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To enhance the thermo-hydraulic performance of cooling channels, this investigation examines the influence of distinct cross-sectional shapes (i.e., triangular, rectangular, and hexagonal) of twisted pin fins and their arrangements in straight and cross rows. An ambient air cooling test platform was established to numerically and experimentally investigate the flow and heat transfer characteristics of 360° twisted pin fins at Re=15 200–22 800. The findings reveal that straight rows exhibit higher Nuvalues than cross rows for triangular and rectangular twisted pin fins, and Nuincreases with Re. In contrast, for hexagonal twisted pin fins, only straight rows at Re=19 000 exhibit superior overall thermal performance compared to cross rows. Notably, the heat transfer performance of the cooling channel with hexagonal twisted fins surpasses both triangular and rectangular configurations, especially at high Reynolds numbers (Re=22 800). Although the heat transfer coefficient of the cooling channel with hexagonal twisted fins is significantly enhanced by 132.71% compared to the flat channel, it also exhibits the highest thermal resistance and relative friction among the three types of twisted fins, the maximum of which are 2.14 and 16.55. Furthermore, the hydrothermal performance factor (HTPF) of the cooling channels with different types of twisted pin fins depends on the Reynolds number and arrangement modes. At Re=15 200, the highest HTPF achieved for the cross-row hexagonal twisted pin fins is 0.99.

Purpose: The purpose of this paper is to develop a coupled lattice Boltzmann model for the simulation of the freezing process in unsaturated porous media. Design/methodology/approach: In the developed model, the porous structure with complexity and disorder was generated by using a stochastic growth method, and then the Shan-Chen multiphase model and enthalpy-based phase change model were coupled by introducing a freezing interface force to describe the variation of phase interface. The pore size of porous media in freezing process was considered as an influential factor to phase transition temperature, and the variation of the interfacial force formed with phase change on the interface was described. Findings: The larger porosity (0.2 and 0.8) will enlarge the unfrozen area from 42 mm to 70 mm, and the rest space of porous medium was occupied by the solid particles. The larger specific surface area (0.168 and 0.315) has a more fluctuated volume fraction distribution. Originality/value: The concept of interfacial force was first introduced in the solid–liquid phase transition to describe the freezing process of frozen soil, enabling the formulation of a distribution equation based on enthalpy to depict the changes in the water film. The increased interfacial force serves to diminish ice formation and effectively absorb air during the freezing process. A greater surface area enhances the ability to counteract liquid migration. [ABSTRACT FROM AUTHOR]

A previous study showed that the thermal performance of the X-lattice cored corrugated honeycomb (XCCH) is better than that of most other periodic cellular materials (PCMs). To further improve the thermal performance of the XCCH, the effects of different ripple amplitudes (i.e., a= 0.5, 0.7 and 1.0) on the characteristics of the flow and heat transfer are numerically investigated by thorough comparisons. In terms of the flow characteristics, with the increase of ripple amplitude, the vortex interaction in the channel becomes stronger, which results in evident increase of kinetic energy of turbulence at the boundary of vortex and reduction in the turbulent kinetic energy dissipation. As far as the heat transfer is concerned, within the Reynolds number range of 3696–7436, the heat transfer increases with the increase of ripple amplitude. The overall Nusselt number of the XCCH with a= 1.0 is 15.7% higher than that with a= 0.5. Within the corresponding range of pumping power, the thermal performance of the XCCH with a= 1.0 is up to 7% higher than that with a= 0.5 at relatively higher Reynolds numbers.

In this paper, plasma actuators are arranged asymmetrically downstream the wall to improve film cooling performance. Effects of blowing ratio, hole configuration and applied voltage on flow characteristics and film cooling effectiveness were investigated numerically on a flat plate. Results show that highest film cooling effectiveness distribution is obtained both in the spanwise and streamwise directions under blowing ratio of 0.5. Average wall film cooling effectiveness of cylindrical hole increases by 251.9% under blowing ratio of 0.5 compared to that under blowing ratio of 1.5. The scale of the counter rotating vortex pairs (CRVP) from fan shaped hole and sister hole are significantly reduced compared to that from cylindrical hole. The console hole has an anti-counter rotating vortex pair (Anti-CRVP), which weakens the entrainment of the CRVP to the coolant air near the wall. Compared with the cylindrical hole, average wall film cooling effectivenesses for fan shaped hole, sister hole and console hole increase by 73.1%, 97.5% and 119.9%. The adherent performance of the coolant air is enhanced after applying plasma actuator. The aerodynamic actuation of the plasma results in the rebound of the fluid close to the wall at 24 kV applied voltage. Average wall film cooling effectiveness of the console hole at 12 kV applied voltage is 10.6% higher than that without plasma.

This paper presents three-dimensional numerical simulations with the established realizable k−εmodel to clarify the underlying and interacting mechanisms between the film cooling and the internal cooling. On the one hand, the effects of three different internal cooling channels, i.e., smooth channel, continuous ribbed channel, and truncated ribbed channel, on the film cooling effectiveness and the discharge coefficients are investigated. On the other hand, the influences of three different film cooling holes, i.e., cylindrical hole, two elliptical holes and two circular-to-elliptical holes, on the heat transfer performances and pressure loss of the internal cooling channel are revealed. Especially, the suction effects of the film cooling holes are analyzed through setting up baselines with only internal cooling channels. Results show that the placement of ribs in the internal channel has different influences on the film cooling effectiveness with respect to different hole shapes depending on the blowing ratio. The discharge coefficient of the film hole can be improved by introducing ribs to the internal channel. Suction of film hole is helpful for enhancing the heat transfer performance and reducing the pressure loss of the internal channel. Besides, ribs instead of the suction effect of film hole play a major role to enhance the heat transfer performance in the internal cooling channel.

Active regenerative cooling with supercritical hydrocarbon fuel is considered as the most promising thermal protection method. The existence of buoyancy force would lead to strongly anisotropic flow and thermal transport characteristics. It is closely related to the cooling performance of the engine. To elucidate the mechanisms of turbulent transport, the large eddy simulation (LES) was performed to assess turbulence statistics within different turbulence scales. The results indicated that the buoyancy and inertial force together dominated the change of turbulent structure. Moreover, the spatial thermal buoyancy effect significantly suppressed the vertical velocity fluctuation. This is due to the laminar motion caused by the buoyancy force, thereby weakening the thermal transport. For the statistics of velocity fluctuation, it was found that the buoyancy force and inertial force greatly weaken the vertical and streamwise velocity fluctuation, respectively. For the statistics of thermal transport, the results pointed out that the near-wall heat transport characteristics need to be paid more attention. The thickness of the temperature mixing boundary layer led to the attenuation of vertical heat flux, which inhibited vertical temperature diffusion and predisposed to extreme conditions of heat transfer deterioration. The results can enhance the academic understanding of the heat transfer mechanism of supercritical fluids, and give guidance for further applications of thermal protection.

Purpose: This paper aims to comprehensively clarify the research status of thermal transport of supercritical aviation kerosene, with particular interests in the effect of cracking on heat transfer. Design/methodology/approach: A brief review of current research on supercritical aviation kerosene is presented in views of the surrogate model of hydrocarbon fuels, chemical cracking mechanism of hydrocarbon fuels, thermo-physical properties of hydrocarbon fuels, turbulence models, flow characteristics and thermal performances, which indicates that more efforts need to be directed into these topics. Therefore, supercritical thermal transport of n-decane is then computationally investigated in the condition of thermal pyrolysis, while the ASPEN HYSYS gives the properties of n-decane and pyrolysis products. In addition, the one-step chemical cracking mechanism and SST k-ω turbulence model are applied with relatively high precision. Findings: The existing surrogate models of aviation kerosene are limited to a specific scope of application and their thermo-physical properties deviate from the experimental data. The turbulence models used to implement numerical simulation should be studied to further improve the prediction accuracy. The thermal-induced acceleration is driven by the drastic density change, which is caused by the production of small molecules. The wall temperature of the combustion chamber can be effectively reduced by this behavior, i.e. the phenomenon of heat transfer deterioration can be attenuated or suppressed by thermal pyrolysis. Originality/value: The issues in numerical studies of supercritical aviation kerosene are clearly revealed, and the conjugation mechanism between thermal pyrolysis and convective heat transfer is initially presented. [ABSTRACT FROM AUTHOR]

• A hybrid RBF-MLP model was tested to achieve a highly nonlinear approximation. • A POD technique was employed to define a low-dimensional reduced-order system. • A POD-ANN model was developed to accurately reconstruct the principal flow features. • The combination of POD and machine learning can reveal the underlying physical mechanisms of flow features. The development of mathematical models, and the associated numerical simulations, are challenging in higher-dimensional systems featuring flows of supercritical fluids in various applications. In this paper, a data-driven methodology is presented to achieve system order reduction, and to identify important physical information within the principal flow features. Firstly, a new hybrid neural network based on radial basis function (RBF) and multi-layer perceptron (MLP) methods, namely RBF-MLP, is tested to achieve a highly nonlinear approximation. When provided with 1000 nonlinear test samples, this model provides an excellent prediction accuracy with a maximum regression coefficient (R) of 0.99 and a minimum root mean square error (RMSE) below 1%. Furthermore, the model is also proven to be flexible enough to capture accurately the turbulent fluctuation characteristics, even at significant nonlinear buoyancy conditions. Secondly, the high-dimensional buoyancy data is collected and integrated into a matrix database. Subsequently, a proper orthogonal decomposition (POD) approach is employed to reduce the high-dimensional database, and to obtain a set of low-dimensional POD basis-spanned space, which defines a reduced-order system with low-dimensional basis vectors. The results reveal that the first five order modes contain dominant flow features, accounting for 93% of the total mode energy, which can be selected to reconstruct the physical flow field. Thirdly, a new data-driven POD-ANN model is established to construct the nonlinear mapping between the full-field buoyancy data and decomposed basis vectors. It is also demonstrated that the POD-ANN model reconstructs the principal flow features accurately and reliably. This POD-ANN model can be used to provide new insights for reduced-order modelling and for reconstructing physical fields of higher-dimensional nonlinear flow cases. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance. Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed. Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared. Detailed flow structures and underlying mechanisms are discussed. The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios, and that swirl strength has significant influence on film cooling performance. Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices. The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157% and 173%, respectively.

Heat conduction in multi-layer and composite materials is one of the fundamental heat transfer problems in many industrial applications. Due to different materials types, interface conditions, and various geometries of these laminates, the heat conduction mechanism is more complicated than that of one-layer isotropic media. Analytical solutions are the best ways to study and understand such problems in depth. In this study, different existing analytical solutions for heat conduction in multi-layer and composite materials are reviewed and classified in rectangular, cylindrical, spherical, and conical coordinates. Applied boundary conditions, internal heat source, and thermal contact resistance as the most critical parameters in the solution complexity investigated in the literature, are discussed and summarized in different tables. Various types of multi-layer structures such as isotropic, anisotropic, orthotropic, and reinforced laminates are included in this study. It is found that although more than half a century has passed since the beginning of the research on heat transfer in multi-layer composites, new researches that can help with a better understanding in this area are still being offered. The challenges and shortcomings in this area are also discussed to guide future researches.

Purpose: The discontinuous Galerkin finite element method (DGFEM) is very suited for realizing high order resolution approximations on unstructured grids for calculating the hyperbolic conservation law. However, it requires a significant amount of computing resources. Therefore, this paper aims to investigate how to solve the Euler equations in parallel systems and improve the parallel performance. Design/methodology/approach: Discontinuous Galerkin discretization is used for the compressible inviscid Euler equations. The multi-level domain decomposition strategy was used to deal with the computational grids and ensure the calculation load balancing. The total variation diminishing (TVD) Runge–Kutta (RK) scheme coupled with the multigrid strategy was employed to further improve parallel efficiency. Moreover, the Newton Block Gauss–Seidel (GS) method was adopted to accelerate convergence and improve the iteration efficiency. Findings: Numerical experiments were implemented for the compressible inviscid flow problems around NACA0012 airfoil, over M6 wing and DLR-F6 configuration. The parallel acceleration is near to a linear convergence. The results indicate that the present parallel algorithm can reduce computational time significantly and allocate memory reasonably, which has high parallel efficiency and speedup, and it is well-suited to large-scale scientific computational problems on multiple instruction stream multiple data stream model. Originality/value: The parallel DGFEM coupled with TVD RK and the Newton Block GS methods was presented for hyperbolic conservation law on unstructured meshes. [ABSTRACT FROM AUTHOR]

To effectively alleviate the heat transfer deterioration phenomenon of supercritical CO2 flow in a vertical circular tube, this paper proposes multiple truncated ribs from a whole O-ring rib but distributed in helical-like distribution. The fluid hydraulics and thermal performance with a verified standard k-ω mode are numerically explored. The effects of the height, the distance and the number of truncated ribs on flow characteristics and heat transfer are observed and analyzed in detail. Results show that the heat transfer coefficient increases significantly with increasing rib height, and as the pitch decreases the fluid re-circulation area behind each rib decreases, resulting in stronger mixing of swirling flow, which enhances turbulent kinetic energy in the downstream and weakens the buoyancy force, thus mitigating heat transfer deterioration. The present study suggests that introducing multiple truncated ribs distributed along helices into circular tubes can be a beneficial way to alleviate heat transfer deterioration and to enhance heat transfer of supercritical CO2 flow.

Due to their exceptional static and dynamic properties along with high-temperature resistance, liquid metal bearings are extensively employed in challenging environments. This paper carried out a multi-objective optimization work for spiral groove journal liquid metal bearings (JLMB) by using a NSGA-II. The clearance of bearing C, spiral angle a, groove depth hg, groove ridge ratio β, groove number N, and groove spacing Pwere chosen as design variables to maximize the load-carrying capacity and the effective stiffness of liquid metal bearing. During optimization process, the Latin hypercube sampling was adopted to generate 41 sample points, and the Kriging surrogate model was used to establish the correlations between design variables and objective functions. The Pareto front with optimal structures was obtained after optimization. Subsequently, optimal parameters were determined from the Pareto front by using the TOPSIS decision method. Finally, a comparative analysis of bearing performance was conducted between the journal liquid metal bearings with optimal parameters and the original parameters. The results indicated that the optimal JLMB parameters are given as follows: C = 10 μm, a = 26°, hg = 5.2 μm, β= 0.7, P = 11.1 mm, N = 10. The static and dynamic performance of optimized JLMB has been significantly improved. Specifically, the load carrying capacity increased to 2781.2N, making a 1313% enhancement over the JLMB with original parameters. While the effective stiffness of the optimized JLMB surged to 1.86 × 108N/m, a more than 20-fold increase.

Purpose: The purpose of this paper is to numerically study the influence of wall conduction on the heat transfer of supercritical n-decane in the active regenerative cooling channels. Design/methodology/approach: A horizontally placed rectangular pipe with a solid zone and another one without a solid zone were used. A drastic variation of thermo-physical properties was emphatically addressed. After the verification of mesh and turbulence models comparing with the experimental results, a mesh number of 4.5 M and the low Reynolds number SST k-ω turbulence model were chosen. The solution of the governing equations and the acquisition of the numerical results were executed by the commercial software FLUENT 2020 R1. Findings: The numerical results indicate that there is a heat transfer deterioration (HTD) potential for the upper wall, lower wall and sidewall with the decrease of mass flux. Due to wall conduction, the distribution of the fluid temperature at spanwise-normal planes becomes uniform and this feature also takes advantage of the relatively uniform transverse velocity. For the streamwise-normal planes, the low fluid temperature appears close to the upper wall at the region near the sidewall and vice versa for the region near the centre. Undoubtedly, the secondary flow at the cross-section plays a crucial role in this process and the relatively cool mainstream is affected by the vortices. Originality/value: This study warns that the wall conduction must be considered in the practical design and thermal optimization due to the sensibility of thermo-physical properties to the heat flux. The secondary flow caused by the buoyancy force (gravity) plays a significant role in the supercritical heat transfer and mixed convection heat transfer should be further studied. [ABSTRACT FROM AUTHOR]

Purpose: In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models with the same geometries and cross-section areas of film holes' exits at three typical blowing ratios (M = 0.5, 1 and 1.5). The two models are an elliptical model and a cylindrical model with 90° compound angle, respectively. Design/methodology/approach: Three different cases are considered in this work and the baseline is the model with a cylindrical film hole. The same boundary conditions and a validated turbulence model (realizable k-ε) are adopted for all cases. Findings: The results show that both the elliptical and cylindrical models with 90° compound angle can enhance the film cooling effectiveness compared with the baseline. However, the elliptical model performs well at lower blowing ratios and in the near region at each blowing ratio because of the wider width of the film hole's exit. The cylindrical model with 90° compound angle provides better film cooling effectiveness in the further downstream area of the film hole at higher blowing ratio because of the less lift-off and better coolant coverage in the larger x/D region along the mainstream direction. Originality/value: Overall, it can be concluded that although the elliptical and cylindrical models with 90° compound angle have identical hole exits, the different inlet direction and cross-sectional geometry affect the flow structures when the coolant enters, moves through and exits the hole and finally different film cooling results appear. [ABSTRACT FROM AUTHOR]

Based on critical velocity model, impact, and capture efficiencies in an AGTB turbine cascade are investigated numerically under various inlet angles of mainstream, blowing ratios, particle sizes and particle densities. The effect of hole configuration on deposition is analyzed based on comparisons of results from combined hole and cylindrical hole. The impact efficiency increases with the increase of particle size. Impact area on pressure side of blade surface expands with increasing of the mainstream inlet angle from 123° to 143°. The capture efficiency decreases with the increase of blowing ratio for 10 µm particles. For particles with densities of 1485 kg/m3, 1980 kg/m3 and 2475 kg/m3, the maximum capture efficiency is reached when the particle size is 5 µm. The particle capture efficiency for the combined hole is up to 3.9% lower than that for cylindrical hole when the mainstream inlet angle is 123°.

Correlations are crucial to the design of cooling channels employed in regenerative cooling systems for scramjets. In this paper, correlations for the aviation kerosene flowing upward and downward in vertical tubes are studied and discussed. Four existing correlations are assessed against the available experimental data. To further improve the prediction accuracy of the heat transfer behaviors of the supercritical aviation kerosene, a new dimensionless parameter (Qi) relevant to the heat flux is proposed and introduced into the construction of a new correlation. Verification shows that the new correlation is more accurate than existing correlations.

Purpose: The purpose of this paper is to investigate the unsteady flow past through a permeable diamond-shaped cylinder and to study the effects of the aspect ratios and Darcy numbers of the cylinder. Design/methodology/approach: The lattice Boltzmann method with D2Q9 lattice model was used to simulate the unsteady flow through permeable diamond-shaped cylinders. The present numerical method is validated against the available data. Findings: The key findings are that increasing the permeability enhances the suppression of vortex shedding, and that the Strouhal number is directly proportion to the Darcy number, Reynolds number and the aspect ratio of the porous cylinder. Originality/value: The present study considers unsteady laminar flow past through single permeable diamond-shaped cylinder. According to the authors' knowledge, very few studies have been found in this field. The present findings are novel and original, which in turn can attract wide attention and citations. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling performance, three configurations are designed to observe the effects of the distance between the center of the ellipse and the side wall(Case 1, l = w/2, Case 2, l = w/3 and for Case 3, l = w/4). Design/methodology/approach: Numerical simulations are conducted under two blowing ratios (i.e. 0.5 and 1) and a fixed cross-flow Reynolds number (Rec = 100,000) with a verified turbulence model. Findings: It is shown that at low blowing ratio, reducing the distance increases the film cooling effectiveness but keeps the trend of the effectiveness unchanged, while at high blowing ratio, the characteristic is a little bit different in the range of 0 = x/D = 10. Research limitations/implications: These features could be explained by the fact that shrinking the distance between the hole and side wall induces a much smaller reserved region and vortex downstream the ribs and a lower resistance for cooling air entering the film hole. Furthermore, the spiral flow inside the hole is impaired. Originality/value: As a result, the kidney-shaped vortices originating from the jet flow are weakened, and the target surface can be well covered, resulting in an enhancement of the adiabatic film cooling performance. [ABSTRACT FROM AUTHOR]

The complex structure at trailing edge reduces the manufacturing precision, which results in an error in the size of the trailing edge structure. In this study, the performance of a stage high-pressure turbine (HP turbine) is calculated out in three dimensions. In the HP turbine guide vane, the trailing edge cutback configuration is adopted. Through three-dimensional simulation, the complex flow around the trailing edge with cutback cooling configuration is presented in this study, and the manufacturing precision reduction due to the complex structure at trailing edge is considered. Furthermore, the effect of trailing edge lip thickness and deflection of the stator on the turbine performance is discussed. Overall, as the press-side lip thickness increasing, the turbine efficiency and turbine inlet flow are reduced. However, the changes in the turbine work output are relatively complex. On the other hand, as the spacing between suction-side lip and press-side lip increases, turbine performance becomes worse. Both of the turbine efficiency and the turbine work output become smaller, while the turbine inlet flow becomes bigger. The effect of the spacing between suction-side lip and press-side lip is obviously greater than that of the press-side lip thickness. The change of the press-side lip thickness has little effect on the relation between the turbine performance and the spacing between suction-side lip and press-side lip. However, when the spacing between suction-side lip and press-side lip deviates from the baseline value, the effect law of the press-side lip thickness on the turbine performance will be affected. As the press-side lip thickness increases, it leads to an increase in the low-velocity zone at both of the pressure-side and suction-side trailing edge. And more main stream is affected or mixed into the wake flow. When the spacing between suction-side lip and press-side lip becomes smaller, the low-velocity zone at the trailing edge is smaller, and the change of vortex with the press-side lip thickness is affected. With a bigger spacing between suction-side lip and press-side lip, the variation is contrary.

•Thermomechanical performances of corrugated core and X core sandwich panels are compared.•Multi-layer and multi-row lightening holes are designed to enhance thermal insulation.•Temperature of X plate is lower about 39 K-63 K than that of corrugated plate.•Three lightening holes of X plate decrease the maximum temperature by 54 K, 60 K and 76 K.•Equivalent stress is below the material yield strength after opening lightening holes.

Purpose The purpose of this paper is to augment heat transfer rates of traditional rib-elements with minimal pressure drop penalties.Design/methodology/approach The novel geometries in the present research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. All turbulent fluid flow and heat transfer results are presented using computation fluid dynamics with a validated v2f turbulence closure model. Turbulent flow characteristics and heat transfer performances in square channels with improved ribbed structures are numerically analyzed in this research work.Findings Based on the results, it is found that rounded transition cylindrical ribs have a large advantage over the conventional ribs in both enhancing heat transfer and reducing pressure loss penalty. In addition, cylindrical ribs increase the flow impingement at the upstream of the ribs, which will effectively increase the high heat transfer areas. The design of rounded transition cylindrical ribs and grooves will be an effective way to improve heat transfer enhancement and overall thermal performance of internal channels within blade cooling.Originality/value The novel geometries in this research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. The combination of cylindrical ribs and grooves to manipulate the turbulent flow. [ABSTRACT FROM AUTHOR]

This paper conducted a multi-objective optimization work for a composite internal and film cooling structure. The pitch-to-height ratio of the ribs, the inclination angle of the ribs, and the inclination angle of the film hole are chosen as the three design variables to enhance the heat transfer performance, improve the film cooling effectiveness and reduce the pressure loss of the internal channel flow. During the optimization process, the Latin hypercube sampling method is adopted to select 26 sample points from the design space. The response values with higher fidelity at the sample points are calculated using computational fluid dynamics (CFD) simulations. Among the 26 sample points, 21 are used to construct a surrogate model of each objective function while the rest of them are adopted to validate the correctness of the established surrogate model. By combining the Kriging surrogate model with a nondominated sorting genetic algorithm, the Pareto optimal front is obtained after the optimization process. Finally, comparison and analysis are conducted with respect to the cooling performance and mechanisms between the reference model and the selected three representative optimized models. Results show that the optimized three models can not only improve the film cooling effectiveness but also reduce the pressure loss of the channel flow and enhance the heat transfer. In addition, it is found that the optimized model induces an anticlockwise rotating vortex, which entrains more coolant near the target surface. The inclined ribs of the optimized models induce a secondary flow along the inclined ribs, which enhances the flow mixing and augments the heat transfer performance.

Based on a combined-hole design, a novel hole arrangement was proposed and tested on a flat plate model by numerical simulation. Replacing one row in two rows of staggered holes with a row of smaller holes, the bigger holes in one row and smaller holes in the other row will form combined-hole units. The kidney–vortex pairs in the combined-hole unit will interact with each other and get weakened, finally enhancing film cooling performance. Compared to the original two rows of staggered holes, the coolant mass flowrate will be reduced by 25% for the new hole arrangements. Results show that the area-averaged film cooling effectiveness of the new arrangements is similar or even higher than that of the original one at different blowing ratios. Replacing the second row of holes with smaller holes provide better cooling performance than replacing the first row of holes. The overall film cooling performance is not sensitive to the row space. The highest improvement of film cooling effectiveness is 24% when the blowing ratio is 1. However, as the coolant accumulation and reattachment phenomenon is weakened by the new arrangements, the film cooling performance is not as good as the original one when the blowing ratio is 1.5.

In this paper, the performance enhancement of a particular type of heater, i.e., water bath heater, with a wide range of industrial applications is proposed and assessed. The idea is centered around using an alternative working fluid with better heat transfer characteristics (heat transfer oil—HTO) to quantify the impacts not only from a technical point of view but also from an economic perspective. The indirect heater of Arkan CGS (located in North Khorasan province of Iran) is selected as the case study, and its laboratory model is constructed by dimensional analysis. The thermal analysis is done at different fluid flow rates in the heating coil of the experimental setup. The results are verified by both numerical simulation and available empirical correlation. The results show that using HTO as the heating medium leads to heater efficiency improvement by up to 158%, and it will also lead to energy savings of up to 36.5%. A comprehensive economic analysis is carried out based on the technical results. It is found that the internal rate of return and dynamic payback period are in the ranges of 42–67% and 1.53–2.17 years, respectively.

A topology optimization strategy with coupled fluid–solid interaction was proposed to maximize the cooling efficiency of a kind of structure applied for scramjets. The Galerkin finite element method (FEM) is used to solve the forced convective heat transfer, and the rational approximation of material properties (RAMP) method combined with the globally convergent method of moving asymptotes (GCMMA) method are used to solve the topological optimization models with different boundary conditions and objective functions. Examples are provided to demonstrate the validity and effectiveness of the optimization strategy. The optimal flow passages of scramjet structures are achieved successfully. Compared with a baseline structure with rectangular straight passages, the optimized flow passages significantly reduce the averaged bulk temperature and pressure loss, and the bulk temperature is more uniform to avoid the occurrence of concentrated high-temperature areas. With the Reynolds number changing from 1000 to 1750, the heat transfer performance of the three-dimensional topology-optimized structure increases by 16.79% to 20.82%.

For the supercritical n-decane horizontally flowing in a rectangular channel of an active regenerative cooling system, a transient thermal–fluid–structure coupling method is employed to investigate the unsteady thermal-hydraulic characteristics and the wall deformation at a starting stage. The temperature distributions of the fluid domain and solid domain along the flow direction are investigated at fixed times as well as at a certain cross section. Streamlines in cross sections are employed to explain the temperature distribution. The velocity and pressure at a fixed point versus time are also given. Besides, the solid deformation is presented according to the uneven pressure distribution and temperature distribution. It is found that the response time is less than 30 s when the heat flux is less than 3.0 MW/m2. A larger heat flux contributes to promoting the steady state. The high-temperature part of the solid domain is close to the heated wall, but the situation is reversed for the fluid domain. This is because a bunch of dead-zone vortices appears in the vicinity of the upper wall of the channel. The maximum deformation is 0.132 mm for the condition of heat flux 3.0 MW/m2 and it is exacerbated by the uneven temperature and pressure distributions on the solid domain.

•Two S-CO2cycle systems integrated thermal protection and power generation for a hypersonic vehicle engine are developed.•Thermal performances of the two systems are evaluated and compared.•Characteristics of the recuperators in the two systems are investigated.•Effects of the recuperators on the two systems are studied.

Internal cooling and film cooling, as two main cooling methods in modern gas turbines, work together to protect the high-temperature components of gas turbines. This paper presents the results of a computational study on cooling performance for a flat plate with both film cooling and internal cooling using a conjugate heat transfer analysis. Three internal delivery channel geometries, smooth channel, channel roughened by square ribs (SR), and channel roughened by crescent ribs (CR), are studied with two film cooling geometries, cylindrical hole, and sister holes (SS). The respective conjugate cooling performances are compared. Detailed flow and heat transfer characteristics are presented and discussed. Results show that both film cooling effectiveness and internal cooling performances are influenced by the delivery channel geometry near the hole inlets. The sink flow effects of film cooling enhance the heat transfer coefficient near the film cooling hole inlet. At the same time, film cooling performance is affected by the internal channel as the flow inside the film cooling hole is influenced by the ribs near the hole inlets. When using sister holes, ribs in the internal channels make the anti-kidney vortex structure created by sister holes more effective by changing the mass flow distribution among the three holes.

•Theoretical comparison on S-CO2/ORC and S-CO2/Kalina combined cycles were made.•Heat transfer characteristic of the evaporators in combined cycle was discussed.•Working medium and parameter optimization were conducted.•Reheating can only improve the ORC thermal efficiency of certain working mediums, but it can improve the overall performance of all mediums.•A detailed heat transfer coupling is performed for the Kalina cycle to recover afterheat near the critical point of CO2.

Purpose -- The employment of continuous ribs in a passage involves a noticeable pressure drop penalty, while other studies have shown that truncated ribs may provide a potential to reduce the pressure drop while keeping a significant heat transfer enhancement. The purpose of this paper is to perform computer-aided simulations of turbulent flow and heat transfer of a rectangular cooling passage with continuous or truncated 45-deg V-shaped ribs on opposite walls. Design/methodology/approach -- Computational fluid dynamics technique is used to study the fluid flow and heat transfer characteristics in a three-dimensional rectangular passage with continuous and truncated V-shaped ribs. Findings -- The inlet Reynolds number, based on the hydraulic diameter, is ranged from 12,000 to 60,000 and a low-Re k-e model is selected for the turbulent computations. The local flow structure and heat transfer in the internal cooling passages are presented and the thermal performances of the ribbed passages are compared. It is found that the passage with truncated V-shaped ribs on opposite walls provides nearly equivalent heat transfer enhancement with a lower (about 17 percent at high Reynolds number of 60,000) pressure loss compared to a passage with continuous V-shaped ribs or continuous transversal ribs. Research limitations/implications -- The fluid is incompressible with constant thermophysical properties and the flow is steady. The passage is stationary. Practical implications -- New and additional data will be helpful in the design of ribbed passages to achieve a good thermal performance. Originality/value -- The results imply that truncated V-shaped ribs are very effective in improving the thermal performance and thus are suggested to be applied in gas turbine blade internal cooling, especially at high velocity or Reynolds number. [ABSTRACT FROM AUTHOR]

Purpose – With the development of electronic devices, including the desires of integration, miniaturization, high performance and the output power, cooling requirement of chips have been increased gradually. Water-cooled minichannel is an effective cooling technology for cooling of heat sinks. The minichannel flow geometry offers large surface area for heat transfer and a high convective heat transfer coefficient with only a moderate pressure loss. The purpose of this paper is to analyze a minichannel heat sink having the bottom size of 35 mm×35 mm numerically. Two kinds of chip arrangement are investigated: diagonal arrangement and parallel arrangement. Design/methodology/approach – Computational fluid dynamics (CFD) technique is used to investigate the flow and thermal fields in forced convection in a three-dimensional minichannels heat sink with different chip arrangements. The standard k-e turbulence model is applied for the turbulence simulations on the minichannel heat sink. Findings – The results show that the bottom surface of the heat sink with various chip arrangements will have different temperature distribution and thermal resistance. A suitable chip arrangement will achieve a good cooling performance for electronic devices. Research limitations/implications – The fluid is incompressible and the thermophysical properties are constant. Practical implications – New and additional data will be helpful as guidelines in the design of heat sinks to achieve a good thermal performance and a long lifetime in operation. Originality/value – In real engineering situations, chips are always placed in various manners according to design conditions and constraints. In this case the assumption of uniform heat flux is acceptable for the surfaces of the chips rather than for the entire bottom surface of the heat sink. [ABSTRACT FROM AUTHOR]

Pressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double‐pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave‐like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power‐law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave‐like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave‐like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29–40, 2008; Published online in Wiley InterScience (). DOI 10.1002/htj.20186

To figure out the abnormal flow characteristics and thermal performance of supercritical fluids, some detailed information of supercritical pressure n-decane flowing in a horizontally round pipe is studied in terms of secondary flow induced by the huge density change or buoyancy force. According to an evaluation of turbulence models, the shear stress transport k–ω is suitable to execute the case of horizontal flow. It is observed that the temperature distributions between the upper wall region and the lower wall region are asymmetric and the location of the maximum buoyancy force coincided with the position of Tpc (pseudo-critical temperature). The generation of a rotating flow arising from the heated wall determines the occurrence of heat transfer deterioration (HTD). In the boom stage of the HTD phenomenon, a dead zone that is close to the upper wall was formed due to the influence of vortices. In contrast, the maximum buoyancy force is located in the core flow zone and it forces the fluid in the mainstream to participate in the cooling process of the heated wall. In addition, the dead zone in the vicinity of the upper wall is broken. This is the main reason why heat transfer deterioration could be inhibited effectively.

Attempts for higher output power and thermal efficiency of gas turbines make the inlet temperature of turbine to be far beyond the material melting temperature. Therefore, to protect the airfoil in gas turbine from hot gas and eventually prolong the lifetime of the blade, internal and film cooling structures with better thermal performance and cooling effectiveness are urgently needed. However, the traditional way of proceeding involves numerous simulations, additional experiments, and separate trials. Optimization of turbine cooling structures is an effective way to achieve better structures with higher overall performances while considering the multiple objectives, disciplines or subsystems. In this context, this paper reviews optimization research works on film cooling structures and internal cooling structures in gas turbines by means of various optimization methods. This review covers the following aspects: (A) optimization of film cooling conducted on flat plates and on turbine blades or vanes; (B) optimization of jet impingement cooling structures; (C) optimization of rib shapes, dimple shapes, pin–fin arrays in the cooling channels; (D) optimization of U-bend shaped cooling channels, and internal cooling systems of turbine blades or vanes. The review shows that through a reliable and accurate optimization procedure combined with conjugate heat transfer analysis, higher overall thermal performance can be acquired for single-objective or multi-objectives balanced by other constrained conditions. Future ways forward are pointed out in this review.

Supercritical fluids (e.g., hydrocarbon fuels, water, carbon dioxide, and organic working medium, etc) have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion, and have been used or selected as the working fluids in engineering fields such as aerospace, nuclear power, solar energy, refrigeration, geothermal energy, chemical technology, and so on. To better understand the interesting characteristic or abnormal behaviors of supercritical fluids, most valuable research works (including experimental results and numerical studies) from domestic and abroad have been documented. As such, this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications. This review focuses on recently available articles published mainly from 2016 up to the present time. The common problems (i.e., heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels) in the supercritical field are summarized and some perspectives on future prospects are also included.

Existing researches on two-row film cooling mainly focused on double-jet film cooling. However, researches on the effects by combining different kinds of hole shapes on film cooling performance are quite limited. In order to improve the film cooling effectiveness, the three-dimensional numerical method is utilized to investigate the effects of a novel structure composed of two-row holes with different shapes and arrangements on the adiabatic film cooling effectiveness with the blowing ratio of M = 1.5. To achieve this purpose, 30 different cases with two-row holes are designed and their film cooling effectiveness are compared with those of other seven cases with a single hole. Cases with two-row holes are designed by setting cylindrical, elliptical, or super-elliptical holes as the first-row, and arranging cylindrical holes with 30 deg, 45 deg, 60 deg, and 90 deg compound angles as the second row. The realizable k–ɛ turbulence model with enhanced wall function is utilized for all cases under identical boundary conditions. Similar film cooling performances are observed for cases with elliptical and super-elliptical holes being the first row, since the maximum deviation of film cooling effectiveness is less than 10%. It is found that the case integrates both a cylindrical hole and a cylindrical hole with 90 deg compound angle can greatly improve the film cooling performance with a higher discharge coefficient. However, the staggered case with an elliptical hole as both first- and second row gives the best film cooling effectiveness and the worst discharge coefficient due to the biggest resistance for the coolant flowing into the film hole.

The shell condenser is one of the key components of underwater vehicles. To study its thermal performance and to design a more efficient structure, a computational model is generated to simulate condensation inside straight and helical channels. The model combines empirical correlations and a MATLAB-based iterative algorithm. The vapor quality is used as a sign of the degree of condensation. Three calculation models are compared, and the optimal model is verified by a comparison of simulated results and available experimental data. Several cases are designed to reveal the effects of various inlet conditions and the diameter-over-radius (Dh/R) ratio. The results show that the inlet temperature and mass rate significantly affect the flow and heat transfer in the condensation process, the heat transfer capabilities of the helical channels are much better than that of the straight channel, and both the heat transfer coefficient and total pressure drop increase with the decrease of Dh/R. This study may provide a useful reference for performance prediction and structural design of shell condensers used for underwater vehicles and may provide a relatively universal prediction model for condensation in channels.

Internal Y-shaped bifurcation has been proved to be an advantageous way on improving thermal performance of microchannel heat sinks according to the previous research. Metal foams are known due to their predominate performance such as low-density, large surface area, and high thermal conductivity. In this paper, different parameters of metal foams in Y-shaped bifurcation microchannel heat sinks are designed and investigated numerically. The effects of Reynolds number, porosity of metal foam, and the pore density (PPI) of the metal foam on the microchannel heat sinks are analyzed in detail. It is found that the internal Y-shaped bifurcation microchannel heat sinks with metal foam exhibit better heat transfer enhancement and overall thermal performance. This research provides broad application prospects for heat sinks with metal foam in the thermal management of high power density electronic devices.

The flow field design of current collectors is a significant issue, which greatly affects the mass transport processes of reactants/products inside fuel cells. Especially for proton exchange membrane (PEM) fuel cells, an appropriate flow field design is very important due to the water balance problem. In this paper, a wavy surface is employed at the cathode flow channel to improve the oxygen mass transport process. The effects of wavy surface on transport processes are numerically investigated by using a three-dimensional anisotropic model including a water phase change model and a spherical agglomerate model. It is found that the wavy configurations enhance the oxygen transport and decrease the water saturation level. It is concluded that the predicted results and findings provide the guideline for the design and manufacture of fuel cells.

According to the particular aerodynamic heating loads which hypersonic aerospace aircrafts suffered from in-service environment, a lightweight integrated thermal protection system (ITPS) named pyramidal core sandwich panel is designed. This is considered not only as an insulation structure but also a load-bearing structure. Compared to traditional thermal protection systems (TPSs), the sandwich panel has simultaneous lightweight, load-bearing, and excellent thermal protection property. The finite-element heat transfer analysis for the pyramidal core sandwich structure is performed, and the distributions of temperature in the structure are presented. Then sequential coupling method is adopted to analyze the thermomechanical performance of the structure and presentations of field of stress and displacement under aerodynamic and thermal load are provided. A comparison between corrugated-core sandwich panels and pyramidal core sandwich panels from the perspectives of heat insulation, strength, and mass is carried out. The results indicate that the particular performance of pyramidal-core structure is superior to that of corrugated-core structure.