25 April 2025, Volume 34 Issue 3
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Journal of Thermal Science. 2025, 34(3): 689-706. https://doi.org/10.1007/s11630-025-2103-8Recent research and development on ramjet and supersonic combustion ramjet (scramjet) engines is concerned with producing greater thrust, higher speed, or lower emission. This is most likely driven by the fact that supersonic/hypersonic propulsion systems have a broad range of applications in military sectors. The performances of such supersonic/hypersonic propulsion systems depend on a series of physical and thermodynamic parameters, such as the fuel types, flight conditions, geometries and sizes of the engines, engine inlet pressure/velocity. As a propulsion system, a stable and efficient combustion is desirable. However, self-excited large-amplitude combustion oscillations (also known as combustion instabilities) have been observed in liquid- and solid-propellant ramjet and scramjet engines, which may be due to acoustic resonance between inlet and nozzle, vortex kinematics (large coherent structures), and acoustic-convective wave coupling mechanisms due to combustion. Such intensified pressure oscillations are undesirable, since they can lead to violent structural vibration, and overheating. How to enhance and predict the engines’ stability behaviors is another challenge for engine manufacturers. The present work surveys the research and development in ramjet combustion and combustion instabilities in ramjet engines. Typical active and passive controls of ramjet combustion instabilities are then reviewed. To support this review, a case study of combustion instability in solid-fueled ramjet is provided. The popular mode decomposition algorithms such as DMD (dynamic mode decomposition) and POD (proper orthogonal decomposition) are discussed and applied to shed lights on the ramjet combustion instability in the present case study.
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Journal of Thermal Science. 2025, 34(3): 707-719. https://doi.org/10.1007/s11630-025-2106-5In this study, we perform a numerical investigation of a steady laminar stagnation flow flame stabilized at a wall with the consideration of heat transport, focusing on a lean hydrogen/air mixture with a fuel/air equivalence ratio 0.6. We discuss the NO emissions and their formation rates under various conditions, such as flow velocity and combustion pressure. It is found that the predominant reaction pathway for NO formation involves NNH radicals, though this changes near the wall surface. Beyond examining the wall’s influence on flame structures, the present work focuses on the impact of combustion process on materials. Specifically, the accumulation of atomic hydrogen at the wall surface is explored, which is significant for the consequent modeling of potential hydrogen embrittlement. Additionally, the growth rate of oxide layers on the material surface increases significantly if the combustion pressure and consequently the combustion temperatures are enhanced. These investigations offer valuable insights into how combustion processes affect material, which is useful for designing engineering components under high-temperature environments.
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Journal of Thermal Science. 2025, 34(3): 720-737. https://doi.org/10.1007/s11630-025-2071-zThe inferior flammability of coal gasification fine slag (CGFS) from entrained-flow gasifiers hampers its resourceful utilization. However, the reasons behind its poor flammability still need to be investigated. This paper conducted a comparative study on the combustion characteristics of three CGFS samples: CGFSGSP, CGFSSN, and CGFSOMB (subscripts GSP, SN, and OMB representing different gasification processes), using experimental techniques such as TG/DTG and combustion kinetic model fitting methods. Additionally, a comprehensive investigation into the physicochemical properties of CGFS was conducted. The objective was to elucidate the causes behind the poor flammability of CGFS. The results revealed that CGFS exhibits lower volatile matter content and higher activation energy than their corresponding raw coal (RC), leading to a significantly higher ignition temperature. The ignition temperatures of RC1, RC2, and RC3 are 361.82°C, 378.66°C, and 404.99°C, respectively. In contrast, the ignition temperatures of CGFSGSP, CGFSSN, and CGFSOMB are 549.08°C, 566.58°C, and 532.67°C, respectively. During the combustion reaction, the temperature (Tmax) at which CGFS reaches its maximum weight loss rate is significantly higher than the temperature (TmaxIII) at which fixed carbon in raw coal reaches its maximum weight loss rate. The TmaxIII of RC1, RC2, and RC3 are 450.90°C, 457.19°C, and 452.77°C, respectively. In contrast, the Tmax of CGFSGSP, CGFSSN, and CGFSOMB are 583.55°C, 608.20°C, and 582.18°C, respectively. The maximum weight loss rate of different types of CGFS is also significantly lower than the fixed carbon combustion maximum weight loss rate of their respective raw coal samples. The physicochemical characterization results of CGFS demonstrate that, compared to the corresponding raw coal, there is a significant reduction in the proportion of active sites in CGFS. Simultaneously, the proportion of C-C/C-H on the surface of residual carbon in CGFS decreases. In contrast, the proportion of O=C-O significantly increases, suggesting a shift toward a more stable state of carbon-containing functional groups. This study is expected to offer essential theoretical support for the efficient combustion utilization of CGFS.
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Journal of Thermal Science. 2025, 34(3): 738-755. https://doi.org/10.1007/s11630-025-2126-1Digital twin is a cutting-edge technology in the energy industry, capable of predicting real-time operation data for equipment performance monitoring and operational optimization. However, methods for calibrating and fusing digital twin prediction with limited in-situ measured data are still lacking, especially for equipment involving complicated multiphase flow and chemical reactions like coal-fired boilers. In this work, using coal-fired boiler water wall temperature monitoring as an example, we propose a digital twin approach that reconstructs the water wall temperature distribution with high spatial resolution in real time and calibrates the reconstruction using in-situ water wall temperature data. The digital twin is established using the gappy proper orthogonal decomposition (POD) reduced-order model by fusing CFD solutions and measured data. The reconstruction accuracy of the digital twin was initially validated. And then, the minimum number of measured data sampling points required for precise reconstruction was investigated. An improved uniform data collection method was subsequently developed. After that, the computational time required for the digital twin and the traditional CFD was compared. Finally, the reconstruction method was further validated by in-situ measured temperature from the in-service boiler. Results indicate that the established digital twin can precisely reconstruct the water wall temperature in real time. Thirty-nine sampling points are sufficient to reconstruct the temperature distribution with the original data collection method. The proposed uniform data collection method further reduces the mean relative errors to less than 0.4% across four test cases, and with the constrained technique, the errors decrease to 0.374% and 0.345% for Cases 1 and 3, which had poor reconstructions using the original sampling point arrangement. In addition, the reconstruction time of the digital twin is also considerably reduced compared to CFD. Engineering application indicates that the reconstructed temperatures are highly consistent with in-situ measured data. The established water wall temperature digital twin is beneficial for water wall tube overheating detection and operation optimization.
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Journal of Thermal Science. 2025, 34(3): 756-770. https://doi.org/10.1007/s11630-025-2142-1This study delves into the theoretical exploration of the effects of injector and orifice arrangement, spray angle, and orifice size on combustion and emission characteristics of horizontal opposed two-stroke engines. By employing numerical simulations, the research systematically investigates how variations in these parameters influence engine performance and emissions. The findings underscore the significance of injector and orifice configuration in optimizing fuel spatial mixing and atomization, resulting in improved indicated thermal efficiency and indicated mean effective pressure. However, it is noted that while emissions of HC, Soot, and CO can be maintained at low levels by injector and orifice configuration, NOx emissions tend to be relatively higher. Moreover, the study highlights the impact of spray angle on combustion dynamics, where an optimum spray angle is identified for achieving peak thermal efficiency and effective pressure due to the improvement between spray distribution and impingement. Additionally, the study reveals the critical role of nozzle diameter in combustion and emissions control, with an optimal diameter leading to enhanced thermal efficiency and reduced emissions of Soot, HC, CO, and CO2 to some extent. Overall, these findings offer valuable insights into optimizing engine performance and emissions control strategies in horizontal opposed two-stroke engines, guiding future research and development efforts in the field.
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Journal of Thermal Science. 2025, 34(3): 771-779. https://doi.org/10.1007/s11630-025-2134-1This study quantitatively examines the impact of magnetic fields on methane flame characteristics, specifically analyzing changes in flame height, width, and velocity. Using flame photography and Particle Image Velocimetry (PIV), the effects of varying magnetic field strengths (ranging from 25 to 45 mT) on flame behavior were measured across equivalence ratios (φ) from 0.8 to 2.0. The results reveal that applying a magnetic field increases flame height by up to 6.75% while reducing flame width by approximately 6% under a field strength of 45 mT at φ=2.0. Additionally, PIV data demonstrate a significant increase in upward flame velocity, with an observed enhancement of 20% at higher magnetic field intensities. The gradient magnetic field was found to reduce flame distortion, leading to a smoother flame profile. Compared to the control group (M0, with no magnetic field), these findings confirm that magnetic fields can effectively adjust flame properties. This study underscores the potential of magnetic fields in optimizing combustion processes.
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Journal of Thermal Science. 2025, 34(3): 780-788. https://doi.org/10.1007/s11630-025-2133-2Soot nanoparticles produced during combustion exhibit diverse nanostructures, which are affected by different combustion parameters such as flame stoichiometry and temperature. This work focuses on characterizing RP-3 jet flame properties and exploring the intricate relationship between the effect of temperature and carbon formation. The observed flame length displayed a notable increase in proportion to the equivalence ratio’s growth. The flame color underwent a great transformation, evolving from pale blue in fuel-lean conditions to bright green at stoichiometric levels, and to brilliant yellow under fuel-rich conditions. Through systematic sampling and thorough observation of soot morphology at different flame heights, there is a clear correlation between the height of the flame and the acceleration of carbon agglomerate growth. Furthermore, an insightful observation is presented wherein the rise in flame height leads to a gradual reduction in the contribution of surface growth to the overall soot particle size. These findings contribute significantly to the understanding of the complex interplay between combustion conditions and soot nanostructures. The trends in flame characteristics, coupled with insights into soot morphology, provide a foundation for comprehending the underlying mechanisms governing soot formation in RP-3 flames. These results contribute to the understanding of combustion dynamics, offering valuable perspectives for optimizing combustion processes and elucidating the environmental implications of flame-formed soot.
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Journal of Thermal Science. 2025, 34(3): 789-800. https://doi.org/10.1007/s11630-025-2131-4This paper investigated the smoke exhaustion characteristics and critical shaft height in a slope tunnel with naturally ventilated shafts based on reduced-scale tunnel experiments. The effects of longitudinal fire location, shaft setting, heat release rate (HRR) and tunnel slope on smoke exhaustion were studied. Experimental results show that the slope has great effect on smoke exhaustion. Moreover, the critical shaft height for complete smoke exhaustion of slope tunnels was studied theoretically and experimentally. The research indicates that the critical shaft height exhibits no dependency on the HRR. Notably, with the increasing of shaft length, the critical shaft height firstly decreases and then remains stable until it finally decreases to zero. Simultaneously, the critical shaft height increases with the increase of the slope and the distance between the shaft and the fire source. In addition, a theoretical model for predicting the critical shaft height was established and verified. The research results can provide some reference for the design of natural ventilation smoke exhaustion with shafts in slope tunnels.
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Journal of Thermal Science. 2025, 34(3): 801-818. https://doi.org/10.1007/s11630-025-2111-8In this study, a three-dimensional numerical investigation was conducted on the front and rear fans of a three-bypass variable cycle engine under various speeds and internal bypass conditions. The impact of internal bypass conditions and speeds on the matching characteristics of the front and rear fans, as well as the factors limiting the variation of bypass ratio, are summarized. The findings reveal that for near stall, design point, and near choke internal bypass conditions, the operating point of the front fan tends to move towards near-stall while that of the rear fan moves towards near-choke when increasing external bypass back pressure. At design speed, external bypass blockage is identified as a limiting factor for increasing the bypass ratio at the internal bypass design point. Additionally, blockage caused by a significant amount of low-energy fluid at the suction surface of the rear fan stator leads to rear fan stall which limits further increase in bypass ratio at external bypass near stall condition. Similarly, leakage flow overflow passage at the top section of first stage rotor blade in front fan results in front fan stall, which restricts decrease in bypass ratio at internal bypass near stall condition. As corrected speed decreases, there is an upper-left shift observed in the curve depicting variation in relative back pressure with respect to change in bypass ratio due to the phenomenon “pre-surge and post-choke”. This indicates increased air flow into external bypass resulting in higher values for lower speeds. Furthermore, limitation on further increase in bypass ratio at external bypass near stall condition with decreasing speed can be attributed to transition from rear fan stall to external bypass blockage.
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Journal of Thermal Science. 2025, 34(3): 819-833. https://doi.org/10.1007/s11630-025-2026-4As one of the hottest components of gas turbine, the blade tip is difficult to be cooled down for the complexity flow field in the tight tip clearance. The blade tip protection requires advanced tip structures. To develop new structures, the effect of ribs on blade squealer tip aerothermal performance and cooling performance were investigated. Ribbed squealers tips (1R, 2R and 3R, compared to the Basic case) were designed and their cooling ability under five coolant blowing ratios (M) were measured by the Pressure Sensitive Paint (PSP) technique, taking film cooling effectiveness (η) as the criterion. Numerical method was validated and then was adopted to analyze the flow field and aerodynamic loss in the tip gap. The results indicated that the cooling coverage and η increase with M for sufficient coolant supply. Compared to the Basic case, the η on the middle section is higher while that on the trailing part is lower for the ribbed squealer tips. The flow field analysis showed that the coolant flows downstream to the trailing edge in the Basic case, bringing additional cooling protect to the downstream region. The ribs induce vortices behind them to involve the local and upstream coolant and prevent upstream coolant from flowing down, leading to the improvement in the local and the degradation in the downstream for the film cooling performance. The aerodynamic results pointed out that the ribbed squealer tips are superior to the Basic case in terms of the aerodynamic performance, even though the tip leakage mass flow of these cases are larger than that of the Basic case. The maximum reduction on pressure loss coefficient is 16.2% for the ribbed squealer tip.
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Journal of Thermal Science. 2025, 34(3): 834-849. https://doi.org/10.1007/s11630-025-2024-6This paper investigates the film cooling characteristics and flow structure of trailing edge cutback in turbine vanes, and explains the unsteady flow mixing mechanism of this cooling structure using Proper Orthogonal Decomposition (POD) method. The Delayed Detached Eddy Simulation (DDES) turbulence model was used to obtain detailed information about the velocity and temperature field for the POD method. To verify the accuracy of the numerical results, fast-response Pressure Sensitive Paint (PSP) and high-frequency Particle Image Velocimetry (PIV) experiments were also conducted, and the results achieved good agreement. As the blowing ratio increases, the effectiveness η of the cutback’s film cooling exhibits a “increase-decrease-increase” trend, with η reaching its minimum point at around a blowing ratio (Mslot) of 0.75. Three kinds of coherent vortex structures are observed in the flow field at different blowing ratios. According to the analysis using the POD method, the first and second order modes of a Karman-like vortex street are observed in the vicinity of the wall at various blowing ratios. This coherent flow structure is directly related to the mixing intensity between the mainstream gas and the coolant. At Mslot=0.75, these modes had the highest energy ratio and formed a stable dominant coherent structure in the flow field. As the blowing ratio increases, the main characteristic modes in the temperature field gradually change, and the mode appears crescent-shaped when the effectiveness of film cooling is at its lowest. This paper combines the vortex structure of the flow field to explain the flow field feature distribution at the lowest effectiveness point η and analyzes its impact on the film cooling characteristics of the protected surface.
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Journal of Thermal Science. 2025, 34(3): 850-879. https://doi.org/10.1007/s11630-025-2100-yThe absorption cycle is a promising technology for harnessing low-temperature heat, playing a crucial role in achieving the objectives of carbon peaking and carbon neutrality. As a significant element in distributed energy systems, the absorption cycle can utilize various types of low-grade heat to fulfill cooling, heating, and electrical energy demands. Therefore, it can be employed in diverse settings to unleash its substantial energy-saving potential. However, the widespread adoption of the absorption cycle is limited to specific scenarios. Hence, further efforts are needed to enhance its technological maturity, gain societal acceptance, and expand its application scope. Focusing on the utilization of different low-grade heat, this paper provides an overview of significant advancements in the application research of various absorption cycles, such as the absorption refrigeration cycle, absorption heat pump, absorption heat transformer, and the absorption power cycle. According to current research, absorption cycles play a critical role in energy conservation and reducing carbon dioxide emissions. They can be applied to waste heat recovery, heating, drying, energy storage, seawater desalination, refrigeration, dehumidification, and power generation, leading to substantial economic benefits. The paper also outlines the primary challenges in the current application of the absorption cycle and discusses its future development direction. Ultimately, this paper serves as a reference for the application research of the absorption cycle and aims to maximize its potential in achieving global carbon neutrality.
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Journal of Thermal Science. 2025, 34(3): 880-898. https://doi.org/10.1007/s11630-025-2034-4The Maisotsenko gas turbine cycle (MGTC), integrated with a combined aftercooling and regenerative saturator, has the potential to challenge traditional wet air turbine cycles. However, its large water consumption limits its applicability. By integrating an intercooler and Organic Rankine Cycle (ORC) into the MGTC, this study proposes a comprehensive design of IMGT-ORC, which can adjust the water capacity of the saturator, and utilize the sensible heat of cooling water and the latent heat of evaporation in exhaust gas to achieve water and energy saving. Firstly, a sensitivity analysis was conducted to investigate the effects of various parameter variations on thermodynamic and economic indicators under different temperature drop ratios. Subsequently, a multi-objective optimization approach was employed to seek for an optimal balance between economic and environmental benefits. The results showed that either the intercooler or ORC integration can improve the thermal efficiency of the system. In the case of joint setting, the thermal efficiency is relatively increased by 6.89% and the water consumption is relatively reduced by 89.07%. Moreover, although high temperature drop ratio reduces the output of ORC, it enhances the energy efficiency of the top cycle. In terms of cost control, ORC integration may increase the levelized cost of electricity (LCOE) slightly, while the intercooler integration helps offset the increase. Finally, the optimization results show that using the optimal parameter combination can reduce the annual equivalent carbon dioxide emissions by 11 600 tons and the annual water consumption of the power plant by 251 027 tons.
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Journal of Thermal Science. 2025, 34(3): 899-912. https://doi.org/10.1007/s11630-025-2138-xSolar radiation and operation condition greatly influence solar aided coal-fired power generation (SACFPG) system. Based on a SACFPG system with its operating strategy considering both different direct normal insolation (DNI) and off-design load, a comprehensive criterion based on gray relation analysis considering the economic, thermal and environmental performance is proposed and used to evaluate of the annual performance of SACFPG system with/without storage under various policy conditions. It is found that solar subsidy, carbon tax, fuel price and the size of the solar field influence system’s performance greatly. The results show that the initial investment of a SACFPG system is higher and the dynamic payback period is longer, but the addition of solar energy makes the total thermal efficiency higher and the environmental performance better. Specifically, the SACFPG system with storage has the highest thermal efficiency of 44.38% and the lowest CO2 emissions of 0.1114 kg/kWh. Under polices of solar subsidy and carbon tax, the economic performance is remedied. Therefore, according to the proposed comprehensive evaluation criteria, SACFPG system with storage is the highest at 0.667, followed by coal-fired plant and SACFPG without storage is the worst. With the development of technology, the costs of SACFPG systems would be lower, and the future of SACFPG is even brighter.
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Journal of Thermal Science. 2025, 34(3): 913-935. https://doi.org/10.1007/s11630-025-2118-1In this paper, a new multi-generation system, incorporating solid oxide fuel cell (SOFC), gas turbine (GT), lithium bromide chiller, gas and heat storage components is proposed to address the issues of volatility in user load and energy source input and mismatching between supply and demand. The dynamic model and control strategy of the system are established, and the system dynamic characteristics in response to solar DNI and external load disturbances are studied. The system can rapidly adjust the key output and input parameters to realize a new supply-demand balance in a shorter period of time by multiple PID control methods. The response processes of two combined cooling, heating and power (CCHP) systems with and without gas storage to cope with load changes are compared. The results show that the CCHP system with gas storage can effectively shorten the response time of load following. The solar collector and the SOFC-GT can reach a new equilibrium within a few tens of seconds under the controller. The response time of the methanol reactor is longer compared to those of solar collector and the SOFC-GT, taking several minutes to stabilize. When the cooling and heating load change, the system can adjust the output to the demand value within 500 and 260 seconds.
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Journal of Thermal Science. 2025, 34(3): 936-952. https://doi.org/10.1007/s11630-025-2085-6The application of multi-energy hybrid power systems is conducive to tackling global warming and the low-carbon transition of the power system. A capacity allocation model of a multi-energy hybrid power system including wind power, solar power, energy storage, and thermal power was developed in this study. The evaluation index was defined as the objective function, formulated by normalizing the output fluctuation, economic cost, and carbon dioxide emissions. Calculations under different initial conditions and output electric power scenarios were carried out with genetic algorithm. The capacity allocation model was validated with the literature results, with errors of less than 5%. Results indicate that the capacity allocation modes of the multi-energy hybrid power system can be divided into thermal power dominated mode, multi-energy complementary mode, and renewable power dominated mode. In addition, the division of capacity allocation modes is not affected by the weather conditions and energy storage ratio. The capacity factor decreases from 0.4 to 0.24 as the power system changes from the thermal power dominated mode to the renewable power dominated mode. When the output electric power is 240 MW, 300 MW, and 340 MW, the optimal energy storage ratio is 10%, 18%, and 16%, respectively. The model developed in this study not only enriches the theory of multi-energy complementary power generation but also guides the engineering design of the wind-photovoltaics-thermal-storage system targeting smart grid and be beneficial for the middle-long-term planning of the green and low-carbon transition of the power system.
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Journal of Thermal Science. 2025, 34(3): 953-969. https://doi.org/10.1007/s11630-025-2109-2The next-generation heating systems, crucial for rational heat distribution and refined management, rely heavily on accurate zone-specific heat load predictions. This paper introduces a method for rapid zone-specific heat load prediction based on heat consumption allocation and data-driven techniques. The approach involves predicting the overall heat load of the building and then redistributing the total heat according to a heat consumption matrix. This eliminates the need for real-time data collection from each room, resulting in cost savings on hardware and improved computational efficiency. The overall building heat load data is obtained through a data-driven algorithm, while the heat consumption matrix is constructed through energy software simulation analysis. Using Building 2 in the Baotou Industrial Park, China, as a case study, the paper analyzes the differences between actual measurements and room estimates. Experimental results indicate an average error of 7.02% for the proposed estimation method. Although not achieving high precision (>95%) in heat load prediction, this level of accuracy is deemed sufficient to meet the requirements of feedforward control.
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Journal of Thermal Science. 2025, 34(3): 970-981. https://doi.org/10.1007/s11630-025-2115-4Cold sintering as a new technology for the fabrication of ceramic composites could overcome the shortcomings of traditional high temperature sintering approach and achieve dense structure in the composite at a relatively low temperature (<200°C). In this work, a shape stabilization phase change composite is fabricated and investigated by dint of such new fabrication approach, in which a mixed nitrate salt of NaNO3-KNO3 is used as phase change material and magnesia powder is acted as structure skeleton. Using of deionized water as sintering additive, the effects of sintering agent content, sintering temperature, uniaxial pressure and time on the composite microstructure characteristics and macroscopic properties are evaluated. The results show that the liquid salt could be effectively accommodated in the magnesia skeleton, forming a dense and stable structure in the composite. There is existence of optimal cold sintering parameters at which a benign combination of mechanical strength and thermal cycling performance could be attained in the composite. Under the sintering temperature of 150°C, duration time of 8 min, uniaxial pressure of 150 MPa, and water mass content of 7%, the fabricated composite exhibits a heat storage density of 610 kJ/kg at its potential utilization temperature range of 30°C–580°C and a compressive strength over 240 MPa with a dense density higher than 98%, demonstrating that it can be a viable alternative used in thermal energy storage domains.
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Journal of Thermal Science. 2025, 34(3): 982-995. https://doi.org/10.1007/s11630-025-2145-yIn this study, the influence of the phase-change cooling storage system on integrating and controlling of the combined cooling, heating, and power system was analyzed through experiments and computational fluid dynamics simulations. The model of three-dimensional phase change material plate and cold storage tank was established and verified. The phase change material selected in this study is a eutectic salt with a phase change temperature of 8°C. The thermodynamic performance of the cold storage tank filled with phase change material plates was calculated, and the energy storage and release efficiency of the phase-change cooling storage system was analyzed. The results indicate that the phase change process correlates positively with the heat transfer fluid flow rate. The heat transfer fluid flow rates of 1.2 m3/h, 1.6 m3/h, and 2.0 m3/h all allow the phase change material within the encapsulation module to completely solidify within 8 hours; the flow rate required for melting is not less than 2.0 m3/h, and the highest energy storage efficiency is up to 72%. Considering the thermodynamic performance of the phase-change cooling storage system, it is recommended to use a heat transfer fluid flow rate of 1.6 m3/h for the cooling charge process and 2.0 m3/h for the cooling release process.
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Journal of Thermal Science. 2025, 34(3): 996-1007. https://doi.org/10.1007/s11630-025-2144-zAl/Al2O3 is crucial encapsulation composites used in solar thermal storage systems. Al/Al2O3 composites with varying SiO2 and MgO contents were prepared using Al powder and Al2O3 powder as raw materials, with SiO2 and MgO as sintering aids, through a cold-press sintering method. The latent heat, thermal conductivity, and bending strength of the composites were measured. The microstructure of the composites and their compatibility with Al-Si (88%-12% in weight) alloy were observed and analyzed. The relationship between thermal properties, mechanical properties, compatibility, and microstructure was investigated. The results show that as the SiO2 content increases and the MgO content decreases, the comprehensive performance of the composites first improves and then decreases. The composites exhibit the best comprehensive performance when the mass contents of SiO2 and MgO are both 1%, with a bending strength of 79.645 MPa, thermal conductivity of 23.903 W/(m·K), and a latent heat of 93.61 J/g. In the compatibility experiment, as the number of thermal cycles increases, the diffusion distance of Si atoms in the composite first increases and then stabilizes, maintaining a distance of approximately 150 µm, indicating good compatibility.
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Journal of Thermal Science. 2025, 34(3): 1008-1036. https://doi.org/10.1007/s11630-025-2078-5Tunnels in high geothermal and water-rich areas usually encounter thermal damage and water seepage problems during the tunnel construction period. Understanding the interaction between seepage and heat transfer in the surrounding rock of the tunnel is an important prerequisite for safe tunnel construction and environmental protection. This study established the tunnelling fractured rock models by using the discrete fracture network method and numerically explored the effects of geometric characteristics of fracture network and geological factors on the hydrothermal field of the rock. By designing orthogonal experiments and analyzing orthogonal cases, the changes of rock equivalent thermal conductivity (ETC) under the combined action of multiple factors were investigated. The priority of each influencing factor on ETC is in the following order: fracture inclination, fracture intensity, water temperature, water head, fracture roughness and fracture aperture. The weighted contribution rates of each factor to the ETC are 30.6%, 24%, 18.5%, 15.5%, 6% and 5.3%, respectively. Finally, a formula including all factors to determine the equivalent thermal conductivity was proposed. The results of this study can provide reference and guidance for quantifying surrounding rock heat transfer during the construction period of high geothermal tunnels.
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Journal of Thermal Science. 2025, 34(3): 1037-1059. https://doi.org/10.1007/s11630-025-2121-6Advancements in high-temperature heat pump technology are pivotal for achieving global carbon neutrality goals, with the working fluid’s heat transfer and flow properties being crucial for efficient condenser design. Nevertheless, research on high-temperature condensation of organic fluids is sparse, necessitating the development of accurate correlations for heat transfer and flow characteristics. This study emphasizes experimental research on R245fa’s condensation heat transfer and pressure drop within a 40°C–110°C saturation temperature range inside a plain tube with a 9-mm internal diameter. Sensitivity analysis highlighted the differences in condensation characteristics between high and low temperatures, and influencing mechanisms are revealed. Then, the measured data are employed to assess the accuracy of previous correlations. Based on the importance factor analysis result, adjustments are made to Reynolds number and flow regime boundaries. Finally, the correlations incorporating high temperature condensation of R245fa are developed, yielding a decrease in deviation from 17.6% to 7.23% for heat transfer and from 15.1% to 7.51% for frictional pressure drop gradient. Utilizing the newly developed models, 877 data points across 14 working fluids are predicted, results in a decrease in deviation from 18.85% to 10.65% for heat transfer coefficient, indicating a significant improvement in both accuracy and generality of the developed correlations.
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Journal of Thermal Science. 2025, 34(3): 1060-1072. https://doi.org/10.1007/s11630-025-2129-yHigh-level water-collecting natural-draft wet cooling towers (HNDWCTs) are commonly employed in super-large thermal and nuclear power units. However, research on the effects of crosswinds is still in the exploratory stage. This paper focuses on the fill packing zone and investigates the influence of various crosswind speeds (ranging from 1 m/s to 18 m/s) on convective and evaporation heat transfer processes in the cooling tower. The results indicate that evaporation heat transfer contributes 90% of the total, asserting a predominant role in the thermal performance of the cooling towers. Therefore, this study examines the impact of crosswinds on evaporation mass transfer in HNDWCTs. It has been observed that the “self-reflux” in high humidity region under low wind speeds is the root cause of generating low mass transfer driving force region. As wind speed exceeds 9 m/s, the “high-humidity reflux” transitions to “low-humidity reflux”, which makes the local mass transfer driving force rise back up, and helps to promote the evaporation mass transfer process. This transition mitigates the negative impact of crosswinds, resulting in the stabilization of the evaporation mass transfer and heat exchange reduction at approximately 60%.
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Journal of Thermal Science. 2025, 34(3): 1073-1090. https://doi.org/10.1007/s11630-025-2127-0The heat transfer characteristics of supercritical carbon dioxide (SCO2) based on natural circulation loop (NCL) are investigated experimentally. A comprehensive analysis is conducted on the impact of single-factor variations in inlet temperature, heat flux, operating pressure, and mass flux on the heat transfer characteristics of SCO2. The results indicate that heat transfer deterioration (HTD) more easily occurs when the inlet temperature exceeds the pseudo-critical temperature. Moreover, the peak of deterioration shifts upstream in the heated section with the increase of heat flux. The inner wall temperature rises with an increase in operating pressure, while it falls with the increase of mass flux. Through an exhaustive analysis of the buoyancy parameter Bo*, it is deduced that buoyancy effect exerts a pivotal influence on the heat transfer process. An improved buoyancy parameter is proposed, enabling precise anticipation of variations in heat transfer coefficients under both normal and deteriorated heat transfer scenarios. Based on experimental data, a novel heat transfer correlation suitable for SCO2 heat transfer in natural circulation is proposed. This new correlation exhibits a more satisfactory predictive accuracy compared to previous correlations; 98.31% and 76.58% of the new correlation predictions under normal heat transfer (NHT) and HTD are within ±20% error range. The research results have significant guiding implications for theoretical research and prediction correlation of HTD phenomenon. This establishes the theoretical groundwork for the implementation of SCO2 natural circulation in Fourth Generation Nuclear Reactors.
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Journal of Thermal Science. 2025, 34(3): 1091-1116. https://doi.org/10.1007/s11630-025-2135-0The mined-out areas formed by ore extraction have promoted the development of seasonal energy storage technology in underground spaces. Currently, most studies on the heat storage/release performance of backfills with embedded heat exchange pipes have idealized the operating conditions, such as constant fluid inlet temperature and flow rate. However, actual operating conditions are influenced by many factors like weather conditions, surface equipment, and heat load fluctuations, making them unstable. Therefore, this paper constructs a solar-assisted heat pump coupled mine backfill body heat storage system (SAHP-MBBHSs) based on TRNSYS simulation software and verifies the accuracy of the backfill heat exchangers (BFHEs) model through experiments. Considering the influence of various external factors on the operating conditions, we investigated the long-term seasonal heat storage/release performance of the BFHEs, focusing on the effects of solar collector area, U-tube spacing, thermal conductivity of backfill materials, and heat storage start/stop time. The results show that reducing the U-tube spacing increases the fluctuation amplitude of the average temperature of the backfill body, with the maximum average fluctuation amplitude difference reaching 16.6°C between the 11th and 15th years. Delaying the onset of thermal storage reduces the storage effectiveness of the U-BFHEs, while increasing the heat release effectiveness. During the thermal storage/release interval, heat loss to the surrounding rock does not exceed 4.7%, with the minimal overall impact. The thermal conductivity of the backfill body has the greatest effect on the heat transfer effectiveness of U-BFHEs, increasing from 1 W·m–1·K–1 to 2 W·m–1·K–1 resulting in respective increases of 58.8% and 39.2% in the heat transfer effectiveness during the 15th year of thermal storage/release. The total heat storage-release effectiveness of the U-BFHEs does not exceed 43.7%, indicating significant room for improvement. Utilizing seasonal thermal storage in the backfill body can effectively enhance the heating performance of SAHP-MBBHSs, with the maximum average APF and HSPF values reaching 3.85 and 5.43, respectively, during the 11th–15th years of operation, maintaining high efficiency even after long-term operation.
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Journal of Thermal Science. 2025, 34(3): 1117-1128. https://doi.org/10.1007/s11630-025-2105-6Traditional salt solutions, due to their susceptibility to crystallization and corrosion, can be replaced by ionic liquids (ILs) to enhance the effectiveness of liquid desiccant dehumidification systems. This study proposes integrating a transcritical-carbon-dioxide heat pump (TCHP) with an IL dehumidification cycle, thereby providing both cooling and heating for IL under large temperature differentials. Thermodynamic analysis is conducted to investigate the influence of key design parameters. The findings reveal that the TCHP is capable of handling the significant temperature rise during IL regeneration. The evaporation temperature is the key factor for matching the supply and demand of cooling and heating in the system. The self-circulation ratio of the solution is limited by the regeneration temperature. When the initial air humidity ratio is 8.0 g/kg and the supply air humidity ratio is 1.0 g/kg, the proposed system’s total heat COP is 31.9% higher than that of the reference systems.
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Journal of Thermal Science. 2025, 34(3): 1129-1147. https://doi.org/10.1007/s11630-025-2146-xThe rapid expansion of data centers has significantly increased energy consumption, with cooling systems accounting for about 40% of total use. Utilizing natural ambient cooling sources provides a simple and effective approach to enhancing energy efficiency. Radiative cooling (RC), though an emerging solution that can considerably reduce energy use, faces challenges in data centers due to the complex, multi-level nature of cooling systems, requiring careful adaptation across different scales, which hinders its widespread adoption in data centers. In this study, we designed radiative coolers for data center cooling systems to enhance efficiency, and then proposed an RC system integrating these structures and analyzed its energy-saving performance. The cooling properties of a real radiative cooling film applied to the cooler surface were experimentally tested, and the data were used for the simulation analysis of the proposed coolers. Five different radiative cooler structures were designed and optimized, and we conducted a comprehensive multi-level performance analysis of the optimized structures, including operational parameters such as flow rate and temperature, as well as the impact of location, climate, and regional adaptability. Subsequently, a novel hybrid cooling system incorporating radiative coolers for data centers was proposed. Comparative studies across different climate zones in China demonstrated that this hybrid system delivers substantial energy savings compared to traditional vapor-compression systems. Results showed that in Beijing, Urumqi, and Guangzhou, the annual temperature difference between the inlet and outlet of the radiative cooler ranges from 2.40°C to 3.28°C, making it feasible for radiative cooling throughout the year in most parts of China. The annual Power Usage Effectiveness (PUE) in Beijing using the novel RC system is 1.19, with an increase in Energy Efficiency Ratio (EER) of 60.74%. This study may contribute to the development of green, energy-efficient cooling technologies for future data centers.
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Journal of Thermal Science. 2025, 34(3): 1148. https://doi.org/10.1007/s11630-024-2095-9
