Conjugate Heat Transfer Effects Research Articles

Finite element simulation of Soret-Dufour and conjugate heating effects on mixed convective heat absorbing hydromagnetic Casson fluid flow with suction/blowing from flat semi-infinite vertical porous plate

The finite element simulations of the Soret-Dufour and angled magnetic field effects on conjugate heat and mass transportation of unsteady heat absorbing hydromagnetic Casson flow across a semi-infinite flat oscillatory plate engrafted in a porous medium with suction/blowing, radiation and chemical reaction is performed. The dimensionless coupled flow guiding nonlinear PDEs of the physical structure is handled numerically by the dynamic Galerkin finite element scheme. The demeanor of the velocity, concentration and the temperature profiles due to the alterations in the regulating flow parameters are examined graphically whereas the wall-friction, mass and heat transfer rates explicated by utilizing the tabular data. The research discovered that radiation; conjugate heat transfer and diffusion thermo effects heighten the temperature and velocity distributions whereas heat absorption has a reverse effect. Likewise, conjugate mass transfer and thermo-diffusion effects intensify the concentration and velocity distributions whereas the chemical reaction display overturns aspect. Increased radiation absorption, inclined magnetic field and porosity parameter stimulate fluid velocity whereas the Casson and magnetic parameters exhibit the converse impact. In the instance of suction, the profiles of concentration, velocity and temperature displayed a downturn nature but for the case of blowing, it was noticed a reversal trend. Further, a comparative analysis between the current findings and existing research works in the literature demonstrates our results are exact and accurate.

Investigation of an improved cold plate design with circuitous minichannel: a computational study involving the effect of conjugate heat transfer

Purpose This study aims to investigate a new circuitous minichannel cold plate (MCP) design involving flow fragmentation. The overall thermal performance and the temperature uniformity analysis are performed and compared with the traditional serpentine design. The substrate thickness and its thermal conductivity are varied to analyse the effect of axial-back conduction due to the conjugate nature of heat transfer. Design/methodology/approach The traditional serpentine minichannel is modified into five new fragmented designs with two inlets and two outlets. A three-dimensional numerical model involving the effect of conjugate heat transfer with a single-phase laminar fluid flow subjected to constant heat flux is solved using a finite volume-based computational fluid dynamics solver. Findings The minimum and maximum temperature differences are observed for the two branch fragmented flow designs. The two-branch and middle channel fragmented design shows better temperature uniformity over other designs while the three-branch fragmented designs exhibited better hydrodynamic performance. Practical implications MCPs could be used as an indirect liquid cooling method for battery thermal management of pouch and prismatic cells. Coupling the modified cold plates with a battery module and investigating the effect of different battery parameters and environmental effects in a transient state are the prospects for further research. Originality/value The study involves several aspects of evaluation for a conclusive decision on optimum channel design by analysing the performance plot between the temperature uniformity index, average base temperature and overall thermal performance. The new fragmented channels are designed in a way to facilitate the fluid towards the outlet in the minimum possible path thereby reducing the pressure drop, also maximizing the heat transfer and temperature uniformity from the substrate due to two inlets and a reversed-flow pattern. Simplified minichannel designs are proposed in this study for practical deployment and ease of manufacturability.

Effects of continuous wettability on the pool-boiling bubble dynamics and heat transfer characteristics of a triangular structure-roughened surface

A phase transition lattice Boltzmann model is used in the current study to simulate the pool boiling process on a triangular structure-roughened surface with conjugate heat transfer effect. Through the verification of the Laplace law and the theoretical film boiling results, the adopted model is ensured to predict pool boiling phenomena accurately with excellent stability. The bubble dynamics, including the nucleation, growth, coalescence and detachment of the bubbles on the triangular structure-roughened surface with continuous wettability, is discussed. Little research has been conducted on the continuous wettability effect on the pool boiling with triangular structures-roughened surfaces. The results show that a hydrophilic surface inhibits bubble growth but facilities bubble detachment with bubble nucleation at the concave corners; a hydrophobic surface increases bubble growth but inhibits bubble detachment with bubble nucleation at hydrophobic areas. It is found that when the direction of the self-drive favors bubble detachment from the surface, the surface which from contact angle θBottom=120° to θTop=90° under the study can achieve better heat transfer over a wider range of superheat, while setting the continuous wettability from θBottom=120° to θTop=60° can achieve a better heat flux density at lower superheat.

Numerical investigation of the heat transfer in a meandering millichannel by a coupled 1D-flow-channel / 3D-surrounding-solid model

Heat exchanger/reactors with corrugated channels are used to implement especially exothermal chemical reactions. Heat conduction effects in their solid material are not negligible and induce in particular heat flows between adjacent channels. In this context, this work proposes a model of a plate-type heat exchanger/reactor with a 2D-meandering millichannel, taking into account these conduction effects by coupling a 1D approach for the channel flow, with correlations for the friction factor and the Nusselt number, to a 3D approach for the solid part. This model is a compromise between the 1D classical reactor models that don’t account for 3D conduction effects in the solid and the 3D simulations of the channel flow with the surrounding solid which are computationnally expensive or unachievable for a large reactor. In the tested case, the 1D/3D and 3D CFD results are in good agreement (5 min vs 4 h computational time), which suggests valid model assumptions and internal model consistency. Simulated and experimental conversion rates of a fast highly exothermic reaction are then compared, showing the relevancy of the model. Further investigations are performed to highlight the effect of conjugate heat transfer in millistructured heat exchangers and to quantify its limitations versus the 1D/3D model.

Cooling performance of an active-passive hybrid composite phase change material (HcPCM) finned heat sink: Constant operating mode

The present study explores a hybrid thermal management technology based on air cooling and hybrid composite phase change material (HcPCM) filled finned heat sink for cooling performance of lower to medium heat flux dissipating electronic devices. Two-dimensional numerical simulations are conducted to study the conjugate heat transfer effects of three types of finned heat sink: air-cooled finned heat sink, HcPCM-cooled finned heat sink, and hybrid (air-HcPCM) cooled finned heat sink. A heat sink with a constant volume faction of plate-fins is designed in all cases and simultaneous effects of hybrid nanoparticles and air are investigated to keep the heat sink temperature at safe operating conditions between 40–60 ∘C. The effect of air is incorporated into the heat sink by applying the convective heat transfer coefficient of hc = 10–100 W/m2.K which tends to create the natural convection and forced convection heat transfer characteristics. The heat flux is varied from 25–40 kW/m2 in the current study. The hybrid nanoparticles of carbon additives (GO and MWCNTs) are dispersed into the RT-35HC, used as a PCM, with a volume fraction of 0% to 6%. Transient simulations are carried out using COMSOL Multiphysics to solve the governing equations for PCM based conjugate heat transfer model. The results showed that forced convection heat transfer improved the cooling performance of the hybrid heat sink compared to natural convection heat transfer. The addition of nanoparticles further enhanced thermal enhancement and uniform melting distribution of PCM inside the finned heat sink. The hc between 30 to 50 W/m2.K shows optimized values for forced convection heat transfer operating conditions. The volume fraction of 2% of GO+MWCNTs nanoparticles in recommended or optimum concentration for uniform melting of PCM inside the finned heat sink.

Computational investigation of single and multi-jet array impingement boiling

Jet impingement boiling has been studied extensively and has been identified as one of the most promising thermal management techniques for high heat flux applications. Unfortunately, only a few numerical studies have been reported in literature and they are mostly limited to single jets. In the present study, both submerged single round jets and confined multi-jet arrays are investigated numerically, using the Eulerian multiphase framework with the Rensselaer Polytechnic Institute (RPI) boiling model to predict heat transfer. The numerical results of the single jet case correlate well with reported experimental data and previously reported numerical results. The numerical results of the multi-jet array correlate well with experimental data reported in the literature, proving that the RPI boiling model can successfully predict the heat transfer of jet array boiling. The effect of conjugate heat transfer in jet impingement boiling heat transfer is also investigated for both single and multiple jet cases. The single-jet results agree with previous reported numerical studies. To improve numerical convergence, especially for higher heat fluxes, use was made of a hydrostatic pressure gradient at the outlet. This allowed for significant improvement in the convergence of the continuity equation. Finally, parametric analyses were conducted for both single and multi-jet arrays in the fully developed nucleate boiling regimes. Parameters included jet-to-surface spacing, Reynolds number and subcooling. The results for the single jet correlate well with the observations of experiments reported in the literature. The results for the multi-jet array showed less sensitivity to changes in jet velocity at low jet-to-surface spacing than the single-jet case. Both single and multi-jet cases showed that reducing the subcooling resulted in an onset of nucleate boiling at lower heat fluxes and that the boiling curve shifted to the left in the nucleate boiling regime.

Conjugate heat transfer effects on flow boiling in microchannels

• Heat distributes nonuniformly around the perimeter of microchannels in evaporators. • In single-phase flow, low aspect-ratio channels yield best heat transfer. • In two-phase flow, the Nusselt number trends vs. aspect-ratio are mixed. • High aspect-ratio channels exhibit larger thermal resistance and higher evaporator temperatures. • Conjugate heat transfer should be included in design models for evaporators. This article presents a computational study of saturated flow boiling in non-circular microchannels. The unit channel of a multi-microchannel evaporator, consisting of the fluidic channel and surrounding evaporator walls, is simulated and the conjugate heat transfer problem is solved. Simulations are performed using OpenFOAM v2106 and the built-in geometric Volume Of Fluid method, augmented with self-developed libraries to include liquid-vapour phase-change and improve the surface tension force calculation. A systematic study is conducted by employing water at atmospheric pressure, a channel hydraulic diameter of D h = 229 µm, a uniform base heat flux of q b = 100 kW / m 2 , and by varying the channel width-to-height aspect-ratio and channel fin thickness in the range ϵ = 0.25 –4 and W f = D h / 8 − D h , respectively. The effects of conjugate heat transfer and channel aspect-ratio on the bubble and evaporative film dynamics, heat transfer, and evaporator temperature are investigated in detail. This study reveals that, when the flow is single-phase, higher Nusselt numbers and lower evaporator base temperatures are achieved for smaller channel aspect-ratios, from Nu ≃ 4 and T b − T s a t ≃ 9 K when ϵ = 4 , to Nu ≃ 6 and T b − T s a t ≃ 2 K when ϵ = 0.25 , for same fin thickness W f = D h / 8 . In the two-phase flow regime, Nusselt numbers in the range Nu = 12 − 36 are achieved. The trends of the Nusselt number versus the aspect-ratio are non-monotonic and exhibit a marked dependence on the channel fin thickness. For small fin thicknesses, W f = D h / 8 and W f = D h / 4 , an overall ascending trend of Nu for increasing aspect-ratios is apparent, although in the narrower range ϵ = 0.5 –2 the Nusselt number appears weakly dependent on ϵ . For thicker fins, W f = D h / 2 and W f = D h , the Nusselt number decreases slightly when increasing the aspect-ratio in the range ϵ = 0.5 –2, although this trend is not monotonic when considering the entire range of aspect-ratios investigated. Nonetheless, due to conjugate heat transfer, Nusselt numbers and evaporator base temperatures follow different trends when varying the aspect-ratio, and channels with ϵ < 1 seem to promote lower evaporator temperatures than higher aspect-ratio conduits.

Heat transfer and flow structures of supercritical n-decane in a regenerative cooling channel loaded with non-uniform heat flux

A harsh and complex thermal environment in the combustor threatens safe working of scramjets. In this study, heat transfer and flow structures of supercritical n-decane under 3 MPa in a regenerative cooling channel loaded with non-uniform heat flux distributions are investigated, including uniform, sinusoidal, increased, and decreased heat flux distributions. A verified k–ω SST turbulence model was employed, and a corresponding mesh independence study was performed. From this work, the fluid temperature at the outlet of the heated channel is only determined by the averaged heat flux, and all the regenerative cooling channels achieve the same temperature although loaded with different heat flux distributions. Compared with the fluid temperature, the wall temperature distribution is more sensitive to the variations of heat flux distribution. The regenerative cooling channels loaded with the sinusoidal heat flux distributions exist in several high-temperature regions, and the channel loaded with linear distributions changes the trend of temperature distribution. A larger temperature gradient is found in the regenerative cooling channel wall with a lower thermal conductivity. This work provides a good insight into the characteristics of the flow and temperature field of regenerative cooling channels loaded with non-uniform heat flux considering the effect of conjugate heat transfer.

Effects of pore scale and conjugate heat transfer on thermal convection in porous media

The study of thermal convection in porous media is of both fundamental and practical interest. Typically, numerical studies have relied on the volume-averaged Darcy–Oberbeck–Boussinesq (DOB) equations, where convection dynamics are assumed to be controlled solely by the Rayleigh number (Ra). Nusselt numbers (Nu) from these models predict Nu–Ra scaling exponents of 0.9–0.95. However, experiments and direct numerical simulations (DNS) have suggested scaling exponents as low as 0.319. Recent findings for solutal convection between DNS and DOB models have demonstrated that the ‘pore-scale parameters’ not captured by the DOB equations greatly influence convection. Thermal convection also has the additional complication of different thermal transport properties (e.g. solid-to-fluid thermal conductivity ratio ks/kf and heat capacity ratio σ) in different phases. Thus, in this work we compare results for thermal convection from the DNS and DOB equations. On the effects of pore size, DNS results show that Nu increases as pore size decreases. Mega-plumes are also found to be more frequent and smaller for reduced pore sizes. On the effects of conjugate heat transfer, two groups of cases (Group 1 with varying ks/kf at σ = 1 and Group 2 with varying σ at ks/kf = 1) are examined to compare the Nu–Ra relations at different porosity (ϕ) and ks/kf and σ values. Furthermore, we report that the boundary layer thickness is determined by the pore size in DNS results, while by both the Rayleigh number and the effective heat capacity ratio, $\bar{\phi } = \phi + (1 - \phi )\sigma$ , in the DOB model.

Aerodynamic port-aligned fins to enhance thermal-hydraulic performance of jet impingement arrays

Jet impingement arrays with interspersed fluid extraction ports can suffer degraded heat transfer near outlets due to flow separation. This study explores the potential to integrate aerodynamic port-aligned fins on the impingement surface to maintain wall-jet attachment and increase heat transfer area. Such fins may also enhance local transport under inlet nozzles. Laminar-flow conjugate heat transfer simulations are performed for a range of Reynolds numbers and geometries to characterize this concept for slot jet impingement arrays. The simulation methodology is validated with conventional slot jet data from the literature and demonstrated to achieve mesh convergence. Overall flow characteristics are evaluated for a representative geometry, and results show a significant increase in relative average Nusselt number (Nu∗‾)and a reduction in peak temperature of the cooled surface. Conjugate heat transfer effects are evaluated, and are found to be significant for lower conductivity fin materials. Parametric studies are performed to generate performance maps for relative average Nusselt number and pressure drop as functions of Reynolds number, fin height, base width, and tip radius. Pareto curves are generated for the geometries that optimally trade heat transfer enhancement and pressure drop penalty to guide design. Teardrop shaped fins are found to be optimal for low Re, whereas continuously narrowing fins are preferable for higher Re. This jet impingement enhancement is shown to deliver up to 25% enhancement in Nu∗‾ at baseline pressure drop.

Design analysis and Work load characteristics of a Micro data Center

Data centers are large-scale data storage and processing systems. It is made up of a number of servers that must be capable of handling large amount of data. As a result, data centers generate a significant quantity of heat, which must be cooled and kept at an optimal temperature to avoid overheating. To address this problem, thermal analysis of the data center is carried out using numerical methods. The CFD model consists of a micro data center, where conjugate heat transfer effects are studied. A micro data center consists of servers aligned with air gaps alternatively and cooling air is passed between the air gaps to remove heat. In the present work, the design of data center rack is made in such a way that the cold air is in close proximity to servers. The temperature and airflow in the data center are estimated using the model. The air gap is optimally designed for the cooling unit. Temperature distribution of various load configurations is studied. The objective of the study is to find a favorable loading configuration of the micro data center for various loads and effectiveness of distribution of load among the servers.

Conjugate Effect on the Thermal Characteristics of Air Impinging Jet

A computational fluid dynamics (CFD) investigation to determine the conjugate heat transfer (CHT) effect on the stagnation and local thermal characteristics due to an impinging process has been carried out in this study using STAR-CCM+ - Siemens PLM commercial code. The transient Navier-Stokes’s equations are numerically solved using a finite volume approach with k-ω SST eddy viscosity as the turbulence model. A fully developed circular air jet with different Reynolds numbers, impinging vertically onto a heated flat disc with different metals, thicknesses, and boundary heat fluxes are employed in the current study to examine the thermal characteristics and provide an enhanced picture for the convection mechanism that used in jet cooling technology. It is found that the thermal characteristics are influenced by the thermal conductivity and thickness of the target upon using air as a cooling jet. The CHT process enhances the local convective heat transfer at the fluid-solid interface due to the variation in transverse and axial conductive heat transfer inside the metal up to a certain redial extent from the stagnation region compared to the process with no CHT. The extent of the radial enhancement depends on the thermal conductivity of the metal. For a given thermal conductivity, the CHT process acts to increase the temperature and convective heat flux of the stagnation region as the metal thickness increases.

The Effect of Hydraulic Diameter on Flow Boiling within Single Rectangular Microchannels and Comparison of Heat Sink Configuration of a Single and Multiple Microchannels

Phase change heat transfer within microchannels is considered one of the most promising cooling methods for the efficient cooling of high-performance electronic devices. However, there are still fundamental parameters, such as the effect of channel hydraulic diameter Dh whose effects on fluid flow and heat transfer characteristics are not clearly defined yet. The objective of the present work is to numerically investigate the first transient flow boiling characteristics from the bubble inception up to the first stages of the flow boiling regime development, in rectangular microchannels of varying hydraulic diameters, utilising an enhanced custom VOF-based solver. The solver accounts for conjugate heat transfer effects, implemented in OpenFOAM and validated in the literature through experimental results and analytical solutions. The numerical study was conducted through two different sets of simulations. In the first set, flow boiling characteristics in four single microchannels of Dh = 50, 100, 150, and 200 μm with constant channel aspect ratio of 0.5 and length of 2.4 mm were examined. Due to the different Dh, the applied heat and mass flux values varied between 20 to 200 kW/m2 and 150 to 2400 kg/m2s, respectively. The results of the two-phase simulations were compared with the corresponding initial single-phase stage of the simulations, and an increase of up to 37.4% on the global Nu number Nuglob was revealed. In the second set of simulations, the effectiveness of having microchannel evaporators of single versus multiple parallel microchannels was investigated by performing and comparing simulations of a single rectangular microchannel with Dh of 200 μm and four-parallel rectangular microchannels, each having a hydraulic diameter Dh of 50 μm. By comparing the local time-averaged thermal resistance along the channels, it is found that the parallel microchannels configuration resulted in a 23.3% decrease in the average thermal resistance R¯l compared to the corresponding single-phase simulation stage, while the flow boiling process reduced the R¯l by only 5.4% for the single microchannel case. As for the developed flow regimes, churn and slug flow dominated, whereas liquid film evaporation and, for some cases, contact line evaporation were the main contributing flow boiling mechanisms.

Effects of flow regime and conjugate heat transfer on particle deposition in heat exchange duct

Deposition of micron particles in heat exchange duct is commonly encountered in many thermal and HVAC engineering applications. Previous studies on this important issue always considered turbulent air flow regime without conjugate heat transfer (CHT). However, the flow regimes and the CHT may have significant influences on particle deposition behaviors. Therefore, this paper aims to study particle deposition characteristics in laminar flow (LF), developing turbulent flow (DTF) and fully developed turbulent flow (FDTF) regimes with and without CHT. The v′2‾−fturbulence model and discrete particle model (DPM) were used to predict gas phase and solid phase, respectively. Moreover, a modified discrete random walk method was adopted to model turbulent particle dispersion. The results showed that particle deposition velocities greatly increase for small particles (dp<20μm) but keep invariable for large particles (dp>20μm) due to thermophoretic deposition. WhenΔT=100Kanddp=1μm, the peak deposition velocity enhancement ratio reaches 3.8, 9.7 and 7.5 for LF, DTF and FDTF regimes respectively. Different flow regimes have obvious effects on the deposition characteristics. Particle deposition velocity for DTF regime is the highest, followed by FDTF case and LF case. Thermophoresis effect is reduced by the CHT, as the temperature difference decreases due to thermal conduction in solid domain. The CHT in DTF or FDTF regime has obviously larger effect on deposition characteristics, compared with the LF regime.

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%.

Theoretical and experimental analysis of overall cooling effectiveness for afterburner double-wall heat shield

The porous heat shield installed in the afterburner can effectively prevent the afterburner cylinder from overheating. Impingement/effusion cooling is one composite cooling technique to effectively improve the overall cooling effectiveness of the heat shield. Designing effective and efficient double-wall configurations requires a detailed understanding of how geometry and operating conditions affect the way coolant cools the afterburner cylinder. In this study, conjugated heat transfer experiments were conducted using IR thermography for double-wall heat shields with three open areas of the impingement plate (σ = 0.5%, 0.7%, 0.8%). The momentum flux ratio was varied in the range 0.01≤I≤0.50. The mainstream Reynolds number, based on the diameter of the film hole, was varied in the range 800≤Reg≤2000. The effects of geometrical and aerodynamic parameters on overall cooling effectiveness were experimentally and numerically investigated with the comprehensive effects of solid heat conduction and convection heat transfer. The experiments were modeled in a low-temperature state (Tg = 603 K, Tc = 298 K), which was based on the analogy theory and matching principle, as if the experiments were conducted under engine operating conditions. The modeling accuracy of experimental results was analyzed by the analogy theory. Results show that the difference in the overall cooling effectiveness between “laboratory” conditions (Tg/Tc = 2) and “engine” conditions (Tg/Tc = 4) is within 0.048. The overall cooling effectiveness is mainly affected by the open area through adiabatic cooling effectiveness and internal heat transfer, and that is mainly affected by the mainstream Reynolds number through external heat transfer. According to the area-averaged results in given experimental conditions, the maximum overall cooling effectiveness raise and drop coefficients after increasing open area and mainstream Reynolds number are 17.3% and 6%, respectively. Thus, the high open area and low mainstream Reynolds number are beneficial to improve the overall cooling effectiveness of the afterburner double-wall heat shield. Furthermore, the experimental measurements provide an important database for the evaluation of computational fluid dynamics simulations of the conjugate heat transfer effects occurring in the double-wall heat shield.

Effect of conjugate heat transfer in single-phase laminar flow through partially heated microtubes

Effect of conjugate heat transfer in single-phase laminar flow through partially heated microtubes

Study of pore-scale coke combustion in porous media using lattice Boltzmann method

In-situ combustion (ISC) for heavy oil recovery is a high-risk process and thus calls for a deep understanding of the coke combustion front. However, simulations for describing pore-scale coke combustion are challenging because of complicated combustion dynamics. This study proposes a multiple-relaxation-time (MRT) lattice Boltzmann (LB) method to simulate solid coke combustion in porous media at the pore scale. The MRT LB model can enhance numerical stability compared with the single-relaxation-time counterpart. This new LB model offers two major advances over existing LB models. First, thermal expansion effects are considered via temperature-dependent density, satisfying the low Mach number flow condition. Second, conjugate heat transfer and species conservation at the coke-fluid interface are modelled by a source term and a bounce-back scheme, respectively, without resorting to iterative methods. Simulations of pore-scale coke combustion are conducted to validate the superior performance of the developed LB model. The results show that this model can reproduce coke combustion dynamics and capture variations in isotherms from the fluid phase to the solid phase at the pore scale. In contrast, without considering effects of thermal expansion or conjugate heat transfer as in previous models, simulations would underestimate the burning temperature and even fail to predict instability caused by a high driving force. Moreover, using the proposed LB model, a parametric study is performed to assess the impact of the inlet air and porous structure on coke combustion. The findings suggest that inlet air temperature and driving force should be controlled within certain ranges, otherwise their influences may become negligible or even negative. Large porosity accelerates coke combustion and leads to a desired combustion front. Heterogeneous coke distribution affects pore-scale combustion details but not the overall combustion intensity, while a random matrix structure may influence combustion dynamics both locally and globally. As a whole, this study develops a reliable LB model to investigate pore-scale coke combustion, which contributes to advancing the knowledge base for heavy oil recovery using the ISC process.

Effect of conjugate heat transfer on the thermo-electro-hydrodynamics of nanofluids: entropy optimization analysis

We investigate, in this analysis, the entropy generation characteristics associated with the transport of nanofluid in a microfluidic channel under the combined influences of applied pressure gradient and electrical forcing. In our study, the nanofluid is subjected to an asymmetric cooling at the channel walls, while the conductive transport of heat through the channel walls is also taken into account. We show that the underlying thermo-electro-hydrodynamics of nanofluids in the channel lead to entropy generation, attributed to the irreversibilities associated with heat transfer, viscous dissipation, and Joule heating effects. We establish that a non-trivial interplay among these irreversibilities gives rise to an optimum value of the geometrical parameter, viz. the channel wall thickness ( $$ \delta $$ ), and the thermophysical parameters, viz. the thermal conductivity of the wall $$ (\gamma ) $$ , Biot number (Bi), and the modified Peclet number ( $$ \overline{\text{Pe}} $$ ), leading to a minimum entropy generation rate of the system. Also, we unveil through this study that changes in the electroosmotic parameter $$ \bar{\kappa } $$ (representative of the EDL thickness) or the composition of the fluid ( $$ \phi $$ , the volume fraction of nanoparticles agglomerates) non trivially alter the optimum values of these parameters. Inferences drawn from this analysis may have consequences in the optimum design of thermal systems/devices, typically used for thermal management in micro-heat exchangers, micro-reactors, and micro heat pipes.

Effect of conjugate heat transfer on the side and horizontal walls on the structure of convective flow in the Rayleigh-Benard convection mode

Rayleigh-Benard convection in rectangular cavities with different relative size with walls of finite thermal conductivity is studied numerically in a two-dimensional conjugate formulation. The influence of relative cavity sizes on the spatial shape and evolution of convective flows with increasing Rayleigh numbers is investigated. Velocity and temperature fields in the liquid, temperature fields, temperature gradients and heat fluxes in solid walls are calculated. The effect of conjugate heat transfer with walls of finite thermal conductivity on the spatial shape and local characteristics of convective heat transfer is studied.