Conjugate Heat Transfer Simulation Research Articles

Accelerating Conjugate Heat Transfer Simulations in Squared Heated Cavities through Graphics Processing Unit (GPU) Computing

This research develops an innovative framework for accelerating Conjugate Heat Transfer (CHT) simulations within squared heated cavities through the application of Graphics Processing Units (GPUs). Although leveraging GPUs for computational speed improvements is well recognized, this study distinguishes itself by formulating a tailored optimization strategy utilizing the CUDA-C programming language. This approach is specifically designed to tackle the inherent challenges of modeling squared cavity configurations in thermal simulations. Comparative performance evaluations reveal that our GPU-accelerated framework reduces computation times by up to 99.7% relative to traditional mono-core CPU processing. More importantly, it demonstrates an increase in accuracy in heat transfer predictions compared to existing CPU-based models. These results highlight not only the technical feasibility but also the substantial enhancements in simulation efficiency and accuracy, which are crucial for critical engineering applications such as aerospace component design, electronic device cooling, and energy system optimization. By advancing GPU computational techniques, this work contributes significantly to the field of thermal management, offering a potential for broader application and paving the way for more efficient, sustainable engineering solutions.

A Modified Enthalpic Lattice Boltzmann Method for Simulating Conjugate Heat Transfer Problems in Non-Homogeneous Media

A Modified Enthalpic Lattice Boltzmann Method for Simulating Conjugate Heat Transfer Problems in Non-Homogeneous Media

Transient simulation of conjugate heat transfer of kerosene with thermal oxidative and surface coking reactions at a supercritical pressure

The regenerative cooling technology in aerospace applications often involves supercritical-pressure heat transfer of a hydrocarbon fuel, in which thermal oxidative reactions of the fuel would lead to surface coke accumulation on the cooling channel wall. In this paper, the long-term transient conjugate heat transfer of kerosene has been numerically investigated in a circular mini tube at a supercritical pressure of 3 MPa. The modified chemical mechanism and kinetics of thermal oxidative and surface coking reactions of kerosene are proposed, which, with an additional surface reaction, are capable of treating large coke deposition in regions with sharp temperature gradients. Transient surface coke accumulation and its effect on heat transfer are handled by a dynamic mesh technique. A series of numerical studies are conducted to elucidate the influences of surface heat flux, dissolved oxygen mass fraction, inlet fuel mass flow rate, and coke layer thermal conductivity on the supercritical-pressure heat transfer and thermal oxidative reactions. The effects of different reaction pathways on surface coke accumulation are analyzed comprehensively, and it is revealed that the oxygen-consuming surface coke deposition is initiated only at the high fuel temperature at around 590 K. The present numerical results would enhance fundamental understanding of the long-term transient heat transfer process of a hydrocarbon fuel at supercritical pressures in the regenerative cooling applications.

Design and optimization of liquid-cooled plate structure for power battery of the pure electric excavator

With the increasing pressure of energy transformation and environmental protection, the trend of electrification of construction machinery is becoming more and more obvious. In this paper, based on a small pure electric excavator which is still in the stages of research and development, a liquid-cooled heat dissipation structure (liquid-cooled plate) is designed according to the power battery pack scheme. The overall shape of the liquid-cooled plate is designed as a symmetrical serpentine flow channel. Geometrically, the symmetrical serpentine flow channel is a combination of a straight flow channel and a runway-shaped flow channel. Then the conjugate heat transfer simulation model was established by using the CFD software Ansys Fluent. The results show that the initial scheme can not guarantee the temperature homogeneity of the battery pack. Therefore, the liquid-cooled heat dissipation scheme was optimized and compared. Firstly, a liquid-cooled plate was added on the original basis, and multiple sets of simulations were carried out with the length of the linear flow channel as a variable. The results show that appropriately increasing the length of the straight flow channel at the entrance of the liquid-cooled plate has a marked effect on improving the heat dissipation performance.

Transient topology optimization for efficient design of actively cooled microvascular materials

Microvascular materials containing internal microchannels are able to achieve multi-functionality by flowing different fluids through vasculature. Active cooling is one application to protect structural components and devices from thermal overload, which is critical to modern technology including electric vehicle battery packaging and solar panels on space probes. Creating thermally efficient vascular network designs requires state-of-the-art computational tools. Prior optimization schemes have only considered steady-state cooling, rendering a knowledge gap for time-varying heat transfer behavior. In this study, a transient topology optimization framework is presented to maximize the active-cooling performance and mitigate computational cost. Here, we optimize the channel layout so that coolant flowing within the vascular network can remove heat quickly and also provide a lower steady-state temperature. An objective function for this new transient formulation is proposed that minimizes the area beneath the average temperature versus time curve to simultaneously reduce the temperature and cooling time. The thermal response of the system is obtained through a transient Geometric Reduced Order Finite Element Model (GRO-FEM). The model is verified via a conjugate heat transfer simulation in commercial software and validated by an active-cooling experiment conducted on a 3D-printed microvascular metal. A transient sensitivity analysis is derived to provide the optimizer with analytical gradients of the objective function for further computational efficiency. Example problems are solved demonstrating the method’s ability to enhance cooling performance along with a comparison of transient versus steady-state optimization results. In this comparison, both the steady-state and transient frameworks delivered different designs with similar performance characteristics for the problems considered in this study. This latest computational framework provides a new thermal regulation toolbox for microvascular material designers.

Computationally Efficient Workflow for Conjugate Heat Transfer With Large Eddy Simulation for Gas Turbine Combustors

Abstract Typical gas turbine combustor (GTC) and high-pressure turbine stage generally employs 10,000 to 100,000 small passages of cooling holes. Such an arrangement protects the solid walls through impingement and effusion cooling. The former provides solid wall internal cooling, and the latter helps to reduce the metal temperature by developing a thin film around it. High-fidelity simulations are primarily utilized in the industry such that accurate prediction from numerical tools can aid advancement in the performance of such machines. In this paper, a numerical study using ansys fluent has been conducted with large eddy simulation (LES), conjugate heat transfer (CHT), and radiation to explore the relative benefits of implicit and explicit fluid–solid thermal couplings. The simulations of LES with CHT are performed for well-documented experiments of heated nozzle exhaust passing over a film-cooled plate (Wernet et al., 2020, “PIV and Rotational Raman-Based Temperature Measurements for CFD Validation of a Perforated Plate Cooling Flow: Part I,” AIAA 2020-1230, Session, AIAA Scitech 2020 Forum, Orlando, FL, Jan. 6–10, 2020). The accuracy of the modeling approach is assessed by comparing CHT predictions of fluid velocity and solid-plate temperatures with experiments. Acceleration techniques for LES–CHT simulations are explored in this paper with an emphasis on thermal coupling, radiation, etc. The effects of mesh sensitivity and flow solution approach are presented in detail. LES–CHT results generally match the experiments at various blowing ratios both qualitatively and quantitatively. The comparisons in the paper allow the selection of best practices for CHT modeling in GTC. A generic combustor model with effusion cooling hole arrays is used in the paper to establish the workflow for modeling LES with CHT in the industrial-type combustor. Various acceleration techniques are utilized to show an overall improvement in solution performance with the same level of accuracy.

Off-lattice Boltzmann simulation of conjugate heat transfer for natural convection in two-dimensional cavities.

This study addresses the inadequacy of isothermal wall conditions in predicting accurate flow features and thermal effects in multicomponent systems. A finite-difference characteristic-based off-lattice Boltzmann method (OLBM) with a source term-based conjugate heat transfer (CHT) model is utilized to analyze buoyancy-driven flows in two-dimensional enclosures. The source term-based CHT model [Karani and Huber, Phys. Rev. E 91, 023304 (2015)1539-375510.1103/PhysRevE.91.023304] is extended to handle curved conjugate boundaries. The proposed CHT-OLBM solver is verified using analytical solutions and reference data from the literature. The effects of wall conduction on conjugate natural convection (CNC) problems in square and horizontal annular cavities are systematically examined with a solid wall of a nondimensional thickness of 0.2. For the square cavity problem, the governing parameters considered are 10^{5}≤Gr≤10^{9} and χ=1,5,10, while for the horizontal annulus problem, the governing parameters are taken as 10^{5}≤Ra≤10^{7} and χ=1,5,10,100, where Gr is the Grashof number, Ra is the Rayleigh number, and χ is the thermal conductivity ratio. Qualitative analysis of the simulation results using isotherms and streamlines and quantitative analysis of the local fluid-solid interface temperature, solid wall temperature distribution, Nusselt number profiles, overall Nusselt number, and effective Grashof/Rayleigh number is conducted. The overall heat transfer reduction inside the cavities due to a solid wall is quantified, and correlations are obtained to represent the overall heat transfer inside both enclosures. The findings demonstrate the significance of CHT analysis, and the CHT-OLBM solver developed in this study can successfully investigate steady, unsteady, and chaotic CNC flows.

Conjugate heat transfer analysis of sidewall-heated rectangular microchannels with different bottom wall materials

In this study, the conjugate heat transfer in a microchannel under four sidewalls (left, right, top, and bottom wall facing upstream) heating conditions is investigated experimentally and numerically. The microchannel has a width of 500 μm and a depth of 100 μm. Micro-Particle Image Velocimetry (Micro-PIV) and Temperature Sensitive Paint (TSP) are respectively applied to measure the velocity and temperature fields at a Reynolds number (Re) of 20. The experimental results demonstrate that the temperature gradient exists in both the left, right, and bottom wall, indicating the existence of conjugate heat transfer. Thus, 3D conjugate heat transfer simulations are subsequently conducted. Good agreements are attained between numerical and experimental data only with the non-ideal boundary condition. Otherwise, there is a significant discrepancy between them. Further parametric studies on bottom wall to fluid thermal conductivity ratio (kb/kf) and Re show that the fully developed overall Nusselt number (Nu‾) in the conjugate heat transfer case is approximately 4.55, much higher than the analytical solution 0.87 without accounting for conjugate heat transfer. As kb/kf is varied from 0.21 to 6.48, there exists a critical kb/kf=1.79, before and beyond which the total heat flux respectively increases and decreases with kb/kf. However, Nu‾ is a monotonically increasing function of kb/kf, with a peak value of 5.75 occurring at kb/kf = 6.48.

Unsteady conjugate heat transfer simulation of wall heat loads for rotating detonation combustor

Rotating detonation engines (RDEs) are the most promising pressure-gain combustion devices, but their long-duration operations are hindered by the harsh thermal environment inside the chamber. This study analyzes the instantaneous and average heat loads on chamber walls of RDEs based on the newly developed unsteady conjugate heat transfer (CHT) OpenFOAM solver named multiRegionBYRFoam. To enhance accuracy in predicting heat transfer characteristics compared to decoupled simulations focusing solely on fluid or solid behavior, three-dimensional CHT simulations are conducted for a premixed H2/air annular RDE coupling the detonation simulation with heat conduction in both inner and outer chamber walls. The transient time evolutions of wall heat flux in RDEs are numerically captured for the first time and agree well with experiments. The calculated peak wall heat flux is 1.98 MW/m2 at the inner wall and 2.63 MW/m2 at the outer wall when a single detonation wave propagates with a mass flow rate of 0.227 kg/s. By investigating the influence of inlet flow conditions and detonation modes, valuable guidelines on designing efficient thermal management systems for RDEs are obtained: larger mass flow rates and multi-wave modes result in higher average wall heat flux; the heat flux at the outer wall exceeds that at the inner wall while both walls require effective cooling for gas turbine engines with a rotating detonation combustor. Furthermore, a novel heat transfer model for RDEs is proposed based on a thermal operation map depicting total heat transfer rates to describe the nonlinear impact of mass flow rate and number of detonation waves, which can be employed to predict total wall heat loads under specific operation conditions of RDE.

A study on the effect of non-uniform spacing on the performance of forced convection cooling of discrete heaters: A numerical investigation

A numerical simulation of forced convection conjugate heat transfer has been performed for flow over discrete, volumetrically heated rectangular obstacles mounted on the lower wall of a horizontal channel. Non-uniform spacing between the heaters is investigated with the help of isotherms, streamlines, heatlines and entropy generation along with cup-mixing temperature by fixing the geometric parameters for flow Reynolds number between 100 and 1500 (100≤ReL≤1500) and a fixed thermal conductivity ratio of 10 (ks/kf). To quantify heat transfer, local and average Nusselt number have been used. Pressure drop is calculated with the help of the apparent friction factor. Together, these two parameters provide the quality factor, which measures the performance of the discrete heaters. It has been found that the effect of spacing variation is not limited to the proximal heaters. Irregular behaviour in heat transfer has also been noticed in the results. As we move downstream of the flow, the heat transfer will decrease; however, there are a few particular cases where it was noticed that the performance of the last discrete heater is better compared to the heater just upstream of it.

C conjugate heat transfer simulation of swirl internal cooling on blade leading edge

Abstract Swirl cooling can not only increase the area of the heat exchange wall covered by the coolant, but also improve the average heat transfer intensity and uniformity of the target surface. SST k-ω turbulence model is utilized in the conjugate heat transfer numerical simulation. Based on C3X blades, leading edge swirl cooling structure of the corresponding areas are modified. The flow and heat transfer characteristics of swirl cooling are analyzed at different cross-sections and positions. It is found that there exists an optimal aspect ratio and hole spacing to minimize the temperature gradient on the swirl cavity wall. The swirling motion in the swirl cavity can significantly increase the heat transfer coefficient of the wall surface.

Conjugated heat transfer simulation of flow mechanism and heat transfer characteristic of sweeping jet impinging on leading edge in turbine cascade

Increasing inlet temperatures of gas turbines is the way to go for the development of advanced aero engines. As the inlet gas temperature of modern gas turbine engines continues to increase, the operating temperature has far exceeded the melting temperature of the typical heated region. Excessive temperatures can cause turbine blade ablation and damage, thus affecting the reliability and safety of the engine. The sweeping jet actuator (SJA) is a fluid oscillator that has attracted considerable attention in the field of enhanced heat transfer and flow control due to its non-constant sweeping characteristics. As a new impinging cooling method, this paper adopts the device to carry out the research work on the flow mechanism and heat transfer characteristics of sweeping jet (SJ) impinging on leading edge in gas turbine blade. Firstly, the numerical investigation of conjugated heat transfer simulation combined with unsteady Reynolds-averaged Navier–Stokes (URANS) is conducted to analyze the cooling performance of SJ. Using a C3X high-pressure turbine blade as a prototype, the temperature drop with the SJ scheme was improved by 1.8 K and 8.7 K compared with the circle jet (CJ) scheme for H/D = 1 and H/D = 5, respectively. Finally, the internal flow field of the blade is reconstructed by combining the proper orthogonal decomposition (POD) method. Through the POD method, we can deeply analyze the mechanism of the effect of SJ on the non-constant heat transfer at the leading edge of the blade, which provides theoretical support for the practical engineering application of SJ in the future industrial field.

Heat Transfer Characteristics of Turbulent Flow in Double-90°-Bend Pipes

This study evaluates the heat dissipation and Nusselt number for an S-shaped double-bend pipe, for which an experimental evaluation is lacking. In terms of the velocity field, the mean velocity and turbulent kinetic energy were measured through particle image velocimetry. Heat transfer characteristics were evaluated in validated conjugate heat transfer simulations, and a k-ω SST turbulence model was used for flow simulation inside the pipe. Heat transfer enhancement was observed at the first bend, as observed in previous studies on single-bend and U-shaped bends, whereas no heat transfer enhancement was observed at the second bend. This result was due to higher turbulent heat flux at the first bend because of higher eddy diffusion on the outside of the bend, whereas eddy diffusion was lower on the outside of the second bend owing to the history of the first bend. The heat transfer characteristics of the S-shaped double-bend pipe elucidated in this study provide valuable insight for devising strategies to reduce heat loss in automotive exhaust pipes with multiple bends. Furthermore, the conjugate heat transfer simulation model used in this study provides a benchmark for heat transfer calculations for multi-bend pipes.

Temperature measurement at turbine outlet achieved by a sensing net and infrared thermometry method

The measurement of turbine outlet temperature is challenging because of an intense swirl and high speed at this position. However, accurate measurement of the turbine outlet temperature is fundamental for characterizing the turbine performance. The paper proposed an infrared thermometry method based on the temperature sensing net (TSN) to measure the temperature distribution at the turbine outlet. First, this article describes the design and operation of the measurement procedure through infrared technology to accomplish this difficult task. Then, the temperature and velocity distribution at the turbine outlet and the adiabatic efficiency of the turbine are obtained using the CFD (Computational Fluid Dynamics) method to verify the feasibility of the proposed scheme. And the CHT (Conjugate Heat Transfer) simulation results for the TSN show that the incoming flow mass rate has a great influence on TSN temperature. In contrast, the influence of the incoming flow temperature gradient on it is almost negligible. Moreover, the fluid flow behavior and static temperature distribution around the temperature-sensing wire (TSW) at different Mach numbers are analyzed, and the heat transfer mechanism between the TSW and the fluid is revealed. The results show that the temperature of the TSN is lower than that of the incoming flow, but the distribution law is similar. The main factor affecting the temperature difference between the TSW and the fluid is the incoming flow velocity.

Hybrid-lattice Boltzmann Method for the Simulation of Magnetohydrodynamic Conjugate Heat Transfer and Entropy Generation in Three Dimensions

Hybrid-lattice Boltzmann Method for the Simulation of Magnetohydrodynamic Conjugate Heat Transfer and Entropy Generation in Three Dimensions

High-Fidelity Conjugate Heat Transfer Simulation of Micro-Channel Heat Exchanger

In this study, high-fidelity conjugate heat transfer simulations are used to model a micro-channel heat exchanger (MCHE) in a crossflow to study its thermal-hydraulic performance. Three different microchannel geometries, namely circular, triangular, and square with louver-shaped fins, are considered. The local flow field showed a strong coupling between the microchannel flow, solid domain, and crossflow. The flow separation and wake regions formed near MCHE resulted in a large variation in the velocity field and temperature in the crossflow. The interaction of the wake region with the fins introduces significant spanwise variations, leading to variations in the thermal boundary layer. The heat conduction in the solid structure provided a non-uniform temperature field with a higher temperature near the microchannel and a slightly lower temperature near the surface exposed to the crossflow. The microchannel flow analysis showed that the internal geometry affects the pressure drop, which is highest for the triangular MCHE and lowest for the circular MCHE. Based on the effectiveness and performance index calculations, the circular MCHE exhibited the best performance, while the rectangular MCHE showed higher heat transfer effectiveness.

Comparison of Thermal Effectiveness and Crevice Corrosion Risk of Fin Geometry on All-Aluminum Microchannel Heat Exchangers

All-aluminum microchannel heat exchangers have recently gained popularity in the heating, ventilation, and air conditioning industry. Despite their attractive thermal performance design, these heat exchangers make coils used in automotive, commercial, and residential applications prone to crevice corrosion. This study uses high-fidelity conjugate heat transfer simulations to model a micro channel heat exchanger system that includes fins and tubes with crossflow to compare their thermal effectiveness to gain insight into potential crevice corrosion of the MCHE alloy. This study considers three fin geometries (louver, step, and saw) with the same tube and circular shape microchannel and identifies the corrosion hot spot and thermal effectiveness. A predicted flow field also identifies crevices between fins and tube surfaces as critical corrosion hot spots often associated with low-velocity regions. The crevice volumes for the louver, step, and saw fin shapes are calculated as respectively. Results also show that the same circular microchannel louver shape fin has higher effectiveness than the step and saw shape fin. The thermal effectiveness for microchannel tubes with louver, step, and saw shape fins are 0.337, 0.20737, and 0.2895, respectively.

A versatile immersed boundary method for high-fidelity simulation of Conjugate Heat Transfer

A numerical strategy based on an immersed boundary method (IBM) is presented for performing high-fidelity simulation of thermal hydraulics while including Conjugate Heat Transfer (CHT). The well documented pipe flow is considered which, despite its academic nature, can be seen as a prototype of complex geometry in the sense that the computational mesh, only regular and Cartesian, is not in any way designed to fit the wall. An original strategy is proposed to impose Neumann boundary conditions in this generic situation where the wall geometry is disconnected from the mesh organization. As a first validation step, the technique is used in the context of heat transfer in pipe flow with isoflux conditions (IF). The actual order of accuracy is assessed in laminar regime and then direct numerical simulation (DNS) results are compared to turbulent data of reference, including first- and second-order one-point statistics, as well as budgets of temperature variance for a Reynolds number Re=5300 and two Prandtl numbers Pr=0.025,0.71. The technique is then used to develop a versatile methodology for CHT simulations, where the coupling between fluid and solid thermal solution is performed by an immersed boundary technique that translates the information from the normal and tangential surface directions into the Cartesian grid directions. Consistent results are presented in laminar and turbulent regimes, through the check of the accuracy order for the former and the analysis of turbulent statistics for the latter, including the assessment of the discontinuity of the temperature variance dissipation across the fluid-solid interface.

Steady-state error estimation and calibration of a shielded total temperature probe for turbomachinery

Accurate measurement of the total gas temperature plays a vital role in the performance research of turbomachinery. The total temperature thermocouple (TC) used in the measurement often needs to be specially designed and calibrated. In the past, the calibration was usually completed by a complex and highly costly experiment. The present work developed a new shielded total temperature probe (NTTP) for relatively low-temperature gas measurement. Meantime, this new design's characteristics and different error sources are analyzed based on the Conjugate Heat Transfer (CHT) simulation method. The CHT results show that the thermal conduction error is kept at a small value in the range of Mach number from 0.2 to 0.6; The velocity error contributes more than 90% of the total error. Four standard temperature probes are selected for the comparison. The maximum measurement error is 1.13 K, which is 331.62%, 119.4%, 61.6% and 59.5% lower than the standard type-A, B, C and D, respectively. Moreover, the detailed flow field and the influence of TC junction position on measurement accuracy are discussed. With the increases of the junction away from the supporting, the total measurement error of the NTTP increases first and then decreases. To vindicate the applicability of the proposed design, the measurement error of the NTTP is verified by a new experimental method with the relatively static fluid as the gas flow source. The testing results show that when the inflow's Mach number is 0.52, the measurement error of the NTTP is about 40% lower than that of the type-C total temperature probe.

A Multi-Disciplinary Approach for the Electrical and Thermal Characterization of Battery Packs—Case Study for an Electric Race Car

A novel, multi-disciplinary approach is presented where experiments, system simulation and Computational Fluid Dynamics are combined for the electrical and thermal characterization of an air-cooled battery pack. As a case study, a Formula Student race car is considered and the procedure proposed consists of three steps: (1) experimental characterization of the battery cells under several thermal conditions; (2) thermal and electrical modeling of the battery stack with system simulation; (3) three-dimensional, time-dependent Conjugate Heat Transfer simulation of the whole battery pack to investigate the cooling performance of the chosen design, and to access fundamental quantities of the batteries, such as state of charge, temperature and ohmic heating. Future improvements of the current work are discussed, including the extension to a liquid-cooled design, battery aging consideration and model integration into a full vehicle system model.