass mixture increased.

    更新日期:2020-01-13
  • Conversion of water caltrop husk into torrefied biomass by torrefaction
    Energy (IF 5.537) Pub Date : 2020-01-13
    Wen-Tien Tsai; Yu-Quan Lin; Chi-Hung Tsai; Mei-Hua Chung; Ming-Hung Chu; Hung-Ju Huang; Ya-Hsuan Jao; Showin-Ing Yeh

    In this work, water caltrop husk (WCH), a special agricultural residue in tropical and subtropical Asian countries, was used as a potential precursor for preparing torrefied biomass at different temperatures (i.e., 200, 240, 280, 320, and 360 °C) and residence times (i.e., 0, 30, 60, and 120 min). To best of our knowledge, this is currently the first study on the thermochemical characteristics of WCH-torrefied products. The mass yields and energy yields of resulting products indicated a decreasing trend with increasing temperature. By contrast, their calorific values and carbon contents generally increased at higher temperatures and longer residence times. These findings were consistently verified by the energy dispersive X-ray spectroscopy (EDS). Based on the thermochemical characteristics, the optimal WCH-torrefied product, which corresponded to mass yield of 45.2%, carbon content of 65.23%, calorific value of 25.3 MJ/kg and energy yield of 65.7%, was obtained at 320 °C for 60 min. According to the classification of solid fuels by the van Krevelen diagram, the optimal torrefied product showed a lignite-like feature. However, this lignite-like biomass fuel would not be appropriate to be directly used in boilers because of its relatively high minerals. Alternatively, it may be blended with coal in existing coal-fired power plants.

    更新日期:2020-01-13
  • A Scenario-Based Approach for the Design of Smart Energy and Water Hub
    Energy (IF 5.537) Pub Date : 2020-01-11
    M. Roustaei; T. Niknam; S. Salari; H. Chabok; M. Sheikh; A. Kavousi-Fard; J. Aghaei

    To exploit various energy carriers simultaneously and optimal distribution of energy in smart electrical infrastructure, a smart energy hub (S. E. Hub) concept was emerged. Therefore, the S. E. Hub is an effective solution for creating an efficient energy system. This paper attempts to provide a new management framework for the smart island which consists of Smart Energy and Water Hub (S. E. W. Hub) and microgrid. Also, optimal planning of multiple energy infrastructures of S. E. W. Hub is done considering operational constraints. Furthermore, the impact of the microgrid which includes wind turbines (WTs), photovoltaic power plant (PVPP) and tidal generation on the optimal planning of the S. E. W. Hub is investigated. The planning minimizes the total investment and operation costs as well as the environmental pollutants costs. In the proposed management framework, the balancing of thermal, electrical and water energy is provided. Due to the uncertainties associated with the considered energy sources, an effective scenario-based method is provided to accurately model such uncertainty factors. The validation of the proposed approach is shown through different cases implemented on a real industrial building and the problem is solved in the GAMS environment using CPLEX solver.

    更新日期:2020-01-13
  • A framework for analyzing trade-offs in cost and emissions in power sector
    Energy (IF 5.537) Pub Date : 2020-01-11
    Pankaj Kumar; Rangan Banerjee; Trupti Mishra

    Current electricity markets operate on a cost minimizing objective for power supply. However, countries across the world need to decarbonize their power systems in line with their policy objectives to mitigate climate change. In this context, this paper presents a framework to analyze synergies and trade-offs in cost and emission minimization strategies in the power sector. Emission minimizing objective can reduce emissions from existing fleets having flexibility in electricity supply, regardless of renewable energy capacity additions. This framework can also provide us with win-win strategies for reducing emissions while keeping costs low. An optimization model is developed for case study of India with data of 568 coal and 199 gas thermal units to analyze alternative real time dispatch and operating strategies. The cost and emission optimal supply strategies are compared in terms of power plant operations, emission reductions, and resulting cost of carbon abatement. The results show that 9.8% of carbon dioxide emissions can be reduced with 19% increment in the cost of electricity in emission minimizing strategy with respect to cost minimization. The operations in emission optimal supply strategy require additional 28 million dollars per day. The cost of carbon abatement is 99–129 dollars per tonne.

    更新日期:2020-01-13
  • Synthesis and simultaneous MINLP optimization of heat exchanger network, steam Rankine cycle, and organic Rankine cycle
    Energy (IF 5.537) Pub Date : 2020-01-11
    Xiaojian Huang; Pei Lu; Xianglong Luo; Jianyong Chen; Zhi Yang; Yingzong Liang; Chao Wang; Ying Chen

    Process plants are typically energy intensive plants and pollutant emission contributors. Energy integration in process plants effectively reduces energy consumption and pollutant emission. In a traditional energy integration concept, a heat exchanger network (HEN) is typically constructed for heat recovery between process streams. However, a large amount of medium-to-low-temperature surplus heat usually occurs in hot streams, where further internal heat integration is impossible, and is inevitably cooled by external cold source. Integrating organic Rankine cycle (ORC) into the process HEN is an effect way in further enhancing the energy recovery. However, the HEN, utility plant, and ORC are traditionally designed and optimized separately or sequentially, resulting in local energy integration or optimization. In the present study, ORC is integrated into a HEN to generate power energy from surplus heat. An improved superstructure is constructed and a mixed integer non-linear programming model is developed for the synthesis and simultaneous optimization of the integration system containing process-process HEN, hot utility-cold stream HEN, process hot stream-ORC HEN, steam utility plant, and cold utility plant. Two case studies of different scale in complexity are elaborated to validate the proposed methodology. Sensitivity analysis of carbon tax and fuel price are finally conducted.

    更新日期:2020-01-13
  • How does the interplay between resource availability, intersectoral competition and reliability affect a low-carbon power generation mix in Brazil for 2050?
    Energy (IF 5.537) Pub Date : 2020-01-11
    Tjerk Lap; René Benders; Floor van der Hilst; André Faaij

    Increasing penetration of solar and wind energy can reduce the reliability of power generation systems. This can be mitigated by e.g.; low-carbon dispatchable hydropower and baseload biomass power plants. However, long-term supply potential for those sources is often uncertain, and biomass can also be used for biofuel production. The purpose of this study is to assesses the interplay between uncertain supply potential of biomass and hydropower, intersectoral competition and reliability on a low carbon power system for 2050, with Brazil as case study, using a soft-link between an energy model and a power system model. Hydropower acts as a balancing agent for solar and wind energy, even under lower hydropower supply potential. When less biomass is available, low carbon transportation is met more with electric cars instead of ethanol cars, leading to an increase in electric load for charging their batteries. The charging strategy determines whether peak load increases substantially; after commuting, or lowers; in off-peak hours. This shows the importance of using a soft-link between the high temporal resolution power system model to assess the reliability, and a least cost-optimization model to assess the interplay between resource availability and intersectoral competition of low-carbon power systems.

    更新日期:2020-01-13
  • Development and uncertainty analysis of radionuclide atmospheric dispersion modeling codes based on Gaussian plume model
    Energy (IF 5.537) Pub Date : 2020-01-10
    Bo Cao; Weijie Cui; Chao Chen; Yixue Chen

    It is necessary to assess the radiological consequences of radioactive leakage accident in the planning and operation of a nuclear power plant, especially an atmospheric radioactive material spill that has a rapid and broad impact on public health. Uncertainty analysis of the assessment results will help to reduce the probability of making mistakes in the emergency response after accident. The Gaussian plume model is the most widely used computational model for atmospheric diffusion assessment. Based on this model, the FORTRAN computer language is used to compile Radionuclides Atmosphere Dispersion Codes. Calculation results based on RADCs are compared with HotSpot Health Physics Codes to verify its calculation accuracy. Based on the Bayesian Markov chain Monte Carlo method, uncertainty of the Gaussian plume model is analysed, and the influence of observation error on the confidence interval is calculated. The results show that the greater the air concentration of radioactivity, the wider the confidence interval; the observation error has a great impact on the confidence interval. Meanwhile, the small observation error will cause a large change in the width of the confidence interval.

    更新日期:2020-01-11
  • Performance comparison of two metallic eutectic solder based medium-temperature domestic thermal energy storage systems
    Energy (IF 5.537) Pub Date : 2020-01-10
    Ashmore Mawire; Chidibiere S. Ekwomadu; Tlotlo M. Lefenya; Adedamola Shobo

    In this study, two thermal energy storage systems based on eutectic solder (Sn63/Pb37) metallic phase change material (PCM) are compared experimentally during their charging and discharging cycles. The first system is a single-PCM system composed of a packed bed of spherically encapsulated eutectic solder capsules. The other system is a two-PCM cascaded system comprising of eutectic solder spherical capsules at the top and erythritol spherical capsules at the bottom in a storage ratio of 50%:50%. The charging experiments are conducted with three different charging flow rates to investigate the effect of the flow rate. Charging experiments are also performed with three different set charging temperatures to investigate their effect. Discharging experiments are conducted with three different discharging flow rates to investigate their effect on the thermal performance. The cascaded storage system demonstrates better energy and exergy charging rates before the bottom PCM melts. After the low-temperature PCM at the bottom melts, the temperature at the bottom of the cascaded system increases, and the single-PCM system demonstrates higher charging energy and exergy rates. Higher discharging energy and exergy rates are obtained with the single-PCM system for longer periods during discharging compared to the cascaded system. The energy and exergy storage efficiencies of the cascaded system are generally higher compared to the single-PCM system. This is possibly because of the release of latent heat during discharging in a single cycle using multiple phase change sequences.

    更新日期:2020-01-11
  • Consistency evaluation and cluster analysis for lithium-ion battery pack in electric vehicles
    Energy (IF 5.537) Pub Date : 2020-01-10
    Jiaqiang Tian; Yujie Wang; Chang Liu; Zonghai Chen

    Consistency is an essential factor affecting the operation of lithium-ion battery packs. Pack consistency evaluation is of considerable significance to the usage of batteries. Many existing methods are limited for they are based on a single feature or can only be implemented offline. This paper develops a comprehensive method to evaluate the pack consistency based on multi-feature weighting. Firstly, the features which reflect the static or dynamic characteristics of batteries are excavated. Secondly, a weighted method of multi-feature inconsistency is proposed to evaluate pack consistency. In which case, the entropy weight method is employed to determine the weight. Thirdly, an improved Greenwald-Khanna algorithm based on genetic algorithm and kernel function is developed to cluster batteries. Finally, nine months of electric vehicle data are collated to validate the proposed algorithms. Meanwhile, the main factor affecting consistency change is analyzed. The results show that with the usage of batteries, the difference between the cells becomes more serious, which weakens the pack consistency. Besides, the relationship between the consistency attenuation rate and the driving mileage can be approximated by a first-order function. The higher mileages will aggravate the pack inconsistency. Moreover, it has been proven that the improved clustering algorithm has stronger robustness and classification performance.

    更新日期:2020-01-11
  • Numerical investigation of hydrogen absorption in a metal hydride reactor with embedded embossed plate heat exchanger
    Energy (IF 5.537) Pub Date : 2020-01-10
    Swaraj D. Lewis; Purushothama Chippar

    In this paper, a Metal Hydride (MH) reactor integrated with an Embossed Plate Heat Exchanger (EPHX) was studied for the first time for its hydrogen absorption rate and thermal performance. A detailed numerical analysis of the various flow-field designs in the EPHX such as parallel-type, pin-type, and serpentine types (vertical and horizontal) was performed. The serpentine flow-field EPHX presented better heat transfer and faster hydrogen storage ability. Also, it showed more uniform temperature distribution in the bed compared with parallel and pin-type flow-fields. Next, the vertical-serpentine flow-field EPHX was compared with the most commonly used Helical Coil Heat Exchanger (HCHX) and the outcomes were discussed. Although, EPHX showed slightly lower overall heat removal from the reactor, it presented similar hydrogen absorption rate and remarkable uniformity in temperature distribution in the reactor.

    更新日期:2020-01-11
  • Dynamic economic emission dispatch with load demand management for the load demand of electric vehicles during crest shaving and valley filling in smart cities environment
    Energy (IF 5.537) Pub Date : 2020-01-10
    Loau Tawfak Al-Bahrani; Ben Horan; Mehdi Seyedmahmoudian; Alex Stojcevski

    A novel algorithm named orthogonal particle swarm optimization (OPSO) is proposed to solve a multi-objective problem, namely, dynamic economic emission dispatch, while applying load demand management (LDM) on 30,000 electric vehicles (EVs) during crest shaving and valley filling (CSVF) regions under several practical operating power constraints. The OPSO algorithm is evaluated by using 10 thermal-generating units from power-generating systems (PGSs) in two Case Studies, with and without LDM on the load demand of EVs. The comprehensive analysis results reveal that this algorithm is capable of solving such a complex problem. This study provides important details about the future operation of PGSs with the large penetration of EVs in smart cities environment.

    更新日期:2020-01-11
  • Vanadium redox flow battery parameters optimization in a transportation microgrid: a case study
    Energy (IF 5.537) Pub Date : 2020-01-10
    Włodzimierz Jefimowski; Adam Szeląg; Marcin Steczek; Anatolii Nikitenko
    更新日期:2020-01-11
  • Providing frequency control reserve with photovoltaic battery energy storage systems and power-to-heat coupling
    Energy (IF 5.537) Pub Date : 2020-01-09
    Georg Angenendt; Sebastian Zurmühlen; Jan Figgener; Kai-Philipp Kairies; Dirk Uwe Sauer

    The number of households with photovoltaic battery storage systems is steadily growing, and so is the number of heat pump installations. An integrated home combines domestic battery systems and a heat pump for power-to-heat coupling. During winter, storage systems in an integrated home are not used to their full capacity due to low solar radiation. This potential can be used to enhance the economics by applying a dual-use scheme. In this publication, an integrated home that participates in the frequency control reserve market is investigated. A major advantage of integrated homes with power-to-heat coupling in comparison to standalone battery storages is the additional flexibility to absorb negative control reserve power in the heating sector. Seasonal variation of feed-in from photovoltaics is considered by an advanced strategy for variable provision of control reserve. Results show that a dual-use operation with participation in the control reserve market can increase the profitability of storage systems. Market participation leads to accelerated battery aging, mainly driven by increased calendar aging. This is overcompensated by the possible incomes. Under consideration of low costs for market participation, a constant provision of at least 3 kW of reserve power could be economical. A variable provision further enhances economic efficiency.

    更新日期:2020-01-11
  • An innovative waste-to-energy system integrated with a coal-fired power plant
    Energy (IF 5.537) Pub Date : 2020-01-08
    Heng Chen; Meiyan Zhang; Kai Xue; Gang Xu; Yongping Yang; Zepeng Wang; Wenyi Liu; Tong Liu

    An advanced waste-to-energy system integrated with a coal-fired power plant has been proposed to improve the energy utilization of municipal solid waste. In the new design, the energy gained from the waste-to-energy boiler is employed to heat the feedwater and partial cold reheat steam of the coal power plant, and the feedwater of the waste-to-energy boiler is provided by the heat regeneration system of the coal power plant. Consequently, the energy obtained from the waste incineration products is injected into the steam cycle of the coal power plant, and the waste-to-electricity efficiency can be significantly boosted. Based on a 500 t/day waste-to-energy plant and a 630 MW coal power plant, the proposed hybrid scheme was evaluated compared with the conventional separate one. The results show that the waste-to-electricity efficiency is promoted by 9.16% points with an additional net power output of 3.71 MW, attributed to the suggested integration. Furthermore, the energy-saving mechanism of the novel concept was revealed by energy and exergy analyses. Finally, the new design was economically examined, which indicates that the dynamic payback period of the proposed waste-to-energy plant is only 3.55 years, which is 5.87 years shorter than that of the conventional one.

    更新日期:2020-01-09
  • The role of data centres in the future Danish energy system
    Energy (IF 5.537) Pub Date : 2020-01-09
    Stefan Petrović; Alessandro Colangelo; Olexandr Balyk; Chiara Delmastro; Maurizio Gargiulo; Mikkel Bosack Simonsen; Kenneth Karlsson

    Data centres (DCs) are expected to satisfy the rising demand for internet services. Denmark alone is expected to host several large-scale DCs, whose demand for electricity in 2040 may reach 33% of 2017 national electricity consumption. Understanding the operation and interactions of DCs with energy systems is key to understanding their impacts on installed capacities, costs and emissions. The present paper makes three contributions in this regard. First, we introduce a thermodynamic model that relates the power consumption of DCs to their production of excess heat (EH). Second, the results are scaled up to represent DCs in a national energy-system model for the analysis of different scenarios. Third, scenarios are generated and analysed to quantify the impact of DCs on the Danish energy system until 2050. The results show that DCs might have significant impacts on Denmark’s power and district heating (DH) sectors. First, the power demand from DCs translates into an additional 3-6 GW of offshore wind capacity. Second, EH from DCs is beneficial to the whole energy system, the entire quantity of EH being utilized in four out of five scenarios. EH recovery from DCs is economically beneficial, providing from 4% to 27% of Denmark’s DH after 2040.

    更新日期:2020-01-09
  • Thermo-mechanical solar receiver design and validation for a micro gas-turbine based solar dish system
    Energy (IF 5.537) Pub Date : 2020-01-09
    Lukas Aichmayer; Jorge Garrido; Björn Laumert

    This work presents the comprehensive development of a solar receiver for the integration into a micro gas-turbine solar dish system. Special focus is placed on the thermo-mechanical design to ensure the structural integrity of all receiver components for a wide range of operating conditions. For the development, a 3-dimensional coupled multi-physics model is established and is validated using experimental data. Contrary to previous studies, the temperature of the irradiated front surface of the absorber is included in the comprehensive validation process which results in a high level of confidence in the receiver design. Finally, a full-scale solar receiver for the integration into the OMSoP solar dish system is designed and its performance determined for a wide range of points to define its safe operating envelope using the validated model. It is shown that the receiver is capable of operating at 800°C with an efficiency of 82.2% and a pressure drop below 1% at the nominal operating point, while at the same time functioning effectively for a wide range of off-design conditions without compromising its structural integrity. At the nominal operating point, the maximum comparison stress of the porous absorber is 5.6 MPa compared to a permissible limit of 7.4 MPa.

    更新日期:2020-01-09
  • Optimizing production of new energy vehicles with across-chain cooperation under China’s dual credit policy
    Energy (IF 5.537) Pub Date : 2020-01-08
    Jizi Li; Yaoyao Ku; Yue Yu; Chunling Liu; Yuping Zhou

    New energy vehicles (NEVs) are becoming more and more prevalent for economic and environmental reasons. This paper investigates the issue of the impacts of subsidy policy and dual credit policy on NEVs and conventional vehicles (CVs) production decision from a across-chain perspective, in a co-opetitive context, where exists a CV supply chain and a NEV supply chain with two important schemes involved, i.e., government subsidies and dual credit. While previous literature has discussed government subsidies excessively, they seldom study the role of dual credit policy in promoting NEVs. To examine the differences between two schemes, a mixed integer linear programing (MILP) is utilized to develop a stylized production model for a CV supply chain and NEV supply chain system that incorporating subsidies and dual credit trading simultaneously. Using a Lagrange heuristic algorithm to provide an optimal solution regarding NEV and CV production decision as well as dual-credit trading. Simulations are performed on realistic profiles that show, (i) implementing the dual credit policy increases the profit of NEV supply chain, whereas the profit of CV supply chain and of whole supply chain system decline simultaneously, and the schedule of CVs/NEVs without across-chain cooperation is arranged more evenly than that with across-chain cooperation during the transit period to NEVs. Meanwhile, (ii) under dual credit policy, gradually-decreasing subsidies can partially offset the negative impacts of dual credit policy on the NEV supply chain, the subsidies can only serve as a temporary supplement to profits. In addition, (iii) there exists an optimal NEV credit price to maximize the overall profit of the whole system, and a corresponding threshold value of for two categories of cars, when above the threshold, the per-CV profit outperforms the per-NEV one and vice versa.

    更新日期:2020-01-09
  • Effect of demand response program of loads in cost optimization of microgrid considering uncertain parameters in PV/WT, market price and load demand
    Energy (IF 5.537) Pub Date : 2020-01-08
    Sahbasadat Rajamand

    Using renewable distributed generators as photovoltaic cell and wind turbine in microgrid includes green and free energy exploitation. However, uncertainty of generated energy from these resources may underestimate energy planning for load demands. The uncertainty may be from market price and load demand in addition to the renewable distributed generators. To overcome the uncertainty challenge, energy storage system and demand response program with cooperation of users on demand side are applied as solutions to plan the energy flow in microgrid to guarantee the voltage stability and essential load supporting. In this paper, price-based demand response for industrial, commercial and house loads are considered in which the effect of demand response on the cost reduction is analyzed and discussed. Electrical and heat demand are considered in the microgrid while uncertainty of renewable distributed generators, market price and load demand are modeled and estimated by point estimation method. Simulation results with three scenarios are performed with and without price-based demand response program and results are compared. As shown in simulation results, demand response has highly reduced total cost (22–28% related to the case without that) where voltage dip (maximum 1.5%) and power deviation (maximum 1.33%) are also improved in the microgird.

    更新日期:2020-01-09
  • Investigation of the fate of nitrogen in chemical looping combustion of gaseous fuels using two different oxygen carriers
    Energy (IF 5.537) Pub Date : 2020-01-08
    Robert F. Pachler; Stefan Penthor; Karl Mayer; Hermann Hofbauer

    The influence of nitrogenous fuel impurities in a 120 kWth chemical looping combustion pilot unit was investigated. Two oxygen carriers were used. An in industrial scale produced perovskite type CaMn0·775Mg0·1Ti0·125O3-δ, called C28 and a copper based oxygen carrier (Cu15) prepared by impregnation were applied. Natural gas was used as fuel and ammonia (NH3) were added as a model NOX precursor up to a fuel-N content of 1.4 wt%, to investigate the path of nitrogen and emissions of nitrogen oxides. The exhaust gas streams of air and fuel reactor were analyzed against NH3 and NOX.

    更新日期:2020-01-08
  • Study on Impacts of Dust Accumulation and Rainfall on PV Power Reduction in East China
    Energy (IF 5.537) Pub Date : 2020-01-08
    Jinxin Chen; Guobing Pan; Jing Ouyang; Jin Ma; Lei Fu; Libin Zhang

    The photovoltaic (PV) power plants’ power generation is affected obviously by the cleanliness of the photovoltaic modules. The dust is the primary source causing the pollution. Natural dust deposition is affected by human activities and meteorological factors such as temperature, humidity, wind speed and PM10 concentration in the region where PV modules are installed. The research efforts so far have been focused on predicting PV power outputs, however, in the real operations the PV outputs can significantly deviate from the prediction due to the dust pollution which, unfortunately, has not been fully investigated. This paper, to the authors’ best knowledge, is the first research to analyze the dust composition and evaluate its impacts on the PV power outputs with the real field test data in East China Collected through a series of experiments completed in the lab of the Institute of Distributed Generation and Microgrid, Zhejiang University of Technology, in East China. A PV output forecasting model was set up first based on the irradiance and the component’s temperature. Then a complete meteorological and electrical data online monitoring system was developed for data acquisition. The morphology of the dust particles on the investigated photovoltaic modules was observed by a scanning electron microscope, and the composition of the dust particles was measured by X-ray fluorescence. The research found that the dust accumulated on the surface of photovoltaic modules tend to form clusters under the influence of rainfall which is one major cause on fast dropping PV outputs. The analysis shows the dust deposit mainly comprises of SiO2 and CaCO3. Further analysis indicates in East China, the average dust density on PV modules is 0.644 g/m2 in a week and consequently the dust reduces the PV output power by 7.4% one week. The research is of significance not only in terms of giving the real-data based analysis on dust properties deposited on PV panels, but also on revealing the relationship between power output attenuation and dust deposition, which helps improve the PV power output prediction accuracy and develop efficient cleaning strategies for photovoltaic modules.

    更新日期:2020-01-08
  • 3D full-space triboelectric-electromagnetic hybrid nanogenerator for high-efficient mechanical energy harvesting in vibration system
    Energy (IF 5.537) Pub Date : 2020-01-07
    Jian He; Xueming Fan; Jiliang Mu; Chao Wang; Jichao Qian; Xiucheng Li; Xiaojuan Hou; Wenping Geng; Xiangdong Wang; Xiujian Chou

    Mechanical energy with low frequency is a widely distributed energy in environment. Triboelectric nanogenerator (TENG) and electromagnetic energy harvester (EMG) are considered as promising methods to harvest low-frequency mechanical energy. In this study, a three-dimensional (3D) full-space triboelectric-electromagnetic hybrid nanogenerator (FSHG) based on a magnetic ball and Polystyrene (PS) spherical shells is presented. The external excitation can be transformed into the relative motion between different units. The mover composed of the PS spherical shell 3 and a magnet ball transforms 3D full-space mechanical energy into electrical energy through friction electrification and electromagnetic induction effect. The results of experiments show that the performance of TENG and EMGs can be influenced by the direction of external vibration and excitation frequency. The output performances of TENG and EMGs increase as the excitation frequency increases. The results show that the maximum output power of TENG is 18 μW at an external loading resistance of 200 MΩ, and the maximum output power of EMG is 640 μW at an external loading resistance of 1000 Ω. The FSHG demonstrates a quick charging ability for capacitor and the capability to power hundreds of LEDs. After storing energy in the capacitor, the DC signal can power a humidity/temperature sensor.

    更新日期:2020-01-07
  • The role of solid oxide fuel cells in future ship energy systems
    Energy (IF 5.537) Pub Date : 2020-01-07
    Francesco Baldi; Stefano Moret; Kari Tammi; Franćois Maréchal

    With rising concerns about emissions from shipping, fuel cells are expected to take an important role in ship propulsion. In particular, solid oxide fuel cells (SOFC) offer high efficiency with the possibility of combined heat and power production. In this paper, we investigate energy, cost, and emission savings on ships resulting from the use of SOFCs using an optimization-based approach. A global sensitivity analysis was used to investigate the effects of the high uncertainty of problem parameters. This setup is applied to two case studies: a cruise ship and a tanker. The results show that SOFCs could provide a reduction in ship greenhouse gas emissions by up to 34% and that when using LNG as fuel, SOFCs are the most cost-optimal solution that allows a significant reduction in GHG emissions. A wider adoption of SOFCs would also lead to a decrease of other pollutant emissions. The sensitivity analysis shows that the lifetime of the stack is the most impacting uncertain parameter, followed by fuel prices and by the investment cost of the SOFC stack. The study highlights that, in a future of stricter constraints on greenhouse gas emissions and where the SOFC technology will be fully industrialized, SOFCs will be able to play an important role in bridging shipping towards decarbonization.

    更新日期:2020-01-07
  • Thermomechanical characterisations of PTFE, PEEK, PEKK as encapsulation materials for medium temperature solar applications
    Energy (IF 5.537) Pub Date : 2020-01-07
    Rajan Gupta; Shraddha Shinde; Aswani Yella; C. Subramaniam; Sandip K. Saha

    Macroencapsulation of phase change material (PCM) is one of the enhancement techniques to maximise heat transfer area between PCM and the surrounding heat transfer fluid (HTF). However, the selection of suitable encapsulation material, that can address the volumetric expansion problem and does not react with the core PCM, while being stable at elevated temperature, possesses a challenge. In this work, the thermo-mechanical characterisation of polymeric material is reported, which can be used for medium temperature (200–350 °C) solar applications. Three materials, such as polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK) and polyether ketone ketone (PEKK) are chosen as an encapsulation material for storing a commercially available organic PCM, A164 in the capsule. Capsules of three materials are fabricated and the mechanical properties of the materials are evaluated after every 10 accelerated thermal cycles near the degradation temperature of the materials to understand their behaviour in extreme conditions. Dimensional and weight analyses of the macro encapsulated capsules is also performed to gauge any change in their physical properties. Thermo-mechanical properties show that the polymers chosen can be used as an encapsulation material for solar applications. Dimensional and weight analysis indicate no significant change in the properties of the polymers. High-temperature stability of these polymers even for extended duration indicates a maximum of 3 wt% change only. The compression test on these materials reveals that the PEKK can be used up to 275 °C with Young's modulus decreases to 0.4 GPa. These results would form the ground for their applications as PCM-encapsulating materials targeting medium temperature solar applications.

    更新日期:2020-01-07
  • Energy and exergy analyses of latent heat storage unit positioned at different orientations – An experimental study
    Energy (IF 5.537) Pub Date : 2020-01-07
    Lokesh Kalapala; Jaya Krishna Devanuri

    The performance of a latent heat storage unit (LHSU) greatly rely on the melting/solidification rate which in turn affected by the orientation of LHSU. The orientation of the LHSU greatly influences the natural convection phenomenon, thereby affects the melting behavior of PCM. The present study is aimed at investigating the performance of a shell and tube LHSU positioned at various inclinations. Four inclinations are considered from vertical to horizontal position. Lauric acid is chosen as PCM with a melting range of 43.45°C–49.94 °C. Both melting and solidification characteristics are analyzed with the help of energy and exergy analyses (PCM average temperature, melt fraction, energy and exergy efficiency, energetic and exergetic effectiveness). From the experimental results, it is observed that the orientation has a major influence on the melting phenomenon and solidification is unaffected by the orientation of LHSU. Melting rate is observed to be higher for horizontal configuration till the PCM in the upper half portion is melted, however total melting time is observed to be less for vertical configuration. In addition, exergy efficiency is found to be higher for vertical configuration while melting, whereas for discharging process the exergy efficiency is same for all the inclinations.

    更新日期:2020-01-07
  • Impact of household demographic characteristics on energy conservation and carbon dioxide emission: Case from Mahabad city, Iran
    Energy (IF 5.537) Pub Date : 2020-01-07
    Mohammad Soltani; Omeid Rahmani; Dara S.M. Ghasimi; Yousef Ghaderpour; Amin Beiranvand Pour; Siti Hajar Misnan; Ibrahim Ngah

    This study explores the impact of different household demographic characteristics on energy conservation and carbon dioxide (CO2) emission in Mahabad city located in the northwest of Iran. The structural model adopted was composed of six variables, including household age, household size, educational qualification, income quintile, gender, and energy conservation concerning demographic characteristics and energy sources and consumptions. To compare predictability power of effects of these variables concerning households’ energy conservation and CO2 emissions, a crisp instruction on how to evolve a statistical technique for analyzing data was provided by partial least squares structural equation modeling (PLS-SEM). To verify the reliability of the PLS-SEM technique, the statistical significance test was performed by investigating path coefficients. The study revealed that households consume approximately 89.71% on liquefied petroleum gas (LPG), 9.87% on electricity while the rest 0.43% on kerosene, petrol, and diesel monthly. Eventually, the results of this study showed that household age, household size, and carbon dioxide emissions, except education background and income level, are significantly correlated with energy conservation.

    更新日期:2020-01-07
  • Numerical investigations on thermal performance enhancement of hydrogen-fuelled micro planar combustors with injectors for micro-thermophotovoltaic applications
    Energy (IF 5.537) Pub Date : 2020-01-06
    Wei Zuo; Qingqing Li; Zhu He; Yawei Li

    In order to address the issue about the low output power of the micro-thermophotovoltaic system, in this work, the inlets of the traditional micro planar combustor are modified into injectors for better thermal performance and higher output power of the micro-thermophotovoltaic system. The thermal performance of traditional and modified micro planar combustors is numerically investigated and compared. It is found that the thermal performance of the modified micro planar combustor is greatly enhanced with the help of the injectors. This is due to that the reduction of the step diameter leads to the rise of the velocity of the inlet flow, resulting in the chemical reaction zone is closer to the center of the combustion chamber in the micro planar combustor. Furthermore, the positive effects and negative effects on thermal performance enhancement brought by the reduction of the step diameter of injectors are vividly discussed under different hydrogen mass flow rate, hydrogen/air equivalence ratio and solid wall material. Finally, some guidelines are proposed for the applications of the micro planar combustors with injectors in the micro-thermophotovoltaic system. This work provides us a simple and practical way to address the issue about the low output power of the micro-thermophotovoltaic system.

    更新日期:2020-01-06
  • Economic potential analysis of photovoltaic integrated shading strategies on commercial building facades in urban blocks: A case study of Colombo, Sri Lanka
    Energy (IF 5.537) Pub Date : 2020-01-06
    Thushini Mendis; Zhaojian Huang; Shen Xu; Weirong Zhang

    Building integrated photovoltaics (BIPV) are becoming a viable solution for clean on-site energy production and utilisation. In tropical climates, although rooftops are ideal for photovoltaic (PV) module integration, the available area may be insufficient to meet building energy demand due to the increase in high-rise urban buildings, causing a requirement for the utilisation of facades. However, the high solar elevation angle means that facades are unfavourably oriented towards receiving incident irradiation. Also, the issue exists of high solar heat gains into built spaces. This paper evaluates the utilisation of horizontally inclined PV integrated shading strategies to combat these issues based on the urban context of Colombo, Sri Lanka. Various strategies are evaluated in terms of their inclination angles and the distance between installations, and urban blocks in Colombo are analysed in terms of how they affect the solar potential in the urban canyon. The results are analysed in terms of economic potential to determine the optimised installation strategies based on urban block type. The results suggest that installations inclined at 30° at a distance-to-length ratio of 4 provide the greatest economic viability in this context.

    更新日期:2020-01-06
  • Comparison of storage density and efficiency for cascading adsorption heat storage and sorption assisted water storage
    Energy (IF 5.537) Pub Date : 2020-01-06
    Matthias S. Treier; Aditya Desai; Ferdinand P. Schmidt

    Storage of thermal energy can be important for compensating the mismatch between demand and supply of energy, especially due to fluctuating renewable energy sources. Within this study, two different system concepts of thermal energy storage involving sorption effects are analysed in a simulation study with the aim of increasing storage efficiency and storage density compared to known systems. Both systems indicate a possible benefit in energy density and storage efficiency but it is also analysed how the choice of system boundary and temperature requirements of the use case influence these two figures of merit.

    更新日期:2020-01-06
  • Will energy transitions impact financial systems?
    Energy (IF 5.537) Pub Date : 2020-01-06
    Yingying Xu

    A low-carbon transition requires changes in the energy structure that may affect the financial system. However, little theoretical and empirical evidence has been produced regarding the interaction between different subsystems. This article presents empirical evidence regarding the relationship between energy and financial systems using the wavelet analysis which considers possible cyclical properties that change over time. The wavelet coherence coefficients based on the data for the United States suggest that the electricity price is closely related to shares of different energy-powered electricity production, but has weak relationships with the interbank connectivity and bank failures. The phase differences show that increases in nuclear energy-powered electricity generation reduce the electricity price at less than one and a half years of scale, but rise it at approximately three years of scale. However, different energy shares have little effect on the interbank connectivity. An increase in renewable energy in producing electricity may reduce the number of failed banks, whereas an increase in nuclear energy has an opposite effect. Therefore, the energy transition affects the financial system and excessively fast investment in nuclear energy may threat the bank sector and thus endanger the financial system. The Nuclear Renaissance program should be treated with caution.

    更新日期:2020-01-06
  • Experimental investigation of cost-effective ZnO nanofluid based spectral splitting CPV/T system
    Energy (IF 5.537) Pub Date : 2020-01-06
    Liang Huaxu; Wang Fuqiang; Zhang Dong; Cheng Ziming; Zhang Chuanxin; Bo Lin; Xu Huijin

    Nanofluid-based spectral splitting concentrating photovoltaic thermal (CPV/T) system enables photovoltaic (CPV) cells and thermal absorbers to operate at different temperatures and realizes the utilization of full-spectrum sunlight. It is important to find one kind of low cost nanofluid that can be applied to nanofluid-based spectral splitting CPV/T system. In this study, the feasibility of using cost-effective glycol-ZnO nanofluid in spectral splitting CPV/T system was experimentally verified. A two-axis sun-tracking nanofluid-based spectral splitting CPV/T system was designed and fabricated. The solar energy conversion efficiency correlation coefficient was utilized to compare the thermodynamic performance of glycol-ZnO nanofluid-based spectral splitting CPV/T system with those of water-polypyrrole and water-Ag-SiO2 nanofluid-based spectral splitting CPV/T system. The effects of ZnO nanoparticles concentration in glycol-ZnO nanofluid on thermal and electrical performances were investigated. The cost comparisons of different types of nanoparticles were also conducted. The results indicated that the correlation coefficient of glycol-ZnO nanofluid-based spectral splitting CPV/T system was 0.218 and 0.05 higher than those of water-polypyrrole and water-Ag-SiO2 nanofluid-based spectral splitting CPV/T system, respectively. The cost of ZnO nanoparticles was 0.13%, 0.08% and 0.17% of cost of Au, Ag and polypyrrole nanoparticles, respectively.

    更新日期:2020-01-06
  • US natural gas consumption prediction using an improved kernel-based nonlinear extension of the Arps decline model
    Energy (IF 5.537) Pub Date : 2020-01-06
    Hongfang Lu; Xin Ma; Mohammadamin Azimi

    Natural gas (NG) is a vital energy in the energy structure transition, and its consumption prediction is a significant issue in energy structure management and energy security. As the second largest energy consumer and producer in the world, the status of NG in the United States (US) energy system has been increasing since the “An America First Energy Plan” was proposed in 2017. Accurate prediction of natural gas consumption (NGC) can provide an effective reference for decision-makers, policymakers, and energy companies. This paper proposes an improved kernel-based nonlinear extension of the Arps decline model (KNEA) to forecast NGC in the US. The grey wolf optimization (GWO) algorithm is used to optimize the regularization parameter and kernel width in the KNEA model, and applies the hybrid model to the NGC datasets of different sectors (including lease and plant fuel usage, pipeline and distribution usage, residential users, commercial users, industrial users, vehicle fuels users, and power generation users) in the US. Compared with the prediction results of five benchmark models, it is shown that the GWO-KNEA model has the best performance in each dataset, and the range of mean absolute percentage error is less than 5%. By comparing the computational time and memory occupancy of the model, it can be concluded that the time and space complexity of the GWO-KNEA model is greater than that of the original KNEA model, but lower than that of other benchmark models. Moreover, this paper uses the newly proposed model to predict the NGC and consumption mix of the US from 2019 to 2025. The main conclusions are drawn: (1) NGC in the US will show a slow growth trend (the average annual growth rate is only 1.2%); (2) The proportion of NGC in power generation will increase significantly, reaching about 39% in 2025; (3) The proportion of residential, commercial and industrial NGC will decline slightly.

    更新日期:2020-01-06
  • A comparative life cycle analysis of wheat straw utilization modes in China
    Energy (IF 5.537) Pub Date : 2020-01-06
    Guishi Cheng; Ying Zhao; Shijiu Pan; Xiaoqiang Wang; Changqing Dong

    There are abundant wheat straw resources in China. Proper treatment of wheat straw can reduce environmental pollution and environmental load while bring certain economic benefits. How to choose the right way to deal with straw is a difficult problem at present. Life cycle analysis of three wheat straw utilization modes: (1)direct combustion for electricity (2)fuel ethanol production and (3)feed production have been conducted to compare their environmental performances. Life cycle analysis results show that fuel ethanol production from wheat straw is an environment-friendly utilization mode because of its great advantages (−412mPt) in human health, ecological environment quality, climate change and natural resources. Direct combustion for electricity has certain advantages in terms of natural resources and treatment efficiency, but has greater impact (308mPt) on climate change and more emissions compared with fuel ethanol production and feed production. Feed production has great economic advantages and moderate environmental load (358mPt). It has the potential for large-scale application. The determination of the specific utilization mode should take into account the actual needs local conditions and other factors.

    更新日期:2020-01-06
  • Simulation and economic assessment of using H₂O₂ solution in wet scrubber for large marine vessels
    Energy (IF 5.537) Pub Date : 2020-01-06
    Yeongryeol Choi; Junghwan Kim

    As emission regulation for marine vessels has become strict since 2016, a new emission control method is required. This paper proposes using the H₂O₂ solution in a wet scrubber for SOx and NOx removal for a conventional large marine vessel that uses a low-speed two-stroke diesel engine and a heavy fuel oil, and aims to evaluate the economic feasibility of this approach compared with other methods. Measurement data for the exhaust gas of the engine are incorporated in a process simulation based on physical properties and kinetics that relate H₂O₂ with emission materials. H₂O₂ consumption rate is determined to be 757.38 and 10.37 kg/h, depending on sailing in an emission control area. The parameters for techno-economic analysis are based on capital cost, operation cost, sailing information, and fuel cost in January 2018. The net present value of the proposed method is calculated to be 3.26% higher than other methods, and the proposed method is more economical than other methods when the sailing ratio in the emission control area is less than 75.98%. Based on these results, the proposed method can be utilized as an alternative emission control method for a marine vessel that considers retrofitting to satisfy strict emission regulations.

    更新日期:2020-01-06
  • Thermodynamic evaluation of an ammonia-fueled combined-cycle gas turbine process operated under fuel-rich conditions
    Energy (IF 5.537) Pub Date : 2020-01-06
    Martin Keller; Mitsuo Koshi; Junichiro Otomo; Hiroshi Iwasaki; Teruo Mitsumori; Koichi Yamada

    Ammonia is a promising energy carrier and carbon-free fuel for power generation using combined-cycle gas turbines. However, its use results in the generation of relatively large amounts of NOx in the combustor. To address this issue, we propose a combined-cycle configuration including exhaust gas recirculation (EGR), in which the gas turbine is operated under fuel-rich conditions and the uncombusted hydrogen is burned in the heat-recovery steam generator (HRSG). Thus, hydrogen in the flue gas of the gas turbine increases the output power and improves the thermal efficiency of the system. Furthermore, in the combined system with EGR, the exhaust gas does not contain O2 and the combustion temperature can be reduced without altering the equivalence ratio. The proposed system is evaluated by thermodynamic modeling, and we find that low NOx emissions can be achieved while maintaining high thermal efficiency. Cold EGR is likely to be required to maintain the turbine inlet temperature below a technically feasible level, and a tradeoff between thermal efficiency and the NOx concentration at the combustor outlet is observed. The ideal operating conditions for this process thus depend on the technically feasible turbine inlet temperature, EGR ratio, and the permissible NOx concentration in the exhaust gas.

    更新日期:2020-01-06
  • Application of Artificial Neural Network for Predicting the Dynamic Performance of a Free Piston Stirling Engine
    Energy (IF 5.537) Pub Date : 2020-01-06
    Wenlian Ye; Xiaojun Wang; Yingwen Liu

    In this study, an artificial neural network model is built to predict the dynamic performance of a beta-type free piston Stirling engine. The influences of six input dynamic parameters on operating frequency, amplitude ratio and phase angle are analyzed. The operating frequency is significantly affected by the spring stiffness and the mass of the pistons. However, the relationships of the dynamic parameters are comprehensive, which are determined by multiple parameters. Then, a number of dynamic output parameters are used as training and testing data. The best results are obtained by 6-6-1, 6-6-1 and 6-10-6-1 network architectures for the operating frequency, amplitude ratio and phase angle respectively. For these network architectures, the back propagation algorithm, namely Levenberg-Marguardt is applied. Stirling engine’s dynamic performance predicted with the network model is compared with the actual values. After training, correlation coefficients (R2) values for training and testing data are close to 1. The mean relative errors of the operating frequency, amplitude ratio and phase angle are 0.85%, 2.78% and 3.19% for the training process. These results show that the artificial neural network model is an acceptable and powerful approach for predicting the dynamic performance of the beta-type free piston Stirling engine.

    更新日期:2020-01-06
  • Thermodynamic analysis of ultralow-temperature district heating system with shared power heat pumps and triple-pipes
    Energy (IF 5.537) Pub Date : 2020-01-06
    Ahmad Arabkoohsar; Ali Sulaiman Alsagri

    An ultralow-temperature district heating system that uses neighborhood-scale heat pumps was recently proposed and investigated. Although the system was found more efficient than any existing solution, there is still potential in this concept for achieving better efficiency and cost-effectiveness. One of the main origins of losses here is through the enlarged pipes. In this work, triple-pipes are proposed to be used instead of twin-pipes to have individual domestic hot water and space heating pipes, reducing the size of heat pumps and decreasing thermal loss rates. The proposed concept is designed, sized and thermodynamically analyzed for a case study in Denmark. The performance is compared with the previous version of this concept as well as the low-temperature district heating system, which is another important competitor to the proposed solution. The results prove that the proposed system outperforms both of the competitors in terms of energy efficiency. For three consecutive days in typical warm/moderate/cold weather in the case study, the proposed solution results in the rates of heat loss of 4.5/10.9/16.5%, respectively. The heat loss rates, for the conventional configuration and the low-temperature design, are 4.9/13.8/19.6% and 5.6/17.8/33.1%, respectively.

    更新日期:2020-01-06
  • Influences of test method and loading history on permeability of tight reservoir rocks
    Energy (IF 5.537) Pub Date : 2020-01-06
    Decheng Zhang; P.G. Ranjith; M.S.A. Perera; C.P. Zhang

    Steady-state and unsteady-state (downstream pressure build-up) gas permeability tests were conducted on low permeability siltstone at a series of upstream pressures during the loading and unloading processes. The characteristics of downstream pressure build-up curves are analysed in detail, and the permeability is calculated based on the data in the stabilization stage. Analysing approaches with and without consideration of the sample pore volume are used to obtain the unsteady-state permeability for both the real pressure and the pseudo pressure. Findings suggest that the permeability based on the pseudo pressure is generally lower than that based on the real pressure, with their ratio ranging from 0.75 to 0.98. The sample pore volume corrected permeability is 1.42–1.51 times of that without the consideration of sample pore volume. The apparent steady-state gas permeability is higher than the sample pore volume corrected permeability due to slip flow, while its intrinsic permeability is lower as the pore pressure is smaller in the steady-state test. The permeabilities decrease with the confining pressure in the loading path especially at lower confinements, while only part of the reductions is recovered during the unloading process. Increase of pore pressure enhances permeability under low confinement conditions. Water permeability is lower than gas permeability in steady-state test due to the water-rock interaction and the residual gas inside the sample.

    更新日期:2020-01-06
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