Conjugate Heat Transfer Research Articles

Conjugate heat transfer simulation of the linear range extender: thermal design considerations for cooling strategy

Conjugate heat transfer simulation of the linear range extender: thermal design considerations for cooling strategy

Transient Modeling and Simulation of a Generic Stable Salt Reactor

A SAM system-level model of a generic stable salt reactor has been developed to investigate thermal-hydraulic behavior and safety performance under steady and transient conditions. The model integrates information generated from a reactor physics analysis using PROTEUS and PERSENT, and a computation fluid dynamics (CFD) analysis using STAR-CCM+. A loose, iterative coupling scheme between PROTEUS and SAM is implemented to calculate the equilibrium power and temperature distributions in the steady-state critical core condition. The converged steady-state model is then used in PERSENT to calculate the four reactivity feedback temperature coefficients (Doppler, fuel density, coolant density, and core radial expansion) and kinetic parameters that are needed in SAM to model the temperature feedback effects in transient simulations. Within the fully enclosed liquid fuel pins, natural convection is the dominant heat transfer mechanism. The STAR-CCM+ model of the fuel pin considers conjugate heat transfer from the liquid fuel salt to the pin cladding and external reactor coolant. The CFD results of the axial and radial temperature profiles are used to empirically determine an effective fuel salt thermal conductivity in the SAM fuel pin model so that the temperatures predicted by the SAM model match as closely as possible the CFD results. In the central region of the fuel pin, the effective thermal conductivity is as high as ~60 times the physical fuel salt thermal conductivity. The whole-plant SAM model is then used to simulate an unprotected station blackout transient. The results of this simulation showed that the large negative fuel axial expansion reactivity feedback reduces fission power to ~2.4% nominal power. The core is cooled by natural circulation, which removes heat in the core to the emergency heat removal system, and ultimately, to the ambient. However, peak fuel salt and cladding temperatures can potentially reach as high as 1500 K, albeit briefly, if the shutdown mechanism fails to operate.

Hollow Direct Air-Cooled Rotor Windings: Conjugate Heat Transfer Analysis

This article focuses on the analysis of a direct air-cooled rotor winding of a wound field synchronous machine, the innovation of which lies in the increase in the internal cooling surface, the cooling of the winding compared to the conventional inter-pole cooling, and the development of a CHT evaluation model accordingly. Conjugate heat transfer (CHT) analysis is used to explore the cooling efficacy of a parallel-cooled hollow-conductor winding of a salient-pole rotor and to identify a cooling performance map. The use of high current densities of 15–20 Arms/mm2 in directly cooled windings requires high cooling intensity, which in the case of air cooling results not only in flow velocities above 15 m/s to ensure permissible operating temperatures, but also the need for coolant distribution and heat transfer studies. The experiments and calculations are based on a non-rotating machine and a wind tunnel using the same rotor coil(s). CHT-based thermal calculations provide not only reliable results compared to experimental work and lumped parameter thermal circuits with adjusted aggregate parameters, but also insight related to pressure and cooling flow distribution, thermal loads, and cooling integration issues that are necessary for the development of high power density and reliable electrical machines. The results of the air-cooling integration show that the desired high current density is achievable at the expense of high cooling intensity, where the air velocity ranges from 15 to 30 m/s and 30 to 55 m/s, distinguishing the air velocity of the hollow conductor and bypass channel, compared to the same coil in an electric machine and a wind tunnel at the similar thermal load and limit. Since the hot spot location depends on cooling integration and cooling intensity, modeling and estimating the cooling flow is essential in the development of wound-field synchronous machines.

Dynamic Simulation of Heat Distribution and Losses in Cement Kilns for Sustainable Energy Consumption in Cement Production

Sustainable energy consumption in cement production involves practises and strategies aimed at reducing energy use and minimising environmental impact. The efficiency of a cement kiln is dependent on the kiln design, fuel type, and operating temperature. In this study, a dynamic simulation analysis is used to investigate heat losses and distribution within kilns with the aim of improving energy efficiency in cement production. This study used Computational Fluid Dynamics (CFD) with Conjugate Heat Transfer, Turbulent Flow, and the Realisable k−ϵ turbulence model to simulate heat transfer within the refractory and wall systems of the kiln, evaluate the effectiveness of these systems in managing heat losses, and establish the relationship between the heat transfer coefficient (HTC) and the velocities of solid and gas phases. The simulation results indicate that a temperature gradient from the kiln’s interior to its exterior is highly dependent on the effectiveness of refractory lining in absorbing and reducing heat transfer to the outer walls. The results also confirm that different thermal profiles exist for clinker and fuel gases, with clinker temperatures consistently peaking at approximately 1450 °C, an essential condition for optimal cement-phase formation. The results also indicate that phase velocities significantly influence heat absorption and transfer. Lower velocities, such as 0.2 m/s, lead to increased heat absorption, but also elevate heat losses due to prolonged exposure. The relationship between the heat transfer coefficient (HTC) and the velocities of solid and gas phases also indicates that higher velocities improve HTC and enhance overall heat transfer efficiency, reducing energy demand.

Numerical investigation on hydrothermal characteristics of microchannel heat sinks with PCM inserts for effective thermal management applications

PurposeThe purpose of the paper is to develop an efficient thermal management system, which effectively dissipate the heat generated from the electronic devices. The present paper focuses at the modeling of microchannel heat sinks (MCHSs) with phase change materials (PCMs) insets to deal with the fluctuating heat generated from the electronic components.Design/methodology/approachIn this paper, a novel approach is introduced to enhance the thermal performance of MCHSs through the integration of conjugate heat transfer and energy storage. Numerical investigations were conducted on six novel models of PCM-based hybrid MCHSs using ANSYS-FLUENT. The hydrothermal characteristics of six PCM-based hybrid MCHS models were analyzed and compared with an MCHS model without PCM.FindingsThe numerical model used for this study exhibited a good agreement with existing experimental and simulation results documented in the literature. The hybrid MCHS models developed in the present analysis showed superior thermal characteristics compared to MCHS without PCM. About 12% improvement in the thermal performance factor and a 7.3% reduction in thermal resistance were observed in the proposed MCHS models. A negligible influence of the PCM channel shape and aspect ratio (AR) was observed on the MCHS performance.Research limitations/implicationsAs the present work is a numerical investigation, the computational time and computational cost requirements are the main implication for the research.Practical implicationsHigh pumping power requirement and expensive manufacturing methods of the microfluidic devices are the main practical implications. Leakage problem is also a challenge for development of these heat sinks.Originality/valueThe surge in the heat generated by electronic components is a limiting factor for the conventional MCHSs. To accommodate the surge, researchers have explored energy storage methods using PCM-based passive MCHS but these are effective only during the phase change process. To address this limitation, novel PCM-based hybrid MCHSs, which combine convective heat transfer with energy storage capabilities, have been modeled in the present work. There is an ample opportunity for further exploration of hybrid MCHSs with PCM.

Solution of the conjugate heat exchange problem for conical heat exchangers

RELEVANCE The article is devoted to the development of new designs of heat exchangers and evaluating the efficiency of their operation. According to the authors, currently of particular interest are conical heat exchangers of the "pipe-in-pipe" type, so the object of research in this paper is a heat exchanger in the form of a truncated cone based on a spring-twisted channel. The introduction of the proposed heat exchange elements and apparatuses into the industry requires additional research. To assess the effectiveness of the application of the considered TA, it is proposed to evaluate its performance in comparison with conical and cylindrical TA based on a smooth-walled pipe. Due to this, two hypotheses will be tested at once: the use of a conical coil heat exchanger is more efficient than a cylindrical one, and the replacement of a smooth-walled pipe with a spring-twisted channel increases the efficiency of the heat exchanger.OBJECT. The aim of the research is to develop a method for setting and solving the conjugate heat exchange problem for a heat exchanger in the form of a truncated cone with a heat exchange element in the form of a spring-twisted channel, analyze the results obtained and evaluate the efficiency in comparison with conical and cylindrical heat exchangers based on smooth-walled heat exchange elements. METHODS. For the numerical solution of the conjugate heat transfer problem, the FEM implemented by means of Ansys was used Fluent. RESULTS. The main results consist in the fact that the authors developed a model and algorithm for calculating conical coil heat exchangers of the pipe-in-pipe type, implemented in the Ansys program, and determined the thermal and hydrodynamic parameters of coil devices. A comparison of coil heat exchangers was also made: a conical one based on a spring-twisted channel with a conical one and a cylindrical one with a smooth-walled heat exchange element. The calculation results showed that replacing a smooth-walled pipe with a spring-wound channel significantly increases the efficiency of heat exchange equipment. CONCLUSION. The significance of the obtained results lies in the possibility of using modern, more efficient and compact heat exchange equipment for technological needs and in the justification of this choice. Thus, with equal initial data, conical heat exchangers are more efficient than cylindrical ones with a heat exchange element in the form of a smooth tube, since they need a smaller heat exchange surface to achieve the necessary thermal and hydrodynamic parameters. The results of calculations prove the prospects of using a conical TA based on a spring-twisted channel and show the need for further study of the influence of the geometric characteristics of both the coil itself and the heat exchange element on the thermal and hydrodynamic characteristics of the proposed HE.

Investigation of drafting-kissing-tumbling movement of two particles with conjugate heat transfer

The conjugate heat transfer at the particle-fluid interface and the collision between particles play a crucial role in the sedimentation process of particles. In this work, the recent volumetric lattice Boltzmann method for thermal particulate flows with conjugate heat transfer is adopted to investigate the drafting-kissing-tumbling movement in the sedimentation process of two particles in a closed channel. This volumetric lattice Boltzmann method is based on double distribution functions, with the density distribution function used for the velocity field and the internal energy distribution function used for the temperature field. It is a single-domain approach, and the nonslip velocity condition within the solid domain can be strictly ensured. The difference in thermophysical properties between the solid and fluid can be correctly handled, and the conjugate heat transfer condition can be automatically achieved without any additional treatments. Based on this particle-resolved simulation, the influences of the solid-to-fluid specific heat ratio, the Grashof number, and the particle’s initial temperature on the drafting-kissing-tumbling movement are discussed in detail. It is found that the fluid cooled by the particle and thus subjected to the downward buoyancy force can promote particle sedimentation. As the specific heat ratio increases, the particle’s temperature rises relatively slowly. In the sedimentation of two cold particles, the drafting duration and tumbling duration of the drafting-kissing-tumbling movement decrease when the heat capacity ratio increases. In contrast, the kissing duration increases as the heat capacity ratio increases. When the Grashof number increases, the heat transfer between the particle and fluid is enhanced, and the drafting duration significantly decreases while the kissing duration and tumbling duration remain almost unchanged in the sedimentation of two cold particles. The particle’s initial temperature greatly affects the occurrence moment of the drafting-kissing-tumbling movement. To be specific, the drafting-kissing-tumbling movement occurs at the earliest moment for the sedimentation of two cold particles, followed by the sedimentation of one cold and one hot particle, and the latest for the sedimentation of two hot particles. The promoting effect of the low particle’s initial temperature on the drafting-kissing-tumbling movement mainly takes place in the dragging stage and kissing stage. The particle’s initial temperature has almost no influence on the tumbling duration.

Conjugate heat transfer in wedged latticework cooling ducts with ejection flow for turbine blades

Conjugate heat transfer in wedged latticework cooling ducts with ejection flow for turbine blades

Loosely Coupled Fluid–Thermal-Ablation Analysis Strategy Based on Dynamic Flight Trajectory

In the context of designing supersonic and hypersonic missiles, it becomes imperative to conduct aerodynamic heating analyses, a task demanding time-dependent conjugate heat transfer (CHT) analyses that can be computationally expensive. This study introduces a time-efficient, loosely coupled fluid–structural thermal analysis method, tailored to the time-dependent flight trajectory. Loosely coupled analysis solves the fluid and structural equations independently and exchanges data at the interface between the two domains. To validate its efficacy, this proposed method is implemented on two distinct missile configurations with separate flight scenarios. The time-dependent temperature data, acquired through the loosely coupled analysis, are compared against results from the tightly coupled approach, actual flight data, and other established reference sources. Additionally, an ablation method using the heat of ablation formulation is coupled to the aerodynamic heating to approximately compute the recession. Also, a test problem is solved to validate the ablation method. The outcomes of this investigation reveal highly promising results. The findings of this research underscore the potential of the loosely coupled analysis strategy as a promising approach for conducting trajectory-based aerodynamic heating analyses of supersonic and hypersonic missiles. Notably, this approach offers reduced computational demand compared to the tightly coupled approach while maintaining the accuracy of the results.

Optimal design of regenerative cooling channels for a ram/scramjet dual-mode aircraft using conjugate heat transfer analysis

Optimal design of regenerative cooling channels for a ram/scramjet dual-mode aircraft using conjugate heat transfer analysis

Unified Solution of Conjugate Fluid and Solid Heat Transfer--Part II. High-Order Conjugate Heat Transfer

Unified Solution of Conjugate Fluid and Solid Heat Transfer--Part II. High-Order Conjugate Heat Transfer

Computational study of conjugate heat transfer and entropy generation of hybrid nano-particles in an enclosure with solid block

Computational study of conjugate heat transfer and entropy generation of hybrid nano-particles in an enclosure with solid block

Conjugate heat transfer simulation of wall temperature in a reverse-flow combustor

Conjugate heat transfer simulation of wall temperature in a reverse-flow combustor

Numerical investigation of thermal barrier coating on performance and emissions of HPDI dual-fuel engine

ABSTRACT Thermal barrier coatings (TBC) represent a promising technology for enhancing the thermal efficiency of internal combustion engines. This study investigates the impact of TBC on in-cylinder combustion processes of a dual-fuel HPDI engine to achieve higher energy conservation with low heat transfer loss. In the present study, a one-dimensional conjugate heat transfer (1D CHT) model is constructed that incorporates TBC material features. By coupling the 1D CHT model with the three-dimensional combustion model of dual-fuel HPDI engines in CONVERGE software, the influences of TBC to the combustion process and temperature distribution within the engine cylinder is illustrated in details. Meanwhile, the adiabatic combustion characteristics of HPDI engines are investigated based on various adiabatic components or porosity. The results demonstrate that the reduction in heat transfer under P_TBC (TBC on top boundary of piston) conditions leads to an increase in the volume proportions of the high-temperature intervals within the cylinder, thus enhancing both mixture activity and heat release rate. The combination of these two factors lead to a 0.4% increase in indicated thermal efficiency under P_TBC conditions compared to the baseline. Under the current injection strategy, P_TBC conditions could effectively eliminate the heat flow area in the piston bowl and step area, thereby significantly reducing heat transfer loss. Since heat transfer loss is basically influenced by both temperature difference between fluid and wall as well as thermal conductivity of TBC, increasing porosity therefore is able to enhance thermal resistance by reducing thermal conductivity of TBC. However, when there is an increased temperature difference between fluid and wall, increasing porosity does not continually lead to a further reduction of heat transfer loss. Finally, it is observed that the utilization of P_TBC with a porosity of 0.1 resulted in an increase of 0.7% in the indicated thermal efficiency compared to the baseline, while marginally reducing CH4 and CO emissions.

The Impact of Conjugate Heat Transfer in Flow Over a Vertical Plate and Application of Artificial Neural Network

Heat conduction properties are important in the flow area for the simulation of engineering applications where heat transfer is needed between both liquid and solid. Conjugate Heat Transfer (CHT) refers to thermal problems involving both conduction within the wall and convection within the fluid. CHT is crucial for heat exchangers, gas turbine blades, nuclear reactor cooling pipes, aircraft engines, and spacecraft. Additionally, the influence of the magnetic field is significant in fields such as electrostatic precipitation, MHD power generators and pumps, aeroheating, and polymer science. The motivation for this study is to understand the combined effects of CHT, mixed convection, magnetic fields, and viscous dissipation on velocity, temperature profiles, local skin friction, and heat transfer parameters over a vertical plate. The boundary layer equations have been derived from the Navier-Stokes and energy equations using similarity methods and solved numerically with the Keller Box technique. A new correlation for local skin friction and heat transfer parameters has been developed. Moreover, Artificial Neural Network (ANN) models have been applied to forecast desired numerical values. The optimal ANN model for local heat transfer has one hidden layer and nine neurons, achieving an R² value of 0.9077607 and an MSE of 0.0003101. For local skin friction, the best-performing model has one hidden layer and fifteen neurons, with an R² value of 0.9470261 and an MSE of 0.0250369.

Numerical investigation and thermal optimization of low-inductance ring-shaped film capacitors with integrated cooling structure for electric vehicle

The advancement of motor controllers for electric vehicles is increasingly focusing on higher power density, efficiency, and miniaturization. Consequently, there is a growing demand for film capacitors that offer not only lower stray inductances but also enhanced high-temperature resistance capabilities. While existing research dedicated to mitigating the stray inductances of film capacitors, studies that address both the capacitors’ stray inductances and the thermal managements remain relatively scarce. Therefore, this paper proposes for the first time a low-inductance ring-shaped capacitor, utilizing an integrated cooling structure to reduce the capacitor’s thermal resistance and enhance its high-temperature tolerance. Firstly, the stray inductances and heat dissipation performances of both ring-shaped and conventional square-shaped capacitors, each with identical capacitances, are compared using Q3D and FLUENT simulations, the results demonstrate that the ring-shaped capacitor exhibits lower stray inductance and superior heat dissipation performance. Then an integrated cooling structure is proposed for the ring-shaped capacitor with the aim of diminishing its thermal resistance and augmenting its tolerance to high temperature. Utilizing FLUENT conjugate heat transfer simulation, the impacts of key factors within the cooling structure such as inlet flow rate, inlet temperature, and ambient temperature on the capacitor’s maximum temperatures are investigated, and the optimal inlet flow rate and inlet temperature are determined by multi-objective optimization. The findings reveal that increasing the inlet flow rate reduces the maximum temperature, although the cooling effect becomes less significant at higher flow rates, leading to increased energy consumption and operating costs. Moreover, the ambient temperature has the largest impact on the capacitor temperature, followed by the inlet temperature. The optimized integrated cooling structure achieves approximately a 73.93% reduction in thermal resistance and lowers the maximum temperature of the ring-shaped capacitor by about 72.24%.

Numerical study of the influence of the geometrical aspect ratio and nanoparticles diameter on forced convection in a micro-channel heat sink of a nanofluid water/CuO based on a Brownian diffusion model

In order to cool electronic equipment with a high efficiency we can use the flow of a nanofluid in a rectangular micro-channel heat sink. The paper reports the results of the study of a hydrodynamically fully developed laminar forced convective heat transfer flow in two different geometries G1and G2. The study is numerical and was achieved using as nanofluid with and a single-phase approach. Calculations were first made with constant thermo-physical properties at and then made using temperature and nanoparticles diameter dependent thermo-physical properties based on a Brownian diffusion model. A three-dimensional conjugate heat transfer model was used and numerical simulations were based on a finite volume method. The simulations were made for a range of Reynolds numbers , for nanoparticle diameter in the range of and for a heat flux through the bottom surface of the heat sinks .The results of thermal and hydrodynamic fields show that nanofluids can provoke an increase in the local and average Nusselt numbers, a decrease of bottom surface local temperature and a slight decrease of the shear stress on the wall, particularly in the case of geometry G2. At the end of the study, the best geometry, volume fraction of nanofluid and nanoparticle diameter to be recommended for cooling were found based on minimum total thermal resistance of the micro-channel heat sink.

Conjugated Heat Transfer of the stator of an synchrounous electrical machine

Electrical energy generation in remote islands and ships are mainly due the energy conversion from chemical (fuel) to mechanical by an engine and converted from mechanical to electrical by an alternator. The losses in the alternator during the energy conversion are responsible for the increase of its temperature. In order to control the temperature level of the equipment, it is necessary to control how heat is evacuated. The present work numerically evaluates the heat dissipation in the stator of an electrical machine and its temperature maximum levels. Heat is generated in the cooper (windings) and steel (stator main body) during the energy conversion and is evacuated due the forced airflow throughout the stator. In order to reduce computational costs, due geometrical symmetry, one quarter of the machine was modeled. In addition to symmetry, the momentum boundary conditions consist in inlet, outlet and noslip at the walls and the thermal boundary conditions consist in imposed heat fluxes. In order to isolate the inlet and outlet boundary conditions, they were positioned at least 10 times the respective channel height far from the stator. The model is transient and the initial flow field is at rest (0 m/s) and at ambient temperature (300 K). The geometry was constructed using Salome-Meca software and the mesh was generated using the snappyHexMesh solver from OpenFOAM v11. The foamMultiRun solver from OpenFOAM was employed to create the numerical model. It solves the mass, momentum and energy equations in transient regime. The numerical schemes employed were linearUpwind (second order) for the advective terms, Gauss for the diffusive terms (linear) and the backward time discretization (second order). The turbulence model employed was the K-omega SST. The model predicted where were the regions inside the stator with intese heat transfer, which implies in lower temperature magnitudes and also where there were temperature peaks. Then correlation between the temperature and flow fields were discussed.

Efficient Numerical Modeling of Oil-Immersed Transformers: Simplified Approaches to Conjugate Heat Transfer Simulation

The development of digital twins for power transformers has become increasingly important to predict possible operating modes and reduce the likelihood of faults. The accuracy of these predictions relies heavily on the numerical models used, which must be both simple and computationally efficient. This work focuses on creating a simplified numerical model for a template oil-immersed power transformer (100 MVA, 230/69 KV). The study investigates how the number of elements and the strategies used to set up the mesh in the domain of interest influence the results, aiming to identify the key parameters that affect the outcomes. Furthermore, a significant effect of resolving thermal boundary layers on the accurate identification of hot spots is demonstrated. Two approaches to resolving thermal boundary layers are explored in this work. This study presents a comprehensive analysis of three numerical models for conjugate heat transfer simulations, each with distinct features and computational domain compositions. The results show that the addition of extra calculation domains leads to the emergence of new vortex structures, affecting the velocity profile at the channel inlet and altering the location of hot spots. This study provides valuable insights into the configuration and composition of calculated domains in numerical models of oil-immersed power transformers, essential for the accurate prediction of hot spot temperatures and ensuring reliable operation.

Conjugate heat transfer effects on bubble growth during flow boiling heat transfer in microchannels

Conjugate heat transfer effects on bubble growth during flow boiling heat transfer in microchannels