Conjugate Heat Transfer Analysis Research Articles

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.

A comparative study of internal heat transfer enhancement of impingement/effusion cooling roughened by solid rib and slit rib

In the present study, we conducted a conjugate heat transfer (CHT) analysis for double-wall cooling with impingement and effusion, incorporating various types of ribs, using the Reynolds-averaged Navier–Stokes (RANS) method and the modified shear stress transport (SST) turbulence closure model (SST-KIC), accounting for the Kato-Launder modification (K), intermittency (I), and crossflow (C) transition effects. We comprehensively discussed the impact of slit type (parallel, inclined, convergent, and divergent), open-area ratio (β = 5%, 20%, and 40%), and jet Reynolds number on the turbulent flow and heat transfer in a double-wall cooling with slit ribs. Our findings indicated that the introduction of slit ribs significantly improved heat transfer and its uniformity on the target wall, albeit with a slight increase in pressure loss. The overall Nusselt number and thermal-hydraulic performance (THP) in cases with slit ribs gradually decreased with β, yet remained up to 17% and 13% higher than those observed on a smooth target wall. Notably, the open-area ratio of the slit rib exhibited a more pronounced effect on heat transfer over the target plate. For the divergent slit rib within the Reynolds number range of 4000–16 000, the heat transfer enhancement ratio reached the highest value at β of 0.05. In addition, we computed the entropy production caused by fluid friction and heat transfer, as well as the overall entropy production in double-wall cooling at different β and Re. The analysis revealed that the slit rib target plate performed better than the solid rib target plate, showing a distinct advantage in terms of total entropy production.

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.

Numerical and correlation analysis of conjugate heat transfer over the discrete braided composites plate

Braided composites, which have excellent mechanical and thermophysical performance, have been considered promising materials widely used in aerospace, renewable energy, and other fields. However, the conjugate heat transfer mechanism between working fluids and braided structures is still unclear. Due to the complicated structure and computational limitation, with a neglection of the structural discrete feature and velocity distortion, current pertinent research primarily relies on the equivalent method of homogenization. In this research, a detailed numerical investigation of conjugate heat transfer over a three-dimensional four-directional (3D4d) braided composite plate with anisotropic and discrete features is presented. The full-size geometric structure of the 3D4d braided plate is first established utilizing the representative volume element (RVE). For such periodic structures, a continuous Eulerian grid generation technique is developed. A local coordinate system approach for the heat conduction spindle based on discretization is subsequently proposed to address the anisotropy of heterogeneous materials. The accuracy of the proposed discrete model processing approaches is verified by comparison with homogenization techniques widely used and experimental data in the literature. It is discovered that the discrete structure with an interfacial thermal dispersion, has a unique physical field distribution in comparison to the homogenization cases. Moreover, a semi-theoretical heat transfer criterion for 3D4d composite is established based on the thermal correction of dispersed interface.

FEM and CFD thermal modeling of an axial-flux induction machine with experimental validation

Axial-flux electrical machines are ideal candidates as in-wheel motors for electrical vehicles (EVs). Due to their characteristics of high power density and compact structure, thermal management is vital for them. Lowering the temperature of the stator windings can protect the insulation material from rapid degradation and reduce the extra copper losses by decreasing their electrical resistance. Contrary to the widely reported axial-flux permanent magnet synchronous machines, thermal modeling methods of axial-flux induction machines are rarely seen in previous literature. Hence, the present work aims at investigating their thermal response based on both the finite element method (FEM) and computational fluid dynamics (CFD) techniques. In addition, a test rig is built to validate the computed results of these two thermal models with the experimental measurement. The CFD conjugate heat transfer analysis is found to be more accurate than the FEM thermal analysis in predicting the temperature distribution of different components in the machine and the temperature rise of the airflow, with lower than 5 ∘C average errors deviating from the corresponding measured data at three rotation speeds. Additionally, the CFD simulation is able to capture the backflow occurring near the outlets of the casing that has been found during the experiments.

Development and Validation of a Segregated Conjugate Heat Transfer Procedure on a sCO2 Dry Gas Seal Test Bench

Abstract Carbondioxide at supercritical state shows particularly favorable thermodynamic properties for closed-loop Brayton and Rankine cycles. High density, close to a liquid, and low viscosity, close to a gas, drive to achieve higher energy conversion efficiency with smaller size turbines and components. Since minimizing the sCO2 leakage flows drives to a further increasing of overall efficiency, dry gas seals (DGS) are considered as a key enabling technology for achieving this purpose and for achieving a carbon footprint in line with the increasingly stringent targets. DGSs are gas-lubricated, mechanical, noncontacting, end-face seals, consisting of a mating (rotating) ring and a primary (stationary) ring. The operating equilibrium clearance of the seal is determined by the balance of opening dynamic forces, mainly depending on angular velocity and grooves shape, and closing forces caused by pressure gradients and spring force. Due to high rotational speeds, typical small size sealing gaps (order of magnitude of Micron), high fluid pressure and density, the heat generated by friction through the seal has a large impact on the temperature distribution, therefore a thermal design is needed to stay below the seal allowable temperature; this requirement has been even amplified in the last years with the DGS application to hot turbomachinery. Nowadays, numerical conjugate heat transfer (CHT) analysis is a good industrial practice to quantify the thermal distribution in turbomachinery components. On the other hand, due to different order of magnitude of secondary flows cavity sizes and DGS seal gaps, simulating the whole fluid domain with three-dimensional (3D) computational fluid dynamic (CFD) calculation could drive to prohibitive computational costs. In this regard, this paper presents a fast numerical iterative procedure based on a commercial one-dimensional flow network modeler (altair flow simulator), with real gas effects included, coupled with a commercial finite element solver (ansys mechanical). Additional 3D CFD simulations are carried out to enhance the predictability of the fluid solver in specific critical areas. The proposed procedure is applied and validated in a DGS specific test bench designed, owned and operated by Flowserve. The validation dataset has been generated operating the DGS in the test bench at 15 different conditions in terms of angular velocity and housing temperature with sCO2 as working fluid aligned with those expected on the unit. Test rig consists of a rotor and housing where the turbomachine operating condition (pressure, speed, temperature and sealing fluid) are mirrored to verify the seal performance. The rig is equipped with test seal and a plug seal mounted in a back-to-back configuration. Data set used for this comparison is composed by thermocouples on the statoric rings, retainers and housing of each seal, operating at five different angular speeds and three minimum levels of housing temperature (100 °C, 210 °C, and 250 °C). These temperatures are designed to mirror turbomachinery conditions around the seal, and, if friction heat is not enough to guarantee them, a series of 18x1 kW heating elements circumferentially distributed in the test bench housing, are activated. The nominal operating condition has been considered as the starting point of the model predictions and, there, several sensitivity analyses have been carried out to align the model to test bench measurements; then, the selected configuration has been frozen and used to assess the model performance on other operating conditions. The numerical results have shown a good agreement with experimental data at each operating condition in terms of punctual temperatures previously described and with extremely low computational times.

Characteristics of a Heat Exchanger in a Liquid Rocket Engine Using Conjugate Heat Transfer Coupling with Open-Source Tools

Since a heat exchanger used in a gas generator of an open-cycle liquid rocket engine was operated in a high-temperature environment, the coupled analysis for heat transfer characteristics and structural integrity should be performed simultaneously. For these reasons, a numerical analysis of the heat exchanger in a liquid rocket engine was performed to elucidate the effects of heat transfer and structural deformation simultaneously using conjugate heat transfer (CHT) analysis and open-source tools. For the baseline heat exchanger, which had an inner helically coiled tube with nine turns (), the heat transfer characteristics were investigated and findings showed that the heat transfer performance was reduced from the sixth turn. Further analysis was performed to examine the effect of the number of turns in terms of heat flux and the corresponding pressure drop and the weight of the structure. The results indicated that the heat exchanger with had a significantly reduced outlet temperature due to an excessively shortened flow residence time. The heat exchanger with showed an outlet temperature similar to that of the baseline; it also presented advantages in terms of the pressure drop and structure weight. In addition, the thermal deformation and stress caused by temperature changes were numerically investigated to consider the structural integrity of the heat exchanger with . Further numerical analyses were performed at various flow rates. As the flow rate of helium increased, the amount of heat received from the high-temperature exhaust gas from the gas generator increased but the outlet temperature of helium decreased gradually. Finally, the temperature difference between the outer and inner walls increased due to the high heat flux in the region around the inlet, resulting in an increase in thermal stress. Based on these results, the optimal shape and flow rate of the system were identified. Furthermore, the heat transfer performance was found to correlate with the flow characteristics of the coiled tube.

Enhancing thermal performance and energy Efficiency: Optimal selection of steel slag crumb rubber blocks through Multi-Criteria decision Making

In today's world, where sustainable building practices are crucial, addressing energy consumption in buildings is vital. Insulation materials are a key to energy efficiency, but their effectiveness depends on properties like thermal conductivity, strength, and sustainability parameters. This research repurposes waste materials to create sustainable building materials. India's tire disposal problem poses environmental risks. To effectively manage those issues, this study targeted towards optimum utilization of wastes; steel slag, fly ash, and crumb rubber to make building blocks. This research focuses on developing blocks from Steel Slag (SS), Fly Ash (FA), Crusher Dust (CD), Lime, and Crumb rubber (CR). Extensive evaluations, including physico-mechanical, thermal assessments, and sustainability analyses, were conducted on these innovative blocks, while optimum selection is done based on heat transfer, Multi-Criteria Decision-Making (MCDM) and Energy analysis using eQuest. The study employs numerical conjugate heat transfer analysis via OpenFOAM software, revealing Grade A crumb rubber averages 11.03 MPa compressive strength, whereas Grade B averages 12.31 MPa compressive strength, and a strength of 22.8 MPa was achieved at crumb rubber incorporation level of 10 %. However, construction material selection entails multifaceted considerations based on physical, mechanical, thermal and sustainability parameters. Consequently, MCDM approach was adopted to identify the optimal alternative. MCDM techniques, including TOPSIS, EDAS, and WPM, consistently endorse Mix M − 6, featuring 10 % crumb rubber as an aggregate replacement, as the paramount choice. These findings underscore the commercial potential of steel slag-lime blocks infused with crumb rubber, offering superior insulation and sustainability performance compared to conventional blocks. This research not only tackles a pressing environmental concern tied to waste materials like crumb rubber and steel slag but also plays a pivotal role in advancing the development of eco-friendly building materials poised to make a significant impact on the construction industry.

Innovative multiphysics approach for designing high-performance thermo-responsive shape memory polymer microvalve

Shape memory polymers (SMPs), classified as smart materials, have emerged as promising candidates for microfluidic devices due to their significant potential. In this study, we present the design and analysis of an SMP microvalve. The thermomechanical response of the SMP microvalve is studied using a recently introduced nonlinear constitutive model that incorporates nonlinear hyperelasticity and viscoelasticity for SMPs. This model is coupled with the fluid field and accounts for heat transfer in both fluid and solid physics. The governing equations for the multiphysics behavior are discussed. Then an overview of the finite element model is provided. The most important characteristics of the SMP valve, such as SMP thickness, flow rate, contact pressure, and pressure distribution, are examined numerically. The results expound upon the significance of employing fluid-solid interaction conjugated heat transfer analysis as a crucial factor in the proficient development of microvalves for diverse applications, with the primary objective being the prevention of overheating and the mitigation of potential failures.

Comprehensive evaluation on conjugate heat transfer and thermal stress performance of film cooling

Film cooling is a commonly used cooling technology in gas turbines, which could reduce heat load by spreading cooling air. However, it faces the problem of stress concentration in structures with holes. The present work focuses on conjugate heat transfer and thermal stress characteristics for a flat film cooling plate through an experimentally validated numerical approach. It discusses the effect of three geometry factors: inclination angle, compound angle, and ellipticity. An engine case simulation and a laboratory case simulation are compared to validate the analogy principle of conjugate heat transfer and thermal stress analysis derived from theoretical analysis. According to the analogy principle, the laboratory flat plate film cooling cases are set to conduct numerical studies. The maximum Mises stress of the film hole is equal to the product of the reference stress and the stress concentration factor. The reference Mises stress is proportional to the overall cooling effectiveness. The stress concentration factor is mainly related to the geometry of the film hole. Reducing the inclination angle of the film hole from 90° to 30° increases the overall cooling effectiveness and drastically increases the stress concentration factor from 2.7 to 5.5. Based on a cylinder hole with a 30° inclination angle, increasing the compound angle enhances the overall cooling effectiveness and slightly increases the stress concentration factor. Based on a cylinder hole with a 30° inclination angle, increasing the ellipticity increases the overall cooling effectiveness and reduces the stress concentration factor. With the increase of ellipticity from 0 to 4, the stress concentration factor decreases from 5.5 to 2. Elliptical film holes are ideal for future low-stress, high-cooling-efficiency turbine blades to extend the life of cooling vanes.

Mini-channel embedded film cooled flat plate: conjugate heat transfer analysis and enhancement study

PurposeMaintaining the turbine blade’s temperature within the safety limit is challenging in high-pressure turbines. This paper aims to numerically present the conjugate heat transfer analysis of a novel approach to mini-channel embedded film-cooled flat plate.Design/methodology/approachNumerical simulations were performed at a steady state using SST k – ω turbulence model. Impingement and film cooling are classical approaches generally adopted for turbine blade analysis. The existing film cooling techniques were compared with the proposed design, where a mini-channel was constructed inside the solid plate. The impact of the blowing ratio (M), Biot number (Bi) and temperature ratio (TR) on overall cooling performance was also studied.FindingsOverall cooling effectiveness was always shown to be higher for mini-channel embedded film-cooled plates. The effectiveness increases with increasing the blowing ratio from M = 0.3 to 0.7, then decreases with increasing blowing ratio (M = 1 and 1.4) due to lift-off conditions. The mini-channel embedded plate resulted in an approximately 21% increase in area-weighted average overall effectiveness at a blowing ratio of 0.7 and Bi = 1.605. The lower uniform temperature was also found for all blowing ratios at a low Biot number, where conduction heat transfer significantly impacts total cooling effectiveness.Originality/valueTo the best of the authors’ knowledge, this study presents a novel approach to improve the cooling performances of a film-cooled flat plate with better cooling uniformity by using embedded mini-channels. Despite the widespread application of microchannels and mini-channels in thermal and fluid flow analysis, the application of mini-channels for blade cooling is not explored in detail.