Effect Of Wall Conduction Research Articles

Effect of Wall Conductivity on Mixed Convection Magnetohydrodynamic Nanofluid Flow with Thermal Non-Equilibrium Approach in Vertical Channel

Effect of Wall Conductivity on Mixed Convection Magnetohydrodynamic Nanofluid Flow with Thermal Non-Equilibrium Approach in Vertical Channel

An overview of conjugate heat transfer augmentation methods for thermal management and recent advancements in microchannel heat sink overall performance

Recent technological advancement creates high-dense circuits development which creates colossal cooling demand requirements. In the future, advanced technology and scientific applications need to balance heat fluxes beyond limitation that catalyse the research opportunities further to achieve cooling requirements. Conventional cooling equipment is inappropriate for extracting heat from microchips within the minimal surface area. Microchannel technology appeared as a next-generation heat exchanger for the given heat duty. In the classical case of accounting, micro-heat exchangers both axial and transverse wall conduction effects is usually neglected. However, from the year 2005 onwards, researchers identified conduction dominance at fluid velocity is zero zones at the interface, which created balance between conduction–convection currents, finally included axial wall/heat conduction effects to a general model. This present study made a comparative evaluation fluid flow, heat transfer characteristics, thermal performance (TP) based on geometrical parameters, substrate materials and discusses previous issues, and current issues-based future research directions. Till today, based on applications of microchannels in thermal management, several experimental and numerical investigations have been reported for further improvement in TP. However, many researchers are still trying to accomplish things over a long period. Therefore, an overview of previous studies is furnished in the present study to assist researchers in this area much useful for further improvement.

Exploring the effect of axial wall conduction on the heat transfer mechanism of hourglass microchannels: Design guidelines for maintaining a constant wall temperature

To accurately estimate the heat transfer mechanisms of microscale thermal devices, it is essential to quantify the effects of axial wall conduction, which can significantly alter the thermal boundary conditions. This study focuses on exploring the effect of axial wall conduction on the thermal mechanism of hourglass microchannels, a topology that has proven useful in several engineering applications. However, there is a lack of research on the impact of axial wall conduction on the heat transfer mechanism of hourglass microchannels, and their potential for maintaining constant temperatures in biological applications has not been explored. To address this issue, a three-dimensional numerical analysis is conducted to investigate the impact of various design variables on the thermal mechanics of hourglass microchannels. An experiment has also been performed to validate the numerical approach employed in the study. The results show that the axial wall conduction effect is insignificant for modified Maranzana number below 0.01. It is further noted that the Nusselt number attains a maximum at an intermediate thermal conductivity ratio. This ratio ranges from 27 to 246 and is moderately dependent on the convergence-divergence angle, width ratio, and thickness ratio. Interestingly, an hourglass shape can maintain a near-isothermal boundary condition with a temperature difference of 1.4K at a lower width ratio. This work also establishes the design criteria for achieving a nearly isothermal condition within prescribed limits for important parameters, such as convergence-divergence angle (8°-16°), width ratio (1–2), thermal conductivity ratio (>646), thickness ratio (>10), and Reynolds number (>300). The established design criteria will pave the way for developing lab-on-chip devices for biological applications, such as PCR, that require the maintenance of constant wall temperature.

Comment on the paper “Optimization and numerical investigation of the effect of wall conduction and magnetic field on the nanofluid flow inside a three-dimensional enclosure using the lattice Boltzmann method, Farhan Khan, Yang Xiao-Dong, Nudrat Aamir, Tareq Saeed, Muhammad Ibrahim, Chemical Engineering Communications, 2023, Vol. 210, No. 5, 955–969”

Some serious errors exist in the above paper.

Effect of domain wall conductivity on domain formation energy

Domain wall (DW) conductivity is nowadays considered as a general ferroelectric phenomenon. As applied to ferroelectric domain reversal, it is capable of providing a strong and instantaneous compensation of the bound polarization charge on DWs by free charges coming from electrodes. We claim that account for this compensation can strongly lower the domain formation energy as compared to that known from the Landauer theory. This facilitates the domain reversal process and resolves the problem of an excessively large depolarization energy. We provide a derivation and detailed analysis of the domain formation energy in the presence of the DW conduction; this is relevant to both the capacitor and atomic force microscopy experimental configurations.

Investigation of Conjugate Effects on Forced Convection in Diamond (Diverging–Converging) Microchannels

Abstract A three-dimensional solid–fluid conjugate model is employed to provide physical insights into the effect of wall conduction on fluid convection in a diamond-shaped microchannel. The study covers the effect of divergence-convergence angle, width ratio, thermal conductivity ratio, thickness ratio, and Reynolds number on peripheral heat flux, temperature, and Nusselt number profiles. Isotherms show a multidirectional thermal gradient for low thermal conductivity ratios, whereas only an axial thermal gradient is seen for higher thermal conductivity ratios. Furthermore, the overall axial surface temperature gradients decrease with increasing divergence-convergence angle and decreasing width ratio. The study also shows that the thermal conductivity ratio significantly influences the Nusselt number, while the thickness ratio has only a moderate influence for all geometries. The analysis also reveals that at a particular intermediate thermal conductivity ratio, the Nusselt number becomes maximum. Lastly, a nondimensional wall conduction number is used to characterize conjugate effects in diamond microchannels. The wall conduction effect is inconsequential in diamond microchannels when the nondimensional wall conduction number is less than 0.01. The present study is beneficial from a practical perspective as it helps design the optimum channel geometries subjected to conjugate effects for many heat transfer applications.

Optimization and numerical investigation of the effect of wall conduction and magnetic field on the nanofluid flow inside a three-dimensional enclosure using the lattice Boltzmann method

The LBM is used to investigate three-dimensional nanofluid (NFs) flow inside a square enclosure with a heat source in this research. The heat source is located in the enclosure's middle and operates at a high temperature. The sidewalls have a thickness, leading to heat transfer (HE-TR) from the sidewalls that are at low temperatures to the internal fluid due to their thermal conductivity. An inclined magnetic field (MF) uniformly affects the fluid flow. The effect of parameters such as Rayleigh number (Ra), thickness and thermal conductivity of the sidewall, dimensions of the heat source, Hartmann number (Ha), the volume fraction of nanoparticles (φ), and the angle of the MF on two- and three-dimensional field flow and HE-TR is investigated. Optimization is made on the parameters for maximum HE-TR. The lattice Boltzmann method has been used to simulate nanofluid flow. The results show that an enhancement in the Ha and the angle of the MF reduces the amount of HE-TR. HE-TR is improved by increasing the thermal conductivity of thick walls. The quantity of HE-TR is increased when nanoparticles are added to water.

Parametric study of heat transfer performance including entropy generation of microchannel heat sink with fan cavity and different rib structure

This numerical study investigates the simultaneous application of axial wall conduction effect and entropy generation minimization as two principles to identify heat transfer performance in a microchannel heat sink with fan cavity and ribs. In this conjugate analysis, three different materials for a microchannel heat sink considered are silicon, aluminium, and copper. In addition to the fan cavity (F), effects of different rib configurations arranged symmetrically inside the fan cavity, that is, backward triangle rib (FB), rectangular rib (FR), forward triangle rib (FF), and diamond rib (FD) with Reynolds numbers ranging from 136 to 588 are studied. The comparative study between silicon and copper in terms of local wall and bulk fluid temperatures, increment in solid wall to fluid thermal conductivity ratio within the range (247.07 < ksf < 669.44), local Nusselt number (Nu x), axial conduction number (M), and entropy generation number ( Ns, a) were furnished and examined. Structural optimization is performed on diamond rib configuration geometrical parameters to observe entropy generation number and wall conduction effects trend as thermal performance is greatly improved to 2.49, at the lowest Ns, a to 0.31 at Re 391.47, with copper in the back to back cavities case. However based on the numerical results, comparative importance of axial wall conduction effect consideration in the present design of microsink, silicon is showing best results in overcoming at Re 588.4, consistently in all optimization cases.

Investigation into the effect of transverse condudction on the thermal performance of a flat-plate pulsating heat pipe

The effect of transverse wall conduction on the thermal performance of a flat-plate pulsating heat pipe (FP-PHP), whose channels are engraved on a flat-plate, is numerically investigated. For this, a numerical model for the FP-PHP that combines a one-dimensional slug/plug flow model for two-phase flow in rectangular channels with a three-dimensional heat conduction model for the solid wall is developed and experimentally validated. Using the proposed model, the effect of thermal interaction between adjacent channels on the thermal performance is numerically investigated. For quantitative examination, the difference in the thermal performance of the FP-PHP without thermal interaction and that of the FP-PHP with thermal interaction is compared for various wall materials, working fluids, and distances between adjacent channels. Finally, a criterion for assessing the importance of thermal interaction between adjacent channels in determining the thermal performance of the FP-PHP is provided: It is confirmed that thermal interaction has a significant influence on the thermal performance and should be taken into account when the Fourier number (Fo) is higher than 5 × 105.

Cooling characteristics and entropy production of nanofluid flowing through tube

In this work, the cooling effectiveness and entropy production of aluminum oxide–water nanofluid flow and heat transfer in the circular tube with the wall conduction effects are explored. All values of heat transfer effectiveness ratios are more than unity in this study. For a constant value of nanoparticles concentration, both heat transfer effectiveness ratios increase as the input temperature of fluid is increased. Both heat transfer effectiveness ratios are increased as the concentration of nanoparticles increases. Predictions show that all values of dimensionless local entropy production ratio are less than unity in this study except in the areas near the entrance of the heating part. This means that the usage of nanofluid is beneficial for decreasing the irreversibility of the system. The dimensionless local entropy production ratio decreases when the input temperature of fluid increases. The maximum value of Biw = 5 × 10-4 was reported for the Biot number in this study, which is far less than 0.1. As a consequence, the tube wall can be regarded as a Lumped system, and it is a reasonable assumption to ignore the radial thermal resistance.

Effect of wall conduction on steady natural convection couette flow in a vertical channel

Effect of wall conduction on steady natural convection couette flow in a vertical channel

Fourier series based 1-D numerical modelling of the dynamics of inclined closed loop buoyancy driven heat exchangers with conjugate effect

A 1-D numerical modelling of the dynamics of inclined closed loop buoyancy driven heat exchangers with inclusion of the wall conduction effect at the heat exchanger is presented in the current study. A Coupled Natural Circulation Loop (CNCL) is an ideal system for studying the closed loop buoyancy driven heat exchanger. The modelling utilises a Fourier series based approach to develop a 1-D model of the Conjugate CNCL system, which is then verified with the 3-D CFD studies of the respective cases. A good agreement is observed with the 3-D CFD data, which demonstrates the suitability of the 1-D model for transient behaviour prediction. The non-dimensional numbers and thermal coupling sensitivity coefficients which govern the dynamics of the Conjugate CNCL are identified and an appropriate parametric study is conducted. Results show that the wall conduction and inclination have a significant effect on the transient behaviour of the Conjugate CNCL system. A jump in the heat transfer coefficient with variation in the inclination of the Conjugate CNCL system is observed. The 1-D model is also able to capture the flow direction reversal with change in the inclination of the Conjugate CNCL system for zero flow field initial conditions.

Optimization and effect of wall conduction on natural convection in a cavity with constant temperature heat source: Using lattice Boltzmann method and neural network algorithm

In this paper, the natural convection (NC) of the Al2O3–H2O nanofluids (NFs) in a cavity with a heat source in its center is numerically investigated. A two-dimensional simulation of the cavity has been performed for this purpose. The D2Q9 LBM was used for the simulation. Then, the largest Nu was obtained using the artificial neural network (ANN). The ANN has been trained in such a way as to be able to automatically modify the input values and to estimate the largest heat transfer. With an increase in the Ra and nanoparticle volume fraction (NPVF), the heat transfer increases, but it decreases with an increase in the Ha number. In addition, the maximum heat transfer rate occurs for parallel magnetic field (MaF) and the heat transfer rate decreases with an increase in the MaF angle. As the size of the isothermal heat transfer and cold walls increase with a rise in the thermal conductivity coefficient, heat transfer also increases. With an increase in the thermal conductivity coefficient, no significant change was observed in the rate of heat transfer after an initial increase in the Nu. The largest Nu occurs at the largest Ra, largest MaF angle, and weakest MaF. The ANN predicted this value to be 7.0703, which is 2.3% different from the exact value resulting from the predicted computations.

Mixed convection flow in a vertical channel in the presence of wall conduction, variable thermal conductivity and viscosity

AbstractThis study theoretically investigates the effects of variable viscosity, thermal conductivity and wall conduction on a steady mixed convection flow of heat generating/absorbing fluid passes through a vertical channel. One of the channel plates moves with a constant velocity while the other is stationary. The governing flow equations are solved analytically using homotopy perturbation method (HPM). The effects of the thermophysical and hydrodynamics parameters are captured in graphs and tables. It has been observed that, both the velocity and temperature distributions decrease with increase in viscosity and boundary plate thickness near the heated plate while a reverse cases were observed near the cold plate. Increase in thermal conductivity ε decreases the fluid flow near the heated plate. When the boundary plate thickness is increased, the critical value of Gre to onset the reverse flow increases while increase in thermal conductivity reduces the critical value of Gre. It’s also noticed that the skin friction and rate of heat transfer at the heated plate decrease with increase in boundary plate thickness d.

Effects of the Domain Wall Conductivity on the Domain Formation under AFM-Tip Voltages in Ion-Sliced LiNbO3 Films

The specified domain patterns were written by AFM-tip voltages in LiNbO3 films composing LNOI (LiNbO3-on-insulator). The domain wall conductivity (DWC) was estimated in the written patterns. This estimate was based on the effects of load resistors RL inserted between DWs and the ground, on the features of occurring domains. In this case, the domain formation is controlled by the ratio between RL and the DWs’ resistance RDW. Starting from the comparison of patterns appearing at different RL, the value of RDW in a specified pattern was estimated. The corresponding DWC is of σDW ≈ 10−3 (Ohm cm)−1 which exceeds the tabular bulk conductivity of LiNbO3 by no less than twelve orders of magnitude. A small DW inclination angle of (10−4)0 responsible for this DWC is not caused by any external action and characterizes the domain frontal growth under an AFM-tip voltage.

Heat‐in‐leak and longitudinal wall heat conduction influence on three‐fluid cross‐flow heat exchanger performance

AbstractThe combined effect of the longitudinal wall heat conduction in the partitioning wall and ambient heat‐in‐leak (HL) from the surrounding to the heat exchanger is a serious factor affecting the performance of a multifluid heat exchanger. The performance of a three‐fluid cross‐cocurrent flow heat exchanger under such circumstances is investigated in this paper. The governing equations for three‐fluids and two separating walls are formulated on the basis of energy balance equations and solved using the finite element method (FEM). Nondimensional parameters (C1,2, C3,2, R1, R3, Ht, Hb, , , , and the number of transfer units [NTU]) are generated and used for the investigation. Effectiveness‐number of transfer plots method is used to analyze the combined effect of wall heat conduction and HL from the surrounding. The combined effect reduces the hot fluid effectiveness significantly for all the parameters considered. The effect of HL alone is predominant as compared with longitudinal wall conduction alone. However, the negligence of the above two parameters in the thermal design of the heat exchanger contributes to a significant loss in hot fluid effectiveness. For a balanced mass flow rate of hot and cold fluid, the drop in the hot fluid effectiveness is found to be 37% approximately (with C3,2 = 0.5, R1 = R3 = 1, Ht = Hb = 0.05, and = = 0.025 at NTU = 10). The results present insight and important considerations involved in the design of such heat exchangers. Also with the application of the FEM, for any number of elements, the stiffness matrix can be generated by writing a program and the exit temperatures are calculated very easily.

Numerical modeling of heat losses in a line focusing solar compound parabolic concentrator with planar absorber

In this work, a three-dimensional steady state thermal model is developed for a compound parabolic concentrator of 2× concentration considering the effects of surface radiation and wall conduction. The performance of the compound parabolic concentrator is modeled to obtain the convective and radiative heat loss under the influence of different parameters such as absorber temperature, absorber emissivity, ambient temperature, external heat loss coefficient, aspect ratio and concentrator tilt. The turbulent natural convection in the concentrator is modeled using standard two equation k-ε turbulent model with enhanced wall treatment. For the surface radiation inside the concentrator, discrete ordinate radiation model is used. The thermo physical properties of air inside the cavity are assumed to be constant except the density which is modeled as incompressible ideal gas. The conduction at the walls is accounted by setting suitable wall thickness for reflectors, glass cover and end walls in the solver. This work clearly demonstrates the need for a three dimensional numerical simulation and coupled natural convection and radiation to exactly reproduce the velocity fields as would be obtained in experiments. The convective Nusselt number, radiative Nusselt Number and thermal stratification are obtained from the parametric study. This study on estimation of heat losses in compound parabolic concentrator is applicable to both solar thermal and solar photo-voltaic collectors with a view of modifying the concentrator design to optimize its thermal performance.

Effect of wall conduction on the heat transfer characteristics of supercritical n-decane in a horizontal rectangular pipe for cooling of a scramjet combustor

Purpose The purpose of this paper is to numerically study the influence of wall conduction on the heat transfer of supercritical n-decane in the active regenerative cooling channels. Design/methodology/approach A horizontally placed rectangular pipe with a solid zone and another one without a solid zone were used. A drastic variation of thermo-physical properties was emphatically addressed. After the verification of mesh and turbulence models comparing with the experimental results, a mesh number of 4.5 M and the low Reynolds number SST k-ω turbulence model were chosen. The solution of the governing equations and the acquisition of the numerical results were executed by the commercial software FLUENT 2020 R1. Findings The numerical results indicate that there is a heat transfer deterioration (HTD) potential for the upper wall, lower wall and sidewall with the decrease of mass flux. Due to wall conduction, the distribution of the fluid temperature at spanwise-normal planes becomes uniform and this feature also takes advantage of the relatively uniform transverse velocity. For the streamwise-normal planes, the low fluid temperature appears close to the upper wall at the region near the sidewall and vice versa for the region near the centre. Undoubtedly, the secondary flow at the cross-section plays a crucial role in this process and the relatively cool mainstream is affected by the vortices. Originality/value This study warns that the wall conduction must be considered in the practical design and thermal optimization due to the sensibility of thermo-physical properties to the heat flux. The secondary flow caused by the buoyancy force (gravity) plays a significant role in the supercritical heat transfer and mixed convection heat transfer should be further studied.

Conjugate Heat Transfer Analysis of PCM Suspensions in a Circular Tube under External Cooling Convection: Wall Conduction Effects

In this paper, a numerical method is used to investigate the conjugate heat transfer of a phase change material (PCM) suspension in a circular tube under external cooling convection. The following parameters and ranges were considered: dimensionless tube wall thickness, t w (0–0.5); wall-to-fluid thermal conductivity ratio, k w f * (0.1–10); volumetric fraction of PCM particles, c v (0.1); Biot number, B i o (1); Stefan number, Ste (0.1); and Peclet number, Pe (1000). The results show that the wall thermal conductivity considerably affects the outer/inner wall temperature of the tube, the average temperature of the working fluid, and the volumetric liquid fraction of PCM particles. Thus, wall conduction effects must be properly accounted for to model heat transfer in a PCM suspension in tube flow.

Effect of axial conduction in integral rough friction stir channels: experimental thermo-hydraulic characteristics analyses

Integral mini-channels fabricated in the metal substrate by friction stir channeling process are different from conventional mini-channels due to irregular shape, and large surface roughness. The effect of axial wall conduction on heat transfer in such mini-channels is significant, which could limit their utilisation as cooling channels in heat transfer based applications. Hence, in this study, we present an experimental analysis of the thermo-hydraulic performance of a friction stir channel to identify the axial wall conduction effect using de-ionized water as working fluid. The thermo-hydraulic performance parameters are analysed in the range of Reynolds number of 500 to 2100. The local wall temperature distribution along the length of the mini-channel is found to be non-uniform due to the significant axial wall conduction effect. The distinct pattern of numerical heat flux distribution is used as evidence to confirm the presence of axial wall conduction effect which is implied by the local wall temperature distribution. The higher average heat transfer and flow characteristics compared to the theoretical predictions for conventional mini-channels are observed as a result of simultaneously developing flow and the presence of surface roughness.