Showing papers in "Heat Transfer Engineering in 2019"
TL;DR: In this paper, the authors proposed a cooling system to dissipate large amount of heat produced over a small area in electronic industry, which will require efficient cooling systems to enable the development in electronic industries.
Abstract: Future developments in electronic industries will require efficient cooling systems to dissipate large amount of heat produced over a small area. In recent years, interest has grown in exte...
72 citations
TL;DR: In this paper, the effect of forward inclined turbulators on the heat transfer enhancement in a duct is investigated, for forced convection, with three diffused turbulators and three diffusers.
Abstract: In the present study, the effect of forward inclined turbulators on the heat transfer enhancement in a duct is investigated, for forced convection. Turbulator configurations with three diff...
52 citations
TL;DR: In this paper, the authors point out possible solutions to the further development of heat pipes by numerical modeling of phase-change heat transfer, which has become a standard technique in the literature.
Abstract: The aim of this paper is to point out possible solutions to the further development of heat pipes by numerical modelling of phase-change heat transfer. Numerical modelling has now become a standard...
51 citations
TL;DR: In this article, a combined analytical and experimental study was carried out to analyze the effects of cryogenic cooling on temperature during turning of AZ31C magnesium alloy and the Finite Element method was employed.
Abstract: A combined analytical and experimental study was carried out to analyze the effects of cryogenic cooling on temperature during turning of AZ31C magnesium alloy. Finite element method was employed t...
45 citations
Abstract: Regenerative cooling is being used to meet the high cooling requirements of advanced hypersonic flight vehicles using the fuel at supercritical pressures as the coolant. The heat transfer and therm...
41 citations
TL;DR: In this paper, a discussion can be made to concurrently contrast HEs to one another under the same conditions to detect maximum effica cation in the same heat exchanger under different conditions.
Abstract: On account of nanofluids influence on heat exchangers (HEs), a vigorous discussion can be made to concurrently contrast HEs to one another under the same conditions to detect maximum effica...
39 citations
TL;DR: In this paper, the authors present a brief perspective on the historical challenges in thermal management and outlines the major length scale regimes where thermal management is being developed, in particular, the expansion of thermal management into the nanoscale is presented due to the consequence that as the feature size of most nano-devices continues to diminish, the impact of thermal transport across solid-solid interfaces on device performance, reliability, and lifetime becomes increasingly important.
Abstract: Since the early days of computing, excess heat has been a major road block in the design and development of faster, more efficient, and more compact electronic devices. Coupled with improvements in thermal management has been a reduction in the size of major electronic components, primarily transistors. This has expanded the field of thermal management down into the nanoscale, where the “rules” of thermal transport become more complicated. This paper presents a brief perspective on the historical challenges in thermal management and outlines the major length scale regimes where thermal management is being developed. In particular, the expansion of thermal management into the nanoscale is presented due to the consequence that as the feature size of most nano-devices continues to diminish, the impact of thermal transport across solid-solid interfaces on device performance, reliability, and lifetime becomes increasingly important.
37 citations
TL;DR: In this article, the effect of perforated circular disk turbulators with and without twisted tape on heat transfer, friction factor and thermal performance of heat exchanger is evaluated experimentally.
Abstract: Heat transfer enhancement in heat exchanger by using passive approach has become a very versatile area of research for the researchers. Although very significant results has been achieved in the thermal performance of heat exchangers, especially in the range of lower Reynolds number, but still these passive approaches of heat transfer enhancement is not effective for the range of higher Reynolds number. In the present work the effect of ‘perforated circular disk turbulators with and without twisted tape’, on heat transfer, friction factor and thermal performance of heat exchanger is evaluated experimentally. The different geometrical parameters used for the experiment include fixed diameter ratio (0. 8), pitch ratios (1, 2, and 3), perforation index (0%, 8%, 16%, and 24%), fixed twist ratio (2) and fixed width ratio (0.4). The experiment is done in the range of Reynolds number lying from 6,500 to 26,500. On the basis of experimental observation, there is 2.2–3.54 times improvement in heat transfer...
34 citations
TL;DR: A comprehensive and critical review of nucleate pool boiling heat transfer, flow boiling and flow critical heat flux (CHF), and two-phase flow phenomena can be found in this article.
Abstract: This paper presents a comprehensive and critical review of studies on nucleate pool boiling heat transfer, flow boiling heat transfer, critical heat flux (CHF), and two-phase flow phenomena...
33 citations
TL;DR: In this article, the authors examined the local heat transfer and friction factor characteristics of pentagonal ribs mounted on bottom heated wall of a rectangular channel and demonstrated that the local augmentation Nusselt number distribution is axisymmetric and shows 2-dimensionalty in heat transfer distribution.
Abstract: Rib turbulators are extensively used in augmentation of convective heat transfer in several applications related to heat exchange and cooling in thermal energy systems. Present experimental investigation examines the local heat transfer and friction factor characteristics of pentagonal ribs mounted on bottom heated wall of a rectangular channel. The emphasis is towards assessing and analysing the potential impact of varying chamfering angle (0 to 20°) and rib pitch to height ratio (6 to 12) on the overall heat transfer enhancement and its distribution on the surface. Experiments are performed at different Reynolds numbers ranging from 9400 to 58850. Liquid crystal thermography is applied to measure surface temperature distribution and finally to demonstrate the local heat transfer coefficient over the ribbed surface. The results depict that the local augmentation Nusselt number distribution is axisymmetric and shows 2-dimensionalty in heat transfer distribution. Pentagonal ribs show a significant ...
32 citations
TL;DR: In this article, a flat plate pulsating heat pipe (FPPHP) was used for parabolic flight in the ESA parabolic mission under vertical orientation, where the energy transfer mode in such conditions is represented either by pure pool boiling inside the channels almost completely filled by the liquid phase or by an annular flow pattern inside the channel mostly filled by refrigerant vapor.
Abstract: A particular flat plate pulsating heat pipe (FPPHP), filled with FC72, is tested during the 62th and 64th ESA parabolic flight campaigns under vertical orientation. The FPPHP is made of a thin copper plate, in which a curved channel disposed with 11 U-turns is milled and closed on the top face by a transparent borosilicate plate. The particular characteristics is that the equivalent hydraulic diameter of the square channel (2.5 × 2.5 mm²) is above the working fluid capillary diameter on ground, inducing a stratification of the liquid/vapor phases under ground and hyper-gravity conditions, whatever the orientation. The energy transfer mode in such conditions is represented either by pure pool boiling inside the channels almost completely filled by the liquid phase or by an annular flow pattern inside the channels mostly filled by the refrigerant vapor. Instead, during the microgravity phases, the fluid regime naturally turns into a slug-plug flow pattern. During the transition from 1.8 g to 0 g a r...
TL;DR: In this paper, the authors present results concerning flow boiling heat transfer in three parallel vertically oriented and asymmetrically heated rectangular minichannels, each minichannel was 1.7mm deep, 16mm w...
Abstract: This paper presents results concerning flow boiling heat transfer in three parallel vertically oriented and asymmetrically heated rectangular minichannels. Each minichannel was 1.7 mm deep, 16 mm w...
TL;DR: In this article, the effect of temperature dependent internal source on the onset of convection and on the heat transfer in a porous layer saturated by a non-Newtonian nanofluid is examined.
Abstract: In this paper, the effect of temperature dependent internal source on the onset of convection and on the heat transfer in a porous layer saturated by a non-Newtonian nanofluid is examined. ...
TL;DR: In this paper, a porous surface is used to enhance boiling heat transfer in the industry, which is influenced by the surface distinctiveness of the boiling region, and the porous surfaces are used to improve the efficiency of boiling regions.
Abstract: Boiling heat transfer enhancement is influenced by the surface distinctiveness of the boiling region. Porous surface is being widely used to enhance boiling heat transfer in the industry. A...
TL;DR: In this paper, nanostructured microporous surfaces were electrodeposited at various electrolyte temperatures on copper substrate to investigate the saturated pool boiling enhancement of distilled water at atmospheric pressure.
Abstract: Nanostructured microporous surfaces were electrodeposited at various electrolyte temperatures on copper substrate to investigate the saturated pool boiling enhancement of distilled water at atmospheric pressure. Surface structure topography and wickability were analyzed to investigate their relation to critical heat flux. Scanning electron microscope showed that the micro-clusters have nanostructures from cubic at 5°C to dendritic at 60°C electrolyte temperature. Rate-of-rise experiments demonstrated that dendritic copper structure has the best capillary performance. The experimental results of pool boiling heat transfer indicate that the critical heat flux increased with surface wickability. Electrodeposited porous surface in hot electrolyte showed the highest critical heat flux and heat transfer coefficient of the 124 W/cm2 and 17 W/cm2K, respectively, which is 50% and 270% higher than that of plain surface. However, the two-step electrodeposition and annealing were used in fabrication of surfaces, but the mechanical strength of layer needs more improvement by changing the electrochemical process parameters.
TL;DR: Fouling is a challenging, longstanding, and costly problem affecting a variety of heat transfer applications in industry as mentioned in this paper, and Mathematical models that aim at capturing and predicting fouling tr...
Abstract: Fouling is a challenging, longstanding, and costly problem affecting a variety of heat transfer applications in industry. Mathematical models that aim at capturing and predicting fouling tr...
TL;DR: In this paper, the thermal characterization of aluminum flat-grooved heat pipes is performed experimentally for different groove dimensions, and three heat pipes with groove widths of 0.2mm, 0.4mm, and 1.5mm are evaluated.
Abstract: The thermal characterization of aluminum flat grooved heat pipes is performed experimentally for different groove dimensions. Three heat pipes with groove widths of 0.2 mm, 0.4 mm, and 1.5 mm are u...
TL;DR: In this article, the authors proposed a flow-boiling-based miniaturization method for microchannels with the combined effect of latent heat of vaporization and forced convection in confined spaces.
Abstract: Flow boiling in microchannels promises high heat transfer due to the combined effect of latent heat of vaporization and forced convection in confined spaces. However, flow boiling based miniaturize...
TL;DR: In this paper, a numerical model has been proposed for predicting the energy performance of a heat pump assisted regenerative solar still using phase change heat storage materials such as phase-change heat storage material.
Abstract: A numerical model has been proposed in this research work for predicting the energy performance of a heat pump assisted regenerative solar still using phase change heat storage materials such as pa...
TL;DR: In this article, the use of magnetic nanofluids (ferrofluids) in a direct absorption solar parabolic trough collectors enhances thermal efficiency compared to conventional solar collectors.
Abstract: The paper is related to the use of magnetic nanofluids (ferrofluids) in a direct absorption solar parabolic trough collectors enhances thermal efficiency compared to conventional solar collectors. By applying the right magnetic intensity and magnetic field direction, the thermal conductivity of the fluid increased higher than typical nanofluids. Moreover, the ferrofluids exhibit excellent optical properties. The external magnetic source is installed to alter the thermos-physical properties of the fluid, and the absorber tube does not have selective surface allowing ferrofluids to absorb the incoming solar irradiance directly. In this paper, an experimental investigation of the performance of direct absorption solar collector using ferrofluids as an absorber. Various nanoparticle concentrations 0% to 1vol% at the operational temperatures between 19°C and 40°C were used in the current study. The results show that using ferrofluids as a heat transfer fluid increases the efficiency of solar collectors. In the presence of the external magnetic field, the solar collector efficiency increases to the maximum, 25% higher than the conventional parabolic trough. At higher temperatures, the ferrofluids show much better efficiency than conventional heat transfer fluid. The study indicated that nanofluids, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies.
TL;DR: In this article, the role of magnetic field and natural convection on the solid-liquid interface motion, flow, and heat transfer during melting of gallium on a vertical wall is reported.
Abstract: The role of magnetic field and natural convection on the solid–liquid interface motion, flow, and heat transfer during melting of gallium on a vertical wall is reported in this paper. The classical geometry consisting of a rectangular cavity with uniform but different temperatures imposed at two opposite side walls, insulated top, and bottom walls is considered. The magnetic field is imposed in the horizontal direction. A numerical code is developed to solve for natural convection coupled to solid–liquid phase transition and magnetic effects. The corresponding streamlines and isotherms predicted by the numerical model serve to visualize the complicated flow and temperature field. The interplay between the conduction and convection modes of heat transfer stimulated by the combination of the buoyancy-driven flow and the Lorentz force on the fluid due to the magnetic field are studied. The results show that the increase of Rayleigh number promotes heat transfer by convection, while the increase of Hartmann number dampens the strength of circulating convective currents and the heat transfer is then mainly due to heat conduction. These results are applicable in general to electrically conducting fluids and we show that magnetic field is a vital external control parameter in solid–liquid interface motion.
TL;DR: In this article, the authors investigated the performance of a rib array placed on the lower wall of a two-pass channel compared to that of the solid rib array for smooth and split-slit-ribbed square channels.
Abstract: This investigation presents the heat transfer enhancement results of flow past repeated permeable ribs mounted on the bottom surface of a two-pass square channel. Spatially periodic flow interruption generated by rib arrays mounted on the walls is extensively used for augmentation of heat transfer in turbine blade cooling passages. To remove the local heat transfer deterioration in the vicinity region of the solid ribs, permeable ribs have been proposed in the literature for single pass coolant passages. This study intends to investigate the performance of permeable ribs array placed on the lower wall of a two-pass channel compared to that of the solid rib array. The heat transfer and friction characteristics are investigated for smooth, solid-ribbed, slit-ribbed, and split-slit-ribbed square channels for the Reynolds numbers of 5,500, 12,800, and 16,400. An array of ribs (consisting of fifteen ribs) has been mounted over the total test section, with seven each in the first and second passes, and ...
TL;DR: The overall heat transfer of a cross flow heat exchanger can be enhanced by using the nanofluids as coolant, which finds application in reducing the size and weight of automobile radiator as discussed by the authors.
Abstract: The overall heat transfer of a cross flow heat exchanger can be enhanced by using the nanofluids as coolant, which finds application in reducing the size and weight of automobile radiator. However,...
TL;DR: In this article, the authors present a study on thermal energy storage for decarbonizing the heating sector, facilitating the use of renewable energy sources, in particular solar thermal energy, which has the potential to decarbonize the heating industry.
Abstract: Thermal energy storage has the potential to decarbonize the heating sector, facilitating the use of renewable energy sources, in particular solar thermal energy. In this paper we present a study on...
TL;DR: In this article, the effect of the swirl number on entropy generation was studied numerically in two research flames and a real combustor problem and it was observed that heat transfer and reactions are dominant causes of entropy generation with the leading contribution of reaction at lower swirl numbers and heat transfer at higher swirl values.
Abstract: In this paper, local and global entropy generation features are studied numerically in two research flames and a real combustor problem. The research flames are the well-known Burner Engineering Research Laboratory and Sandia flame D experimental flame databases and the real combustor is a gas-turbine can-type combustor. The main focus is on investigating the effect of the swirl number, in the range 0.0–2.4, on entropy generation characteristics due to different phenomena, including viscous, mass transfer, heat transfer, heat-mass coupling, reaction, and specifically radiation. For this purpose, the surface and volumetric local entropy generation rates are formulated based on the first-order spherical harmonics model known as “P1,” a frequently used model in combustion applications. It is observed that heat transfer and reactions are dominant causes of entropy generation with the leading contribution of reaction at lower swirl numbers and heat transfer at higher swirl values. The radiation entropy...
TL;DR: Pulsating heat pipes (PHPs) are promising heat transfer devices due to their high heat transfer rate, simple construction, and low manufacturing cost as mentioned in this paper. But, most previous investigations focused mainly on...
Abstract: Pulsating heat pipes (PHPs) are promising heat transfer devices due to their high heat transfer rate, simple construction, and low manufacturing cost. Most previous investigations focused mainly on...
TL;DR: In this article, the enhancement of heat transfer rate through staggered pin fins of different shapes with different perforation geometries was investigated, namely circular, diamond shaped and elliptical.
Abstract: The present work investigates the enhancement of heat transfer rate through staggered pin fins of different shapes with different perforation geometries, namely circular, diamond shaped and ellipti...
TL;DR: In this paper, the authors deal with the numerical and experimental analyses to study the detailed behavior of the thermally induced flow of water in an open vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon, and quantify the effect of heating on design parameters such as liquid and wall temperatures, mass flow rate, and heat transfer coefficient.
Abstract: The present work deals with the numerical and experimental analyses to study the detailed behavior of the thermally induced flow of water in an open vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon. Spatio-temporal behavior of fluid flow is also studied for variety of heat fluxes. The annuli in the present study have a radius ratio of 1.184 and aspect ratio (length to annular gap) equal to 352. The objective of the present work is to quantify the effect of heating on design parameters such as liquid and wall temperatures, mass flow rate, and heat transfer coefficient. Experiments have also been conducted on a similar system with water at constant heat flux of 1 kW/m2, 2.5 kW/m2, 5 kW/m2, 7.5 kW/m2, 10 kW/m2, 12.5 kW/m2 and 15 kW/m2. For numerical purpose, a two-dimentional solver has been developed for direct numerical simulation of the essential thermally induced flow dynamics The numerical solution was thus performed for Rayleigh numbers ranging between, 4.4 ×...
TL;DR: In this paper, the authors studied the heat-shielding performance of a beetle forewing to explore how it has excellent thermal protective properties, with an experimental setup of a self-developed heating system.
Abstract: This paper studies the heat-shielding performance of a beetle forewing to explore how it has excellent thermal protective properties. With an experimental setup of a self-developed heating ...
TL;DR: In this paper, the effect of channel size, heat flux, vapor quality, and mass flux on heat transfer in microchannels is addressed, and the authors address the effects of the channel size and heat flux.
Abstract: Flow boiling heat transfer in microchannels is used today in many diverse applications. The previous studies addressing the effect of channel size, heat flux, vapor quality, and mass flux on heat t...