28 February 2025, Volume 34 Issue 2
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Journal of Thermal Science. 2025, 34(2): 337-351. https://doi.org/10.1007/s11630-024-2075-0To achieve low-carbon economic operation of hydrogen-doped integrated energy systems while mitigating the stochastic impact of new energy outputs on the system, the coordinated operation mode of hydrogen-doped gas turbines and electrolyzers is focused on, as well as a hybrid energy storage scheme involving both hydrogen and heat storage and an optimized scheduling model for integrated energy systems encompassing electricity-hydrogen-heat-cooling conversions is established. A model predictive control strategy based on deep learning prediction and feedback is proposed, and the effectiveness and superiority of the proposed strategy are demonstrated using error penalty coefficients. Moreover, the introduction of hydrogen energy exchange and ladder carbon trading is shown to effectively guide the low-carbon economic operation of hydrogen-doped integrated energy systems across multiple typical scenarios. A sensitivity analysis is conducted based on this framework, revealing that increases in the hydrogen doping ratio of turbines and the carbon base price led to higher system operation costs but effectively reduce carbon emissions.
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Journal of Thermal Science. 2025, 34(2): 352-373. https://doi.org/10.1007/s11630-025-2091-8The supercritical carbon dioxide (sCO2) cycle can be powered by traditional as well as clean energy. To help users obtain more accurate results than the literatures with pre-set compressor efficiency, we proposed a complete model to establish a link between the performance, sizes of compressors and parameters such as power WC, inlet temperature Tin, inlet pressure Pin and pressure ratio ɛ. Characteristic sizes of compressors lc, profile loss Yp and clearance loss Ycl are all proportional to powers of WC with powers of 0.5, –0.075 and –0.5 to 0 respectively; the scaling laws are constant in the range of capacities from 20 MW to 200 MW. The compressor isentropic efficiency ηtt grows as the WC increases, and the curves become gentle. Compressor efficiency improves over the full power range when the speed is changed from standard speed to the optimal speed; the ηtt curves turn soft as the n increase. As the Pin and Tin approach the critical point, the ηtt increase. Compressor efficiency follows a parabolic curve as the ɛ increases, this parabolic distribution results from the tradeoff between the change in losses and the pressure distribution of blades. The ηtt versus Pin, Tin and ɛ relations are similar at various capacities because of insignificant changes in the distribution of losses. Compressor efficiency maps facilitate the estimation of system performance, while scaling law for irreversible losses and characteristic lengths, along with constant criterion analyses, aid in comprehending the characteristics of compressors across various capacities.
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Journal of Thermal Science. 2025, 34(2): 374-388. https://doi.org/10.1007/s11630-025-2017-5With a broad range of application prospects, hydrogen fuel cell technology is regarded as a clean and efficient energy conversion technology. Nevertheless, challenges exist in terms of the safe storage and transportation of hydrogen. One proposed solution to this problem is the utilization of methanol on-line steam reforming technology for hydrogen production. In this paper, an integrated system for in-situ steam reforming of fuel coupled with proton exchange membrane fuel cells (PEMFC) power generation is proposed, and sensitivity analysis and exergy sensitivity analysis are conducted. Through the gradual utilization of waste heat and the integration of the system, fuel consumption is reduced and the power generation efficiency of the system is improved. Under the design operating conditions, the power generation efficiency and exergy efficiency of the system are achieved at 44.59% and 39.70%, respectively. This study presents a proven method for the efficient integration of fuel thermochemical conversion for hydrogen production with fuel cells for power generation, highlighting the advantages of complementary utilization of methanol steam reforming and PEMFC.
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Journal of Thermal Science. 2025, 34(2): 389-399. https://doi.org/10.1007/s11630-025-2094-5Thermally regenerative electrochemical cycle (TREC) is a novel and effective heat-to-electricity technology for harvesting low-grade heat. Currently, reported TREC analyses have been based on the Stirling cycle of ideal infinite heat source and infinite time for heat transfer. However, this will lead to inaccuracy when the scenario deviates from the ideal case. In this study, a systematic thermodynamic analysis on TREC is performed to address this problem. Based on different heat transfer situations, the description of thermodynamic processes and the corresponding mathematical models are established. At the same time, the TREC system, with the solar collector as the high-temperature heat source and the environment as the low-temperature heat source, is employed as a case. And the study delved into discrepancies arising from incongruences between the practical operational process and the traditional ideal analytical methodologies, along with an investigation of the different thermal environment impact on system performance. The findings suggest that the finite analysis method should be used when the actual operating time of the system is shorter than the desired equilibrium period. On the contrary, the use of the infinite analysis method, in this case, produces an error, the magnitude of which is directly related to the operating time, whereas when the time reaches 80% of the equilibrium time the error can be controlled to less than 2%. The influence of the heat source on the operating phase of the system is mainly in the temperature equilibrium and the rate of temperature equilibrium. This effect is proportional to the thermal capacitance and is also positively related to the system performance. Therefore, to improve system performance, it is recommended that a high-temperature heat source with a high ratio of thermal capacitance to system thermal capacitance should be selected and that the response time should slightly exceed the system equilibrium duration.
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Journal of Thermal Science. 2025, 34(2): 400-412. https://doi.org/10.1007/s11630-025-2082-9The exploitation of photovoltaic/thermal (PV/T) systems, which facilitate concurrent conversion of solar radiation into electrical and heat energies, presents substantial potential in the solar-abundant northwestern zone of China. This investigation endeavors to evaluate the efficacy of a micro heat pipe (M-HP) PV/T system via exhaustive experimental analysis conducted in Lanzhou. To improve the performance of M-HP-PV/T system, a comparison was made between the optimal angles for each day and the entire year. The system inside greenhouse exhibited an average photovoltaic conversion efficiency (PCE) and thermal conversion efficiency (TCE) of 12.32% and 42.81%. The system of external environment registered average PCE and TCE values of 12.99% and 21.08%. To further understand the system’s operational results, a mathematical model was constructed through the integration of experimental data, exhibiting good agreement between the simulated outcomes and empirical observations. The average solar irradiance of daily optimum angle was 728.3 W/m2; the annual optimum angle was 29° with an average solar irradiance of 705.6 W/m2. The average annual total powers at the optimal angle outside the greenhouse and inside the greenhouse were 448.0 W and 398.7 W. The average annual total efficiencies at the optimal angle outside the greenhouse and inside the greenhouse were 40.8% and 56.9%. The total power in the greenhouse was lower by 49.3 W, while total efficiency in the greenhouse was higher by 16.1%.
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Journal of Thermal Science. 2025, 34(2): 413-428. https://doi.org/10.1007/s11630-024-2084-zWater is a recyclable resource and the largest energy carrier on Earth. New hydropower generation technologies hold great promise for the future. However, there is a lack of evaluation standards for power generation performance. And, the mechanism of hydrovoltaic power generation lacks systematic clarity. In this study, a thermodynamic analysis method about hot and humid air energy conversion based on the principle of hydropower generation is established. To author’s knowledge, it is the first time that the maximum available energy of hydropower generation is analyzed by exergy and parametric calculations. The greater the difference, the higher the available energy. Also, a series of experiments were conducted to explore the power generation device materials, structural composition, and structural parameters, further clarifying the principle of electricity generation. And, the influence of temperature and relative humidity on the power generation performance was also studied. The increase in temperature can effectively increase the output electrical performance of the power generation. The open-circuit voltage and short-circuit current of water evaporation power generation with Al2O3 nanoparticles are higher than 2.5 V and 150 nA respectively. Through analysis, we propose relevant application strategies to provide theoretical and practical support for the development of green energy.
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Journal of Thermal Science. 2025, 34(2): 429-447. https://doi.org/10.1007/s11630-024-2068-zHybrid nanofluids are known for their attractive thermophysical properties and enhanced heat transfer potential. This study thoroughly investigates the impact of particle mixing ratios on the thermophysical and heat transfer characteristics of MgO-SiO2/water hybrid nanofluid. The mixing mass ratio (MR) of MgO:SiO2 was systematically altered including ratios of 100:0, 80:20, 60:40, 50:50, 40:60, 20:80, and 0:100 at a fixed particle concentration of 0.01% in volume. Experimental assessments of thermal conductivity and viscosity were conducted within the temperature range of 25°C–50°C at 5°C intervals. Thermal conductivity was measured by analysing sonic velocity of sound in nanofluid medium. Viscosity was determined by Ostwald viscosity apparatus. Sensitivity analysis was performed to examine the influence of mixing ratio and temperature on thermal conductivity and viscosity. Sustainability and economic analysis were conducted to guide future applications. The findings highlight the substantial influence of MR on thermal conductivity and viscosity enhancements within the hybrid nanofluid. The thermal conductivity exhibited a positive correlation with temperature elevation, with the hybrid nanofluid at MR=60:40 and 50°C displaying the highest thermal conductivity enhancement at 20.84% compared to water. In contrast, viscosity decreased with increasing temperature, with MR=50:50 at 50°C showing the maximum viscosity increase at 5.06% compared to water. New data-driven correlations for precise predictions of thermal conductivity and viscosity of hybrid nanofluid have been proposed. Sensitivity analysis revealed that mixing ratio had a more pronounced impact than temperature elevation. Sustainability and economic analysis concludes that MR=60:40 is an optimal, economical and sustainable choice for achieving peak heat transfer performance.
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Journal of Thermal Science. 2025, 34(2): 448-464. https://doi.org/10.1007/s11630-025-2098-1To address the intermittent challenges of new energy and waste heat recovery as well as counteract the issues of corrosion and overcooling in phase-change materials, this study develops and investigates a medium-temperature phase-change capsule (PCC) through experiments and numerical simulations. The thermal cycle stability testing of the developed PCC, subjected to 150 cycles to evaluate its performance, demonstrated that the capsule’s surface remained intact with no signs of leakage. The enthalpy-porosity method combined with the volume-of-fluid method was used to establish a numerical model to simulate the phase-change process in capsules with two structures: one with a central cavity and the other with a top cavity. Results indicated that when using 304 stainless steel as the wall material for both structures, the PCC with the centrally located cavity melted 28.3% faster than that with the cavity at the top. When using different materials as wall coverings, the melting rate of the PCC made of polytetrafluoroethylene (PTFE) was 22.1% slower than that of the capsule made of 304 stainless steel. Conversely, the modified PTFE PCC melted 15.2% faster than the stainless steel-based PCC. Furthermore, when using PCCs having different diameters, the time differences for complete melting between the PTFE and stainless steel-based PCCs were 118 s and 66 s for the capsules having diameters of 24 mm and 16 mm, respectively, indicating that the time difference decreased with decreasing capsule diameter.
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Thermal Contact Resistance and Heat Transfer Enhancement Mechanisms at Non-Smooth Contact InterfacesJournal of Thermal Science. 2025, 34(2): 465-497. https://doi.org/10.1007/s11630-025-2086-5As an important and effective indicator of contact heat transfer, thermal contact resistance is a widespread phenomenon in engineering. It can directly affect product reliability, full-load performance, power consumption and even life cycle in energy, aerospace, electronic packaging, cryogenic refrigeration, etc. Therefore, enhancing the interface heat transfer and suppressing thermal contact resistance have become increasingly important. Against this background, this paper seeks to elaborate on conceptions of thermal contact resistance and the ways to reduce it. After reviewing the existing methods of measuring thermal contact resistance and characterizing the interface morphology, we highlight the theoretical underpinnings of thermal contact resistance, including the two-dimensional mathematic characteristics of the contact interface and the theoretical and empirical models for quantifying it. Three categories of influencing factors, i.e., thermal, geometrical and mechanical states, are then presented. Based on the macroscopic formation mechanism, the paper summarizes the existing methods for suppressing thermal contact resistance, with close attention paid to polymer composite thermal interfacial materials and metal interfacial materials filled with high thermal conductivity filler. In light of the findings, this review provides five promising directions for future research on thermal contact resistance. It suggests that the failure modes and service life of interface materials are essential to apply such technologies to suppress thermal contact resistance in practice. This review will be a guide for future research in thermal contact resistance and for the widespread use of composite interface materials.
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Journal of Thermal Science. 2025, 34(2): 498-509. https://doi.org/10.1007/s11630-025-2096-3In the field of nano energy, investigating the specific heat capacity and coordination number of nano-confined water is highly significant for gaining a better understanding of the energy and microstructure of confined water. In this work, we employed the method of molecular dynamics (MD) simulation to calculate the specific heat capacity at constant volume and coordination number of water molecules confined in carbon nanotubes (CNTs) under different conditions (T=600–700 K, P=21.776 and 25 MPa, CNT diameter=0.949–5.017 nm). The results showed that near the critical point, the specific heat capacity at constant volume of confined water was lower than that of bulk water, and the energy fluctuation showed a trend of first increasing and then remaining unchanged with the increase of temperature and CNT diameter. Among them, the saturation point of temperature is 650 K (reduced pressure Pr=1) and 660 K (Pr=1.15), and the saturation point of CNT diameter is 2.034 nm. Additionally, the pseudo-critical temperature of confined water was the same as bulk water, and it increased with the increase of critical pressure. Moreover, with the increase of CNT diameter, the coordination number of confined water increased rapidly, and reaches the saturation state when the CNT diameter is 2.034 nm. This investigation revealed the mass and energy characteristics of nano-confined water near the critical point, which could provide guidance for the critical phase transition of nano-confined water.
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Journal of Thermal Science. 2025, 34(2): 510-523. https://doi.org/10.1007/s11630-025-2032-6Backward Monte Carlo method of the complicated and exact three-dimensional turbine with the spectral emission and reflection characteristics of the turbine blades materials and the spectral absorption and emission characteristics of combustion gas is established. The factors affecting the accuracy of the radiation temperature measurement are analyzed. The results show that reducing the distance from the probe to the target surface can reduce the effect of the environment on the measurement accuracy. Increasing the temperature and emissivity of the target surface can improve the measurement accuracy. The reflection characteristics of the surfaces have little influence on the radiation temperature measurement, so the blades can be considered as diffuse reflectors in order to improve the calculation efficiency. The temperature measurement accuracy decreases rapidly as the temperature of the combustion gas increases. The temperature measurement accuracy decreases with the increase of total gas pressure and H2O concentration. When measuring the temperature of rotating blades, the apparent emissivity of the target surface is inversely proportional to the measurement accuracy.
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Journal of Thermal Science. 2025, 34(2): 524-541. https://doi.org/10.1007/s11630-024-2073-2SCRamjet is exposed to severe thermal environments during hypersonic flights, which poses a serious challenge to the engine cooling technology. Regenerative cooling with hydrocarbon fuel is considered promising, in which the hydrocarbon fuel flows through micro channels (200 μm–3 mm) to absorb the combustion heat release. With strictly limited hydrocarbon fuel onboard, heat transfer deterioration and over-temperature are highly possible. In this paper, micro ribs with staggered side gaps are introduced and numerically studied to enhance the heat transfer. Compared with the straight channel and channel with straight micro ribs, the staggered side gaps alleviate the local low velocity zone and intensify the longitudinal and transverse vortexes. The heat transfer is obviously enhanced. Larger rib height enhances the heat transfer by stronger side gap effects at the cost of larger pressure loss. The best overall heat transfer factor η is achieved in the case of hrib/H=0.1, which increases by 204.5% comparing to the straight channel. When the rib interval is too small or too large, it approaches to the straight channel. The best overall heat transfer factor η is achieved in the case of L/prib=100, which increases by 212.9% comparing to the straight channel. It is known the improvement in the geometry of the ribs, i.e., the staggered-side-gap micro ribs, induces extra transverse vortex and improves the heat transfer performance more effectively. The research of this paper provides support for the cooling design of the SCRamjet.
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Journal of Thermal Science. 2025, 34(2): 542-554. https://doi.org/10.1007/s11630-024-2063-4Tubular moving bed heat exchangers (MBHEs) present inherent advantages for efficiently and stably recovering sensible heat from high-temperature granular bulk. In this study, we introduce a viable and practical approach based on the combined approach of Computational Fluid Dynamics with Discrete Element Method (CFD-DEM) and employ it to conduct a comprehensive investigation into the effects of operation parameters on tubular MBHEs. These parameters include inlet particle temperature (ranging from 500°C to 700°C), tube wall temperature (ranging from 50°C to 250°C), and particle descent velocity (ranging from 0.5 mm/s to 12 mm/s). Our analysis reveals that the heat radiation and gas film heat conduction predominantly govern the heat transfer process in the particle-fluid-wall system, collectively contributing to approximately 90% of the total heat flux of tube wall (Qwsimu). The results indicate that increasing the inlet particle temperature and reducing the tube wall temperature intensify heat transfer by enlarging the temperature difference. More interestingly, Qwsimu exhibits three distinct stages as particle descent velocity increases, including an ascent stage, a descent stage, and a stable stage. Furthermore, the simulation attempts suggest that the optimal descent velocity for maximizing Qwsimu falls within the range of 1.3–2.0 mm/s. These findings not only uncover the precise influence mechanisms of operation parameters on heat transfer outcomes but also offer valuable insights for heat transfer enhancement efficiency in MBHE system.
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Journal of Thermal Science. 2025, 34(2): 555-566. https://doi.org/10.1007/s11630-025-2101-xIn this work, the interactions between the environmentally friendly refrigerant propane (R290) and Polyol Ester (POE) including solubility parameters, diffusion coefficients, binding energies, and radial distribution functions were investigated using molecular dynamics (MD). Specifically, the effect of chain length of Pentaerythritol esters (PEC) as the representative component of POE on the interaction of PEC/R290 was discussed. The solubility parameters difference exhibits the PEC and R290 are more easily miscible as increasing chain length of PEC, and there is plateau as the chain lengths is above 8 units. In addition, it was also found that solubility parameters are various for the isomers due to the different spatial structure. Moreover, the presence of PEC would reduce the diffusion coefficient of R290 in the mixed system of R290/lubricant with the reduction of 20% on average. It is also found that van der Waals forces are dominant in the R290/PEC system. The PEC molecules start to be bound to the H atoms of R290 at the first neighbor shell layer with a radius of 0.219 nm. Finally, the molecular simulation model of POE22 considering various actual components was innovatively developed. The results showed that the solubility of R290 with typical POE lubricant is affected by the composition and proportions of based oil and additives.
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Journal of Thermal Science. 2025, 34(2): 567-578. https://doi.org/10.1007/s11630-024-2069-yThe through-flow method still plays an important role in the design of modern aero-engine, and its accuracy depends on the loss and deviation model. The presence of tip clearance will impact the deviation distribution, while the retained lift is somewhat related to this effect. To achieve a more precise deviation model, this paper utilises the machine learning approach. The database comprises cascades with tip clearances in training, from which obtains a span-wise deviation model and executes its validation by comparing with experiment result. The database is obtained by calculating 16 different geometries of the cascades with tip clearance in different working conditions, introducing the geometrical parameters of the cascades and retained lift as feature engineering. The deviation and the retained lift follow the same trend with tip clearance size and operating conditions variation. We predict the span-wise distribution of the retained lift using the k-nearest neighbour regression, and then combine with the traditional model to get the distribution of the deviation. The results show that the coefficient of determination of the retained lift coefficient prediction in the test set reaches 81.02%, and the mean absolute error is around 1.32%. Moreover, the trend predictions of cascade deviation distribution for different tip clearance size are all in good agreement with the experimental results. The coefficient of determination of the prediction with the simulation is 75.23%, and the mean absolute error is 1.74%.
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Journal of Thermal Science. 2025, 34(2): 579-589. https://doi.org/10.1007/s11630-025-2093-6The utilization of a part-span connector (PSC) has the potential to enhance the blade frequency, but with the penalty of aerodynamic performance. In this study, we numerically investigate the aerodynamic performance of two types of bionic structure snubbers: (1) Harbor seal whisker (HSW) and (2) Atropus’s body shape (ABS). The investigation is conducted by solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations and utilizing the SST turbulent model. In this study, the performance impact of classical snubbers on a cascade blade has been examined by modeling it with and without an ellipse-shaped snubber. The vortex induced by the snubber predominantly manifests on the suction side and can be categorized into three primary vortices: upper, lower, and tail. The upper and lower vortices serve as the primary contributors to loss. Compared to the conventional ellipse snubber, the ABS snubber exhibits a reduction in the total pressure loss coefficient by 0.11% and an increase in the mass flow rate by 0.41%. On the contrary, the implementation of the HSW snubber has the potential to mitigate parameter fluctuations. However, it is important to note that this comes at the cost of a 0.10% increase in the total pressure loss coefficient and a 0.20% decrease in mass flow rate. This article further examines the factors contributing to these disparities.
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Multi-Objective Optimization Method for Performance Prediction Loss Model of Centrifugal CompressorsJournal of Thermal Science. 2025, 34(2): 590-606. https://doi.org/10.1007/s11630-024-2081-2The selection of loss models has a significant effect on the one-dimensional mean streamline analysis for obtaining the performance of centrifugal compressors. In this study, a set of optimized loss models is proposed based on the classical loss models suggested by Aungier, Coppage, and Jansen. The proportions and variation laws of losses predicted by the three sets of models are discussed on the NASA Low-Speed-Centrifugal-Compressor (LSCC) under the mass flow of 22 kg/s to 36 kg/s. The results indicate that the weights of Skin friction loss, Diffusion loss, Disk friction loss, Clearance loss, Blade loading loss, Recirculation loss, and Vaneless diffuser loss are greater than 10%, which is dominant for performance prediction. Therefore, these losses are considered in the composition of new loss models. In addition, the multi-objective optimization method with the Genetic Algorithm (GA) is applied to the correction of loss coefficients to obtain the final optimization loss models. Compared with the experimental data, the maximum relative error of adiabatic the three classical models is 7.22%, while the maximum relative error calculated by optimized loss models is 1.22%, which is reduced by 6%. Similarly, compared with the original model, the maximum relative error of the total pressure ratio is also reduced. As a result, the present optimized models provide more reliable performance prediction in both tendency and accuracy than the classical loss models.
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Journal of Thermal Science. 2025, 34(2): 607-625. https://doi.org/10.1007/s11630-024-2060-7The influence of the hole length-to-diameter ratio on film-cooling performance is numerically investigated for a cylindrical hole and laidback fan-shaped hole with an inlet groove. Numerical analysis of film-cooling is conducted by solving three-dimensional Reynolds-averaged Navier-Stokes equations (RANS) with a Realizable k-ε turbulence model. Rectangular and triangular grooves are applied to the inlet of cylindrical and laidback fan-shaped holes. The ratio of the hole length (L) to the diameter (D), i.e., L/D, is varied between 6–12 at blowing ratios (M) of 0.5 to 1.5 for the cylindrical hole and 0.5 to 3.0 for the laidback fan-shaped hole. For cylindrical holes with an inlet groove, the film-cooling effectiveness decreases as the L/D increases, regardless of the blowing ratio. However, in the case of laidback fan-shaped holes, the cooling performance with the length-to-diameter ratios shows different tendencies for each blowing ratio. At low blowing ratios (M=1.0), relatively high effects were observed with more than 5% increases in the effectiveness at L/D=10 and 12 compared to that of L/D=6. However, the performance is maximized at L/D=8 under high-blowing-ratio conditions (M=3.0). The cooling efficiency is enhanced up to 148% for square grooves and 124% for triangle grooves compared to those of L/D=6.
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A Comparative Study of Purge Flow Aero-Thermal Performance under Pre-Swirl and Rotational ConditionsJournal of Thermal Science. 2025, 34(2): 626-638. https://doi.org/10.1007/s11630-025-2104-7Investigating the interaction between purge flow and main flow in gas turbines is crucial for optimizing thermal management, and enhancing aerodynamic efficiency. Measuring the high-speed rotating rotor poses challenges; however, employing the pre-swirl method to model rotational effect can facilitate experimental measurements. This study evaluates the validity of the pre-swirl method for modeling rotational effects. Numerical simulations are conducted under both stationary conditions, with seven swirl ratios, and rotational conditions. The investigation focuses on the underlying mechanisms of pre-swirl and rotation. Pre-swirl and rotation impart circumferential velocity to the purge flow relative to the blade, resulting in a diminishing effect on endwall cooling. On the other hand, pre-swirl reduces the adverse pressure gradient, and the rotation generates Coriolis forces acting on the passage vortex, both contribute to an increasing effect on endwall cooling. Under pre-swirl condition, the diminishing effect is dominant, while in rotational condition, neither the diminishing nor the increasing effect exhibits an overwhelmingly dominant trend.
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Journal of Thermal Science. 2025, 34(2): 639-652. https://doi.org/10.1007/s11630-025-2088-3Microwave-assisted ignition (MAI) is a promising technology to improve the ignition stability in internal combustion engines under lean conditions. To investigate the interplay between the microwave pulses and the electrical characteristics of ignition plasma, the high-time-resolved electrical characteristics of MAI are measured based on the discharge voltage and current profiles with microwave power varying from 0 to 1000 W. The effects of microwave pulse on the electrical characteristics in the breakdown and glow discharge phases are discussed respectively. The results show that the microwave-induced-voltage-decline (MIVD) occurs during the glow discharge phase, which originates from the increment of free electrons and the additional microwave field. However, this voltage decline is insignificant in the breakdown phase. Moreover, as the free electron number reaches a critical value, a shining plasma can be observed between the gap of electrodes and the voltage decline is stabilized to a “saturated voltage curve”. Ultimately, the effect of microwave plasma on the enhancement of ignition kernel area is explored. The result indicates that the enhancement effect increases with plasma duration rising. Those enhancements of earlier-generated plasmas are more significant than those of subsequent plasmas due to the distance limit of the plasma propulsive effect.
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Journal of Thermal Science. 2025, 34(2): 653-671. https://doi.org/10.1007/s11630-025-2021-9Preheating combustion/gasification technology enables efficient and environmentally friendly utilization of coal resources, but the research on the flow and reaction characteristics of high-temperature gas-solid mixed fuels produced by the technology still needs to be further explored. The flame can intuitively show the jet, mixing and reaction of fuel and oxidant at the outlet of the burner. Therefore, this study investigates the jet flame characteristics of high-temperature gas-solid mixed fuels on a self-designed test platform. High temperature and gas-solid mixing are the special features of the fuel in this study, which are different from other studies. Therefore, we first qualitatively compare the jet flame characteristics of high-temperature gas-solid mixed fuel with traditional fuel. The preliminary results indicate that high-temperature gas-solid mixed fuels exhibit higher reactivity and a faster reaction rate compared to pulverized coal. As a result, it shows different characteristics in flame shape, ignition delay and ignition mode. The jet flame shape of high-temperature gas-solid mixed fuels closely resembles that of the pulverized coal group combustion flame, displaying a continuous cloud-like structure similar to the shape of a gas-fueled flame. Furthermore, the flame image does not show any significant ignition delay phenomenon. Building upon these results, this study also quantitatively analyzes the geometric parameters, temperature distribution and oscillation frequency of the high-temperature gas-solid mixed fuel jet flame under different secondary air equivalence ratios and primary air equivalence ratios, so that we can have a deeper understanding of the influence of operating parameters on the combustion/gasification process.
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Journal of Thermal Science. 2025, 34(2): 672-688. https://doi.org/10.1007/s11630-025-2102-9Experimental and numerical investigations have been carried out on the effects of multi-swirl interaction patterns on self-excited unstable combustion characteristics based on a five-nozzle can combustor. The multi-swirl interaction patterns include equal swirl intensity interaction and strong-weak swirl interaction. The thermo-acoustic instability characteristics indicate that increasing the central nozzle swirl intensity transforms the interaction pattern from equal swirl intensity interaction to strong-weak swirl interaction, which can significantly weaken the thermo-acoustic coupling effect under low equivalence ratio conditions, and substantially reduce the dynamic pressure amplitude during unstable combustion. The instantaneous flame structures show that the multi-swirl flames exhibit chaotic oscillations under low equivalence ratio conditions. With equivalence ratios greater than 0.71, a clear flame interaction boundary appears, and the flames can exhibit periodic oscillations in a regular structure. However, different interaction patterns result in the completely different phase oscillations in the central and outer flames. The time-averaged flame structures also indicate that strong-weak swirl interaction leads to an increase in the flame angle and a decrease in the flame length for both the central and outer flames, and the variations in the flame angle and length have great impacts on the thermo-acoustic instability mode. The fuel-staging combustion characteristics demonstrate that the instability combustion conditions with a dominant frequency of 100 Hz are greatly broadened by the strong-weak swirl interaction pattern, and the overlapping operating conditions between this mode and other modes are greatly increased. This implies that it is more flexible to adjust the thermo-acoustic unstable mode, which is conducive to the passive suppression of thermo-acoustic instability.
