Conjugate Heat Transfer Analysis Research Articles

Cooled MarkII blade surface pressure and temperature distribution by a conjugate heat transfer analysis using Reynolds stress baseline turbulence model

Cooled MarkII blade surface pressure and temperature distribution by a conjugate heat transfer analysis using Reynolds stress baseline turbulence model

Conjugate heat transfer and fluid flow analysis on printable double-wall effusion cooling with internal topology-optimized TPMS structures

Double-wall effusion is a highly efficient cooling technique in modern gas turbine blades. This study uses topology optimization infilled with triply periodic minimal surface structures (TPMS) to design high-performance internal cooling structures, improving cooling effectiveness and mitigating thermal stress for the double-wall channel. The flow, heat transfer, and static structural characteristics of the topology-optimized TPMS model are compared with the results of the smooth and circular pin fin configurations. Results show that the optimized model provides a uniform flow inside the channel and the effusion holes, reducing the jet lift-off and keeping the coolant attached to the effusion wall. Within the blowing ratios of 0.5–1.7, the optimized model improves impingement heat transfer by 9.5 %–12.5 % compared to the pin fin configuration. The averaged overall cooling effectiveness is also 4.2 %–4.6 % with lower pressure loss. The thermal stress and total deformation are evenly distributed and show 22.9 % and 12.0 % lower than the pin fin model. Moreover, a 3D laser scanning microscope and high-resolution CT scan are used to evaluate the manufacturability of the optimized sample, printed by laser powder bed fusion with an actual gas turbine blade scale. The results benefit the fabrication improvement for next-generation gas turbine blades.

Stokes-type conjugate heat transfer and thermoelasticity analysis of a hollow spherical particle in a slip flow

Conjugate heat transfer around a spherical particle submerged in a viscous heat-conducting fluid at very low Reynolds numbers is analytically investigated. The cases of spherically symmetric and axisymmetric temperature fields are solved. The temperature jump condition of dilute gas dynamics is assumed. The induced thermal stresses in the sphere in the case of spherical symmetry are analytically solved as well. The effect of temperature jump, heat conductivity ratio between the solid and fluid media, the heat generation and the inner radius of the sphere on the temperature, displacement, radial stress and circumferential stresses are studied. Furthermore, an exact correlation is proposed between the Reynolds, Knudsen and Nusselt numbers as well as the drag coefficient of the sphere, which is valid for slip flow at the Stokes limit. Whether it is accurate at higher Reynolds numbers would need further research.

Investigation of temperature assisted corrosion failure of an aircraft turbine blade

In this study, the root cause of a recurring corrosion problem at the tip of an internally cooled high-pressure turbine blade (HPT) of a turbofan engine was investigated. A two-pronged strategy was utilized involving (i) experimental techniques to identify the blade material and corrosion products, and (ii) computational methods to analyze the fluid flow over the blade. In the experimental thrust, an array of techniques was employed to determine the chemical composition, microstructure, corrosion products and microhardness values while the airflow, pressure distribution and thermal profile over the blade were found through computational paradigms. The blade was a Ni-based superalloy containing typical gamma (γ) and gamma prime (γ′) phases, with an average microhardness value of 389 HV at room temperature. SEM analysis of the corroded area revealed oxides of iron, calcium, magnesium, aluminium, and silicon (FCMAS) most of which were not part of the base alloy. To determine the temperature profile and pressure distribution on the blade, a conjugate heat transfer analysis using Ansys CFX was conducted. A combination of experimental data from the engine ground running test station and analytical equations was used to find the required boundary conditions for the computational analysis. Pressure distribution over the entire blade was found which showed higher flow velocities and cross flows at the blade tip which potentially cause erosion at that region in the presence of impurities in the incoming air. Temperature distribution over the entire blade was also obtained, and it was found that the highest temperatures for the internally cooled blade occurred at the tip region which were in the range of ∼1060 °C–1250 °C (average ∼1114 °C). The temperature on the tip was high enough to cause the melting of the impurities that ingress the coating and cause its degradation during thermal cycling. This exposes the base alloy to FCMAS and causes corrosion. These high temperatures (1060–1250 °C) also induced phase transformation and increased the brittleness (∼22 % increase in hardness) which aggravated the presence of corrosion and resulted in crack formation and blade rejection.

The Development of a Next-Generation Latticed Resistojet Thruster for CubeSats

CubeSat and small satellite resistojet heat exchanger designs are based on conventional concepts that have been used since the 1960s, being primarily limited to helical or twisted tape heat exchangers. The design flexibility enabled by new additive manufacturing technologies is yet to be properly harnessed. This study introduces a novel resistojet concept that incorporates a highly miniaturized lattice structure as the heat exchanger. A conjugate heat transfer analysis determined that the lattice with a diamond unit cell had superior thermal performance compared to the same lattice with a gyroid unit cell and increased the heat transfer rate by up to 11% compared to a helical heat exchanger of the same volume. Performance testing of the prototype thruster with integral diamond lattice indicated that specific impulses of up to 94 s were possible with a 30-Watt heater using nitrous oxide as the propellant. The prototype thruster weighed only 22 g and demonstrated a 67% reduction in the power required to achieve the same specific impulse as previous nitrous oxide resistojets designed for the small satellite platform. The development of highly miniaturized latticed resistojets is shown to be feasible and highly attractive for CubeSats, where mass and power are of the utmost importance.

Conjugate heat transfer analysis on the action mechanism of centrifugal force and centrifugal buoyancy in staggered labyrinth seals

The heat transfer characteristics of smooth and honeycomb staggered labyrinth seals were investigated using the conjugate heat transfer method. Three pressure ratios (π = 1.2, 1.6, and 2.0), three rotational speeds (RPM = 0, 10,000, and 20,000), and two wall-to-fluid temperature ratios (TR = 0.4 and −0.67) are considered to explore the influence of centrifugal force and centrifugal buoyancy. The results indicate that the heat transfer coefficient of staggered labyrinth seals increases with pressure ratio due to the increased flow velocity and the thinner boundary layer. As a result of the interaction of inertia force and centrifugal force, some enhancement positions of heat transfer coefficient shift slightly. Notably, centrifugal buoyancy has a negative impact on heat transfer at TR = −0.67, but a positive impact at TR = 0.4. When TR = −0.67, there is a peak of the heat transfer coefficient with increased rotational speed due to centrifugal buoyancy. In addition, the heat transfer coefficient at TR = −0.67 is lower than that at TR = 0.4, especially at high rotational speeds. It is proposed that heat transfer correlations be developed by incorporating the Taylor number and rotating Grachev number.

POD–ANN as digital twins for surge line thermal stratification

This paper describes a hybrid proper orthogonal decomposition (POD) and artificial neural network (ANN) strategy to construct digital twins of a pressurizer surge line under thermal stratification conditions. The one-way coupled conjugate heat transfer and thermal stress analysis was conducted by use of parametric modeling and the introduction of the inverse distance weighted interpolation for the grid mapping, which allows for the mapped grids to have the same number of nodes regardless of variations of surge line geometries. A snapshot-based POD was utilized to obtain truncated lower-order modes and the full-order system response was projected onto these modes with reduced state coefficients. Then the ANN was employed to establish a surrogate model between the five chosen design variables of interest and the reduced state coefficients, resulting in a surrogate-assisted digital twin for a pressurizer surge line. Prediction of fluid–structure interface temperature and thermal stress distribution was thus achieved in an in-line real-time manner for a wide range of parameter variations. We publicly share all code implementations, and we believe that our efforts open a door for the digital twining of thermo–fluid–structure interaction problems

Conjugate heat transfer analysis of developing region of square ducts for isothermal and isoflux boundary conditions

Purpose This paper aims to present a comprehensive analysis of conjugate heat transfer phenomena occurring within the developing region of square ducts under both isothermal and isoflux boundary conditions. The study involves a rigorous numerical investigation, using advanced computational methods to simulate the complex heat exchange interactions between solid structures and surrounding fluid flows. The results of this analysis provide valuable insights into the heat transfer characteristics of such systems and contribute to a deeper understanding of fluid–thermal interactions in duct flows. Design/methodology/approach The manuscript outlines a detailed numerical methodology, combining computational fluid dynamics and finite element analysis, to accurately model the conjugate heat transfer process. This approach ensures both the thermal behaviour of the solid walls and the fluid flow dynamics are well captured. Findings The results presented in the manuscript reveal significant variations in heat transfer characteristics for isothermal and isoflux boundary conditions. These findings have implications for optimizing heat exchangers and enhancing thermal performance in various engineering applications. Practical implications The insights gained from this study have the potential to influence the design and optimization of heat exchange systems, contributing to advancements in energy efficiency and engineering practices. Originality/value The research introduces a novel approach to study conjugate heat transfer in square ducts, particularly focusing on the developing region. This unique perspective offers fresh insights into heat transfer mechanisms that were previously not thoroughly explored.

Conjugate heat transfer analysis of helium–xenon gas mixture in tight rod bundles

Helium-xenon gas mixture (He-Xe) and tight rod bundles are widely used in gas-cooled space nuclear reactors. However, few studies have been conducted on the effects of pitch-to-diameter ratio (P/D) on thermal–hydraulic characteristics while considering conjugate heat transfer. This paper numerically investigated He-Xe heat transfer in a fuel-gas gap-cladding-coolant structure of tight rod bundles. The numerical model is validated using experimental data and the maximum error of wall temperature is less than 5 %. The results show that conjugate heat transfer significantly affects the heat transfer. The heat transfer coefficient without conjugate heat transfer is only 8.85 % of that with conjugate heat transfer in the quasi-triangular pipe. The decrease in P/D enhances the convective heat transfer and causes larger pressure drops. A new performance evaluation criterion (PEC) is presented considering the effects of heat transfer, pressure drop and volume. PEC first increases and then decreases with the increase in P/D and the best comprehensive performance occurs at P/D = 1.113. The analysis of the temperature difference in the viscous sublayer (y+ < 5) shows that the decrease in P/D enhances the turbulent effect of He-Xe and reduces the thickness of the viscous sublayer, resulting in the heat transfer enhancement. This study contributes to the optimal design of advanced space reactors.

Improving heat transfer and compressed air consumption in low pressure die casting of aluminum wheels

Automotive wheels made from aluminum alloys are generally manufactured using the Low-Pressure Die Casting (LPDC) method. The molten aluminum is pressurized and filled into the cavities between the molds, and it is cooled using cooling channels in the LPDC. While the cooling fluid can be either air or water in industrial applications, only air cooling is utilized within the scope of this study. The primary expenditures of the process are attributed to the cycle time and the consumption of compressed air. In industrial settings, the primary coolant supply, emanating from either one or two inlet sources, is systematically channeled through a series of nozzles. These nozzles are strategically designed to impinge air onto specific areas of the mold pockets, ensuring efficient cooling.This research focuses on enhancing the cooling channels and mold pocket regions in LPDC through a combination of experiments and Computational Fluid Dynamics (CFD) integrated with Conjugate Heat Transfer (CHT) analyses. The study involves designing cooling channels to achieve a uniform mass flow distribution at the nozzle outlets, and optimizing the mold pocket regions. This optimization resulted in a 46% reduction in compressed air flow while maintaining comparable levels of heat transfer in the optimized mold pocket design. Moreover, flow rate non-uniformity at nozzle outlets was reduced from 11.5% to 2.0% to achieve uniform cooling and temperature distribution across the wheel spokes. An experimental setup with a cooling pipe network allowed simultaneous flow rate measurements from 20 outlets using flow rate sensors.The improved cooling channel and mold pocket design were adapted to the LPDC, and 20 aluminum alloy wheels were successfully cast with a 46% lower mass flow rate. All these wheels were tested in accordance with the relevant test specifications and the results obtained were assessed as compliant according to certain limits.

Numerical simulation of composite swirl/film double-wall cooling structures and chamber designs for enhanced overall cooling effectiveness

A novel double-wall with composite swirl/film cooling structure is proposed in this work to enhance the cooling effectiveness of contemporary gas turbine blades. The influence of different shaped chambers and Biot numbers on the overall cooling effectiveness (OCE) are investigated by Reynolds time-averaged Navier-Stokes simulations and conjugate heat transfer analysis. The results suggest that the proposed composite cooling configuration exhibits outstanding OCE in the simulated range. When the Rm is 1.00 and the Biot number is 0.11, the OCE of the composite structure is improved by 8.92 % over the conventional double-wall structure, and the distribution is more uniform. In addition, the optimal flow and cooling performance of the composite swirl/film cooling structure at high Rm conditions are obtained. The OCE is very sensitive to the variation of the Biot number. Finally, the empirical correlations obtained by the multivariate nonlinear regression fitting method are in good agreement with the simulations, with errors within 10 %. The results also provide important guidance for the development of advanced gas turbine blades double-wall cooling structures.

Simulation and analysis on heat leakage structure of cold compressor in large-scale refrigeration system

Large-scale helium cryogenic refrigeration facilities are indispensable equipment for many cutting-edge researches, and the cold compressor is the most advantageous pressurization scheme in superfluid helium systems with capacity of more than 200 watts. Due to the extremely low operating temperature zone of the cold compressor, the efficiency of the compression process decreases as the external heat leakage increases, especially when building systems with greater cooling capacity, this phenomenon becomes more significant. In order to reduce the influence of heat leakage, a conjugate heat transfer analysis is carried out on the cold compressor using commercial CFD software, and the internal structures, including thermal anchor, thermal insulation materials, are analysed and optimized base on the simulations.

Thermal and Structural Analysis of A Vascular Cooled Composite Radome

To increase the efficiency of aircraft radome structures, the potential to integrate structural, cooling, and electromagnetic (EM) transmission functions into a composite radome is being investigated. The radome configuration includes micro-channels, used for flow of cooling fluids, and embedded copper layers, used to alter the EM transmission characteristics, incorporated into a composite panel. Concepts have been developed using low dielectric loss composite for manufacturing the multilayer structure required to incorporate these multifunctional characteristics. Structural analyses and conjugate heat transfer analyses have been performed to assess the effects of channel size and position on load-carrying capability and cooling capability. Results from the analyses have been used to identify candidate configurations that will be fabricated. Fabrication concepts and results of the structural and thermal analyses are presented.

Conjugate heat transfer analysis of the transient thermal discharge of a metallic latent heat storage system

Thermal energy storage systems utilizing metallic phase change materials exhibit great potential as a technology for mobile applications, offering high storage densities and high thermal discharge rates. First experimental investigations show the functionality and performance characteristics of this system. For a deeper understanding of the thermal discharge, this paper presents a numerical model and analysis of the transient conjugate heat transfer. For validation of the numerical model, the results of the simulations are compared to the available experimental data. The investigated storage is based on an aluminum silicon alloy and a box-shaped graphite container design. In this system, heat extraction is achieved by forced convection of ambient air. The transient thermal discharge was simulated from 650 °C to 100 °C, and the solidification of the storage material at around 577 °C was simulated using an enthalpy-porosity approach. The discharge time and total heat flow show good agreement with the experimental data, indicating the model’s successful validation. An empirical study was carried out to determine the thermal contact resistance at the interface between the storage material and the graphite container. The present study contributes new physical insights regarding the thermal discharge of a novel metallic latent heat thermal energy storage system.

Conjugate Heat Transfer Advancements and Applications in Aerospace Engine Technology

Over the past few decades, conjugate heat transfer (CHT) technology has been instrumental in predicting temperature fields within aerospace engines, guiding engine design with its predictive capabilities. This paper comprehensively surveys the foundational technologies of CHT and their applications in engine design, backed by an extensive literature review. A novel coupling iteration methodology, su-F-TFTB, was proposed. Following this, it introduced grid splicing technology tailored for heat flux conservation, which significantly enhances the adaptability of CHT grids. Ultimately, this study employed the self-developed Aerospace Engine Numerical Simulation (AENS v4.0.1) software to perform CHT analyses on NASA-C3X turbine blades equipped with ten radial cooling systems. A comparative analysis of pressure distributions across various density meshes was undertaken to affirm mesh independence. Furthermore, the impacts of the Spalart–Allmaras (SA) one-equation model and k–ω Shear Stress Transport (SST) two-equation model on the temperature distribution in conjugate heat transfer were investigated. The results indicated that the k–ω SST model exhibited superior performance, aligning closely with NASA experimental data. This validation confirmed the effectiveness of the software.

An integrated 2D/3D numerical methodology to predict the thermal field of electric motors

The present work aims at providing a predictive numerical methodology for the thermal characterization of electric motors. The methodology relies on a 2D-FE simulation for the estimation of the electromagnetic (iron and joule) losses. The latter are then exploited in a 3D-CFD Conjugate Heat Transfer analysis for the evaluation of the thermal field.The CFD model includes both the solid components and the fluid domains. The main novelty of the paper is represented by the copper coil modelling. In fact, copper, air, epoxy resin and enamel are synthetized in a single homogeneous body able to reproduce the thermal behaviour without including the single components, to reduce the computational cost.The methodology is validated against experimental data on a three-phase squirrel-cage induction motor. As for the experimental data (available at three different operating conditions), temperature distributions are measured by thermocouples at the test bench for the validation of the 3D-CFD CHT model. In addition, experimental estimations of the losses are available for the validation of the 2D electromagnetic simulations.The numerical results in terms of motor performance, electromagnetic losses and thermal field are discussed and are proved to be close to the experimental counterparts, for all the investigated conditions.

A combined combustion and conjugate heat transfer analysis of a hybrid draft biomass cookstove

A cookstove comprises both fluid and solid regions, with combustion gases representing the fluid domain and the combustion chamber wall and insulation forming the solid regions. These solid regions are made of different materials and make significant contributions to stove performance. So far, most studies conducted on biomass stoves have only analysed the fluid domain, neglecting solid regions. The current study integrates combustion and conjugate heat transfer analysis, encompassing both fluid and solid domains, to investigate the fluid flow and heat transfer behaviour of a hybrid draft biomass cookstove (HDBC) using CFD. This analysis aims to gain insights into the impact of stove materials on its performance. The study analysed six cases of HDBC, testing different combinations of materials: two for the combustion chamber (ceramic-cement and stainless-steel) and three for insulation (ceramic wool, perlite, and vermiculite). The combustion of biomass and the formation of soot are modelled using reaction kinetics and a one-step soot model, respectively. The CFD findings for thermal efficiency, CO, and PM2.5 emissions derived using combustion and soot model demonstrated closed alignment with the experimental result with variations of 3%, 19%, and 23%, respectively. It was observed that stoves with stainless-steel combustion chamber material exhibit better thermal and emission performance compared to ceramic-cement stoves, with perlite taking the edge over other insulation materials. The success of these materials is attributed to their superior thermophysical properties, which play a significant role in material selection.

Flow and Heat Transfer Characteristics of Superheater Tube of a Pulverized Coal-Fired Boiler Using Conjugate Heat Transfer Modeling

This study is a numerical study to predict the temperature of the heat exchange tubes inside the pulverized coal-fired boiler through the conjugate heat transfer analysis. Due to the aspect ratio and number of tubes inside the pulverized coal-fired boiler, actual tube modeling analysis has rarely been conducted. Most of the research has been conducted through the porous media method, resulting in limited information on the temperature distribution of each tube. However, for the development of a digital twin model for improving the performance of the boiler and reducing maintenance costs, information on the local temperature of the tubes is required. In this study, all the tubes inside the boiler were modeled, and conjugate heat transfer analysis was performed to confirm the local temperature distribution. For this purpose, the analysis was conducted using Fluent 2020 r2, and the analysis model was constructed using more than 300 million structured grids. The calculation was performed considering conjugate heat transfer in the pulverized coal-fired boiler, heat exchange by steam inside the tubes, and conductive heat transfer of the tubes. As a result, it was confirmed that there is a significant deviation in the local temperature for each tube position. Furthermore, the maximum temperature of the PrSH tube ranges widely, between 492 and 532 degrees, depending on the tube’s position. It was observed that the point of the highest temperature inside the tubes also varies for each tube due to the flow of external combustion gas. Based on these results, it is expected that strategic approaches to boiler design and maintenance can be achieved. Furthermore, it is anticipated to contribute to the high efficiency of power facilities by being utilized as basic data for the development of a digital twin model for the boiler.

Conjugate heat transfer analysis on double-wall cooling configuration including jets impingement and film holes with conformal pins

Abstract A double-wall cooling configuration including impingement holes and film holes with conformal pins is studied by CFD numerical simulation in this paper. The influences of three different injection directions of film holes at six blowing ratios ranging from 0.4 to 2.5 on conjugate heat transfer characteristic are investigated. Impingement-only arrangements with corresponding pin directions are adopted to illustrate the film cooling gains and the impingement cooling contribution. The results indicate that the effect of different pin directions on overall cooling effectiveness is non-significant. At low blowing ratio, the forward injection arrangement has higher overall cooling effectiveness since greater gain of film cooling, and is transcended by reverse injection arrangement as coolant supplement increases. Moreover, although the cooling effectiveness for normal injection case is the lowest within the whole range of mass flow rate, it possesses the most uniform distribution of cooling effectiveness in downstream region at high blowing ratio.

A novel microchannel-twisted pinfin hybrid heat sink for hotspot mitigation

Thermal hotspots cause excessive localized temperature rise, leading to significant temperature gradients across the microprocessor, which is the primary reason for its inadequate performance and early failure. This study proposes microchannel-pinfin hybrid heat sinks incorporating twisted and non-twisted pinfins of various cross-sectional shapes (hexagonal, pentagonal, square, and triangular) to demonstrate energy-efficient hotspot mitigation in a microprocessor with highly non-uniform power distribution. Microchannels and pinfins are positioned at low- and high-heat-flux zones, respectively, to reduce the temperature variations utilizing their unequal heat transfer capabilities. Here, high- and low-heat-flux zones represent the microprocessor-core area (hotspot) and remaining chip area (background zone), characterized by heat fluxes of 300 W/cm2 and 50 W/cm2, respectively. The pinfin twisting angle varies from 0° to 360° at a step of 45°. Conjugate heat transfer analyses are conducted through numerical solutions of the continuity, Navier-Stokes, and energy equations. The performance of the proposed hybrid heat sinks is compared with the non-hybrid (NH) and hybrid circular pinfins (HCP) heat sinks at Re = 120–440. The hybrid heat sink featuring triangular pinfins twisted at 225° angle (HTP-225) exhibits a remarkable reduction of 48.2 % in the total thermal resistance (Rth) and 58.4 % in the temperature non-uniformity (δT,bs) as compared to the NH heat sinks at Re = 440. Compared to the HCP design, the HTP-225 design shows 26.9 % and 35.8 % lower Rth and δT,bs, respectively. Moreover, the HTP-225 heat sink outperforms the NH heat sink with 46.0 % and 57.0 % lower Rth and δT,bs, respectively, at an equal pumping power of 18.6 mW. Furthermore, the HTP-225 heat sink demonstrates a 96.4 % and 38.5 % higher critical hotspot heat flux dissipating capacity than the NH and HCP heat sinks, respectively, making it a viable and effective solution for alleviating hotspots in high-power-density devices.