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research-article  
Matthew Ralphs, Chandler Scheitlin, Robert Y. Wang and Konrad Rykaczewski
J. Heat Transfer   doi: 10.1115/1.4041539
Thermally conductive soft composites are in high demand and aligning the fill material is a potential method of enhancing their thermal performance. In particular, magnetic alignment of nickel particles has previously been demonstrated as an easy and effective way to improve directional thermal conductivity of such composites. However, the effect of compression on the thermal performance of these materials has not yet been investigated. This work investigates the thermal performance of magnetically aligned nickel fibers in a soft polymer matrix under compression. The fibers orient themselves in the direction of the applied magnetic field and align into columns, resulting in a 3x increase in directional thermal conductivity over unaligned composites at a volume fraction of 0.15. Nevertheless, these aligned fiber columns buckle under strain resulting in an increase in the composite thermal resistance. These results highlight potential pitfalls of magnetic filler alignment when designing soft composites for applications where strain is expected such as thermal management of electronics.
research-article  
Muhammad Farooq, Shakeel Ahmad, Mubashar Javed and Aisha Anjum
J. Heat Transfer   doi: 10.1115/1.4041497
In this attempt, melting heat transfer characteristic of unsteady squeezed nanofluid flows in non-Darcy porous medium is interrogated. The nanofluid model incorporates Brownian diffusion and thermophoresis to characterize the heat and mass transport in the presence of thermal and solutal stratification. Similarity solutions are implemented to acquire non-linear system of ordinary differential equations which then evaluated using Homotopic technique. Flow behavior of involved physical parameters is examined and explanations are stated through graphs. We determine and analyze skin friction co-efficient, Nusselt and Sherwood numbers through graphs. It is evident that larger melting parameter results decrement in temperature field, while horizontal velocity enhances for higher melting parameter. Moreover, temperature and concentration fields are dominant for higher Brownian diffusion parameter.
TOPICS: Flow (Dynamics), Melting, Heat transfer, Nanofluids, Temperature, Diffusion (Physics), Heat, Skin friction (Fluid dynamics), Differential equations, Nonlinear systems, Porous materials
research-article  
Mansour Nasiri Khalaji, Isak Kotcioglu, Sinan Caliskan and Ahmet Cansiz
J. Heat Transfer   doi: 10.1115/1.4041498
This paper presents the second law analysis of a cross flow forced convection heat exchanger consisting of the pin fins in cylindrical, square and hexagonal shapes placed in a rectangular duct. The pin fins are placed periodically at the top and bottom plates of the duct perpendicular to the flow direction, structured in-line and staggered sheet layouts. Distribution of entropy generation is investigated to demonstrate the rate of irreversibilities in the flow domain. To determine the energy and exergy efficiencies, irreversibility, thermal performance factor and entropy generation number, the heat exchanger is operated at different temperatures and the flow rates by using hot and cold fluids. Optimization of the design parameters and winglet geometry associated with the performance of the heat exchanger are determined by entropy generation minimization. The variation of the entropy generation number due to the heat transfer, fluid friction and optimal cases as a function of Reynolds number for the different pin fins is presented. The Reynolds number is determined according to the experimental plan and performance analysis is accomplished in terms of e-NTU method. It was determined that the increment in fluid velocity enhances the heat transfer rate, which in turn decreases the heat transfer irreversibility.
TOPICS: Thermodynamics, Heat exchangers, Cross-flow, Entropy, Heat transfer, Fins, Flow (Dynamics), Reynolds number, Ducts, Fluids, Viscosity, Temperature, Exergy, Design, Forced convection, Geometry, Shapes, Optimization, Plates (structures)
research-article  
X.Y. Zhang, Y. Peng and X.F. Li
J. Heat Transfer   doi: 10.1115/1.4041419
In this paper, a non-Fourier model of heat conduction and moisture diffusion coupling is proposed. We study a hygrothermal elastic problem within the framework of time-fractional calculus theory for a centrally symmetric sphere subjected to physical heat and moisture flux at its surface. Analytic expressions for the transient response of temperature change, moisture distribution, displacement and stress components in the sphere are obtained for heat/moisture flux pulse and constant heat/moisture flux at the sphere's surface, respectively, by using the integral transform method. Numerical results are calculated and the effects of fractional order on temperature field, moisture distribution, and hygrothermal stress components are illustrated graphically. Sub-diffusive and super-diffusive transport coupling behavior as well as wave-like behavior are shown. When fractional-order derivative reduces to 1st-order derivative, the usual heat and moisture coupling is recovered, which obeys Fourier heat conduction and Fick's moisture diffusion.
TOPICS: Heat, Temperature, Diffusion (Physics), Heat conduction, Stress, Waves, Transients (Dynamics), Displacement
Technical Brief  
Mohsen Rostam and Elham Omidbakhsh Amiri
J. Heat Transfer   doi: 10.1115/1.4041324
The efficiency of industrial heat equipment can be increased using baffles. The shape of baffles is one of the effective parameters. In this work, the effect of shapes of asymmetric baffles on the thermal performance has been investigated. Four different shapes as Rectangular diagonal, Trapezoidal, Triangular and Semi Ellipsoid, as well as, vertical Rectangle (as the base model) were used. Also, four non-Newtonian fluids were used as the working fluid. The governing equation which models the physical phenomenon was solved with the finite volume method. The results showed that better thermal performance could be observed with Semi Ellipsoid baffle for all four non-Newtonian fluids. However, for different models of non-Newtonian fluids, the average of increasing of thermal performance with different percent was achieved. By comparing different models of non-Newtonian fluids, Shear-thinning model shows better thermal performance than other models.
TOPICS: Non-Newtonian fluids, Shapes, Finite volume methods, Heat, Fluids, Shear (Mechanics)
research-article  
S.Y. Misyura and Vladimir Morozov
J. Heat Transfer   doi: 10.1115/1.4041323
Evaporation of layers of aqueous solutions of salts (LiBr, CaCl2, NaCl, MgCl2, BaCl2, CsCl) is studied experimentally. Experimental data are compared with evaporation of the water layer. The solution is placed on a horizontal surface of a cylindrical heating section. Experiments on surface crystallization of salts are carried out. For aqueous solutions of salts LiBr, LiCl and CaCl2 there is an extremum for the heat transfer coefficient al. For water and for solutions of salts NaCl and CsCl the extremum is absent. The first factor is a decreasing function of time, and the second factor is an increasing function of time. For the water layer, both factors continuously increase with time, and the maximum evaporation rate corresponds to the final stage of evaporation. The heat balance for interface layer is made up. The role of the free gas convection in the heat balance strongly depends on the salt concentration and varies with the rise of evaporation time. For low salt concentrations the influence of free convection in the gas phase on heat transfer in the liquid phase can be neglected; however, for high concentrations this effect is comparable with other factors. The curves for the rate of crystallization have been built. More than two times difference between the experiment and the calculation is associated with the kinetics of dendritic structures.
TOPICS: Evaporation, Water, Heat, Crystallization, Convection, Heat transfer, Heating, Heat transfer coefficients, Natural convection
research-article  
Amirhossein Mostafavi, Shunkei Suzuki, Sumeet Changla, Aditya Pinto, Shigetoshi Ipposhi and Donghyun Shin
J. Heat Transfer   doi: 10.1115/1.4041241
Recent studies have shown that doping nanoparticles into a molten salt eutectic can induce salt molecules to form a stelliform nanostructure that can enhance the effective heat capacity of the mixture. This phenomenon can result from a unique characteristic of a eutectic molten salt system, which can self-form a nanostructure on a nanoscale solid surface. Hence, such an enhancement was only observed in a molten salt eutectic. Similarly, a stelliform nanostructure can be artificially synthesized and dispersed in other liquids. Mixing polar-ended molecules with a nanoparticle in a medium can induce the polar-ended molecules ionically bonded to a nanoparticle to form a stelliform nanostructure. Hence, this may enhance the effective heat capacity of the mixture. In this study, we disperse various nanoparticles and polar-ended materials into a sodium acetate trihydrate at different ratios to explore the effect of nanoparticle type and concentration as well as polar-ended materials and their concentrations on the resultant heat capacity of sodium acetate trihydrate. The result shows the specific heat capacity was the highest with silica nanoparticle at 1 % concentration of weight and polar-ended material at 4 % concentration.
TOPICS: Specific heat, Sodium, Nanoparticles, Heat capacity, Nanoscale phenomena, Weight (Mass)
research-article  
Shirin Niroomand, Melanie Fauchoux and Carey J. Simonson
J. Heat Transfer   doi: 10.1115/1.4041185
This paper investigates frost formation on a flat horizontal surface, with humid air flowing over the surface and a cold liquid desiccant flowing below the surface. Two different surfaces, a semipermeable membrane and an impermeable plate are tested. The condensation/frosting limit, that is, the lowest air humidity ratio, Wair at a constant liquid temperature, Tliq, or the highest Tliq at a constant Wair that leads to condensation/frosting, is determined for each surface. The main aim of this study is to find the effect of moisture transfer through the semipermeable membrane on the condensation/frosting limit. It is found that the semipermeable membrane has a lower condensation/frosting limit, due the moisture transfer through the semipermeable membrane, which dehumidifies the air flow. For a given Wair, the surface temperature can be approximately 5 to 8°C lower when using a semipermeable membrane, compared to an impermeable plate, before condensation/frosting occurs. Furthermore, it is shown that at some operating conditions, frost appears on the semipermeable membrane only at the air flow entrance of the test section, while the impermeable plate was fully covered with frost at the same operating conditions. Moreover, it is shown that increasing the moisture transfer rate through the semipermeable membrane, decreases the frosting limit and delays frost formation.
TOPICS: Condensation, Membranes, Temperature, Air flow, Delays
research-article  
Jianyang Yu, Zhao Wang, Fu Chen, Guojun Yan and Cong Wang
J. Heat Transfer   doi: 10.1115/1.4041186
The dielectric barrier discharge (DBD) plasma actuator, in which electrodes are asymmetric arranged, has already demonstrated its ability in flow control. In the present work, the configuration of DBD plasma actuator defined as DBD-VGs, which can induce streamwise vortices, has been employed in the flow control of the inclined jet in crossflow. The coherent turbulent structures around the cooling hole are examined by the large eddy simulation (LES) method with the improved plasma model. The mechanism of coherent structure controlled by the DBD-VGs is also elucidated in the processes of parametric study with the actuation conditions. The calculation results show that the DBD-VGs provides us an effective approach to further enhance the performance of the film cooling. When it is applied into the flow, symmetrical streamwise vortices are induced to break down the coherent vortex structure, leading to more coolant gathered on the surface, especially at the lateral area of the coolant jet. What's more, an overall improvement of the film cooling performance can be obtained when the actuation strength is strong enough.
TOPICS: Plasmas (Ionized gases), Jets, Actuators, Large eddy simulation, Film cooling, Vortices, Flow control, Coolants, Electrodes, Flow (Dynamics), Cooling, Turbulence, Symmetry (Physics)
research-article  
Bugra Sarper, Mehmet Saglam and Dr. Orhan Aydin
J. Heat Transfer   doi: 10.1115/1.4041187
In this study, convective heat transfer in a discretely heated parallel-plate vertical channel which simulates an IC package is investigated experimentally and numerically. Both natural and mixed convection cases are considered. The primary focus of the study is on determining optimum relative lengths of the heat sources in order to reduce the hot spot temperature and to maximize heat transfer from the sources to the air. Various values of the length ratio and the modified Grashof number (for the natural convection case) / the Richardson number (for the mixed convection case) are examined. Conductive and radiative heat transfer is included in the analysis while air is used as the working fluid. Surface temperatures of the heat sources and the channel walls are measured in the experimental study. The numerical studies are performed using a commercial CFD code, ANSYS FLUENT. The variations of surface temperature, hot spot temperature, Nusselt number and global conductance of the system are obtained for varying values of the working parameters.
TOPICS: Heat, Electronic packages, Temperature, Mixed convection, Natural convection, Heat transfer, Radiative heat transfer, Fluids, Electrical conductance, Computational fluid dynamics, Convection
research-article  
Mehdi Karabi and Ali Jabari Moghadam
J. Heat Transfer   doi: 10.1115/1.4041189
The hydrodynamic and thermal characteristics of electroosmotic and pressure-driven flows of power-law fluids are examined in a semi-circular microchannel under the constant wall heat flux condition. For sufficiently large values of the electrokinetic radius, the Deye length is thin; the active flow within the electric double layer drags the rest of the liquid due to frictional forces arising from the fluid viscosity and consequently a plug-like velocity profile is attained. The velocity ratio can affect the pure electrokinetic flow as well as the flow rate depending on the applied pressure gradient direction. Since the effective viscosity of shear-thinning fluids near wall is quite small compared to the shear-thickening fluids, the former exhibits higher dimensionless velocities than the later close to the wall; the reverse is true at the middle section. Poiseuille number increases with increasing the flow behavior index and/or the electrokinetic radius. Due to the comparatively stronger axial advection and radial diffusion in shear-thinning fluids, better temperature uniformity is achieved in the channel. Reduction of Nusselt number continues as far as the fully-developed region where it remains unchanged; as the electrokinetic radius tends to infinity, Nusselt number approaches a particular value (not depending on the flow behavior index).
TOPICS: Flow (Dynamics), Heat transfer, Electroosmosis, Non-Newtonian fluids, Pressure gradient, Fluids, Electrokinetics, Shear (Mechanics), Viscosity, Diffusion (Physics), Poiseuille flow, Microchannels, Heat flux, Temperature uniformity, Pressure
research-article  
Yuanwei Lyu, Jing-zhou Zhang, Yong Shan and Xiao-ming Tan
J. Heat Transfer   doi: 10.1115/1.4041183
A series of tests were performed for the pulsating jet impingement heat transfer by varying the Reynolds number (5000?Re?20000), operation frequency (10Hz<=f<=25Hz) and dimensionless nozzle-to-surface distance (1?H/d?8) while fixing the duty cycle at DC=0.5(280 measurement data in total). Specific attention was paid to examine the relationship between the pulsating jet impingement and the steady jet impingement. By using a modified Strouhal number (Sr(H/d)), the test data are analyzed according to three classifications of the enhancement factors a=Nupulsation jet/Nusteady jet (such as a=?(Min,0.899), a?(0.95, 1.049) and a?(1.1, Max)). The results show that the identification of pulsating jet impingement in related to the steady jet impingement is suitable by using the modified Strouhal number (Sr(H/d)). Within the scope of this study, the most possibilities for the heat transfer enhancement by using pulsating jet impingement are suggested as the following conditions: Re<=7500 and Sr(H/d)>=0.04, Re>=17500 and 0.01<=Sr(H/d)<=0.03; 10Hz<=f<=20Hz and Sr(H/d)>=0.04; H/d>=6 and most of current Sr(H/d). While under such conditions, 7500<=Re<=15000 and Sr(H/d)<=0.02; f>=20Hz and Sr(H/d)>=0.04; H/d<=2 and Sr(H/d)<=0.02, the pulsating jet impingement makes the heat transfer weaker than the steady jet impingement more obviously.
TOPICS: Heat transfer, Flat plates, Reynolds number, Nozzles, Cycles
Technical Brief  
Mustafa Turkyilmazoglu
J. Heat Transfer   doi: 10.1115/1.4041184
This short brief is to address the boundary layer flow of motion due to a rotating as well as stretchable/shrinkable flexible cone in an otherwise still fluid. It is shown that the relevant information on the progress of the triggered boundary layer structure can be obtainable from the limiting traditional deformable rotating disk flow of von Karman, recently published in the literature. Thus, the physical parameters of great interest from the engineering point of view concerning a cone of a particular apex angle can be easily deduced as a multiplying factor corresponding to the deformable rotating disk flow.
TOPICS: Flow (Dynamics), Heat transfer, Fluids, Boundary layers, Rotating Disks
research-article  
Subhasisa Rath and Sukanta K. Dash
J. Heat Transfer   doi: 10.1115/1.4040954
Natural convection heat transfer over horizontal solid cylinders has been studied numerically by varying the Rayleigh number in the range of (10^4<=Ra<=10^8) and (10^10<=Ra<=10^13) for both laminar and turbulent flows, respectively. The computations were carried out for three different geometries of 3, 6 and 10 cylinders in a stack arranged in a triangular manner having same characteristic length scale. The present numerical investigation on natural convention is able to capture a very interesting flow pattern and temperature field over the stack of horizontal cylinders which has never been reported in the literature so far. Visualization of plume structure over the horizontal cylinders has also been obtained pictorially in the present work. From the numerical results, it has been observed that the total heat transfer is marginally higher for 3 cylinders stack in the laminar range. In contrast, for turbulent flow, starting from Ra=10^10, heat transfer for 6 cylinders case is higher but when Ra exceeds 5×10^11 heat transfer for 10 cylinders stack is marginally higher. Whereas, average surface Nusselt number is higher for 3 cylinders stack compared to 6 and 10 cylinders cases for all range of Ra in both laminar and turbulent regime. A correlation for average Nusselt number has also been developed as a function of Rayleigh number which may be useful for researchers and industrial purposes.
TOPICS: Heat transfer, Natural convection, Cylinders, Turbulence, Rayleigh number, Visualization, Computation, Plumes (Fluid dynamics), Flow (Dynamics), Temperature
research-article  
Andrey Gusarov
J. Heat Transfer   doi: 10.1115/1.4040958
The statistical multiphase approach proposed in the first part of this work to evaluate radiative properties of composite materials is applied to porous structures of opaque material and biological tissues. Radiative thermal conductivity is calculated for the bundle of circular rods, packed pebble beds, and metal foams. The results generally agree with the reference calculations by other methods. The small difference can be explained by different approaches to scattering and assumptions about the temperature distribution. Attenuation of light in skin tissues is calculated by the diffusion approximation. The attenuation coefficient generally agrees with the reference Monte Carlo simulation. The difference observed at certain combination of parameters can be due to the assumption of regular arrangement of vessels at the Monte Carlo simulation.
TOPICS: Diffusion (Physics), Radiative heat transfer, Scattering (Physics), Composite materials, Simulation, Radiation scattering, Electromagnetic scattering, Thermal conductivity, Biological tissues, Approximation, Metal foams, Rods, Skin, Temperature distribution, Thin wall structures, Vessels
research-article  
Zahir Shah, Saeed Islam, Hamza Ayaz and Saima Khan
J. Heat Transfer   doi: 10.1115/1.4040415
The present research aims to examine the micropolar nanofluid of Casson fluid between two parallel plates in a rotating system with effects of thermal radiation. The effects of Hall current on the micropolar nanofluids are have been taken into account. The flow of micropolar nanofluid has been assumed in steady state. The rudimentary governing equations have been changed to a set of differential nonlinear and coupled equations using suitable similarity variables. An optimal approach has been used to acquire the solution of the modelled problems. The convergence of the method has been shown numerically. The impact of the Skin friction on velocity profile, Nusslet number on temperature profile and Sherwood number on concentration profile have been studied. The influences of the Hall currents, rotation, Brownian motion and thermophoresis analysis of micropolar nanofluid have been mainly focused in this work. Moreover, for comprehension the physical presentation of the embedded parameters have been plotted and deliberated graphically.
TOPICS: Flow (Dynamics), Heat, Mass transfer, Fluids, Plates (structures), Nanofluids, Steady state, Temperature profiles, Rotation, Brownian motion, Skin friction (Fluid dynamics), Thermal radiation, Hall effect
research-article  
Giuseppe Romano and Alexie Kolpak
J. Heat Transfer   doi: 10.1115/1.4040611
Nanostructured semiconducting materials are promising candidates for thermoelectrics due to their potential to suppress phonon transport while preserving electrical properties. Modeling phonon-boundary scattering in complex geometries is crucial for predicting materials with high conversion efficiency. However, the simultaneous presence of ballistic and diffusive phonons challenge the development of models that are both accurate and computationally tractable. Using the recently developed first-principles Boltzmann transport equation (BTE) approach, we investigate diffusive phonons in nanomaterials with wide mean-free-path (MFP) distributions. First, we derive the short MFP limit of the suppression function, showing that it does not necessarily recover the value predicted by standard diffusive transport, challenging previous assumptions. Second, we identify a Robin type boundary condition describing diffuse surfaces within Fourier's law, extending the validity of diffusive heat transport in terms of Knudsen numbers. Finally, we use this result to develop a hybrid Fourier/BTE approach to model realistic materials, obtaining good agreement with experiments. These results provide insight on thermal transport in materials that are within experimental reach and open opportunities for large-scale screening of nanostructured thermoelectric materials.
TOPICS: Phonons, Nanostructures , Boundary-value problems, Model development, Heat, Scattering (Physics), Semiconductors (Materials), Radiation scattering, Electromagnetic scattering, Electrical properties, Mean free path, Modeling, Nanomaterials
research-article  
Marcelo J.S. de Lemos and Paulo Carvalho
J. Heat Transfer   doi: 10.1115/1.4039915
This work presents a study of double-diffusive free convection in a porous square cavity under turbulent flow regime and with aiding drive. The thermal non-equilibrium model was employed to analyze the energy and mass transport across the enclosure. Governing equations were time- and volume averaged according to the double-decomposition concept. Analysis of a modified Lewis number, Lem, showed that for porous media this parameter presents opposite behavior when varying the thermal conductivity ratio or the Schmidt number, while maintaining the same value for Lem. Differently form free flow, the existence of the porous matrix contributes to the overall thermal diffusivity of the medium, whereas mass diffusivity is only effective within the fluid phase for an inert medium. Results indicated that increasing Lem through an increase in Sc reduces flow circulation inside porous cavities, reducing Nuw and increasing Shw. Results further indicate that increasing the buoyancy ratio N promotes circulation within the porous cavity, leading to an increase in turbulence levels within the boundary layers. Partial contributions of each phase of the porous cavity (solid and fluid) to the overall average Nusselt number becomes independent of N for higher values of the thermal conductivity ratio, ks/kf. Further, for high values of ks/kf, the average Nusselt number drops as N increases.
TOPICS: Porous materials, Turbulence, Equilibrium (Physics), Buoyancy, Convection, Cavities, Flow (Dynamics), Fluids, Thermal conductivity, Boundary layers, Thermal diffusivity, Natural convection
research-article  
Salam Hadi and Mustafa Rahomey
J. Heat Transfer   doi: 10.1115/1.4039642
Numerical simulations are carried out for fluid flow and natural convection heat transfer induced by a temperature difference between a hot inner cylinder with different geometries (i.e. circular; triangular; elliptic; rectangular; and rhombic) and a cold outer square enclosure filled with nanofluid superposed porous-nanofluid layers. The Darcy-Brinkman model is applied for the saturated porous layer with nanofluid. Moreover, the transport equations (mass, momentum, and energy) are solved numerically using the Galerkin weighted residual method by dividing the domain into two sets of equations for every layer with incorporating a non-uniform mesh size. The considered domains in this investigation are closely examined over a wide range of Rayleigh number (103 = Ra= 106), Darcy number (10-5 = Da = 10-1), the thickness of porous layer (0% = Xp = 100%), thermal conductivity ratio (1 = Rk = 20) and nanoparticle volume fraction (0 = ? = 0.1), respectively. The nanofluid is considered to be composed of Cu-nanoparticle and water as a base fluid. The results showed that the obtained total surfaces-averaged Nusselt numbers of the enclosure, in all cases, at the same operating conditions, the rate of heat transfer from the enclosure which the triangular cylinder is located inside is better. Also, as the thickness of the porous layer is increased from 20% to 80%, the free convection performance will decrease significantly (to about 50%) due to the hydrodynamic properties of the porous material.
TOPICS: Natural convection, Circular cylinders, Cylinders, Nanofluids, Heat transfer, Nanoparticles, Thermal conductivity, Momentum, Fluid dynamics, Temperature, Fluids, Porous materials, Computer simulation, Rayleigh number, Water
research-article  
Francisco Valentin, Narbeh Artoun, Masahiro Kawaji and Donald McEligot
J. Heat Transfer   doi: 10.1115/1.4039585
High pressure/high temperature forced and mixed convection experiments have been performed with helium and nitrogen at temperatures and pressures up to 893K and 64 bar, respectively. The test section had a 16.8-mm ID flow channel in a 108-mm OD graphite column. Flow regimes included turbulent, transitional and laminar flows with the inlet Reynolds numbers ranging from 1,500 to 15,000. Due to strong heating, the local Reynolds number decreased by up to 50% over the 2.7-m test section. In addition, heat transfer degradation and flow laminarization caused by intense heating led to Nusselt numbers 20~50% lower than the values given by the modified Dittus-Boelter and modified Gnielinski correlations. Flow laminarization criteria were considered based on a dimensionless acceleration parameter (Kv) and buoyancy parameter (Bo*). Upward turbulent flows displayed higher wall temperatures than downward flows, due to the impact of flow laminarization which is not expected to affect buoyancy-opposed flows. Laminar Reynolds number flows presented an opposite behavior due to the enhancement of heat transfer for buoyancy-aided flows. At low Reynolds numbers, downward flows displayed higher and lower wall temperatures in the upstream and downstream regions, respectively, than the upward flow cases. In the entrance region of downward flows, convection heat transfer was reduced due to buoyancy leading to higher wall temperatures, while in the downstream region, buoyancy-induced mixing caused higher convection heat transfer and lower wall temperatures.
TOPICS: Flow (Dynamics), High pressure (Physics), Graphite, High temperature, Buoyancy, Reynolds number, Wall temperature, Heating, Heat transfer, Turbulence, Convection, Mixed convection, Entrance region, Laminar flow, Temperature, Helium, Nitrogen

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