26 June 2025, Volume 34 Issue 4
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Journal of Thermal Science. 2025, 34(4): 1149-1161. https://doi.org/10.1007/s11630-025-2159-5The modification with dark metallic oxide is identified as the crucial strategy to enhance optical absorptions of calcium-based materials for the direct solar-driven thermochemical energy storage. The effect of modification on the heat release behavior in carbonation of calcium-based material has been widely investigated, but its effect on the heat storage behavior in calcination is lacking of sufficient research, typically for low-cost calcium resource such as carbide slag. The Fe-modified and Mn-modified carbide slags for CaCO3/CaO heat storage were synthesized and their optimum decomposition temperatures, effective heat storage conversions, heat flows and heat storage rates in endothermic stage were investigated. Although the Fe modification exacerbates the CaO sintering due to the formation of Ca2Fe2O5, that is still effective in reducing the regeneration temperature of CaO in CaCO3/CaO cycles. The Mn modification enhances significantly sintering resistance by forming the CaMnO3 and its transformation into Ca2MnO4. The effective heat storage conversion of Mn-modified carbide slag after 30 cycles is 3.2 times as high as that of untreated carbide slag. Mn-modified carbide slag exhibits the lowest regeneration temperature and the highest heat storage rate after cycles. The loose and stable porous structure of Mn-modified carbide slag contributes to its superior endothermic performance. Therefore, Mn-modified carbide slag seems to be the potential candidate for calcium looping thermochemical heat storage.
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Journal of Thermal Science. 2025, 34(4): 1162-1176. https://doi.org/10.1007/s11630-025-2172-8Thermal storage is a key technology in concentrating solar thermal power (CSP) system, which can provide continuous and stable high quality electricity, improve the efficiency of the power system and extend the system life. Molten salt is an important material for heat storage and heat transfer in solar thermal power generation, the addition of nanoparticles can synergistically and effectively enhance both specific heat capacity and thermal conductivity. In this study, a base salt with mass percentage of 31.5% Na2CO3-31.5% Li2CO3-37% K2CO3 was employed. SiO2 nanoparticles with varying particle sizes, different concentrations of SiO2 and Al2O3, as well as composite nanoparticles, were dispersed in a salt solution to create ternary carbonate nanofluids using a two-step solution method. The melting point, specific heat capacity, crystal structure, and surface microstructure of nanofluids were measured using a differential scanning calorimeter, X-ray diffractometer and scanning electron microscope, respectively. The results show that among the selected nanoparticles, SiO2 nanoparticles are the most effective at enhancing the specific heat capacity and thermal conductivity of the ternary carbonates. The mass addition of 1.0% of 30 nm SiO2 results in 83.5% increase in specific heat capacity in the solid phase and 159.4% increase in the liquid phase compared to pure ternary carbonates, and the thermal conductivity increases by 20.8%. Meanwhile, scanning electron microscopy has revealed the formation of rod-like nanostructures after adding nanoparticles to ternary carbonates. XRD results confirm that there are no chemical reactions between ternary carbonates and the added nanoparticles. After exposure to a constant high temperature of 600°C for 100 h and undergoing 100 cycles of large temperature differences (ranging from room temperature to 600°C), the thermophysical properties of this composite material remain relatively stable, demonstrating good long-term and heating-cooling cycle thermal stability.
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Journal of Thermal Science. 2025, 34(4): 1177-1191. https://doi.org/10.1007/s11630-025-2179-1Air source heat pump has insufficient heating performance under the low ambient temperature conditions; meanwhile, the thermal storage device in heat pump system has a wide range of application. This study proposes a thermal storage air source heat pump heating system (HSASHP) with a novel structure, and has established both the mathematical models and simulation models of each component of the single-stage and the thermal storage air source heat pump heating systems in MATLAB/Simulink respectively, with three operation modes proposed for the latter (i.e., the thermal storage air source heat pump heating system); by using the outdoor ambient temperature during the heating period in Baotou, China, the heating capacity of the two heat pump systems are simulated and the economy of both systems’ operation are investigated. The results show that within a 7-day heating period, the total heat production of the thermal storage heat pump unit and the single-stage heat pump unit is 442.58 kW·h and 355.68 kW·h, respectively, with HSASHP 24% higher; the average heating Coefficient of Performance (COP) of the two heat pump units is 2.11 and 1.51, respectively, with HSASHP 39.74% higher; the power consumption of the two heat pump units is 202.74 kW·h and 239.74 kW·h, respectively, with HSASHP 15.44% lower. These all illustrate the effectiveness of the new structure in improving the performance of heat pump units. However, the total power consumption and operational economy of both air source heat pump heating systems do not differ significantly.
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Journal of Thermal Science. 2025, 34(4): 1192-1210. https://doi.org/10.1007/s11630-025-2185-3Latent heat storage technology plays a critical role in storing and utilizing geothermal energy. By combining cascaded phase change materials (PCM) with mine filling technologies, mine geothermal energy can be stored thermally more effectively. Therefore, this paper designed a physical model of double casing cascaded latent heat storage (CLHS) system in mine. Paraffin RT28 and RT35 were encapsulated in annular gap 1 and annular gap 2, respectively, and this backfill mode was defined as Case 1. The scheme whose backfill sequences of the two PCM were exchanged is defined as Case 2. The heat transfer process of backfill body and PCM was simulated and analyzed by using FLUENT software, and compared with the single stage latent heat storage process. The temperature, liquid fraction (LF), heat transfer capacity, and heat transfer rate were used to evaluate the thermal properties of the CLHS process. It was necessary to study the effect of the filling sequence of PCMs on the heat storage and release process of the backfill body using these results as a starting point. The results show that the main factor affecting latent heat storage in cascaded system is the heat transfer of surrounding rock. Compared with the single-stage heat storage process, the heat storage time of cascaded heat storage process is reduced by 73 min, which is significantly decreased by 20.9%. Moreover, the whole liquid phase fraction (β) of the single-stage has little change during the heat release, while the PCM of the cascaded heat release process can fully release the latent heat. In terms of layout order of PCM, compared with Case 1, the latent heat storage time of Case 2 is increased by about 40 min, and the heat release rate (εs) is significantly lower than that of Case 1. In the initial heat release stage, the heat release rate of Case 2 reaches 95.6 W, which is 30.6% lower than that of Case 1. In comparison, the heat storage and release effect of Case 1 is better than that of Case 2. This paper provides a reference for the improvement of heat storage and release rate of the backfill coupled cascaded latent heat storage system (BCCLHS).
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Journal of Thermal Science. 2025, 34(4): 1211-1222. https://doi.org/10.1007/s11630-025-2167-5The improvement of composite phase change materials in energy storage density and thermal conductivity is significant for the efficient use of energy. This study proposed novel composite materials based on forsterite with high specific heat as matrix materials, chloride salts (NaCl-KCl) with high latent heat as phase change materials and SiO2 nanoparticles as fillers. The results indicated that forsterite and chloride salts exhibited excellent chemical compatibility, and the composite materials containing 40% (in weight) chloride salts achieved an energy storage density of 882.5 J/g within the range of 100°C to 800°C, a latent heat of 108.1 J/g, and a thermal conductivity of 0.68–0.81 W/(m·K) at 300°C–500°C. Furthermore, the addition of SiO2 enhanced the thermal conductivity and energy storage density of composite materials due to the formation of unique nanostructures. More importantly, the removal of structural water during heat-treatment process resulted in the formation of micropores and increased specific surface area of forsterite particles, which facilitated the adsorption and stabilization of molten chloride salts. Combined with the stabilization effect of forsterite and synergistic effect of SiO2 nanoparticles, the obtained composite materials with 2.0% (in weight) SiO2 nanoparticles exhibited good thermal stability with 1.80% weight loss and 2.34% reduction in latent heat after 150 cycles, indicating a promising application in high-temperature thermal energy storage.
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Journal of Thermal Science. 2025, 34(4): 1223-1240. https://doi.org/10.1007/s11630-025-2182-6As the total amount and share of new energy installed capacity continue to rise, the demand for flexible regulation capability of the power system is becoming more and more prominent. The current conventional molten salt energy storage system has insufficient peaking capacity. A solar-molten salt energy storage system based on multiple heat sources is constructed in this study. The heat generated from the solar field and the steams are used for the peaking process to further enhance the peaking capacity and flexibility. The installation multi-stage steam extraction and the introduction of an external heat source significantly improve the system performance. The simulation models based on EBSILON software are developed and the effects of key parameters on performance are discussed. The feasibility of the proposed system is further evaluated in terms of exergy and economy. The results demonstrate that the proposed SF-TES-CFPP (solar field, thermal energy storage system, coal-fired power plant) system exhibits the enhancement of peaking capability and flexible operation. In comparison with the conventional TES-CFPP, the integration of solar energy into the peaking process has enabled the SF-TES-CFPP system to enhance its peaking capacity by 20.60 MW while concurrently reducing the coal consumption rate by 10.26 g/kWh. The round-trip efficiency of the whole process of the system can be up to 85.43% through the reasonable heat distribution. In addition, the exergy loss of the principal components can be diminished and the exergy efficiency of the system can be augmented by selecting an appropriate main steam extraction mass and split ratio. The economic analysis demonstrates the dynamic payback period is 9.90 years with the net present value (NPV) across the entire life cycle reaching 1.069 02×109 USD.
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Journal of Thermal Science. 2025, 34(4): 1241-1256. https://doi.org/10.1007/s11630-025-2124-3Upstream blade wake turbulence fluctuation may affect compressor blade forced response caused by wake sweeping. In order to investigate the effect of wake turbulence fluctuation and predict the blade vibration more accurately, this paper proposes a forced response calculation model that considers the excitation of upstream blade wake turbulence fluctuation on the basis of the conventional forced response calculation method. Using a three-stage axial compressor as the research subject, a quasi-three-dimensional large eddy simulation is conducted using the blade profile at 77.8% of the span of the inlet guide vane. Analysis of the flow field around the inlet guide vane indicates noticeable total pressure fluctuation in the wake of the inlet guide vane. The influence of upstream wake turbulence fluctuation is incorporated into the forced response calculation model in the form of total pressure fluctuation to obtain more accurate excitation forces. Specifically, the relationship between the amplitude of total pressure fluctuation and total pressure loss is established according to the results of large eddy simulation, and different formulas are set according to the position zoning of suction surface and pressure surface. Computational results show that, if only wake sweeping is considered, the maximum amplitude is 27% lower than the test result. However, when wake sweeping and wake fluctuation are considered, the calculated result better matches the test result, with only a 6% reduction compared to the test result. The results confirm the effectiveness of the proposed model.
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Journal of Thermal Science. 2025, 34(4): 1257-1270. https://doi.org/10.1007/s11630-025-2180-8To address the complex spatiotemporal characteristics of impeller axial clearance leakage flow in a liquid-ring vacuum pump, plasma actuation with radial centripetal, circumferential reverse, and counter discharge layout types was designed to control the leakage flow. The regulation effects and interference mechanisms of plasma actuation on clearance leakage flow were explored. The results show that under plasma flow control of the three layout types, the vacuum degree of the pump changes not obviously, but the shaft power is reduced and the efficiency is improved to a certain extent. Among them, the circumferential reverse has a more obvious control effect on the hydraulic performance of the pump and has more advantages in controlling the medium- and high-intensity leakage flow in the compression zone, while the radial centripetal has a more effective control effect on the low-intensity leakage flow in the transition zone. All three layout types of plasma actuation can effectively weaken the medium-intensity leakage flow near the beginning of the compression zone, but their suppression effect on the high-intensity leakage flow near the end of the compression zone is weak. Due to the weak leakage in the transition region, the plasma actuation induced airflow and low-intensity leakage flow are coupled with each other, which will further aggravate the complexity and variability of the flow in the clearance. For unsteady clearance leakage flow, the circumferential reverse has a more stable control effect. About the control of medium-intensity leakage flow, the radial centripetal plasma actuation effect is better than the circumferential reverse. The research results can provide theoretical and methodological references for the performance optimization of liquid-ring vacuum pumps.
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Journal of Thermal Science. 2025, 34(4): 1271-1286. https://doi.org/10.1007/s11630-025-2186-2The complex three-dimensional flow within the last turbine stage under low-load condition intensifies internal flow instabilities, decreasing turbine efficiency and operational reliability. In this paper, to investigate the flow instability characteristic of air turbine used in Compressed Air Energy Storage (CAES) systems, three-dimensional unsteady numerical simulations are conducted on two-stage axial flow turbines, namely a small-scale turbine (AT-S) and a large-scale turbine (AT-L). Two low-load conditions of AT-S with a radial inlet chamber (RIC) were firstly analyzed. At the lowest relative mass flow (mrel) of 0.18, no rotating instability (RI) and rotating stall (RS) phenomena were observed in AT-S, which features an aspect ratio of 2.4 for the last-stage rotor blades (R2). However, vortex instability was observed in the RIC, and it was not related to the occurrence of RI or RS. Thus, analysis on four low-load conditions of AT-L without RIC was conducted, where the R2 aspect ratio is 5.4. When mrel was reduced to 0.28, RI occurred. As mrel furtherly decreased to 0.18, RS occurred. The RI and RS phenomena were accompanied by disturbance clusters appearing at the blades top. Different flow modes were observed in RI and RS, which features with different combinations of Through-flow mode (TM), Choke mode (CM), and Separation mode (SM). This study not only considers the influence of the RIC, but also the factors of blade length on flow instabilities of CAES turbine.
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Journal of Thermal Science. 2025, 34(4): 1287-1300. https://doi.org/10.1007/s11630-025-2140-3Paraffin (PA) is a common phase change material, which is widely used in battery thermal management systems (BTMS) because of its high latent heat and temperature uniformity, simple system structure, and no increase in battery energy consumption. In this work, sulfur-free expanded graphite (EG) is prepared by oxidation intercalation without H2SO4 in the preparation process, which avoids the harm to devices caused by the S element. The sulfur-free EG exhibits a high expanded volume of 324 mL·g–1, which can adsorb PA well to prevent leakage. When the mass filling ratio of EG is 5.0%, EG/PA-5.0 composite films show high latent heat of phase transition (253.08 J·g–1), and thermal conductivity (2.56 W·m–1·K–1). EG/PA films are attached to the external surface of the lithium iron phosphate battery for a heat dissipation performance test. When the discharge rate is 1C at room temperature, the surface temperature and maximum temperature difference between temperature measurement points of the battery with EG/PA-5.0 film are 32.1°C and 1.2°C. After charge-discharge at 1C for 100 cycles, the thermal properties of EG/PA remain basically unchanged, and it has good cycle stability. The simulation results are in good agreement with the actual temperature changes of the battery at different discharge rates. This work indicates that sulfur-free EG/PA composite has a good application prospect in BTMS of the power batteries.
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Journal of Thermal Science. 2025, 34(4): 1301-1313. https://doi.org/10.1007/s11630-025-2099-0With the growing need for greater cooling capacity in electronic and heat exchange systems, significant attention has been directed toward improving the heat transfer by incorporating nanoparticles into the base fluid. While the use of nanoparticles in spray cooling shows promise for enhancing heat transfer, additional clarification is required. The paper compiles empirical data from existing literature focusing on spray cooling using nanofluids. Its objective is to clarify how nanoparticles impact the efficiency of spray heat transfer and investigate the effects of factors such as spray Weber number, nanoparticle concentration and droplet spread. Gathered data reveal that when compared to water droplets, nanofluid droplets exhibited more extensive surface spreading at low impinging droplet Weber numbers. Data also show that the heat transfer effectiveness of nanofluid sprays at the critical heat flux and film boiling temperature decreases with the increase in the spray Weber number. At the critical heat flux temperature and for intermediate spray Weber numbers, sprays utilizing nanofluids are more effective than sprays utilizing pure water; however, the situation reverses when dealing with exceedingly high Weber numbers. The data indicate that for surfaces heated within the film boiling range, it remains unclear whether sprays containing nanoparticles demonstrate higher heat transfer efficiency compared to sprays using pure water alone. For surfaces heated to the critical heat flux temperature, there is a critical nanoparticle concentration below which spraying with pure water is more effective than spraying with a nanofluid. However, for surfaces heated to temperatures near the Leidenfrost point, there is no clear indication that nanoparticle concentration plays a role. With the introduction of nanoparticles into sprays, there is a tendency for both the critical heat flux and the Leidenfrost temperatures to shift to a higher temperature range and to increase with the increase in nanoparticle concentration.
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Journal of Thermal Science. 2025, 34(4): 1314-1327. https://doi.org/10.1007/s11630-025-2117-2In response to the challenges posed by the transformation of China’s reed industry, leading to difficulties in reed utilization, and the significant increment in raw soil from the expansion of urban infrastructure, the authors proposed a novel method of coupling reed with raw soil to produce an ecological building insulation material. The aim is to enhance the thermal comfort of rural buildings and achieve building energy saving. The research has applied theoretical and experimental methods as the core means of exploration for key factors in the preparation of the novel ecological insulation material. These factors include raw soil content and curing methods. Key performance indicators such as thermal insulation, mechanical properties, fire resistance, water resistance, moisture resistance, and acoustic performance have been utilized for evaluation. The research results indicate that the proposed process and method for the preparation of the ecological insulation material effectively utilize reed and raw soil, achieving excellent multi-target performance. When the content of raw soil is in the range of 0–40%, the material’s thermal conductivity ranges from 0.097 W/(m·K) to 0.104 W/(m·K), compressive strength from 0.70 MPa to 0.79 MPa, water absorption rate from 29.42% to 38.95%, moisture absorption rate from 13.33% to 31.48%, and the maximum sound absorption coefficient is 0.80, with a maximum sound insulation of 56.66 dB. Additionally, a non-combustible A-grade fire resistance was achieved. To expand the application space and scope of the novel material, the research team further explored on-site construction material preparation processes and conducted experimental research, focusing on the key aspect of the “curing process”. The low temperature curing method of industrial heating blanket was proposed. The research results indicated that the method is feasible. At an environmental temperature of 25°C, with different curing times and curing temperatures, the material’s thermal conductivity ranges from 0.089 W/(m·K) to 0.109 W/(m·K), and the compressive strength is between 0.14 MPa and 0.70 MPa, meeting the relevant parameter requirements. This research opens up avenues for other types of biomass with high economic added value applications and can be directly applied to improving the thermal environment of residential buildings, contributing to building energy saving, rural revitalization, and the implementation of dual-carbon strategies in China.
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Journal of Thermal Science. 2025, 34(4): 1328-1340. https://doi.org/10.1007/s11630-025-2120-7The paper utilizes a combination of entropy production theory and numerical simulation to analyze the energy dissipation of Francis turbines. The distribution law of local entropy production rate (LEPR) in various components of hydraulic turbines is explored under different operating conditions. A detailed examination of hydraulic losses within the Francis turbine reveals that the primary contributors are the runner and draft tube, with comparatively smaller losses occurring in the spiral casing and guide vane areas. The study further explores the formation reasons behind these losses. Within the runner area, the LEPR mainly concentrates in the inlet area of the blade channel, as well as the pressure and suction surfaces of the runner blades. The main reason for hydraulic losses in the runner area is the movement of vortex structures in the blade channel. Within the draft tube area, the hydraulic losses mainly occur on the walls of the straight cone section and the elbow section. There is a backflow phenomenon in the draft tube, which is the main reason for hydraulic losses in the draft tube area. This article can provide a certain theoretical reference for exploring the influencing factors of hydraulic losses in hydraulic turbines.
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Journal of Thermal Science. 2025, 34(4): 1341-1357. https://doi.org/10.1007/s11630-025-2070-0Constructed by a solar chimney power plant (SCPP) and a honeycomb photocatalytic reactor (HPCR), the system can remove non-CO2 greenhouse gases on a large scale. A mesoscopic-scale fluid flow heat transfer model of the photocatalytic reaction region within the SCPP-HPCR system has been established based on the Lattice Boltzmann method (LBM). Multiple distribution functions have been introduced to simulate the distribution of flow, temperature, and concentration of the photocatalytic region. The performance of photocatalytic methane in the SCPP-HPCR system has been analyzed under the influence of different operating and structural parameters. The results show that increasing the inlet methane flow rate can improve the efficiency of photocatalytic and purification rate of CH4, and lead to the increase in carbon dioxide generation rate. When the solar radiation Gr=857 W/m2 and the inlet flow rate Qp=750 mL/min, the photocatalytic efficiency can reach 30.67%. Furthermore, decreasing the aperture size results in enhanced photocatalytic efficiency, purification rate of CH4, and equivalent CO2 reduction rate. When the inlet flow rate Qp=1000 mL/min and the aperture size Dp=0.5 mm, the photocatalytic efficiency can reach 40.23%. Conversely, an increase in the temperature leads to a slight decrease in all evaluated criteria, and the highest photocatalytic efficiency is 24.79% at a temperature of 298 K. These findings provide valuable insights and guidance for subsequent simulation studies on a more microscopic scale.
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Journal of Thermal Science. 2025, 34(4): 1358-1386. https://doi.org/10.1007/s11630-025-2112-7Fourier heat conduction in functionally graded materials (FGMs) has attracted considerable scientific interest due to its simplicity in modeling. FGMs, characterized by a gradual variation in material composition and properties, exhibit unique thermal conductivity behaviors that differ from conventional homogeneous materials. Understanding and analyzing heat transfer in FGMs is crucial for optimizing their thermal performance in various applications. The analytical analysis of Fourier heat conduction in FGMs has facilitated a more profound understanding of the heat transfer phenomena that occur within these advanced materials. This paper provides a comprehensive overview of the research conducted on Fourier heat conduction in FGMs, highlighting the key methodologies, findings, and implications. The literature review showed that the thermal conductivity in FGMs varies spatially, affecting the temperature distribution and heat flux within the material. The gradual variation in material properties in FGMs necessitates the development of specialized analytical solutions to accurately describe the heat transfer behavior. Additionally, the choice of appropriate analytical functions has been found to significantly impact the accuracy and efficiency of the analytical solutions. Researchers have explored various functions, including power functions, exponential functions, and polynomial functions, to represent the temperature distribution within FGMs. It has been observed that the choice of these functions should be based on compatibility with the analytical solution of the heat conduction equation, ensuring accurate predictions of temperature profiles and heat transfer rates.
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Journal of Thermal Science. 2025, 34(4): 1387-1407. https://doi.org/10.1007/s11630-025-2113-6Non-Fourier heat conduction models are extended in response to heat transfer phenomena that cannot be accurately described by Fourier’s Law of heat conduction. This paper provides a review of heat conduction in functionally graded materials (FGMs) employing non-Fourier models. FGMs are designed materials with a gradual transition in composition, microstructure, or thermal conductivity throughout their volume. The spatial variation in thermal conductivity can lead to deviations from Fourier’s Law, resulting in non-Fourier heat conduction behavior in certain situations, such as at very short time scales or in materials with high thermal conductivity gradients. Researchers utilized various models, such as, Cattaneo-Vernotte, parabolic two-step model, hyperbolic two-step, phonon kinetic, dual-phase lag, and three-phase lag models to describe non-Fourier heat conduction phenomena. The objective of this review is to enhance the understanding of non-Fourier heat transfer in FGMs. As a result, the analytical studies conducted in this particular area receive a greater emphasis and focus. Various factors affecting non-Fourier heat conduction in FGMs including gradient function, material gradient index, initial conditions, boundary conditions, and type of non-Fourier model are investigated in various geometries. The literature reviews reveal that a significant portion of research efforts is centered around the utilization of dual phase lag and hyperbolic models in the field of non-Fourier heat conduction within FGMs.
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Journal of Thermal Science. 2025, 34(4): 1408-1416. https://doi.org/10.1007/s11630-025-2116-3The regulation of interlayer van der Waals forces and the engineering of heterostructures represent effective strategies to reduce the thermal conductivity and improve the thermoelectric performance of materials. In this study, molecular dynamics simulations and the density functional theory were employed to study the thermal conductivity of bilayer MoSe2, bilayer MoS2, and MoS2-MoSe2 heterostructures. The analysis of thermal conductivity indicates that an increase in van der Waals forces results in a reduction of thermal conductivities in both bilayer MoSe2 and MoS2. Interestingly, for the MoS2-MoSe2 heterostructure, the thermal conductivity initially increases and then decreases with growing van der Waals forces. Among the structures studied, bilayer MoSe2 exhibits the highest thermal conductivity, followed by the MoS2-MoSe2 heterostructure, and then bilayer MoS2. The major factors affecting heat transfer, including heat capacity, phonon group velocity, and phonon lifetime, demonstrate a positive correlation with thermal conductivity. Additionally, it is observed that MoS2 has a more pronounced impact on the heterostructure compared to MoSe2.
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Journal of Thermal Science. 2025, 34(4): 1417-1430. https://doi.org/10.1007/s11630-025-2136-zThe Heat Recovery Steam Generators (HRSGs) are designed to recapture heat from gas turbine exhaust to generate electric power by a steam turbine. Finned tubes are critical heat transfer components of HRSG, whose design and optimization play an essential role in realizing effective energy utilization in power plants. In this study, an optimization method with multi-layered neural network (MNN) and tree-structured parzen estimator (TPE) is proposed for the finned tube heat exchanger with curved serration. This method has high fitting accuracy and global optimization efficiency, and is suitable for complex heat transfer design and optimization problems caused by novel irregular finned tubes. The developed thermal-fluid model is validated with existing experimental data, and a satisfactory agreement is found in terms of Nusselt number and Fanning friction factor. It is shown that increasing the curved serration angle is beneficial to destroy the thermal boundary layer and enhance turbulent kinetic energy. When the Reynolds number is between 5000 and 25 000, the heat transfer factor of finned tubes with a curved serration angle of 10° is 20% higher than that of flat serrated finned tubes on average. The optimized geometric parameters are obtained from the optimization approach, and the optimal solution has achieved excellent results in comprehensive performance. Compared with the baseline design, the optimized results show a 9% higher heat transfer factor, which is better than those based on commonly used optimization methods.
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Journal of Thermal Science. 2025, 34(4): 1431-1449. https://doi.org/10.1007/s11630-025-2143-0The junction film cooling has been proposed to deal with the situation of insufficient film cooling performance under limited coolants. Numerical investigations are performed for baseline case and four junction film hole cases (3_junction, 4_junction, 5_junction and 6_junction cases) at the coolant mass flow rate varying from 0.0016 kg/s to 0.0064 kg/s. From the results, due to the expanded film hole exit and the interactions between branch film jets, junction film hole cases can suppress the “injection phenomenon” of film jet and the “entrainment effect” of mainstream, thus to improve film cooling performance, especially the film spanwise coverage. By comparison, under low coolant mass flow rate, the 5_junction case can generate the most obvious film cooling performance improvement. To be specific, at the coolant mass flow rate of 0.0016 kg/s, it achieves 76.92% improvement in area-averaged adiabatic film cooling effectiveness, and at the coolant mass flow rate of 0.0032 kg/s, the improvement is up to 703.85%. Through flow loss analysis, the results show that at low coolant mass flow rate, the junction film hole cases improve film cooling performance and pay a little cost of pressure loss; but under high coolant mass flow rate, they can improve film cooling performance and reduce total pressure loss concurrently. Among them, the 5_junction case generates the lowest total pressure loss coefficient; corresponding to the coolant mass flow rate of 0.0048 kg/s and 0.0064 kg/s, it decreases by 15.90% and 41.58% respectively. Through this study, the junction film cooling for improving cooling performance is provided, which is conducive to further raising turbine intake temperature, thereby improving the kinetic and thermodynamic properties of gas turbines.
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Journal of Thermal Science. 2025, 34(4): 1450-1473. https://doi.org/10.1007/s11630-025-2080-yVegetable oils and animal fats-sourced biodiesel are considered a promising alternative to conventional diesel fuel. However, they possess convinced restrictions like inadequate cold flow properties, poor lubricity, and complex emissions of nitrogen oxides (NOx). However, various nano-additives have emerged to overcome those limitations and enhance the performance of biodiesel in diesel engines. The impact of different additives on diesel engine characteristics that have been conducted recently with the combination of biodiesel is thoroughly analyzed in this review paper. Additionally, to provide a thorough summary of experimental research done in this area, the article addresses the several kinds of additives that are frequently employed and their effects on engine performance, combustion, emissions, wear, and durability. The evaluation of nano-additives’ impacts in diesel-biodiesel engines highlights significant improvements in emissions, combustion efficiency, and engine durability. For example, the multi-walled carbon nanotubes (MWCNT) are found to increase Brake Thermal Efficiency (BTE) by up to 36.81%, while cerium oxide (CeO2) can reduce Brake Specific Fuel Consumption (BSFC) by as much as 30%. Additionally, titanium dioxide (TiO2) achieves a minimum NOx reduction of 22.57%, and graphene nanoplatelets (GNPs) have produced a minimum 65% reduction in carbon monoxide (CO) emissions, albeit with higher hydrocarbons (HC) emissions. However, long-term engine durability studies are needed to assess the compatibility of nano-additives with engine components and their impact on engine longevity which could be the future research direction aiming to investigate new nanoparticle possibilities and reduce pollutants to maximize biodiesel performance.
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Journal of Thermal Science. 2025, 34(4): 1474-1482. https://doi.org/10.1007/s11630-025-2114-5To compare structures of turbulent gas and spray flames is helpful for understanding the effect of evaporating droplets on turbulence and turbulent combustion. Presently some investigators did studies on the effect of turbulence on droplet evaporation and the effect of droplet combustion on turbulence, and most of studies paid attention to the time-averaged results. In this paper, the specific feature is to give a review for comparative studies on instantaneous structures of turbulent methane-air jet gas flame, ethanol jet spray flame, methane-air swirling gas flame and heptane-air swirling spray flame by large-eddy simulation (LES) using a second-order moment (SOM) combustion model. The results show that evaporating droplets enhance turbulence and turbulent combustion.
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Journal of Thermal Science. 2025, 34(4): 1483-1496. https://doi.org/10.1007/s11630-025-2108-3To achieve deep NOx control, we investigated a purification-combustion system consisting of devolatilizer, swirl burner and down-fired combustor, and explored the influences of primary and secondary air ratios (λp and λ2) on two-stage modification, combustion and NOx emission of pulverized coal in a 30 kW purification-combustion experimental bench. In devolatilizer and swirl burner, the temperature in different positions increases with λp and λ2 rising. Moreover, the location of main burning zone in swirl burner could be changed by increasing λp rather than λ2. CO and H2 are the main burnable components in modified gases, and their concentrations decrease with λp and λ2 increasing. By contrast, the CH4 concentration is extremely low. Purification system composed of devolatilizer and swirl burner outperformed single-stage devolatilizer in increasing specific surface area, pore volume, pore diameter and fuel conversion rate of pulverized coal as well as improving its carbon microcrystalline structure, and these indexes of modified char are better and better with λp and λ2 increasing properly in this system. In down-fired combustor, as λp and λ2 increase, the temperature changes slightly in reduction region, while it decreases in complete combustion region only at lower λ2. Properly rising λp and λ2 will reduce the NOx emission with high efficiency of above 99.00%, but the emission reduction driven by λ2 is limited.
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Journal of Thermal Science. 2025, 34(4): 1497-1511. https://doi.org/10.1007/s11630-025-2110-9Flame propagation speeds are reported for ammonia/hydrogen/air mixtures with equivalence ratios in the range of 0.5–1.5, preheated gas temperatures ranging from 298 K to 673 K and hydrogen volume fractions of 0%, 20%, and 50%. The measurements were conducted using a Bunsen burner and an optical schlieren system. The results show that the flame propagation speed and combustion stabilities of the premixed gases increase with increasing preheating temperature. The combustion stability is significantly improved under the 20% hydrogen volume fraction condition. For the NH3/H2 mixtures with a hydrogen volume fraction of 50%, the flame propagation speed at 673 K with a stoichiometric ratio is approximately 4.85 times that at 298 K. The experimental results show that at 673 K, the flame propagation speed of the NH3/H2/air mixture increases by 7.8 times when the hydrogen volume fraction increases from 20% to 80%. The numerical results predicted with the Mei, Shrestha, and Stagni mechanisms are compared with the experimental data. The mechanisms proposed by Shrestha and Stagni overestimate the flame propagation speed, especially at high preheating temperatures. The results predicted with the Mei mechanism are consistent with the available data. The concentrations of OH, H, O and NH2 are increased by the hydrogen addition; thus, the ammonia consumption is accelerated.
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Journal of Thermal Science. 2025, 34(4): 1512-1526. https://doi.org/10.1007/s11630-025-2119-0This study employs a new SATES (Self-Adaptive Turbulence Eddy Simulation)-FGM (Flamelet Generated Manifold)-CRN (Chemical Reactor Network) coupling method to numerically predict the combustion pollutions of CO and NOx together in a methane/air turbulent diffusion flame (Sandia Flame D). Two SATES models are developed based on the underlying realizable k-ε and BSL k-ω turbulence models. The prediction accuracy of the combustion field and the CO pollutant distribution are compared and analyzed by coupling two SATES models and two RANS (Reynolds-Averaged Navier-Stokes) models with FGM combustion model. Furthermore, CRN is utilized to construct the NOx distribution characteristics for different scales and rules using the unsteady high-fidelity combustion field results obtained from SATES-FGM. The results demonstrate that SATES-FGM can accurately predict the turbulent diffusion flame and improve the sensitivity of different RANS models to flow patterns in the framework of the SATES method. However, the results show a large deviation in predicting the main combustion zone. The SATES-FGM method can efficiently and accurately simulate flow fields of the free-jet turbulent flame. Additionally, it performs well in predicting the pollution products associated with combustion process, such as CO, while the SATES-CRN coupling method can accurately predict the post-combustion pollutants like NOx. The number of CRN zones can be adjusted to fit the combustor. Excessive reaction zones not only reduce the efficiency but also result in a deviation in the NOx prediction. The unsteady SATES-CRN coupling method is better suited for complex partitioning rules. The developed SATES-FGM-CRN method can offer a new and efficient approach to simultaneously predict the distributions of CO and NOx pollutions.
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Journal of Thermal Science. 2025, 34(4): 1527-1540. https://doi.org/10.1007/s11630-025-2097-2The effect of different fuel mixtures (C2H2, C3H6, C3H8, C2H2+C3H6, C2H2+C3H8) on the acceleration of the gas detonation flame under the same detonation tube gun structure has been studied using numerical simulation. The trends of the internal parameters of the gun, as well as the variations of the gas flow velocity, temperature and pressure at the gun outlet with time were analyzed. At equivalence ratio of 1, the simulation results demonstrate that acetylene fuel produces the shortest detonation time and reaches the highest average gas flow velocity of 1031.6 m/s at the gun exit, and the acetylene detonation reaches the highest average temperature of 2750.6 K. The fastest speeds of OH and other parameters were produced by the detonation of C2H2 and its mixture fuels, which represents the fastest flame propagation. Propane detonation at the outlet of the gun to reach the maximum pressure of 0.66 MPa; internal to the gun, detonation of CO2 produced by the majority of the distribution of the wall region. Different fuel compositions lead to variations in the detonation spray effects, and altering the fuel composition can meet diverse requirements for detonation and spray particle characteristics.
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Journal of Thermal Science. 2025, 34(4): 1541-1553. https://doi.org/10.1007/s11630-025-2171-9A series of C2H2 jet flames were investigated with respect to the soot formation, species distribution, and velocity fields from both experimental and numerical point of view. The flame flow velocities were measured by a particle image velocity (PIV) with a newly-designed continuous laser of 18 W. The experimental results show a significant difference in flame velocity between lean and rich conditions. The lean condition exhibits higher flame velocity, while the rich condition leads to more intense reactions and the formation of vortices at the flame base. A 2-dimensional computational model was employed to investigate the influence of equivalence ratio Φ on combustion characteristics. As Φ increases from 0.8 to 1.5, the distributions of key free radicals such as OH, H, and O are affected. A further increase in Φ results in the generation of soot. Moreover, the increased Φ also affects the processes of axis soot nucleation, oxidation and surface growth rate. The continuous laser PIV system constructed in this paper can provide C2H2 jet flame velocity, which can be also used in other flow field to measure the flow field velocity.
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Journal of Thermal Science. 2025, 34(4): 1554-1568. https://doi.org/10.1007/s11630-025-2149-7The present work aims to provide preliminary support and research foundation for developing integrated technology of CO2 utilization and tar-rich coal pyrolysis to produce high-value chemicals and fuels. The chemical properties of tar produced by tar-rich coal pyrolysis under traditional N2 and N2/CO2 atmospheres were investigated in a fixed-bed reactor at different temperatures (600°C–800°C) and atmospheric pressures. The results showed that tar-rich coal pyrolysis under CO2 atmosphere can promote tar production (mass fraction 8.42% increased) compared with that of traditional pyrolysis (under N2), with the maximum value up to 21.26% (in weight). It should be noted that the generation of coal tar and CO small molecule gas can be promoted by increasing the concentrations of CO2 in pyrolysis atmosphere gases. GC-MS and simulated distillation results showed that the CO2 atmosphere can promote the production of light oil components such as phenols, alcohols, and olefins, while inhibiting the production of heavy components such as asphalt simultaneously. Elemental analysis results showed the H/C ratio of coal tar increased under CO2 atmosphere indicating that the high quality of coal tar is improved, which is consistent with that of simulated distillation and GC-MS test. Finally, a possible reaction pathway of tar-rich coal under CO2 atmosphere pyrolysis is also proposed.
