ABSTRACT Ceiling diffusers are one of the most important elements of ventilation and air-conditioning installations. They have a significant impact on the speed and temperature distribution of air. The basic task of these devices is to provide the required air stream while maintaining its appropriate parameters in the occupied zone and low noise levels in the room. Square ceiling diffusers are designed

ABSTRACT In the present work, three-dimensional numerical investigations are carried out to study the influence of top wall confinement on unsteady flow and heat transfer characteristics of sinusoidal wavy channels. Different channel confinements considered in the present study are channels having sinusoidal bottom wall and plane, in-phase, and out-of-phase configurations of the top wall. Computations

ABSTRACT The insertion of a broken twisted tape (BTT) in tube is a novel passive heat transfer augmentation method, which constitutes the subject of the present investigation. Effect of BTT on heat transfer performance in novel triangular axial corrugated tubes is investigated experimentally and numerically. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered

ABSTRACT Heat transfer operations in microchannel are of special relevance in designing micro-devices involving accumulation of high heat flux. The current study explores simultaneously developing, unsteady laminar flow inside a twisted sinusoidal wavy microchannel and heat transfer involved. A square cross-sectioned channel is taken for the study. The channel is wavy in nature as well as twisted about

Abstract This paper considers the previously discovered by the authors non-monotonic effect of the water velocity on the nucleate boiling of a subcooled flow. We present experimental results for the following conditions: initial pressure 0.18 and 0.48 MPa, subcooling level 54 and 120 K, initial flow velocity in the range from 0 to 1.85 m/s, and carry out numerical analysis of the model for nonstationary

Abstract Thermosetting materials are commonly used as an insulative material in medium and high voltage applications. Production of large volume elements is causing several problems related to a mold filling or an exothermic polymerization reaction which may lead to quality issues. To improve the quality, numerical simulations are commonly used for a production process prediction and optimization.

Abstract There has been a remarkably increasing interest in applying acoustofluidics in micro-electro-mechanical systems and lab-on-a-chip systems in the past decades. This paper investigated the heat transfer performance in a straight microchannel heat sink which applies standing surface acoustic waves (SSAW) to disturb the flow. Two-dimensional numerical simulations of the SSAW-driven flow are performed

ABSTRACT The paper describes the results of boiling heat transfer during FC-72 flow in minichannels, obtained on the basis of time-dependent experiments. The main goal of the work was to determine the heat transfer coefficient by means of the finite element method with the spacetime Trefftz-type basis functions based on the Hermite interpolation. The crucial part of the experimental stand was the test

ABSTRACT In the paper, the results of tests on pool boiling heat transfer on open microchannel surfaces were discussed. Nucleate pool boiling from copper microchannel surfaces was examined using ethanol as a working fluid. Parallel microchannels fabricated by machining were about 0.2 to 0.4 mm wide and 0.2 to 0.5 mm deep. In the mathematical model the heat transfer process was in steady state. The

Abstract In the operating nuclear power plants, piping and components installed in the in-service testing systems connected to the reactor coolant system are potentially exposed to fatigue caused by thermally stratified flow, possibly threatening its integrity. The emergency core cooling system (ECCS) is one of candidates for which the thermal stratification phenomenon can occur. Because temperature

ABSTRACT Fluid-structure interaction problem - unsteady channel flow with a moving indentation problem, which represents flow features of oscillating stenosis of a blood vessel, is numerically simulated here. The flow phenomenon inside the channel with a moving boundary is found to be unsteady and complex mainly due to the presence of the moving boundary and its interaction with flowing fluid. In this

ABSTRACT A numerical investigation of the condensing flow of isobutane inside microchannel has been performed. Impact of mass flux, hydraulic diameter, and vapor quality on the heat transfer rate and pressure drop is determined. To this purpose, steady-state numerical simulations of condensation flow of isobutane have been performed at mass fluxes ranging from 200 to 600 kg/m2s inside a single circular

Abstract The urban heat island effect amplifies the global warming phenomenon with sensible aftermaths on the building energy consumptions. The absence of green areas, open water channels as well as the lack of free unsurfaced spaces creates a sort of urban cap and a heat reflection effect, from the bottom upwards, which persists in the early hours of the night. This heating effect exacerbates the

ABSTRACT The objective of the current research work is to provide the optimum experiment and heating times in dimensionless form to be used for the simultaneous estimation of thermal properties when running a plane source-based experiment. In detail, they are thermal conductivity, volumetric heat capacity and contact resistance. These optimum times are limited to high-conductivity materials and are

ABSTRACT Natural convection from a horizontal plate with identically-heated top and bottom sides, enclosed in gas- or liquid-filled square cavities cooled at sides, is studied numerically. A computational code based on the SIMPLE-C algorithm for pressure-velocity coupling is used to solve the system of the governing conservation equations of mass, momentum and energy. Simulations are performed using

ABSTRACT The dimensions of an electronic control unit are extremely important in the developing of any new product design. It is well known that a large area of the PCB (printed circuit board) increases thermal performance. For any developed product, when the PCB area is enlarged, the volume, the mass, and the surroundings also increase. The current paper presents how the shape is more important than

Abstract Transport and storage of liquefied natural gas (LNG) requires special double-walled cryogenic tanks. To provide a liquid state of LNG throughout entire storage time a temperature inside the tank should be equal −160 °C under the pressure of around 7 bar. Maintaining these parameters requires a vacuum insulation system and internal supports designed to minimize heat leakage into the tank. Additionally

Abstract The heat transfer coefficients of flow boiling in a small semi-circular channel of plate once-through steam generator were tested by experimental method in this paper. Based on the experimental data, the numerical simulation of flow boiling in the semi-circular channel was carried out using STAR-CCM + software. The numerical models are the homogenous flow model, the Rohsenow model and the

Abstract One of the main disadvantages of conventional fixed-bed adsorption chillers is the low coefficient of performance due to the high voidage of the sorbent beds. The common method, which can help to handle this problem, is modifying the beds’ design, including the application of fluidization. An innovative idea, shown in the paper, constitutes in the use of the fluidized bed of sorbent, instead

Abstract A numerical study is conducted for a thermal-hydraulic performance analysis and secondary side screw-type tube inlet orifice design of a once-through steam generator. Various tube-plugging conditions and power levels are considered, and the secondary coolant flow rate is adjusted to maintain a constant level of thermal power. Comprehensive numerical solutions are acquired to evaluate the thermal-hydraulic

Abstract In the presented paper a thermal network approach was proposed for a quick and accurate study of the thermal performance of two interconnected and unsymmetrically energized switchgears. The method base on the full computational fluid dynamics (CFD) simulation of a single standalone switchgear which was used to provide unknown input parameters for a constructed thermal network. Next, a thermal

Selected Papers from the 12th International Conference on Computational Heat and Mass Transfer (ICCHMT2019). Heat Transfer Engineering. Accepted .

Abstract In the present study, the lateral heat transfer and fluid flow characteristics between two-phase impinged jet flow and two-phase channel flow were compared. The effects of volumetric quality (0 – 0.9) on the lateral variation of the Nusselt number were considered. The working fluids are air and water. A circular jet of 470 mm long with a 5.86 mm inner diameter is used. The water jet Reynolds

Abstract Temperature uniformity is an important factor in the thermal management of electronic devices. The present study investigates the effect of bypass injection on the wall temperature distribution of a single-phase mini/micro-channel using water as the coolant. Experimental studies were conducted on an 18 mm thick copper substrate heated by a cartridge heater, with the bypass inlet located midway

Abstract Prediction of dryout location is essential to identify reliable heat flux margins for the safe operation of different thermal systems. The present study proposes a simple model to predict the dryout type critical heat flux location in a circular tube and an annulus. Based on the flow topology, the annular flow boiling regime is demarcated into two zones viz., vapour flow in the core region

Abstract A comparative investigation is carried out to reveal the effect of plate-fin type variation on the performance of compact heat exchangers (CHX) with a mini-channel flat tube. The compact heat exchanger prototypes with plain, louver and offset strip fins with the same frontal area are tested in the same air tunnel under the same experimental conditions to provide a better comparison. Besides

Abstract In this study, the thermal and hydraulic performances of three curved-rectangular vortex generators (VG_1, VG_2 and VG_3) in a compact fin-and-tube heat exchanger were numerically investigated. The secondary flow theory and field synergy principle were employed to characterize the effects of VGs on the flow characteristics and hence the heat transfer enhancement. The thermal and volume-goodness

Abstract Nucleate boiling has been a topic of great interest due to its heat transfer enhancement capability. In the present work, a highly resolved numerical model is developed combining two submodels, a microlayer evaporation submodel and phase change sub model, to get insights on various sub-processes like bubble inception, growth, departure, waiting time and scavenging effect. Here, a new approach

ABSTRACT In this experimental study, heat transfer and pressure drop characteristics of R134a evaporating flow are investigated inside a horizontal internally grooved tube with discrete inclined grooves. The test evaporators are made of smooth and grooved copper tubes of 20 mm inner diameter. The length, width, and depth of grooves are 6, 2, and 0.5 mm, respectively, and the angle of the grooves with

Abstract Extensive results are reported on the flow and heat transfer for Bingham plastic fluids for the same configuration as in Part I over the ranges: Reynolds number ( 5   −   200 ) , Prandtl number ( 1 − 100 ) , and Bingham number ( 0 . 01 − 100 ) and the gap ratio ( 0 . 3   −   0 . 7 ) . At small Bingham numbers, the results deviate a little from that in Newtonian fluids except for the pockets

Abstract Forced convection heat transfer in power-law fluids has been investigated numerically around four identical circular cylinders in a diamond array in a square enclosure. For the laminar flow, the governing equations have been solved numerically over the following ranges of parameters: Reynolds number (5 - 200), Prandtl number (0.7 - 100), power-law index (0.2 - 2) and center-to center gap between

Abstract A coal fired pusher type reheating furnace is simulated with the help of an efficient numerical model. The authors have improved over a numerical model developed in previous work to save more than 50% of computational time and thus making it feasible to use the model in large number of parametric studies. The transient movement of the billets is modelled as a steady-state problem with suitable

Abstract A numerical study on mixed convection is carried out through a partially filled brass wire mesh in a vertical channel. A heater embedded with aluminum plates is placed at the center of the vertical channel. The aluminum heater assembly is wrapped with brass wire mesh to facilitate more heat transfer. The vertical channel that consists of aluminum heater assembly with the brass wire mesh is

Abstract Natural convection heat transfer in a concentric horizontal annulus with annular fins is numerically studied. Due to the low thermal conductivity of water, CuO-water and Al2O3-water nanofluids were used as heat transfer fluids. The effect of three different parameters, including fin spacing, fin eccentricity, and fin thickness at different fin diameters and Rayleigh number range of 104 to

ABSTRACT Understanding and predictions of the local thermal-hydraulic performance of supercritical CO2 in channels of printed circuit heat exchanger geometries are of great importance to the design and optimization of the pre-cooler and recuperators in supercritical CO2 cycle. The local flow and heat transfer of supercritical CO2 in horizontal semicircular zigzag channel during cooling near the critical

ABSTRACT Plate heat exchanger (PHE) has been widely used in energy transport fields for its high efficiency and compact structure. However, fouling is an intractable issue which reduces heat transfer efficiency and increases pressure drop. In this study, an experimental investigation on composite fouling characteristics of Ni-P-PTFE nanocomposite coating in corrugated PHE was conducted to evaluate

Abstract The mathematical modeling of heat transfer in nanofluids based on the effects of additional particle forces was investigated with computational fluid dynamics simulations of titania-water nanofluid in a heated pipe flow. The additional particle forces analyzed were Brownian force, thermophoresis, Saffman’s lift force and Magnus lift force. The results were validated with an experimental work

A macrolayer formation model for predicting the critical heat flux (CHF) in saturated and subcooled pool boiling was proposed. The concept of this model was based on the bubble coalescence process, which was observed using a high-speed camera. In the present model, the thickness of the macrolayer was calculated assuming that the liquid volume remaining under the lower part of the bubble should contribute

The aim of the present study is to numerically investigate the thermal performance of a heat exchanger tube fitted with vortex generator inserts. In the present paper, three configurations of vortex generators—straight, double-curved, and triple-curved—are proposed to achieve the optimum configuration design that provides the highest thermal performance. The thermal performance results of the tubes

Multi-objective optimization of nanofluids in a microchannel heat sink was conducted to determine the highest Nusselt number and the lowest pressure drop. This was done by creating a design study consisting of four nanoparticles of Al2O3, CuO, ZnO and SiO2 with four diameters of 10, 30, 60 and 100 nm, nanoparticle volumetric concentrations of 0.001, 0.005, 0.01 and 0.05 and four base fluids of water

Numerical investigations of heat transfer and fluid flow have been carried out to study the effect of variation of longitudinal and transverse pitch-to-diameter ratios for a cross-flow heat exchanger with elliptical tubes. A total of seventeen configurations of varying compactness are investigated. This investigation also covers the effect of aspect ratio (0.40, 0.53, 0.78, 0.92 and 1.00) and tube

In this study, mixed convection heat transfer of silver-water nanofluid was experimentally investigated under laminar flow regime inside a horizontal rectangular channel filled with an open-cell copper foam. Thermophysical properties of silver-water nanofluid at 1000, 2000, and 4000 ppm concentrations were also measured. The morphological properties of copper foam were further measured by image processing

Fluid flow and heat transfer characteristics past four elliptic cylinders arranged in square configuration are numerically investigated in this study. An in-house finite element method code based on streamline upwind Petrov - Galerkin algorithm has been used for simulations of two-dimensional, incompressible and laminar flow of air. Analyses are carried out by changing geometric parameters such as

The public domain is inundated with discrepancies in numerical and experimental findings on the natural convection heat transfer performance of nanofluids in a cavity. This paper presents the experimental investigation of the natural convection of deionized water (DIW)-based zinc oxide (ZnO) nanofluid in a rectangular cavity. The ZnO nanoparticles (20 nm) were dispersed in DIW to formulate nanofluids

Oxidized carbon nanohorn water based nanofluids are attracting more and more attention for solar harvesting applications because of their peculiar features: stable suspension without any surfactant, higher solar absorbance values as compared to the base fluid, etc. However, these nanofluids are still matter of research because not all their properties have been comprehensively studied yet. This paper

Thermosyphons are amongst the most efficient passive heat transfer devices known nowadays. Due to heat and mass transfer limitations of working fluids, much effort is invested in developing a new generation of enhanced fluids, such as nanofluids. Previous studies reported improved thermal capacity when water was replaced by nanofluid. The interplay between nanoparticles and the evaporator surface is

Nanofluids have been used in several thermal management systems, as they contribute to the augmentation of the heat dissipation rates in many applications, especially those where heat pipes, pulsating heat pipes and loop heat pipes are used. Long term use of this type of device is required in order to increase their reliability, which requires chemical compatibility between the base fluid and the nanoparticle

In this study, microparticle coatings and nanoparticle coatings were fabricated on copper surfaces by an electrochemical deposition method and an electrophoretic deposition method, respectively. Pool boiling of NOVEC-649 was experimentally studied on the coated surfaces, concerning heat transfer, bubble dynamics and critical heat fluxes. Compared with a smooth surface, heat transfer coefficients and

This study focuses on the experimental characterization of fluid dynamics and heat transfer processes occurring at the interaction between a nanofluid droplet and a heated smooth surface. Time resolved thermography is used to detail the understanding of the role of the particles in wetting modification that affects the heat transfer mechanisms within different characteristic time scales. Gold and silver

We report in this study the experimental investigation of the dynamic viscosity of purified multi-walled carbon nanotubes (MWCNT) water and water-propylene glycol based nanofluids in the temperature range 10-80 °C. Four weight concentrations of MWCNTs are considered, between 0.005 and 0.1 wt.%. Triton X-100, a common nonionic surfactant, is used to disperse the nanotubes and stabilize the nanofluids

Commonly, heat transfer performance of a nanofluid is enhanced by increasing the mass fraction of nanoparticles due to an improvement of the thermo-physical properties. However, increasing the number of nanoparticles in the base fluid will result in an increase of the nanofluid viscosity. This research aims to investigate natural convective heat transfer for an electric heater filled with various Al2O3-water

Developing materials that efficiently combine cutting-edge technology with competitive costs so as to meet technical, economic and, last but not least, environmental challenges are a must in the field of materials engineering and beyond. Ionic liquids are heat transfer fluids that offer a wide range of advantageous properties. One of the most recent applications of these complex ionic liquids and nanomaterial

In order to enhance the heat transfer performance, the screen mesh wick and the inside wall of the container of a heat pipe were pre-coated with a silica nanoparticle layer. When the screen mesh was coated, the thermal resistance decreased by 47% on average. This would be attributed to enhanced wicking performance of screen mesh by the nanoparticle layer. When the container inside wall was coated,

In this paper, the numerical analysis of an impinging jet of Al2O3-water nanofluid in laminar and turbulent flow is carried out by using ANSYS. The main purpose of the paper is to describe the effects on heat transfer through a parametric analysis by varying jet-to-plate distance, volume fraction of nanoparticles and Reynolds number based on jet diameter. To assess how all these parameters affect the

In this paper a numerical investigation in metal porous structures with Kelvin cell model is carried out on water/Al2O3 nanofluids using the single-phase model. The examined foams are characterized by a porosity of 0.95 and different values of cells per inch (CPI), equal to 10 and 20 CPI. Three different values of Al2O3 nanoparticle volume concentrations equal to 0, 2 and 4% are used. Results are presented

Selected Papers from the 1st International Conference on Nanofluids (ICNf). Heat Transfer Engineering. Accepted .

The objectives of the present research work are the three-dimensional computational analysis and predictions on double-diffusive natural convection in a cubic cavity filled with Cu-Al2O3/water micropolar hybrid nanofluid. The governing equations are carefully modified employing vorticity-vector potential formulation and are solved by the finite volume method. Performance enhancement of Cu-Al2O3/water

This study reports on a mathematical model for predicting the fluid and heat flow characteristics of a Z-shaped corrugated foam heat sink. Experiments were carried out to validate local as well as overall pressure drop predictions. The mathematical model was further validated against corrugated carbon foam experimental measurements from the literature. A general flow parameter emerges from the formulation

In this study, heat transfer, flow characteristics, and entropy generation of turbulent TiO2/water nanofluid flow in the spiral coil tube were analytically investigated considering the nanoparticle volume fraction, curvature ratio, flow rate and inlet temperature between 0.01-0.05 percent, 0.03-0.06, 1.3-3.3 l/min, and 15-27 °C, respectively. Results showed that the augmentation of the nanoparticle

Condensation heat transfer on stainless steel tube utilizing superhydrophobic coatings was investigated. The electrophoretic deposition and spraying methods were employed to coat the tubes’ outer surface. The mixture that was synthesized for spray coating was a hybrid paint. It incorporated polyurethane matrix and a colloidal suspension containing organic nanoparticles. The hybrid paint had a proper