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  • Numerical simulation for nonlinear radiated Eyring-Powell nanofluid considering magnetic dipole and activation energy
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-17
    M. Waqas; Shagufta Jabeen; T. Hayat; S.A. Shehzad; A. Alsaedi

    The boundary-driven magnetized flow of non-Newtonian nanofluids have several applications in the processing and manufacturing of electronic devices, medicine and medical equipments, glass fiber, paper production, polymer sheets and filaments. Due to all such potential implications, we characterized the Powell-Eyring fluid over a stretching surface in the regime of magnetic dipole. Rheological flows with heat transfer have superficial roles in the modern industries. We evaluated the transportation of heat under nonlinear thermal radiation. Convective heat condition is taken into account. Furthermore, the Brownian and thermophoresis aspects of nanofluid with activation energy are explored. Appropriate transformations are implemented to convert the nonlinear system of partial differential expressions into system of ordinary differential ones. The governing dimensionless equations are solved by shooting scheme. The outcomes of sundry variables are demonstrated through graphs and numerical benchmarks.

    更新日期:2020-01-21
  • CVFEM simulation for Fe3O4-H2O nanofluid in an annulus between two triangular enclosures subjected to magnetic field and thermal radiation
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-18
    A.S. Dogonchi; Zeeshan Asghar; M. Waqas

    Here CVFEM is accounted for modeling natural convectived Fe3O4 − H2O nanomaterial flow in an annulus between two triangular enclosures. Flow analysis subjected to magneto-hydrodynamics has been elaborated. Heat transportation characteristics are described under radiation and heat source/sink aspects. Influences of effective variables for instance, Rayleigh number, heat (source,sink) factor, radiation factor, Hartmann number, aspect ratio, nano-particles shape factor and nanoliquid volume fraction versus heat transportation and flow fields have been scrutinized. Besides, a relationship describing average Nusselt number is introduced.

    更新日期:2020-01-21
  • Thermal-hydraulic analysis for alumina/water nanofluid inside a mini-channel heat sink with latent heat cooling ceiling-An experimental study
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-20
    C.J. Ho; Yu-Jie Hsieh; Saman Rashidi; Yasin Orooji; Wei-Mon Yan

    In this paper, an experimental investigation is carried out to evaluate the heat dissipation performance of the parallel mini-channel heat sink with the latent heat cooling ceiling. The heat sink is under the influence of an isothermal heating from the below. To enhance the cooling capacity of the system, the alumina/water nanofluid with various mass fractions of nanoparticles is considered as the working fluid. A micro-encapsulated phase change material layer is installed on the ceiling of the heat sink to cool down the fluid along the length of the heat sink. The experiments are performed for different values of mass fraction of nanoparticles, Reynolds number, mean temperature of bottom wall, inlet temperature of fluid, and mean temperature of cooling upper plate. The effects of these parameters on the friction factor, the mean Nusselt numbers dependent on the inlet and bulk temperatures difference, and the coefficient of performance are investigated. The experimental results indicate that the inlet temperature of the nanofluid has negligible effects on the friction factor for the base fluid Reynolds numbers of 483 and 968. However, the friction factor decreases as the inlet temperature increases for the base fluid Reynolds number of 161. The mean Nusselt numbers dependent on the inlet and bulk temperatures difference decrease by using a working fluid with the higher inlet temperature. The coefficient of performance increases with increasing the mean temperature of bottom wall from 50 °C to 55 °C. Finally, the mean temperature of cooling upper plate has negligible influences on the coefficient of performance.

    更新日期:2020-01-21
  • Heat transfer and convection of evaporating sessile droplets in transition from superhydrophilic to superhydrophobic structured wall: Optimization of functional properties
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-13
    S.Y. Misyura

    The free convection and heat transfer of evaporating water droplets on a textured wall have been studied. The analysis of the influence of micro- and macrotextures on the heat transfer coefficient has been performed. Structured surfaces were created by two different methods: mechanical surface treatment and laser exposure. The behavior of heat transfer on a structured wall was compared with that on a smooth surface. The wettability of the wall varied over a wide range of contact angles (the transition from a superhydrophilic to a superhydrophobic surface was considered). Simple relations have been obtained to estimate the separate influence of several key factors (the drop height, the surface area of the wetted spot of the drop, the convection velocity in the liquid and the temperature difference in the drop). The obtained data are important for designing heat exchangers with structured walls and for optimizing the functional properties.

    更新日期:2020-01-13
  • Experimental evaluation of the melting behaviours of paraffin within a hemicylindrical storage cell
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-10
    Nabeel S. Dhaidan; Abbas F. Khalaf

    Phase change materials (PCM) have been widely used as latent energy storage media due to their useful high energy density with small storage volume at nearly constant temperatures throughout solidification and melting. In this paper, experimental evaluation of the melting of a paraffin wax (RT58) PCM inside a hemicylindrical storage cell is outlined. The cell is heated on its straight vertical wall by means of flowing hot water, while the curved side of the cell is thermally insulated. The temperatures of the PCM at various locations are measured using thermocouples, while a digital camera is used to visualise the melting process. A set of experiments is performed to examine the influence of variation of hot water temperature on various melting characteristics including the temperature field of the PCM, the progress of the melting front, the melt fraction, the stored energy, and the Nusselt number. The experimental findings reveal that increasing hot water temperature leads to a reduction of melting time and increases in the stored energy and the Nusselt number. The melting process is expedited by 15.4 and 16.5% when the temperature of hot water increases from 80 °C to 85 °C, and from 85 °C to 90 °C, respectively.

    更新日期:2020-01-11
  • An experimental investigation on natural convection of non-covalently functionalized MWCNTs nanofluids: Effects of aspect ratio and inclination angle
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-08
    Asma Samadzadeh; Saeed Zeinali Heris; Ishak Hashim; Omid Mahian

    An experimental analysis was conducted to study natural convection heat transfer of water-based nanofluids. Two enclosures with the length × width × height(cm) dimensions of 10 × 10 × 10 and 20 × 10 × 10 and the inclination slopes of 0, 45 and 90° were considered. One of the walls was cooled and the opposite wall was heated. Multi-walled carbon nanotube (MWCNT)/water nanofluids were used as the heat transfer fluid while the MWCNTs were non-covalently functionalized by gum Arabic (GA). The MWCNT-GA/water nanofluids were prepared using 0.005, 0.05 and 0.1 wt% nanoparticles. According to the results, adding MWCNTs to water reduced free convection heat transfer in both enclosures. The effect of increasing MWCNT concentration on Nusselt number was found to be greater than the impact of changing Rayleigh number. Furthermore, free convection heat transfer increased with reducing inclination angle from 90° to 0° at high Rayleigh numbers. It was noticed that changing inclination angle has no considerable influence on Nusselt number at lower Rayleigh numbers. Moreover, free convection heat transfer increased about 8.77% with increasing the aspect ratio from 1 to 2. The highest reduction of Nusselt number was attributed to a system with the aspect ratio, concentration and inclination angle of 1, 0.1 wt% and 90°, respectively.

    更新日期:2020-01-09
  • Study of conjugate heat transfer from the impingement of an inclined free slot jet onto the moving hot surface
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-08
    Shashikant Pawar; Devendra Kumar Patel

    A dimensionless numerical investigation of turbulent flow and heat transfer characteristics due to the impingement of a free inclined slot jet onto the moving hot surface has been performed using the k − ω turbulence model. The parameters considered for the investigation are: the Reynolds number, impingement angle and plate velocity. The influence of parameters on the properties such as the pressure and velocity profiles, skin-friction coefficients, Nusselt number, interface temperature, and the location of stagnation has been presented. The displacement of stagnation point depends primarily on ϕ, whereas the effect of plate velocity is less significant. These relocations are found in between X = − 2 to 0. The effect of plate velocity on average skin-friction coefficient is continuously decreasing with increase in jet angle. A continuous increase in average Nu has been found with increase in Re for all values of ϕ and Up considered in the present study. It is revealed that the change in plate velocity has more influence on the average Nu for lower angles of impingement. Further reduction in the impingement angle shows an adverse effect on the average Nu. Correlations have been developed for Nusselt number at different zones based on the parameters considered for the study.

    更新日期:2020-01-08
  • Numerical approach for modeling fractal mobile/immobile transport model in porous and fractured media
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-08
    O. Nikan; J.A. Tenreiro Machado; A. Golbabai; T. Nikazad

    The fractal mobile/immobile model of the solute transport is based on the assumption that the waiting times in the immobile region follow a power-law, and this leads to the application of fractional time derivatives. The model covers a wide family of systems that include heat diffusion and ocean acoustic propagation. This paper develops an efficient computational technique, stemming from the radial basis function-generated finite difference (RBF-FD), to solve the fractal mobile-immobile transport model (FMTM). The time fractional derivative of the FMTM is discretized via the shifted Grünwald-Letnikov formula with second-order accuracy. On the other hand, the spatial derivative is approximated using the local RBF-FD method. The main benefit of the local collocation technique is that we only need to consider discretization points present in each of the sub-domains around the collocation point. The stability and convergence analysis of the proposed method are proven via the energy method in the L2 space. The numerical results for the FMTM on regular and irregular domains confirm the theoretical formulation and efficiency of the proposed scheme.

    更新日期:2020-01-08
  • Influence analysis of thermophysical properties on temperature profiles on the breast skin surface
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-08
    Alisson A.A. Figueiredo; Henrique C. Fernandes; Fernando C. Malheiros; Gilmar Guimaraes

    This work presents a simplified approach for the early detection of breast cancer using thermographic images, showing that several thermophysical properties of the bio-thermal problem does not need to be previously known to locate the geometric center of tumors. A 3D hemispheric breast model composed of different layers (muscle, gland, fat and skin) was constructed to evaluate the thermal behavior on the skin surface from numerical simulations using commercial software COMSOL. The effects of changes in depth, size, metabolism, blood perfusion and thermal conductivity of the tumor at surface temperatures were systematically analyzed to provide important information and guidelines for future medical diagnoses. Variations in blood perfusions and thermal conductivities of healthy tissue layers were also evaluated. It has been found that changing the size, metabolism, blood perfusion and thermal conductivity of a centralized tumor in the same coordinate does not modify the profiles of normalized temperature variations on the breast skin surface. Regarding the properties of healthy tissue, if a specific region of the breast surface is taken, there is the possibility that the normalized temperature profiles also do not depend on these properties. Thus, knowing that one of the main limitations in the estimation of tumors from thermographic images is related to the difficulty of previously knowing the thermophysical properties of human tissues, the results obtained in this study provide valuable simplifications for the early diagnosis of breast cancer using infrared thermography.

    更新日期:2020-01-08
  • Thermal analysis of tubular arrangements submitted to external flow using constructal theory
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-06
    V.A. Pedroti; C.C. de Escobar; E.D. dos Santos; J.A. Souza

    Present work performs a numerical study about the energy removal in a heated tubular array submitted to an external flow. Taking into account that a large variety of tubular arrangements can exists, in this work it is developed a tubular array that does not use any kind of initial predefined arrangement. Using the principles of Constructal Theory (or Law) and a positioning function dependent on the velocity and temperature fields, it is calculated, in a deterministic way, the location where each tube should be positioned. Pressure drop is not taken in to account in this first algorithm implementation as a performance indicator. In order to validate the proposed methodology, the Constructal Array is compared with standard aligned and staggered arrangements suggested in literature. The minimum distance between tubes (p) is considered as a degree of freedom. Four variations are studied: p = 1D, p = 1.25D, p = 1.5D and p = 2D, where D is the tube diameter. It is considered here the simulation of a transient, incompressible and laminar flow of a Newtonian fluid in a two-dimensional domain with forced convection and Prandtl number equal to 0.71. Results are computed when the flow reaches to the steady state condition. It is evaluated three values for Reynolds number: ReD = 10, 50 and 100. Thermal analysis of the formed patterns has shown that best thermal performance was not obtained with p = 1D, neither with p = 2D, i.e., tube distance has an influence on its formation and, consequently, on the heat transfer exchange. In all performed analyzes, Constructal arrays configuration showed higher energy removal (up to 71%) than the aligned and staggered arrangements, which highlights the capacity of proposed method. Constructal Array for p = 1.5D showed the most homogeneous distribution and proved to be the most effective in 4 of the six studied cases.

    更新日期:2020-01-07
  • Optimization of heating-cooling generators with porous components/cryogenic conductors on natural convection in a porous enclosure: Using different two-phase models and single-phase model and using different designs
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-06
    Pouya Barnoon; Davood Toghraie; Sara Rostami

    In the present study, the effect of the use of heating and cooling generators along with cryogenic conductors on flow and heat transfer characteristics in a porous chamber are investigated. The finite volume method (FVM) is used to simulate the phenomena. Single-phase and two-phase models (Mixture model and Eulerian-Eulerian model) have been used to predict heat transfer. Water-Copper oxide nanofluid is assumed to be Newtonian, incompressible, and steady. Several cases have been investigated in order to evaluate the heat transfer rate and streamlines visualization accurately. Investigations include a change in the number of heating and cooling generators, a change in the size of the cryogenic conductors, and the use of porous components as an alternative to cryogenic conductors. The volume fraction is assumed to be constant in the whole simulation and is 3%. The Rayleigh and Darcy numbers ranges are 104 ≤ Ra ≤ 107 and 10−2 ≤ Da ≤ 10−4, respectively. The Darcy-Forchheimer model is used for fluid flow and heat transfer in a porous medium. The results of this study are compared with the results of a regular enclosure that has been studied by many previous researchers. The findings show that the effect of using heating-cooling generators is favorable and that cryogenic conductors can also help to improve heat transfer. However, in some conditions using a regular porous enclosure yields better results. In addition, the difference in the results of single-phase and two-phase models depending on the operating conditions can be low or high. The goal is to achieve the highest heat transfer rate using the available tools. It is hoped that using the results of this research can be a useful guide to better understanding the phenomena and optimum and better designs.

    更新日期:2020-01-07
  • Entropy optimized dissipative flow of effective Prandtl number with melting heat transport and Joule heating
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-03
    T. Hayat; F. Shah; A. Alsaedi; B. Ahmad

    Melting heat in mixed convective magnetohydrodynamic flow of viscous material bounded by a stretchable plate is examined. Thermal expression consists of Joule heating and heat generation. Here (γAl2O3 − H2O and γAl2O3 − C2H6O2) nanofluids are analyzed. Boundary layer flows is determined for both Prandtl number and effective Prandtl number. Melting heat is accounted. Second law of thermodynamics is utilized to determine entropy generation. Entropy generation is minimized and discussed graphically through different parameters. Furthermore the drag forces and heat transfer rates have been examined through tabulated values.

    更新日期:2020-01-04
  • Assisting and opposing mixed convection with conjugate heat transfer in a differentially heated cavity filled with coarse-grained porous media
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-03
    Manu Chakkingal; Julia de Geus; Saša Kenjereš; Iman Ataei-Dadavi; M.J. Tummers; Chris R. Kleijn

    We report numerical simulations of assisting and opposing mixed convection in a side-heated, side-cooled cavity packed with relatively large solid spheres. The mixed convection is generated by imposing a movement on the isothermal vertical walls, either in or opposite to the direction of natural convection flow. For a fluid Prandtl number of 5.4 and fluid Rayleigh numbers of 106 and 107, we varied the modified Richardson number from 0.025 to 500. As in fluids-only mixed convection, we find that the mutual interaction between forced and natural convection, leading to a relative heat transfer enhancement in assisting - and a relative heat transfer suppression in opposing - mixed convection, is most prominent at a Richardson number of approximately one, when the Richardson number is modified with the Darcy number Da and the Forchheimer coefficient Cf = 0.1 as Rim = Ri × Da0.5/Cf. We focus on local flow and heat transfer variations in order to explain differences in local and average heat transfer between a coarse grained and fine grained (Darcy-type) porous medium, at equal porosity and permeability. We found that the ratio between the thermal boundary layer thickness at the isothermal walls and the average pore size plays an important role in the effect that the grain and pore size have on the heat transfer. When this ratio is relatively large, the thermal boundary layer is locally disturbed by the solid objects and these objects cause local velocities and flow recirculation perpendicular to the walls, resulting in significant differences in the wall-averaged heat transfer. The local nature of the interactions between flow and solid objects cannot be captured by a volume averaged approach, such as a Darcy model.

    更新日期:2020-01-04
  • Heat transfer enhancement through periodic flow area variations in microchannels
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2020-01-03
    Kai Xian Cheng; Zi Hao Foo; Kim Tiow Ooi

    In this study, annular microchannels with a microscale gap of 300 μm were implemented through the concentric superposition of two macro-sized cylinders. Flow area variations along the streamwise direction were created by introducing sinusoidal wave profiles on either the inner or outer wall of the annular gap while keeping the other wall flat. These variations introduced re-entrant effects along the flow direction. Numerical studies using the finite volume method were performed to elucidate the single-phase, steady-state thermal and hydrodynamic performances of the wavy channels, using water as the fluid medium, with an operating Reynolds number range of 800–2200. The predicted results were validated using the available measured data and classical correlations. This study demonstrated the viability of attaining enhanced heat transfer rates of up to 360% of the original straight channel through the inducement of flow area variations with single wavy-walled channels. Despite magnifications of the friction factors, the single wavy-walled channels attained a 120% increment in heat transfer coefficient when evaluated at the same pumping power. Overall, single-walled wavy passages were deemed suitable for heat exchanger designs demanding very high heat removal rates and efficiencies while the conventional serpentine channels were apt for moderately enhancing heat transfer while requiring low pumping power.

    更新日期:2020-01-04
  • Enhancing thermal-hydraulic performance of counter flow mini-channel heat sinks utilizing secondary flow: Numerical study with experimental validation
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-30
    Amitav Tikadar; Titan C. Paul; Saad K. Oudah; Nabeel M. Abdulrazzaq; Azzam S. Salman; Jamil A. Khan

    Continual growth of hydraulic and thermal boundary layers along stream wise direction in conventional straight fin mini-channel heat sink (MCHS) causes gradual deterioration of their thermal performance. To enhance thermal-hydraulic performance by breaking and re-development of the boundary layers, this research aims to introduce a novel water cooled inter-connected counter flow mini-channel sink (ICMCHS). Two inter-connectors (ICs) were positioned transversely between two counter flow mini-channels (CMCs) which segmented the flow domain into three zones (zone 1–3). Secondary flow was generated through the ICs utilizing the pressure difference of the adjacent CMCs resulting in disruption of the hydraulic and thermal boundary layers. To examine the effect of the ICs location and width on the thermal-hydraulic characteristics of the counter flow mini-channel heat sink (CMCHS), the present numerical studies were carried out for nine different cases (case 1–9) by varying ICs width from 1 mm to 1.5 mm and ICs location from 4 mm to 9 mm. A corresponding conventional CMCHS was chosen as the base case in contrast to the newly proposed ICMCHS. Experiments were also carried out for CMCHS to validate numerical results, and excellent agreement was found between measured values and the corresponding numerical results. At the lowest considered Re (Re = 150), a maximum value of Performance Evaluation Criterion (PEC) was achieved to ~1.22 for the highest length of zone 1 and 3 and the lowest ICs width (case 7), whereas at the highest Re (Re = 1044), the maximum PEC value (~1.42) was recorded for the intermediate length of zone 1 and 3 and the highest ICs width (case 6).

    更新日期:2019-12-30
  • PTFE-modified porous surface: Eliminating boiling hysteresis
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-25
    Ya-Qiao Wang; Jia-Li Luo; Yi Heng; Dong-Chuan Mo; Shu-Shen Lyu

    Boiling hysteresis is a side effect that usually occurs with overshot temperature before steady boiling, often noted as a start-up problem. This phenomenon tends to emerge when porous surfaces are used to enhance boiling heat transfer performance. It is important to reduce or eliminate hysteresis before various micro−/nanoporous surfaces can be deemed acceptable in the thermal management industry. In this study, a two-layer composite surface (TLCS) with a copper forest structure at the bottom and micro-nano biporous structure at the top showed good enhancement at a heat transfer coefficient of 340% and critical heat flux of 67% compared to a plain copper surface with water as the working fluid at atmosphere. However, boiling hysteresis occurred on TLCS; the highest wall superheat temperature difference between steady boiling and the start-up process was approximately 13.5 K at 140 W cm−2. When TLCS was modified with Polytetrafluoroethylene (PTFE), the temperature difference at the same heat flux was less than 0.5 K, demonstrating that the boiling hysteresis phenomenon was successfully eliminated.

    更新日期:2019-12-26
  • Numerical investigation of total entropy generation in a rectangular channel with staggered semi-porous fins
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-14
    Mohammad Amniyeh Vatanparast; Siamak Hossainpour; Alireza Keyhani-Asl; Sadra Forouzi

    A numerical investigation was performed to study total entropy generation due to forced convection inside the partially heated channel with staggered semi-porous fins. A finite volume code has been utilized to solve the governing equations which are based on the volume-averaging method. Results declared that increasing Reynolds number to Re = 100 comes up with about 44% more total entropy generation compared to Re = 50. At particular semi-porous fin percentage (SFP = 40) generation of total entropy encounters a minimum point, which is identical for all Reynolds numbers. Utilizing semi-porous fins with Darcy number below 10−4 has not any noticeable effect on total entropy generation through various SFPs, but at higher Darcy number such as Da = 10−2, total entropy generation decreases almost 14% compared to Da = 10−8. Also, there is a minimum point for total entropy generation for Da ≥ 10−4, which is different for each Darcy number and the minimum point moves toward higher SFP values as the Darcy number increases. In addition, applying higher Ke and increasing fins' length or width results in more total entropy generation.

    更新日期:2019-12-26
  • Entropy generation minimization: Darcy-Forchheimer nanofluid flow due to curved stretching sheet with partial slip
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-14
    Tasawar Hayat; Sumaira Qayyum; Ahmed Alsaedi; Bashir Ahmad

    This paper explores the Darcy-Forchheimer two-dimensional flow of nanofluid due to curved stretching sheet. Brownian motion and thermophoresis effects are taken in to account. Bejan number and entropy generation are analyzed in presence of MHD, convective boundary conditions, partial slip and viscous dissipation. Nonlinear ordinary differential systems are developed through transformations. Convergent series solutions are constructed by using NDSolve of MATHEMATICA. Behavior of involved variables on flow characteristics is shown through graphs. Velocity reduces for higher slip parameter and Forchheimer number. Temperature and concentration have direct relation with thermal and solutal Biot numbers. An increase in entropy generation is seen for higher curvature parameter, porosity parameter and Brinkman number. Decrease in Bejan number is observed for higher estimations of Brinkman number and slip parameter. Comparative study of present results with previous information in a limiting sense is made.

    更新日期:2019-12-26
  • The stabilized lower-order and equal-order finite element methods for the hydrostatic Stokes problems
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-18
    Lingzhi Qian; Jinru Chen; Xinlong Feng

    In this paper, we propose a family of stabilized lower-order and equal-order finite elements(FE) schemes for the hydrostatic Stokes problems or primitive equations of the ocean. It is known that two “inf-sup” conditions appear associated to the two constraints of this problem: namely incompressibility and hydrostatic pressure. The focus of this paper is to develop the stabilized lower-order and equal-order(velocity-velocity)-pressure pairs for the hydrostatic Stokes problems. Then, the new schemes offer a number of attractive properties: avoiding extra “inf-sup” condition, achieving optimal accuracy with respect to the solution regularity and unconditional stability, implementing simply and straightforward. Finally, ample numerical experiments are presented supporting the excellent stability and accuracy of the newly proposed methods.

    更新日期:2019-12-26
  • A modified Fourier approach for analysis of nanofluid heat generation within a semi-circular enclosure subjected to MFD viscosity
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-20
    A.S. Dogonchi; M. Waqas; Seyyed Masoud Seyyedi; M. Hashemi-Tilehnoee; D.D. Ganji

    In this study, the heat transfer behavior in a semi-circular cavity filled with Fe3O4-H2O nanofluid is analyzed using the modified Fourier formula. MFD (magnetic field dependent) viscosity is considered for ferrofluid viscosity. The salient features elaborating transportation of heat namely the heat sink/source aspect is accounted. The control volume finite element method (CVFEM) is employed for numerical computations of the nonlinear system. The effects of different parameters such as Hartmann number, heat source/sink parameter, thermal relaxation parameter, Rayleigh number, nanoparticles volume fraction and shape factor on heat transfer and fluid flow properties are investigated. Based on the active parameters of the study, a correlation was obtained for the average Nusselt number. According to the results, the average Nusselt number is proportional to nanoparticles volume fraction, thermal relaxation factor, and Rayleigh number. The results also indicate that the magnetic field can be applied as a regulatory factor to the system. It is also concluded that the spherical shape nanoparticles provide lesser heat exchange while the platelet nanoparticles shape represents better heat exchange.

    更新日期:2019-12-26
  • Accelerating phase-field modeling of solidification with a parallel adaptive computational domain approach
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-20
    Peng Ding; Zhe Liu

    We developed a parallel adaptive computational domain method for accelerating the simulation of solidification in two dimensions using the phase-field model. The algorithm is paralled with the MPI library based on the domain decomposition approach. We discuss the implementation details of the parallel adaptive computational domain method and the domain decomposition based strongly implicit linear solver. We examined the performance of our algorithm by comparing with the algorithm based on the fixed computational domain and show that it greatly reduces the computational cost of solving the phase-field model. We also simulate the competitive growth process of the second and ternary dendritic arms successfully.

    更新日期:2019-12-26
  • Development of a new correlation to determine the viscosity of ternary hybrid nanofluid
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-19
    Rashmi Rekha Sahoo; Vikash Kumar

    In this study, the experimental investigation on the effects of temperature and concentrations of nanoparticles on the dynamic viscosity of water-based Al2O3-CuO-TiO2 ternary hybrid nanofluid has been presented. The experiments were performed in the solid vol. fraction range of 0.01–0.1%, and temperature range of 35°C to 50 °C. Furthermore, the SEM image, together with an EDX analysis of 0.05% vol. fraction ternary hybrid nanofluid has been investigated. Experimental results revealed that the dynamic viscosity enhances with an increase in the solid vol. fractions and decreases with increasing temperature. However, the maximum enhancement of dynamic viscosity of 55.41% and 17.25% has been observed for 0.1% vol. fraction of ternary hybrid nanofluid compared to water-based Al2O3-TiO2 and Al2O3-CuO hybrid nanofluids, respectively, at a temperature of 45 °C. Due to the increase in the interior resistance of fluid and ternary hybrid, nanofluids have a weaker result on the viscosity. Also, with an increment of the temperature from 35 °C to 45 °C, a 23.64% decrement in dynamic viscosity is observed for ternary hybrid nanofluid. Finally, an accurate correlation with a maximum deviation of 1.5% has been proposed to predict the dynamic viscosity of Al2O3-CuO-TiO2/water ternary hybrid nanofluid.

    更新日期:2019-12-26
  • Compressible Fanno flows in micro-channels: An enhanced quasi-2D numerical model for turbulent flows
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-20
    Marco Cavazzuti; Mauro A. Corticelli; Tassos G. Karayiannis

    Fanno theory provides an analytical model for one-dimensional confined viscous compressible flows. The model holds under the assumptions of adiabatic flow and constant cross-section channel. From theory, the differential of every flow-related quantity is expressed as a function of Mach number and friction factor. One-dimensional flow numerical models can be derived by discretizing Fanno equations. However, theory does not assess how to evaluate friction, while the model works properly only if friction is estimated correctly. Compressibility and turbulence act by deforming the velocity profile making it flatter. Assuming the friction factor function of the Reynolds number alone, in line with incompressible flow theory, is thus not correct. Better correlations should include the Mach number to address compressibility effects. Here, the impact of turbulence and compressibility on the velocity profiles in a micro-channel is analysed by means of CFD simulations. Friction factor correlations are deduced for turbulent micro-flows. The impact of the velocity profile on other quantities, such as dynamic pressure and bulk temperature, needed for the numerical model operation, is also evaluated. Additional correlations for these quantities overcome the instrinsic limits of the one-dimensional model, necessarily unaware of local velocity profiles, in a quasi-2D fashion significantly improving its predicting capabilities.

    更新日期:2019-12-26
  • Application of graphene oxide IoNanofluid as a superior heat transfer fluid in concentrated solar power plants
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-23
    Armin Hosseinghorbani; Mehrdad Mozaffarian; Gholamreza Pazuki

    This study presents the fabrication of a highly stable Ionic liquid nanofluid (IoNanofluid) without any surfactant application by dispersing 0.5%, 1% and 2% mass fractions of functionalized graphene oxide (GO) nanoparticles in 1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2]). Various analyses were employed to investigate the chemical structure and morphology of the synthesized nanoparticles. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) results were taken into account to assess the stability of IoNanofluid. Thermophysical properties of the IoNanofluid including density, viscosity, thermal conductivity and specific heat capacity were measured experimentally, and compared with the base fluid's experimental data. The results showed the dramatic improvement of thermal conductivity and specific heat capacity of up to 6.5% and 27%, respectively. Therefore, application of the prepared IoNanofluid in concentrated solar power (CSP) plants as heat transfer fluid (HTF) could lead to enhancement of the overall efficiency of the system. Accordingly, in order to estimate the heat transfer performance of IoNanofluid, Dittus-Boelter, the correlation commonly used for turbulent flow was applied. Compared to the base fluid, the maximum heat transfer coefficient enhancement was 7.2% via application of 0.5% mass fraction of GO nanoparticles. Thus, it seems that GO IoNanofluid at low mass fractions has desirable advantages for using as HTF in CSP plants.

    更新日期:2019-12-26
  • Mass and heat transfer control in the GMAW process utilizing feedback linearization and sliding mode observer
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-23
    Saeed Soltani; Mohammad Eghtesad; Yousef Bazargan-Lari

    Controlling the gas metal arc welding (GMAW) process is investigated utilizing feedback linearization with heat input, detaching droplet diameter and melting rate as controlled variables while accounting for actuator saturation. The control algorithm is employed using a state space model with eight dynamic states. Stability and internal dynamics of the process are studied thoroughly. Sliding mode state observers are implemented to determine the arc current and contact tip to work piece distance as well as the stick out length (which constitute the internal states of the system). Several simulation reports are provided to demonstrate successful regulation and tracking of detaching droplet diameter, heat input rate and melting rate. Finally, simulations indicate that the method is capable of overcoming parametric uncertainty.

    更新日期:2019-12-26
  • Heat transfer from a non-isothermal rotating rough disk subjected to forced flow
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-24
    Muhammad Usman; Ahmer Mehmood; Bernhard Weigand

    This communication aims to report heat transfer characteristics from a non-isothermal wavy disk rotating in a forced flow. The primary objective of this kind of studies is to seek a suitable mechanism for the quick removal of heat energy from a rotating disk surface. The achievement of an efficient mechanism which ensures a further higher rate of heat transfer is a fundamental goal in such studies. In this regard active and passive techniques are of fundamental importance whereby the current study utilizes a combination of both. There are three key elements, namely, the non-uniform disk temperature; surface roughness, and a radial free flow, which are responsible for the augmentation of the heat transfer. The analysis has been carried out for a variety of fluids depicting the increased rate of heat transfer due to a variation of these different elements. In doing so, the local and global heat transfer rates are manipulated in order to obtain a clear picture of the heat transfer process at a corrugated disk. The considered rough non-isothermal disk (with two sinusoids) rotating in the uniform stream of air (Pr = 0.71) leads to a significant (about 263%) enhancement in the overall heat transfer rate compared to that of a flat free rotating disk having surface temperature as quatratic function of the radial coordinate. Moreover, some threshold values (which correspond to seizing the heat transfer process) of the used power-index of the disk temperature (Tw − T∞ = c0rn∗) are also identified which are observed to vary slightly due to the surface irregularities and the relative motion of fluid and disk.

    更新日期:2019-12-25
  • Numerical simulation of aggregation effect on nanofluids thermal conductivity using the lattice Boltzmann method
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-24
    Hamed Tahmooressi; Alibakhsh Kasaeian; Ali Tarokh; Roya Rezaei; Mina Hoorfar

    The standard enhancement in nanofluids thermal conductivity due to the addition of nanoparticles is well understood. Despite this, the reason behind observed anomalous increases is still controversial. Limitations in nano-scale experimental observations would make it even harder to approach into this topic. To address this issue, researchers have proposed many different macroscopic (continuum-based)/microscopic (molecular scale) numerical schemes as an alternative for experimental investigations. However, the overall thermal effect of suspended nano-scale particles cannot be observed in neither macroscopic nor microscopic scale due to collective interrelated behaviors such as nanoparticles aggregation. In this paper, a mesoscopic approach, Lattice Boltzmann method (LBM), aims to consider microscopic phenomena in a broader context (mesoscopic scale), been implemented to investigate the nanoparticles aggregation as a probable working mechanism behind the anomalous increase in nanofluids thermal conductivity. The stochastic and dynamic nature of nanoparticles aggregation is captured through generation of fractal random microstructures. The effects of size, shape and distribution regime of aggregates are studied and optimum values are calculated. The results indicate that the aggregation can anomalously enhance nanofluids effective thermal conductivity (ETC). The LBM results are found to be in great agreement with the available numerical/experimental data in the literature.

    更新日期:2019-12-25
  • Optimization of the interface heat transfer coefficient model based on the dynamic thermo-physical parameters in the pressure-temperature coupled field
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-10
    T. Chang, C.M. Zou, H.W. Wang, Z.J. Wei, X.J. Zhang

    Based on the inverse method, the dynamic thermo-physical parameters of the sand mold in the pressure-temperature coupled field were used for calculation. The optimized inverse method model of interface heat transfer coefficient (IHTC), which combined with the three-layer Dufort-Frankel difference equation, was developed to reveal the effects of pressure on IHTC. The results showed that the IHTC was the maximum at the beginning due to high heat flux at the interface under the influence of pressure, then a rapid reduction on account of the forming of air gap and variation of thermo-physical parameters, then slowly stabilize. Compared with the classical inverse model using the static thermo-physical parameters, the accuracy of the calculated temperature field obtained by the optimized inverse model was improved by 18% at most.

    更新日期:2019-12-11
  • Non-Newtonian behavior of an electrical and magnetizable phase change material in a filled enclosure in the presence of a non-uniform magnetic field
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-09
    Mohammad Ghalambaz, Seyed Mohsen Hashem Zadeh, S.A.M. Mehryan, Kasra Ayoubi Ayoubloo, Nima Sedaghatizadeh

    This work aims to study the non-Newtonian behavior of a magneto- and ferro-hydrodynamic phase change material (PCM) inside a differentially heated enclosure. The enclosure is occupied with a Power-law non-Newtonian PCM, and a non-uniform magnetic field is imposed on the adjacent hot wall. The left and right of the enclosure are subjected to the high and cold temperatures, and the top and bottom of the enclosure are insulated. A deformed mesh technique along with the Stephan condition is applied to track the interface of the solid and molten regions. The impacts of the alterable parameters including the Rayleigh number (104 < Ra < 106), the Power-law index (0.7 < n < 1), the Hartman number (0 < Ha < 250) and the magnetic parameter (0 < Mnf < 7000) on the melting front, normalized melt volume fraction (NMVF), and the Nusselt number are studied. The simulation shows that a decrease in the Power-law index can significantly increase the melting rate. In addition to this, results show that augmentation of the Hartman number and magnetic parameter weakens and enhances the NMVF, respectively.

    更新日期:2019-12-11
  • Effect of nonhomogeneous nanofluid model on transient natural convection in a non-Darcy porous cavity containing an inner solid body
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-10
    Ammar I. Alsabery, Muneer A. Ismael, Ali J. Chamkha, Ishak Hashim

    Transient natural convection of an alumina-water nanofluid saturated in non-Darcy porous media is investigated in this paper. The domain of the nanofluid is an annulus composed from a square cavity confining a solid conductive body. The nanoparticles are assumed to be slipping in the base fluid according to Buongiorno model. The Brinkman-Forchheimer-extended Darcy formulation has been adopted for the porous medium. The dimensionless governing equations are solved by implementing the finite difference method. In this study, a special focus is given on the following model parameters; porosity of the porous medium, Darcy number and the nanoparticles average volume fraction. The results show that the nanoparticles possess high uniformity in the base fluid and the Nusselt number augments with increasing values of the Darcy number. The porosity increases the average Nusselt number at a higher Darcy number while its influence remains negligible at a low Darcy number. For the given porosity, there is a critical value of the nanoparticles volume fraction when the average Nusselt number is maximal.

    更新日期:2019-12-11
  • Established prediction models of thermal conductivity of hybrid nanofluids based on artificial neural network (ANN) models in waste heat system
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-10
    Jiang Wang, Yuling Zhai, Peitao Yao, Mingyan Ma, Hua Wang

    The properties of water (W)/ethylene glycol (EG) mixtures vary significantly with the proportion of EG and temperature, so it is suitable to use such fluids as exchange heat mediums in a waste heat system with temperature fluctuations. The experiments were conducted with 1.0 wt% Cu/Al2O3- EG/W hybrid nanofluids at temperatures ranging from 20 to 50 °C, where the base fluid (EG/W) mixture ratio was varied from 20:80 to 80:20. To search individuals which contain optimal weights and thresholds, a genetic algorithm (GA) and a mind evolutionary algorithm (MEA) coupled with a back-propagation neural network (GA-BPNN and MEA-BPNN, respectively) were used to improve the accuracy in the predicted thermal conductivity. The results show that the thermal conductivity increases nonlinearly with the ratio of water to ethylene glycol and temperature, due to the higher thermal conductivity of water and stronger collision frequency between molecular and nanoparticles. Binary Polynomial Regression (BPR) was fit with (coefficient of determination) R2 = 0.9984 as functions of temperature and mixture ratio. Comparisons of the prediction performance and capability of BPR, the performance of R2 increases by 0.11% and 0.13% for GA-BPNN and MEA-BPNN. It indicates that the combined BPNNs both predicate more accurately, particularly MEA-BPNN has the highest prediction accuracy.

    更新日期:2019-12-11
  • Transient thermo-hydraulics and performance characteristics of single-phase natural circulation loop using hybrid nanofluids
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-09
    Mayaram Sahu, Jahar Sarkar, Laltu Chandra

    Transient analysis of vertical heating and horizontal cooling rectangular single-phase natural circulation loop with various water-based hybrid nanofluids (Al2O3 + Ag, Al2O3 + Cu, Al2O3 + TiO2, Al2O3 + CNT, Al2O3 + Graphene) with 1% volumetric concentration is studied numerically. Temporal fluctuation and time required to attain the steady-state, transient mass flow rate and energy-exergy performance parameters (effectiveness and total entropy generation) using hybrid nanofluids are compared with water. The effect of power input and geometry parameter (diameter and height) of the loop on transient performances is studied as well. The result reveals that the fluctuation of mass flow rate and time required to attain the steady-state are less for hybrid nanofluids as compared to water. However, platelet and cylindrical shaped nanoparticles yield a lower stability as compared to spherical shaped. The mass flow rate is enhanced with hybrid nanofluids, except Al2O3 + CNT and Al2O3 + Graphene, as compared to water. The energy-exergy performance of hybrid nanofluids is higher than water. The maximum increment in mass flow rate is shown by Al2O3 + Ag hybrid nanofluid (3%), whereas Al2O3 + Graphene shows the highest increment in effectiveness (25.4%) and highest decrement in total entropy generation (14.3%) as compared to water. Smaller diameter and lower height of loop are found preferable for the flow stability.

    更新日期:2019-12-09
  • Effect of twisted-tape inserts and nanofluid on flow field and heat transfer characteristics in a tube
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-09
    Wei He, Davood Toghraie, Amin Lotfipour, Farzad Pourfattah, Arash Karimipour, Masoud Afrand

    In the present study, the flow and heat transfer of CuO-water nanofluid in different solid concentrations (1–4 vol%) in a tube have been simulated by using the single- and two-phase (mixture) models. The simulations have been conducted under the turbulent flow regime in different Reynolds numbers ranging from 3000 to 36,000. The effects of using CuO-water nanofluid on the Nusselt number, friction factor, and performance evaluation criterion have been investigated. It is found that employing the two-phase mixture model leads to having closer results in reality compared to the single-phase model. The results revealed that the maximum performance efficiency coefficient in the tube with one twisted tape is 2.18 (for the two-phase model, Re = 36,000 and φ = 4%), while for a tube with two twisted tapes under the same conditions, it is 2.04. Thus, the use of one twisted tape is more favorable from the thermal-fluid dynamics viewpoint.

    更新日期:2019-12-09
  • An extended weighted-sum-of-gray-gases model to account for all CO2 ‐ H2O molar fraction ratios in thermal radiation
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-09
    Hadi Bordbar, Guilherme C. Fraga, Simo Hostikka

    All published weighted sum of gray gases models (WSGGM) were either developed for a limited number of molar fraction ratios, MR, or include MR as a variable in their formulations. Either way, they are not able to adequately support moisture-rich regions of combustion environments, such as the outer regions of unwanted fires, fires during water-based suppression, and some air-injection regions of furnaces. In this article, we provide an extension to a previously published WSGGM by coupling it to a new accurate set of WSGGM coefficients for pure carbon dioxide and water vapor. The coupling follows a linear interpolation methodology, which is justified by a detailed analysis of the line-by-line (LBL) absorption spectra and by plotting the total emissivity of CO2 ‐ H2O mixtures with large and small values of MR for various temperatures and path lengths. The proposed model is discussed and validated in four benchmarks, using a solution obtained by LBL integration as reference. The results indicate that, while the previously available WSGGMs either have excessive computational costs or yield inaccurate results in the regions of large MR, the new model can be safely used for all gas compositions in a computationally efficient manner.

    更新日期:2019-12-09
  • Natural convection heat transfer from horizontal annular finned tubes based on modified Rayleigh Number
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-06
    H. Nemati, M. Moradaghay, S.A. Shekoohi, M.A. Moghimi, J.P. Meyer

    The modification of the Rayleigh number, Ra, has been studied in the past. These studies have shown that the physical interpretation of the modified Rayleigh number which is commonly used is questionable. Moreover, although most of the available correlations work well, their behaviours in extremes (low or high Ra) are not correct where only a few correlations are available in low Ra. Therefore, a numerical simulation of heat transfer from annular circular finned tubes was conducted to present a comprehensive correlation for the modified Rayleigh number. As shown in this study, the flow forms a circular path around the tube. Based on this fact, a new modified Rayleigh number definition and correlation are proposed, which are valid for Nusselt numbers from 1 to 20,000. This range of Ra provides a complete picture of natural convection over circular annular finned tubes, especially at relatively low Ra. Finally, the end behaviours of the proposed correlation were compared with those of existing correlations.

    更新日期:2019-12-07
  • Experimental study of evapowration and crystallization of brine droplets under different temperatures and humidity levels
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-04
    Jie Qu, Luis Escobar, Jianzhi Li, Zhonghao Rao, Ben Xu

    The evaporation of brine droplets has critical impacts on the zero-liquid-discharge thermal desalination process. A good understanding of the evaporation of brine droplets provides guidelines for the design of thermal desalination systems, and offers insights for applications when solvent droplet evaporation processes are involved. In this study, brine droplets with different salt mass concentrations were placed in a chamber with controlled temperature and relative humidity. The evaporation and crystallization processes were then visualized through a high speed camera by employing the pendant droplet method. The results showed that the evaporation rate increases with the decrease of relative humidity, the increase of temperature, and the decrease of salt mass concentration. After the evaporation was finished, we can observe that the crystal grew along the filament during the evaporation and remained on it. A salt shell was formed at the outside, while the droplet still contained some amount of brine inside, when the evaporation rate was low. Consequently, the evaporation mechanism was changed once the salt shell was formed, the water molecules needed to overcome the pressure difference inside and outside the salt shell, and diffused through the shell for further evaporation. A multi-variable fitted quadratic regression model was developed with R2 = 0.974 to describe the relationship among the evaporation rate, mass concentration, relative humidity and temperature. Because the regression model was based on experimental data with temperature varying from 30 °C to 60 °C, a predicted result of brine droplet's evaporation rate with various mass concentrations under 75 °C and 0% RH showed a good agreement with the experiment data. Therefore the developed regression model can be extended for high temperature (<100 °C, no boiling) applications.

    更新日期:2019-12-05
  • Experimental study of temperature and mass fraction effects on thermal conductivity and dynamic viscosity of SiO2-oleic acid/liquid paraffin nanofluid
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-03
    Zhixiong Li, Sajad Asadi, Arash Karimipour, Ali Abdollahi, Iskander Tlili

    This paper presents the study of the influence of SiO2 nanoparticles, temperature and nanoparticles mass loads on the thermal conductivity of SiO2/liquid paraffin nanofluid in existence of oleic acid. Different temperatures and nano sized particles mass fractions ranging from 25 to 70 °C and 0.005% to 5%, respectively, were considered within the experimentations. The results clearly exhibited that the thermal conductivity of the nanofluid altered significantly with the temperature enhancement and by increasing in the mass fraction of the SiO2 nano sized particles in the basefluid, the thermal conductivity of the nanofluid raised. The empirical relation of the current research exhibits that for the relative thermal conductivity of SiO2-oleic acid/liquid paraffin nanofluid as parameters of nanoparticles mass fraction and temperature the extent of data deviation is lower than 10% and for that of the relative viscosity of the SiO2-oleic acid/liquid paraffin the data deviation is also <10%.

    更新日期:2019-12-04
  • 3D mixed convection MHD flow of GO- MoS2 hybrid nanoparticles in H2O– (CH2OH) 2 hybrid base fluid under effect of H2 bond
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-04
    S.S. Ghadikolaei, M. Gholinia

    In this achievement, the physical perspectives on 3D natural convection MHD flow of GO- MoS2 / Water (H2O)-Ethylene glycol (C2H6O2) (50:50 Vol%) hybrid nanofluid under the effect of thermal ray, shape and slip factors has been presented using Runge- Kutta Fehlberg 5th order (RKF-5) numerical procedure. The infiltration of diverse parameters for instance: suction/ injection parameters, thermal radiation, and nanoparticle shapes (Cylinders, Platelets, and Bricks), on velocity and temperature profiles are exemplified qualitatively through graphs. Outputs indicate that: Lorentz force created by augmenting magnetic square parameter (M) causes diminution in the velocity profile. The radiation parameter has used to breakdown hydrogen bonds of fluid molecules. Additionally, strong hydrogen bonding of hybrid nanofluid (GO- MoS2) causes a sharp increase in thermal conductivity and, consequently, increment in temperature profile (H2 bondHybrid‐phase > H2 bondNano‐phase). Increasing the shape factor has always increased temperature profile and heat transfer rate, so the number of hydrogen bonds also decreases.

    更新日期:2019-12-04
  • Thermal performance of phase change nano-emulsion in a rectangular minichannel with wall conduction effect
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-12-03
    C.J. Ho, Chao-Sheng Huang, Caiyan Qin, Wei-Mon Yan

    The minichannel heatsink is one of the small heat exchangers, having high heat capacity and being able to remove substantial heat within a very small volume, in line with the current demand for heat dissipation of electronic components. In the present study, the convection cooling characteristics in a rectangular minichannel considering wall conduction effect was investigated numerically. Numerical simulations are performed under 2% and 10% volume fractions of PCM particles (n-eicosan). The results reveal that the axial wall conduction plays a more pivotal role in the minichannels at the lower Reynolds number. Besides, the employment of phase change nano-emulsion in the working fluid in the rectangular minichannel suppresses the wall temperature and improves the heat transfer performance up to 4.23% and 9.36%, respectively, compared with the application of pure water. In addition, it is demonstrated that a high concentration of PCM particles may have detrimental effect on pressure drop and extended wall heat dissipation efficiency under certain circumstances thus the concentration of PCM particles needs careful selection.

    更新日期:2019-12-03
  • 更新日期:2019-11-30
  • Dynamism of magnetohydrodynamic cross nanofluid with particulars of entropy generation and gyrotactic motile microorganisms
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-29
    Rahila Naz, Mughira Noor, Tasawar Hayat, Maryiam Javed, Ahmed Alsaedi

    The current study presents the dynamics of entropy generation in magnetohydrodynamic Cross nanofluid containing gyrotactic microorganisms. The system of nonlinear coupled differential equations is acquired through boundary layer approximation and appropriate similarity transformations. The system of equations is solved using the Optimal Homotopy Analysis Method (OHAM). The impressions of several emergent parameters are obtained and presented graphically. Contour plots are conferred for entropy generation and the Bejan number to explore the dynamism of flow in detail. Numerically calculated values of heat flux, mass flux, and fluxes for the concentrations of nanoparticles and motile microorganisms are exhibited in tabular forms. It is remarkable to note that the concentration of nanoparticles can be enhanced by controlling the Brownian motion parameter whereas the process of entropy generation can be controlled through temperature difference parameter.

    更新日期:2019-11-30
  • Effects of diameter ratio and inclination angle on flow and heat transfer characteristics of sister holes film cooling
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-30
    Junfei Zhou, Xinjun Wang, Jun Li, Haikong Lu

    In order to investigate the flow and heat transfer characteristics of sister holes cooling method, sister holes cooling structures have been applied on a flat plate with four primary to sister hole diameter ratios and three inclination angles under three blowing ratios. Single cylindrical hole film cooling structure is also established as a benchmark structure. The numerical results of the single cylindrical hole case and one sister holes case are validated with the experimental results available in literatures. The tangential velocity vectors and total vorticity distributions are studied and compared. The spanwise averaged film cooling effectiveness and the adiabatic temperature contours are studied and compared. Results show that the development of the kidney vortex induced by primary hole is impeded by the sister hole induced kidney vortex and thus the film cooling performance is promoted. The blowing ratio and diameter ratio heavily affect the flow and heat transfer characteristics of sister holes cooling cases, the influence of the inclination angle is much smaller. In this paper, the best film cooling performance of sister holes cooling cases is obtained under the smallest diameter ratio.

    更新日期:2019-11-30
  • Effects of heterogeneous catalysis in porous media on nanofluid-based reactions
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-30
    Chunyan Liu, Mingyang Pan, Liancun Zheng, Ping Lin

    This paper studies a new type of homogeneous(HOM)-heterogeneous(HET) reactions in Al2O3-water-based nanofluid flowing through porous media over a stretching plate. Prior investigators have focused mainly on the catalytic effects on the plate, we model the influence of heterogeneous catalysis in porous media on these reactions. The HET reactions on the surfaces of porous media and plate are both governed by the first-order kinetics, while the HOM reaction in the fluid is given by the isothermal cubic autocatalytic kinetics. In addition, the thermal conductivity of four distinct shapes of nanoparticle, sphere, brick, cylinder, and platelet, is taken into consideration with the Hamilton-Crosser model. The obtained nonlinear differential systems simplified by using similarity transformations are numerically calculated by the bvp4c algorithm. Results demonstrate that the increase of interfacial area of porous media enhances the rate of surface-catalyzed reaction and therefore porous media can greatly shorten the chemical reaction time. Moreover, we find that platelet nanoparticles exhibit the highest convective heat transfer capacity.

    更新日期:2019-11-30
  • An ingenious fluidic capacitor for complete suppression of thermal fluctuations in two-phase microchannel heat sinks
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-28
    Durga Prasad Ghosh, Deepak Sharma, Anurag Kumar, Sandip Kumar Saha, Rishi Raj

    Rapid bubble growth within the confinement of microchannels leads to undesired flow oscillations. The flow regime cycles between single-phase, bubbly/slug, backflow, dryout, and rewetting regimes. The large difference between the heat transfer coefficient (HTC) in these regimes induces significant thermal fluctuations (≈ ± 5 ° C) and the overall HTC is low. The intensity of backflow and the time-span of dryout increases with heat flux. As a result, a gradual deterioration in HTC followed by a premature CHF is encountered. Here we introduce an ingenious pulse-dampener for complete mitigation of two-phase thermofluidic fluctuations in microchannel heat sinks. An inflatable latex bladder in the outlet manifold acts as a fluidic capacitor to accommodate the excess vapor. Such on-demand vapor removal weakens backflow to avoid extended dryout. In sharp contrast to the heat sinks without pulse-dampener, a relatively high and monotonically increasing HTC without any thermal fluctuations is observed in experiments with pulse-dampener. A maximum HTC of ≈270 kW/m2. K at a heat flux of ≈2 MW/m2 was observed with a nanostructured microchannel heat sink. The monotonically increasing HTC suggests that the true potential of this pulse-dampener-based heat sink design is much larger than the maximum heat flux of ≈2 MW/m2 tested in our work.

    更新日期:2019-11-29
  • Effect of multiple reactions on the transport coefficients in pulsatile flow through an annulus
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-28
    Ashis Kumar Roy, Apu Kumar Saha, Sudip Debnath

    The present problem is on the mass transport process through an annular tube, where a chemical species is discharged into a flowing stream driven by a harmonic pressure gradient. The species may undergo linear reversible and irreversible reactions at the outer boundary of the annulus. Also, two non-linear chemical decay are assumed within the bulk flow and at the outer wall. However, the degree of the non-linearity of these reactions are different. The problem is analyzed based on the three-time scale, and thus the homogenization method is utilized to average the two-dimensional mass transport problem. We establish analytical expressions for different transport coefficients in terms of rigorous mathematical calculations. The results exhibit some paradoxical behavior with the radius ratio. The transport coefficients linearly increase with the associated reactions rate but decrease with the wall absorption rate.

    更新日期:2019-11-29
  • Experimental and comparative theoretical study of thermal conductivity of MWCNTs-kapok seed oil-based nanofluid
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-26
    Ahmad Mukhtar, Sidra Saqib, Fatma Safdar, Ayesha Hameed, Sikander Rafiq, Nurhayati Binti Mellon, Rabia Amen, Muhammad Saad Khan, Sami Ullah, Muhammed Ali Assiri, Muhammad Babar, Mohamad Azmi Bustam, Wajid Ur Rehman, Z.M.A. Merican

    Despite the significant potential of nanofluids in energy storage applications, the experimental determination of thermophysical properties is relatively costly and time-consuming. Therefore, the modeling techniques can be used for the accurate estimation of thermo-physical behavior. The predictive models are useful for the understanding of thermo-physical behavior. Due to restrictions on classical models, there is a need to develop more reliable models to simulate the thermophysical behavior of nanofluids. This paper deals with the synthesis and experimental thermal conductivity measurement of the multi-walled carbon nanotubes (MWCNTs)-Kapok seed oil nanofluid. Additionally, two new correlations based on multiple non-linear regression analysis along well as dimensionless analysis are proposed to estimate thermal conductivity with high precision compared to the classical models. Based on the statistical analysis, the prediction accuracy of the proposed model was ranked. Finally, the sensitivity analysis has been carried out in combination with the residual analysis to assure the accuracy of the model parameters of both proposed models and adequacy of estimated values of model parameters, respectively. The results revealed the global minimum values for all parameters at 0% perturbations indicating that the model parameters were estimated with high accuracy and adequacy.

    更新日期:2019-11-28
  • Influence of cooling gallery structure on the flow patterns of two-phase flow and heat transfer characteristics
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-24
    Deng Lijun, Zhang Jian, Hao Guannan

    In research of the accurate relation between two-phase flow pattern and heat transfer characteristics in distinct cooling gallery structures, a dynamic transient visualization test bench was established recording flow of fluid real-time. Meanwhile, multiphase flow model and dynamic mesh were also employed to carry out simulation calculation concerning the dynamic characteristics of two-phase flow and heat transfer characteristics. Compared with the experimental results, the calculation results were extremely close to the actual state. It can be clearly seen that “liquid slug” of engine oil in Kidney shaped cooling gallery emerged mostly during upstroke and the half of downstroke when crankshaft angle was roughly at 90°and 270° while that in water droplet shaped cooling gallery emerged mostly near the entry and exit of engine oil during downstroke of piston. However, liquid slug of engine oil in ellipse shaped cooling gallery appeared in more locations relatively.

    更新日期:2019-11-28
  • ISPH simulations for a variable magneto-convective flow of a ferrofluid in a closed space includes open circular pipes
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-25
    Abdelraheem M. Aly, Sameh E. Ahmed

    The time-dependent ferrofluid flow in a square enclosure that includes an open circular pipe has been studied. A variable magnetic field resulting from a magnetic source that is located at a specific point outside the enclosure is taken into account and different thermal conditions are assumed for the inner circular pipe. The mixture consists of water as a based ferrofluid and Fe3O4 as nanoparticles. In addition, basics of the magnetohydrodynamics (MHD) and the ferrohydrodynamics (FHD) are considered during the mathematical formulations of the current physical model. The novel Incompressible Smoothed Particles Hydrodynamics (ISPH) method is applied to solve the dimensionless governing equations. The controlling parameters for this situation are the Hartmann number, magnetic number, solid volume fraction and different locations of the heated part on the inner circular pipe. It is found that maximum values of the stream function are reduced by 74.3% when the Hartmann number Ha is increased from 0 to 30. In addition, insertion the heated part at the bottom right part of the inner pipe gives a best rate of the heat transfer compared to other thermal conditions.

    更新日期:2019-11-28
  • An experimental investigation on the evaporation characteristics of lubricating oil film in different grooves
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-24
    Yejian Qian, Qiancheng Hu, Zhaoyuan Li, Shun Meng, Kongjin Zhu, Xiaozhang Cheng, Changfa Tao

    The pre-ignition of lubricating oil is the main cause of super knock in gasoline direct injection (GDI) engine. This paper investigates the effect of thermal radiation, cylinder material and film thickness on evaporation characteristics of lubricating oil film using a radiation device under the condition of open space. The experimental results show that the mass loss rate of lubricating oil film is proportional to the film thickness. The thermal conductivity of the material which coated with lubricating oil film has a significant influence on the evaporation characteristics of oil film. There are three obvious stages in the mass change curve of lubricating oil film and a formula is developed to estimate the mass loss rate of the lubricating oil film during the second stage.

    更新日期:2019-11-28
  • Numerical assessment of Ag-water nano-fluid flow in two new microchannel heatsinks: Thermal performance and thermodynamic considerations
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-23
    Liu Yang, Jia-nan Huang, Mao Mao, Weikai Ji

    The present paper is devoted to the first and second law analysis of a aqueous nano-fluid (NF) containing suspended Ag nanoadditives in two new microchannel heatsinks. The influences of nanoadditives volume fraction (φ) and Reynolds number (Re) on performance indicators based on the first and second law of thermodynamics are taken into account and analyzed. The outcomes reveal that the augmentation of Re and φ causes an intensification in the convective heat exchange coefficient and a decrease in the CPU temperature, thermal irreversibility rate and enhance the CPU temperature uniformity. However, grow of Re intensifies both the pumping power and irreversibility due to flow friction. Additionally, the outcomes depicted the superior performance of NF compared to the base fluid. Moreover, the irreversibility inside the studied heatsinks is mainly due to the heat transfer compared to the flow friction. Finally, the results demonstrate that the heatsink with more path changes is more efficient form the viewpoint of the first and second laws of thermodynamics.

    更新日期:2019-11-28
  • MHD thermogravitational convection and thermal radiation of a micropolar nanoliquid in a porous chamber
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-25
    Mohsen Izadi, Mikhail A. Sheremet, S.A.M. Mehryan, I. Pop, Hakan F. Öztop, Nidal Abu-Hamdeh

    This work studies the thermogravitational transmission and thermal radiation of micropolar nanoliquid within a porous chamber in the presence of the uniform magnetic influence. The model includes the single-phase nanofluid approach, local thermal equilibrium approximation and Darcy law for the processes within the porous structure. The Galerkin finite element method with the structured non-uniform mesh is used to calculate the formulated equations. The key characteristics are the Darcy–Rayleigh number Ra = 10–1000, Darcy number Da = 10−5–10−1, porosity ε = 0.1–0.9, nanoparticles concentration φ = 0–0.04, radiation parameter Rd = 0–2, vortex viscosity characteristic Δ = 0–2, and Hartmann number Ha = 0–50. It has been ascertained the energy transport intensification with thermal radiation parameter, Darcy–Rayleigh number, porosity and nanoparticles concentration. Also, the results indicate that the average Nusselt number reduces with an increment of the Hartmann number for high values of the Rayleigh number, while for low magnitudes of the Rayleigh number a weak change of the average Nusselt number can be found.

    更新日期:2019-11-28
  • Thermal characteristics and uniformity of microstructures during temperature controlled mold continuous casting profiled copper alloy strip
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-27
    Xuefeng Liu, Wanneng Liao, Yaohua Yang

    Nonuniform temperature field at cross section of profiled billets during conventional continuous casting always results in serious defects and inhomogeneous microstructures. In this paper, a 3D temperature controlled mold continuous casting (TCMCC) model for preparing profiled copper strip was established and verified to calculate the magnetic and temperature field during continuous casting process. Under different controlled temperatures of TCM and casting speeds, the temperature fields in the TCM and melt were numerically calculated, and the variation of temperature fields in the mushy zone was analyzed. The calculated temperatures are in good agreement with the measured values. The results indicate the uniformity of temperature gradient (uG) at the profiled section improves significantly when the controlled temperature of TCM is higher than the liquidus temperature of alloy, further, the uG gradually reaches the minimum and then increases with increasing casting speed. Based on the calculated results, the profiled KFC copper alloy strips with good surface quality were successfully prepared by the TCMCC under controlled TCM temperature of 1423 K and casting speeds of 15–60 mm/min. The value of the uniformity of primary dendrite spacing at the cross section of the profiled strips reaches the minimum with the casting speed of 45 mm/min.

    更新日期:2019-11-28
  • Pore-scale investigation on flow boiling heat transfer mechanisms in open-cell metal foam by LBM
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-26
    J. Qin, Z.G. Xu, Z.Y. Liu, F. Lu, C.Y. Zhao

    The flow boiling heat transfer mechanisms inside open-cell metal foam are investigated by Lattice Boltzmann method. The 2D reconstructed model of open-cell metal foam is proposed based on the scan image and the thermal responses of metal foam are considered. The effects of Reynolds number, porosity and Rayleigh number on bubble motion and heat transfer performance are revealed. The results show that the dominant force shifts from buoyant force to shear force with increasing Re number, thus the “sweeping off” effect is further intensified by the accelerating sliding bubbles. The superposition of enhanced boiling heat transfer and thermal conduction are responsible for the wall superheat reduction at the central heating areas. Bubble departure diameter decreases with increasing Reynolds number due to the high bubble sliding velocity. The failure of “sweeping off” effect results in the formation of vapor film which worsens the flow boiling heat transfer performance of metal foam with low porosity (ε = 0.94). The convection heat transfer is depressed by bubble motion confinement inside the metal foam at low Rayleigh number.

    更新日期:2019-11-28
  • Study on cooling process of copper tube after three-roll planetary rolling
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-26
    Yi Han, Xiao-Bo Zhang, Zi-Xin Wang, Yao Xiao, Xin-Liang Gao, Yu-Qian Zhao

    Copper tubes are efficient heat exchange parts in refrigeration industry, and their quality has a bearing on the grade of corresponding products. The cooling process of copper tube after three-roll planetary rolling is a key step in the production of copper tube by the casting and rolling method, and its cooling effect matters to the quality of copper tube products. Aiming at the characteristics of motion of a rolled piece in the through water cooling with a cooling water jacket, the method of “stepwise” moving cooling water jacket was used in this paper to achieve equivalence to the motion of the rolled piece, realizing finite element simulation of the whole process of three-roll planetary rolling and cooling of copper tube. The velocity field and pressure field of the fluid in the cooling water model were analyzed, and it was found that there existed a flow “dead zone” with the velocity below 8 m/s, there was a “negative pressure” phenomenon, and there were more eddy currents occurring. Through the study on the temperature field during the cooling process of the rolled piece, it was found that there was a phenomenon of non-uniform temperature distribution in the cooling process of the rolled piece. With the maximum temperature difference at each monitoring point in the cooling process of rolled piece as the evaluation criterion for the uniformity of temperature distribution in the cooling process of rolled piece, the process parameters affecting the rolled piece cooling effect, including the size of water inlet, the size of water outlet, and the pressure of entering water, were studied respectively, and the optimum process parameter values for improving the quality of rolled pieces were finally obtained. The accuracy of the model was verified by comparatively analyzing the metallographic microstructure and microhardness between the factory produced sample and the thermally simulated sample.

    更新日期:2019-11-28
  • Experimental investigation of the effect of bypass inlet on flow boiling in a mini/micro-channel
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-26
    Raamkumar Loganathan, Ahmed Mohiuddin, Sateesh Gedupudi

    The present work reports the findings from an experimental study on the effect of bypass inlet on the performance of flow boiling of water in a copper mini/micro-channel of dimension 2.5 mm wide x 0.6 mm deep x 25 mm long. The mass fluxes considered were 430 kg/m2 s, 640 kg/m2 s and 850 kg/m2 s and the heat flux was in the range 87–548 kW/m2. The results show a significant increase in heat transfer coefficient with the increase in bypass ratio for the subcooled boiling conditions and the enhancement decreases with the increase in the exit quality. An increase in pressure drop was also noticed due to the bypass inlet. The study indicates potential for further investigation and optimization.

    更新日期:2019-11-28
  • Interacting influences of Lorentz force and bleeding on the hydrothermal behaviors of nanofluid flow in a trapezoidal recess with the second law of thermodynamics analysis
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-26
    M. Atashafrooz, H. Sajjadi, A. Amiri Delouei

    This study deals with the analysis of the interacting influences of Lorentz force and bleeding on the hydrothermal behaviors of magnetohydrodynamic (MHD) nanofluid flow and entropy generation in a trapezoidal recess. This trapezoidal recess is created by two inclined steps in a horizontal channel. The Lorentz force is appeared due to the existence of a magnetic field in the flow domain. The Brownian motion influences on the effective characteristics of CuO -water nanofluid are considered to have more accuracy. The effects of bleeding coefficients (−0.005 ≤ Vw ≤ + 0.005), Hartmann number (0 ≤ Ha ≤ 60) and concentration of solid nanoparticles (0 ≤ ϕ ≤ 0.04) on the flow characteristics, heat transfer and flow irreversibility rates are investigated. The results show that the trends and values of friction coefficient, Nusselt number and entropy generation number can be different at the various magnitudes of Ha and Vw, whereas the ϕ parameter only increases the values of them. These differences are related to the variations of streamlines contours against the Ha, Vw and ϕ parameters.

    更新日期:2019-11-28
  • One-dimensional heat flux estimation by sequential method using feedback control system: AFSMC approach
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-24
    S.D. Farahani, Amir Hossein Rabiee

    In this article, a novel sequential method for estimation of heat flux in inverse heat conduction problems is proposed. This technique is based on the feedback control system theory in which adaptive fuzzy sliding mode controller (AFSMC) is utilized. The objective is to estimate the input heat flux associated with a flat plate according to the time history of measured output temperature. In this closed-loop control system, at each time instant, the AFSMC calculates the proper heat flux value to track the measured temperature with the desired input temperature. Some experiments are designed to investigate the ability and accuracy of proposed method in estimating the heat flux of a one-dimensional flat plate. The effects of noise in data and sensor location on the exactness of proposed method are also assessed. Moreover, the distribution of heat flux is considered to be in three forms: constant, step and triangular. The influential parameters of suggested method are tuned once and then used in all subsequent numerical tests. This method does not rely on scanning the entire time history of measured temperatures, and successfully operates in an online manner for a wide range of heat flux distribution functions and their associated abrupt changes.

    更新日期:2019-11-28
  • Influence of structured surface roughness peaks on flow and heat transfer performances of micro- and mini-channels
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-27
    Munib Qasim Ansari, Guobing Zhou

    The effect of surface roughness peaks (SRP) on laminar air-flow and heat transfer performances in rough micro- and mini-channels is analyzed by 3D computational fluid dynamics (CFD) simulation method. The variations of channel height, SRP height, pitch and width, aligned and off-set SRP, and hybrid SRP in rectangular channels are studied. The parametric ranges of channel height, SRP height and constricted diameter of the channel are 150 μm to 400 μm, 15 μm to 45 μm, and 179 μm to 663 μm, respectively. The results showed that heat transfer performance of smooth micro- and mini-channels with low aspect ratio is higher than the conventional predictions. The maximum convective heat transfer depends on the optimum combination of channel size and roughness height. Furthermore, increasing SRP pitch has less impact on the heat transfer while increasing roughness width improves the performance index. Hybrid SRP in a channel is more effective than constant SRP at lower Reynolds number with the performance index improved up to 12%. Aligned peaks are more efficient than the off-set arrangement and the average rise of performance is 9% under present conditions. Relative roughness with varying parameters can be configured for practical purposes without compromising the compactness.

    更新日期:2019-11-28
  • Influence of Cattaneo-Christov model on Darcy-Forchheimer flow of Micropolar Ferrofluid over a stretching/shrinking sheet
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-22
    Zahir Shah, Ebraheem O. Alzahrani, Abdullah Dawar, Asad Ullah, Ikramullah Khan

    This work deals with the study of Darcy-Forchheimer flow of micropolar ferrofluid on a porous and dynamic (stretching/shrinking) sheet under the influence of thermal radiations subjected to both suction and injection. The effects of the external electric and magnetic fields are considered as well. Water is used as a base fluid and Fe3O4 (iron oxide) as electro-magnetite nanoparticles. The mathematical equations developed in this study are based on the Cattaneo-Christov model consisting of coupled nonlinear partial differential equations. These equations are transformed into a set of coupled ordinary differential equations (ODEs) by using similarity transformations. These ODEs are solved by applying the standard mathematical technique of homotopy analysis (HAM). The effects produced by different parameters on the velocity, micro-rotational velocity and temperature profiles are shown graphically for positive as well as negative mass transfer flow and for both stretching and shrinking cases. It has been observed that the velocity profile increases (decreases) with the increasing electric field strength and microrotation parameter during the stretching (shrinking) of the surface in both suction (S > 0) and injection (S < 0) cases. Furthermore, similar results has been observed for the velocity profile with the increasing inertial coefficient, porosity, magnetic and boundary parameters during flow over the stretching (shrinking) surface for both S > 0 and S < 0. The micro-rotational velocity increases with higher values of microrotation parameter for stretching, while decreases for the shrinking of the surface. The temperature profile displays an increasing trend with the increasing values of heat energy source and sink terms and thermal radiation parameter for stretching as well as shrinking of the sheet for S > 0 as well as S < 0. The temperature profile also changes with the variation in thermal relaxation parameter and Prandlt number.

    更新日期:2019-11-26
  • Investigation of entropy generation in a square inclined cavity using control volume finite element method with aided quadratic Lagrange interpolation functions
    Int. Commun. Heat Mass Tranf. (IF 4.127) Pub Date : 2019-11-22
    Seyyed Masoud Seyyedi, A.S. Dogonchi, M. Hashemi-Tilehnoee, M. Waqas, D.D. Ganji

    One of the most concerned subjective in Mechanical science is natural convection study in a cavity. Furthermore, the investigation of entropy generation can be useful for better designing of the thermal systems. In the present study, natural convection flow and entropy generation are numerically investigated in the presence of a magnetic field in a square inclined cavity which known as the effect of magneto-hydrodynamic (MHD). Firstly, governing equations, including mass, momentum, and energy balance equations are applied to the problem. Then, governing equations are rewritten in dimensionless form using non-dimensional parameters, vorticity, and stream function. Furthermore, the entropy generation equation is written as a non-dimensional equation. Then, the contribution of the heat transfer entropy generation into the total entropy generation rate is determined using the Bejan number. A new measure for evaluation of the thermal performance of the cavity is presented that is the so-called ecological coefficient of performance (ECOP) based on the second law of thermodynamics. Flow and heat transfer characteristics are investigated for different values of the Rayleigh number, inclination angle, and Hartmann number. The new correlations of entropy generation as a function of Rayleigh number are obtained using the two-dimensional version of quadratic Lagrange interpolation functions (QLIFs). The obtained values for the average Nusselt number and the entropy generation number are compared with those of the literature and excellent agreement is observed. The results show that the entropy generation number rises with increasing of Hartmann number and whereas it has a maximum value for a specified inclination angle. Also, ECOP increases with increasing of Hartmann number for low values of Rayleigh number. The results discover that the optimum values of the inclination angle are 20°, 35° and 48°for Hartmann number 0, 25 and 75 at Ra = 105, respectively. Also, with increasing Ha from 25 to 75, the contribution of the Ngen due to magnetic field decreases from 23% to 9% for β = 0° and it decreases from 24% to 6% for β = 45°.

    更新日期:2019-11-22
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