Study Of Conjugate Heat Transfer Research Articles

A Comparative Study of Film Cooling with Combined Impingement and Film Cooling

In order to cool the gas turbine vane or blade and raise the operating temperature, two standard convective cooling methods are used: jet impingement cooling and film cooling. The current study uses computational analysis to analyze and compare film cooling effectiveness with and without multi-jet impingement cooling on a flat plate. Ansys Fluent software is used to perform computational analysis on a flat plate. The computational results were compared with the experimental result using K-ω SST turbulence model and validated with literature data. The flat plate is used for the conjugate heat transfer study on the hot surface (named interaction surface), cold surface (called target surface), and inside the film hole. Different heat transfer parameters such as heat flux, Nusselt's number, and effectiveness are compared for the two cases, i.e., film cooling with impinging jets (IFC) and film cooling without impingement cooling (FC). It is observed that the FC case shows lower effectiveness as compared to the IFC case. The average Nusselt number for the IFC cases is almost three times larger than FC. The film exit temperature values are higher FC case, but it is more uniform in the IFC case. Interaction surface heat flux and Nusselt number values show higher values on the upstream wall of the film hole for IFC than in the FC case.

Numerical study on conjugate heat transfer in a liquid-metal-cooled pipe based on a four-equation turbulent heat transfer model

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metal-cooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor’s safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquid-metal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Prt, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal’s CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k−ε turbulence model and the Manservisi kθ−εθ heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson’s experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquid-metal-cooled fast reactor.

Pore-scale fluid flow and conjugate heat transfer study in high porosity Voronoi metal foams using multi-relaxation-time regularized lattice Boltzmann (MRT-RLB) method

This study aims to investigate pore-scale flow and conjugate heat transfer in high-porosity open-cell metal foams. Five representative elementary volume (REV) samples with different values of porosity (0.80, 0.85, and 0.90) and pore density (10, 20, and 30 PPI) are generated using the Laguerre-Voronoi tessellation (LVT) algorithm. To perform direct numerical simulations, a decoupled lattice Boltzmann solver is developed utilizing multi-relaxation-time (MRT) model for flow and regularized lattice Boltzmann (RLB) model for advection-diffusion. As a novelty, this solver is able to simulate advection-diffusion in the non-Darcy regime. To consider thermal conduction in REV samples more prominently, a constant high temperature is assigned to the solid ligaments on the inlet plane. The flow results show that the transition from the Darcy to the non-Darcy regime occurs at lower Reynolds numbers in foams with lower porosity, whereas the pore density does not affect the transition point significantly. According to the heat transfer results, metal foams cool down rapidly at high flow velocities while the temperature rise in the fluid is minimal. Also, increasing pore density from 10 PPI to 30 PPI and decreasing porosity from 0.90 to 0.80 increase the h-ReK slope in the non-Darcy regime by 190% and 17.5%, respectively.

Conjugate heat transfer study of various cooling structures and sensitivity analysis of overall cooling effectiveness

The conjugate heat transfer of a turbine blade is influenced by several factors. To analyze the influence of each factor, the published one-dimensional conjugate heat transfer model was improved through theoretical analysis in this study. An overall cooling effectiveness equation containing three dimensionless parameters (adiabatic film cooling effectiveness η, Biot number on the mainstream side Big, and ratio between the heat transfer coefficients of the external and internal walls hg/hi) was obtained. The sensitivity of the overall cooling effectiveness ϕ to these three parameters was obtained through a multi-parameter sensitivity analysis. The results showed that increasing η could improve ϕ the most effectively. The interactions between the dimensionless parameters were analyzed by developing sensitivity charts. The results showed that increasing η from 0.4 to 0.5 could reduce the sensitivity of ϕ to the other two parameters by approximately 15%, whereas increasing Big had little effect on the sensitivity of ϕ to each dimensionless parameter. Increasing hg/hi could improve the sensitivity to η. The above conclusions could also be applied to the plate film hole and plate impingement effusion structures. The effects of different internal cooling structures and film hole structures on the three dimensionless parameters were studied by performing numerical simulations, which verified the accuracy of the one-dimensional conjugate heat transfer model in this study. The results showed that the internal cooling structures had little effect on the distribution of η and Big. The heat transfer coefficient on the coolant side could be effectively improved by installing film holes. The film hole structures mainly affected ϕ by influencing the distribution of η.

Flow and heat transfer studies of multijet impingement cooling for different configurations: A review

AbstractIncreasing the gas turbine engine's turbine intake temperature has long been a potential strategy for increasing the specific work output of the engine. However, the melting temperature of the turbine blades and vane material limits the maximum intake temperature. As a result, internal and external cooling techniques are commonly used to maintain the vane material in a safe condition. This study provided an overview of internal impingement cooling to highlight the significance of geometrical variations, such as flat plate, curve plate, and actual vanes. It was observed that flat and curved plate impingement heat transfer studies were reported extensively, whereas limited studies were found on the conjugate effects on airfoil surfaces. The importance of conjugate heat transfer studies and their impact has recently been described in the literature. In most of the literature, a wide range of instruments, such as Laser Doppler Velocimeter, Particle Image Velocimeter, liquid crystal sheets, and so forth, were used for experimental investigations. According to most studies, the local value of internal surface temperature and heat transfer coefficient are vital factors of local flow behavior. Jet‐to‐jet spacing, jet‐to‐plate spacing, jet hole diameter, and jet Reynolds numbers played a crucial role in both numerical and experimental analyses. Different geometric variations strongly influence flow behavior. Therefore, the usual method for determining interior temperature distributions and heat transfer coefficients by considering generalized geometries like the flat and curved plate may not produce accurate conjugate solutions. Most of the computational studies on the flat and curved plate indicate the usage of κ−ω shear stress transport and κ–ε realizable model to predict the heat transfer coefficient.

A computational conjugate heat transfer study of a rectangular minichannel undergoing sinusoidal flow pulsations

The development of current and next generation high performance electronic devices has led to smaller components in more densely packed spaces. The increasing power levels have resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling systems is viewed as a potential solution to the problems involving high heat flux densities. A review of published literature indicates a lack of time-resolved and space-resolved links between the hydrodynamic pulsating characteristics and associated heat transfer perturbations. The scope of this work involves the development of a validated three-dimensional conjugate heat transfer computational model to investigate hydrodynamically and thermally fully developed pulsating flows in a heated rectangular minichannel. Simulations were performed for a sinusoidal waveform with a fixed pulsation amplitude for varying pulsation frequencies in the range of 0.02 Hz to 25 Hz, corresponding to Womersley numbers in the range of 0.5 ≤Wo≤ 18.33. Low pulsation frequencies exhibited the well known parabolic profile for the fluctuating hydrodynamic and thermal parameters, i.e., velocity, wall shear, and wall temperature. As a result, the axial pressure gradient, velocity, and wall shear stress profiles were in phase and similar results were obtained for the oscillating wall and bulk fluid temperatures. For the inertia dominated high frequency flows, an increase in axial pressure gradient leads to a phase lag of π/2 when compared with the velocity and wall shear profiles. The shorter time period pulsations exhibit unique attributes in the form of flow reversal effects at local near wall regions. High near wall thermal gradients were observed as a result of stronger viscous effects due to a narrowing thermal boundary layer; consequently the transverse diffusion of heat was ineffective. A phase lag and a subsequent drop in the peak magnitudes existed between the oscillating bulk and wall temperatures for high frequency flows. Fluctuations in near wall heat flux profiles showed a dependency on the imposed pulsation frequencies. For the chosen pulsation profile and frequencies, the overall time averaged thermal performance indicates that pulsating flow performs worse than steady flow for a flow rate amplitude of 1. The highest thermal performance was achieved for Wo=5.1 while maintaining a low friction factor.

Numerical and experimental study of the transient conjugate heat transfer and fluid flow of passive residual heat removal heat exchanger

The transient heat transfer performance of passive residual heat removal heat exchanger (PRHR HX) with C-tube bundle directly influences nuclear reactor safety under accident condition. This paper presents an investigation of transient conjugate heat transfer and fluid flow phenomena and characteristics of scaled-down single C-tube submerged in water tank under atmospheric pressure at the initial period before saturation pool boiling occurs. Empirical calculation model, experimental setup and numerical model were established separately, and both numerical and experimental studies were carried out. The distributions of tube outlet temperature and water temperatures at horizontal and vertical monitoring points in tank were obtained. Detailed comparisons of the results show good agreements. Also, the change tendencies of heat flux, heat transfer coefficients and heat load were analyzed. The fluctuation of heat flux along normalized length from tube inlet firstly increases but finally tends to keep stable with the change of temperature difference and transformation of heat transfer mechanism. The heat transfer coefficient inside tube shows a slight downtrend along normalized length from tube inlet, but the heat transfer coefficient outside tube shows obvious change in the transient process. The total heat load continuously decreases with time. Furthermore, the volume fraction of vapor is relatively low during the subcooled boiling period. The two-phase flow enhances the agitation in water tank and the fluid velocity near tube outside wall is much larger.

Probing the Accuracy of Experimental Data on Nusselt Numbers Within Miniature Heat Sinks

Abstract Achieving accurate experimental data in conjugate heat transfer studies to calculate Nusselt number can be challenging due to its complex three-dimensional thermal hydraulics nature. This study is devoted to evaluating the accuracy and reliability of experimental approaches used to calculate the Nusselt number in miniature heat sinks. It is observed that three major parameters including (1) axial heat conduction within the solid substrate of heat sinks, (2) thermal contact resistance, and (3) assumed uniform wall temperature, as well as wall heat flux distributions, influence the reported experimental data in the literature. The results obtained from the developed analytical and computational models in this study revealed that the assumptions of local uniform wall temperature and heat flux distributions for small-scale heat sinks result in underestimated Nusselt numbers calculated from experiments. At lower Reynolds number (<200) flows in miniature heat sinks with a high solid to fluid thermal conductivity ratio (>> 1), it is shown that the fluid bulk temperature should be measured away from the heat sink inlet and outlet to minimize the effect of axial heat conduction within the solid substrate of the microscale heat sinks on calculated Nusselt numbers. As the third important parameter, the influence of thermal contact resistance on the Nusselt number calculation in a miniature heat sink is studied where thermal slip length is considered. Finally, the concurrent effects of thermal contact resistance and thermal developing region are considered to explicate the obtained trends in the experimental Nusselt numbers dataset.

Computational modeling and conjugate heat transfer study for in situ design of artificial porous media at varied orientations

Computational modeling and design of artificial porous media has gained immense attention in recent years due to its numerous applications, particularly in the biomedical and electrical industries. Conjugate heat transfer study of porous media in an enclosure is performed in several applications to study generated heat dissipation. The present work investigates the characteristics of conjugate heat transfer on various orientations of computationally modeled artificial porous media structure. In the study, the rate of heat transfer is compared for horizontal and vertical orientations of the porous structures which mainly consists of holes and pores. The study also investigates the effect of porosity on heat transfer. Furthermore, the study establishes that for both horizontal and vertical orientations, an increase in porosity results in an increase of the heat transfer rate from the porous media. The work also discusses, the heat transfer occurring due to forced convection in porous structures. Also, we considered a range of velocities from 1 m/s to 4.5 m/s for analyzing the effect of flow rate on the average heat flux.

Conjugate heat transfer study of hypersonic flow past a cylindrical leading edge composed of functionally graded materials

Aero-thermodynamic analysis of a cylindrical leading edge placed in a hypersonic stream is carried out using an in-house developed conjugate heat transfer (CHT) solver. Isotropic and functionally graded materials (FGM) are tested as heat shields to understand the effects of the material property on the flow structure and aerodynamic heating associated with the mutual coupling of fluid flow and heat transfer. A simplified partitioned approach is employed to couple the independently developed fluid flow and heat transfer solvers to perform conjugate heat transfer studies. This framework employs a cell-centred finite volume formulation with an edge-based algorithm. Both strong and loose coupling algorithms are implemented for the data transfer across the fluid–solid interface. A test case of hypersonic flow over a cylindrical leading edge composed of an isotropic material is considered to validate the accuracy and correctness of numerical formulation adopted in the in-house solver. The significance of solid domain materials on the conjugate heat transfer has been studied by considering both isotropic material and FGM. The loosely coupled CHT solver required 10 times less simulation time when compared with the strongly coupled CHT solver. The interface heat flux evolution over time showed a decreasing trend, whereas an increasing trend was for the interface temperature. The current study strongly recommends CHT analysis for the design of thermal protection system of space vehicles. The thermal performance of FGMs composed of various volume fractions of Zirconia and Titanium alloy (Ti6Al4V) is assessed. The temperature distributions obtained from the CHT analysis shows that FGM with a power index of unity is a good material choice for thermal protection systems.

Development of a Novel DEMO divertor target: spiral plate module

In DEMO, the divertor must endure steady state loads of 10 MW m−2 and transient thermal cycling up to 20 MW m−2. A novel divertor target, termed the Spiral Plate Module (SPM) and designed to meet these loads, was initially optimized by a one-dimensional, steady-state model. The best design was a trade-off between the wall overheat (τ s )—a figure of merit for cooling performanceand the pumping ratio (η P )—a comparison of the pressure drop and the incident heat flux on a target surface. A three-dimensional, steady-state, conjugate heat transfer study showed significant correlation to the one-dimensional model. Compared to other divertor target concepts, the SPM achieved the lowest wall overheat of any target design. The hydraulic performance was also on par with comparable designs, demonstrating a very low pumping ratio. This novel, modular divertor target could be used in future fusion power plants to effectively cool the plasma facing components with low pressure drop.

Conjugate heat transfer analysis of rectangular cooling channels using modeled and direct numerical simulation of turbulence

We carry out a computational study of conjugate heat transfer in rectangular cooling channels typical of liquid propellant rocket engines, with the goal of establishing the predictive capability of Reynolds averaged Navier-Stokes (RANS) solvers. A classical Spalart-Allmaras RANS solver is here used, which is iteratively coupled with a Fourier solver which solves for conduction within the duct walls. Comparison is made with the reference solutions of the same problem obtained with a direct numerical simulation (DNS) approach, which allows to describe the full features of flow and heat evolution in the channel. Numerical simulations are carried out for different values of the fluid-solid thermal conductivity ratio to bring out conjugate heat transfer effects. Finite conductivity of the solid is found to imply reduced thermal efficiency of the overall system as a result of both increased thermal resistance, and asymmetric heat loading on the fluid. We find that, despite the absence of the secondary motions, the RANS/Fourier solver can accurately estimate the pressure drop. Differences in the prediction of thermal effects are generally larger. However, the wall temperature distributions are predicted by RANS with reasonable accuracy, and discrepancy in the overall heat transfer coefficient is no larger than 10%.

Numerical Study Using Microstructure Based Finite Element Modeling of the Onset of Convective Heat Transfer in Closed-Cell Polymeric Foam.

The thermal performance of closed-cell foams as an insulation device depends on the thermal conductivity. In these systems, the heat transfer mode associated with the convective contribution is generally ignored, and studies are based on the thermo-physical properties that emerge from the conductive contribution, while others include a term for radiative transport. The criterion found in the literature for disregarding convective heat flux is the cell diameter; however, the cell size for which convection is effectively suppressed has not been clearly disclosed, and it is variously quoted in the range 3–10 mm. In practice, changes in thermal conductivity are also attributed to the convection heat transfer mode; hence, natural convection in porous materials is worthy of research. This work extends the field of study of conjugate heat transfer (convection and conduction) in cellular materials using microstructure-based finite element analysis. For air-based insulating materials, the criteria to consider natural convection () is met by cavities with sizes of 9.06 mm; however, convection is developed into several cavities despite their sizes being lower than 9.06 mm, hence, the average pore size that can effectively suppress the convective heat transfer is 6.0 mm. The amount of heat transported by convection is about 20% of the heat transported by conduction within the foam in a , which, in turn, produces an increasing average of the conductivity of about 4.5%, with respect to a constant value.

Designing of microsink to maximize the thermal performance and minimize the Entropy generation with the role of flow structures

Designing a novel microsink with geometric structures for better cooling of compact tiny-sized electronic devices at lower pressure drop is the utmost desire of recent technological development. A three-dimensional numerical study of conjugate heat transfer has been carried out to propose a microsink with the disruptive structures placed symmetrically about the vertical midplane in a rectangular microchannel. The channels are made of silicon with the structures like triangular cavity (TC), secondary branches (SB) and blockage (B) with water as a working fluid. The effects of these structures are illustrated by heat transfer, friction factor, thermal performance (TP), entropy generation (EG) due to heat transfer, entropy generation (EG) due to pressure drop and entropy generation number (EGN) over the range of Reynolds number (Re) from 146 to 618. The best channel has been identified from the rigorous analysis among the microchannels with the only triangular cavity (TC), triangular cavity with the secondary branch (TCSB) and triangular cavity along with secondary branch and blockage (TCSBB) from the highest TP and minimum EGN. These two models have been chosen to find out a best channel as criteria of highest heat transfer with the same pumping power from the highest TP and minimum temperature of electronic sink from the lowest EGN. The highest TP and lowest EGN are obtained from the channel TCSBB compared to other three channels. The parametric variation of relative angle of the secondary branch, length of cavity, width of secondary branch and cavity, pitch distance have been varied to find the maximum TP and the minimum EGN. The values have been obtained equal to 2.01 and 0.41 respectively at Re of 480. The significant roles of longitudinal vortex on the augmentation of heat transfer and minimizations of EG mechanism with the alteration of geometrical parameters are exploited and described explicitly. Finally, the correlations of heat transfer enhancement and rise in pressure drop dependent on geometric parameter have been inscribed based on Response surface methodology.

Conjugate Heat Transfer Study of Innovative Pin-Fin Cooling Configuration

The Paper involves experimental and numerical heat transfer analyses of four pin-fin cooling configurations in a rectangular channel. Two design concepts were studied with two separate pin-fin (cylindrical and triangular) geometries. The first design includes a single-wall pin-fin configuration where the coolant flows through an array of full-length cylindrical (PF) and triangular pin fins (TF). The second configuration involves a double-wall pin-fin–jet configuration where the coolant jet impinges on the target wall, then flows through the array of partial-length cylindrical pin fins with jets (PFC) and partial-length triangular pin fins with jets (TFC). IR thermography was used to measure the steady state wall temperature of the target surface to estimate the overall cooling effectiveness . A transient heat transfer experiment was conducted to evaluate the internal heat transfer coefficient from the transient wall temperature. It is found that the double-wall pin-fin–jet (PFC and TFC) configurations show higher cooling effectiveness compared to the single-wall pin-fin (PF and TF) designs and the triangular pin fin (TF and TFC) showed a higher heat transfer augmentation compared to the cylindrical pin fin (PF and PFC) design. Numerical study later confirmed that the triangular pin fin creates a pair of streamwise vortices that augments the local heat transfer. The presence of the pin fin in the double-wall configuration prevents the development of a strong crossflow that negatively affects the heat transfer of the impinging jet. In addition, the triangular pin fin not only prevents the strong crossflow but redirects the coolant in the lateral direction that eventually contributes to the formation of a counterrotating vortex pair in the streamwise direction and thus augments local heat transfer and improves overall cooling effectiveness. Pressure drop measurement showed that the full-length triangular pin fin has a higher-pressure loss but the partial-length pin fin can lower the pressure loss considerably without compromising additional cooling performance.

Conjugate heat transfer study comprising the effect of thermal conductivity and irreversibility in a pipe filled with metallic foams

A parametric study is proposed in this paper to examine heat dissipation rate and entropy generation of a forced convection in a horizontal pipe which is filled with high porous metallic foams. The study quantifies the effect of thermal conductivity and pore density on entropy generation when the pipe is fully filled with copper, aluminium and nickel metallic foams of 0.6 m length in the fluid flow direction. To predict fluid flow and heat transfer features through these metallic foams the Darcy-extended Forchheimer (DEF) flow and the local thermal non-equilibrium (LTNE) models are employed. The characteristics of laminar, transition and turbulent in the non-foam region of the pipe are captured by considering the appropriate flow models. To affirm the methodology adopted in this work, the results of the present numerical solutions are validated with the available experimental results reported in the literature. Colburn j factor and thermal performance factor are the important factors that decide the performance and efficiency of any heat exchange device. Hence, these parameters are critically evaluated and are observed to increase with increasing pore densities of the metal foams and decrease with increasing flow rates of the fluid. Furthermore, the numerical analysis is extended to obtain the results of wall temperature, Nusselt number, heat transfer enhancement ratio, frictional irreversibility and Bejan number.

Conjugate heat transfer study of the impact of ‘thermo-swing’ coatings on internal combustion engines heat losses

To comply with the very strict emissions regulation the automotive industry is succeeding in developing ever more efficient engines, and there is scope for more improvements. In this regard, some investigations have suggested that insulating the combustion chamber walls of an internal combustion engine (ICE) yield low thermal losses. Most of the literature available on this topic presents simplified models that do not allow studying in detail the coating impact on engine efficiency. A more precise approach that consists in the combination of Computational Fluid Dynamics (CFD) and Conjugate Heat Transfer (CHT) simulations is used in this paper to predict the heat losses through the combustion chamber walls of a spark ignition (SI) engine. Two configurations are considered for the single cylinder engine: the metallic case and the same engine with coated piston and cylinder head. The insulation material has a low thermal conductivity ( k[Formula: see text]1.0 W/( mK)). The numerical results are validated by comparison with the results of a 1D heat transfer model and with experimental data for a medium load operation point (3000 rpm −7 bar IMEP). The solutions obtained are analysed in detail in terms of wall temperature distribution and heat transfer. The impact of the coating on the engine efficiency is thus assessed. The CFD-CHT calculations yields very good results in terms of heat transfer prediction during the whole engine cycle.

Conjugate heat transfer study of backdisc cooling of a radial turbine

Radial turbines used in turbochargers and micro-turbines are subjected to high inlet temperature. This creates high thermal stress in the turbines, and possible creep of turbine inducer blades, and can reduce turbines’ reliability. With the ever-stringent engine emission regulations and the continuous drive for engine power density, turbine inlet temperature is significantly increased recently and the risk of thermo-mechanical failure of turbine rotor is heightened. To solve this problem, an innovative turbine cooling method is proposed by injecting a small amount of compressor or intercooler discharge air onto the upper backdisc region of turbine rotor to cool the disc and the inducer blades. A conjugate heat transfer simulation was carried out to investigate the effects of this cooling method with a turbocharger turbine. Flow conditions and geometric configurations were investigated for their influences on the cooling effectiveness of the method. The results show that using the compressor discharger air after intercooler with only 0.5–2.0% of turbine mass flow, the averaged cooling efficiency of the turbine backdisc is promoted by 23–43%; only four to six jets may be needed to cool the entire backdisc; and turbine efficiency is reduced by less than 1% point.

Shock wave boundary layer interactions in hypersonic flows over a double wedge geometry by using conjugate heat transfer

AbstractShock wave boundary layer interaction phenomena play a critical role in the design of supersonic and hypersonic vehicles. Consequently, this paper mainly focuses on hypersonic flow over a double wedge model, flow fields around concave corners are relatively complicated, and produce several classical viscous flow features depending on the combination of the first and second wedge, and the important characteristic phenomena are mainly the shock‐boundary layer and shock‐shock interaction. For these interactions, aerodynamic heating and pressure loads increase greatly when interactions are present. The conjugate heat transfer (CHT) technique is expected to exactly predict the separation bubble length, heat flux, skin friction coefficient, and pressure distributions in double wedge studies in hypersonic applications. In the present CHT studies, the different wall materials used are thermal insulation, Macor, and SiC, it is clearly shown that while using Macor and thermal insulctation wall material in CHT studies, the interface temperature, skin friction coefficient, heat flux distribution along the length change significantly with increase in simulation time. In comparing the CHT results with the fluid flow solver with the wall, considering isothermal and adiabatic boundary results, it is clearly indicated that the fluid flow solver results are either underpredicting or overpredicting the interface properties, but CHT studies give an accurate prediction of the separation length and interface properties.

The Role of Flow Structures on the Thermal Performance of Microchannels With Wall Features

Abstract Innovative design of microchannel heat sinks (MCHS) remains a contemporary research need to meet the increasing cooling demand of modern electronic industries. A transient three-dimensional conjugate heat transfer study has been carried out here for different combinations of constrictors like ribs or protrusions along with cavities on the sidewalls of a microchannel (MC). A facing pair of cavities with circular arc sections, together called a fan-shaped cavity (FC), has been considered. Each in the facing pair of ribs (R) or protrusions (P) is in the form of a part of cylinder or sphere, respectively. The results include the variations of Nusselt number, friction factor, and thermal performance over a range of Reynolds numbers from 140 to 605 in microchannels with rib (MCR), protrusion (MCP), or cavity pairs alone (MCFC), as well as with cavity-rib pairs (MCFCR) or cavity–protrusion pairs (MCFCP). Contrasting the highest thermal performance of 1.6 reported in an earlier study on MCFCR, a value as high as 1.76 has been obtained around Re of 550 for MCFCP with the relative values of cavity length, width, and pitch of 0.015, 0.5, and 0.0625, respectively, along with protrusion length and width of 0.01 and 0.4, respectively. The mechanisms leading to spiraling transverse streamlines in both MCFCR and MCFCP have been explained. The superior performance of MCFCP has presumably arisen from the vortex structure with no interference with the boundary layers at the top and bottom walls.