27 December 2024, Volume 34 Issue 1
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Journal of Thermal Science. 2025, 34(1): 1-23. https://doi.org/10.1007/s11630-024-2076-zLi-ion battery is an essential component and energy storage unit for the evolution of electric vehicles and energy storage technology in the future. Therefore, in order to cope with the temperature sensitivity of Li-ion battery and maintain Li-ion battery safe operation, it is of great necessary to adopt an appropriate battery thermal management system (BTMS). In this paper, the current main BTM strategies and research hotspots were discussed from two aspects: small-scale battery module and large-scale electrochemical energy storage power station (EESPS). The practical application situation, advantages and disadvantages, and the future development trend of each heat dissipation method (air, liquid, PCM, heat pipe, hybrid cooling) were described in detail. Among them, the air cooling and liquid cooling were reviewed in-depth based on the engineering application. The PCM, heat pipe and hybrid cooling were reviewed extensively based on the latest explorations. The research provides a comprehensive understanding for the BTMS in all scales.
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Journal of Thermal Science. 2025, 34(1): 24-33. https://doi.org/10.1007/s11630-024-2087-9Numerical simulations of the flow and heat transfer characteristics of four shell-and-tube molten salt electric heaters with different perforation rates was conducted. Shell-and-tube electric heaters have the same geometry and tube arrangement, and all of them use single segmental baffles, but there exist four different baffle openings (φ), i.e., 0%, 2.52%, 4.06%, and 6.31%. The results indicated that the reasonable baffle opening could significantly reduce the shell-side pressure drop, effectively decreasing the shell-side flow dead zone area. They can eliminate the local high-temperature phenomenon on the surface of electric heating tubes, but the heat transfer coefficient is slightly decreased. All perforated schemes significantly reduce shell-side pressure drop compared to the baseline solution without open holes. In particular, the φ=6.31% scheme exhibits the optimal performance among all the schemes, with a maximum reduction of up to 50.50% in shell-side pressure drop relative to the unopened holes scheme. The heat transfer coefficient is the highest for φ=0%, exhibiting a range of 5.26% to 5.73%, 5.14% to 5.99%, and 7.31% to 8.54% higher than φ=2.52%, 4.06%, and 6.31%, respectively, within the calculated range. The composite index h/(Δp)1/3 was higher for all open-hole solutions than that for the unopened-hole solution. The best overall performance was for φ=6.31%, which improved the composite index by 15.29% to 17.18% over the unopened-hole solution.
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Journal of Thermal Science. 2025, 34(1): 34-49. https://doi.org/10.1007/s11630-024-2061-6Turbulent agglomeration is viewed as a promising technology for enhancing fine particle removal efficiency. To better understand particle transport, agglomeration behaviors, and fluid-particle interactions, we numerically explored these phenomena under cylindrical vortex wake influence using a coupled large eddy simulation and discrete element method (LES-DEM) approach. The validity of the LES approach was verified by comparison with available direct numerical simulation (DNS) results. We adopted the Johnson-Kendall-Roberts (JKR) contact model for particle-particle interactions. The particle dispersion and agglomeration characteristics of particles with different diameters (dp=2–20 μm) in the laminar and transition of shear layer (TrSL) flow regimes were analyzed. Fine particles were concentrated at the vortex centers, while larger particles accumulated around the vortices. The agglomeration efficiency exhibited an M-shaped profile spanwise (y-direction). With increasing Reynolds number, the agglomeration efficiency and turbulence intensity improve. The particle agglomeration efficiency peaks at a certain Reynolds number. However, at higher Reynolds numbers, reducing the residence time of particles in the flow field decreases the agglomeration efficiency.
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Journal of Thermal Science. 2025, 34(1): 50-61. https://doi.org/10.1007/s11630-024-2056-3Heat exchangers have the potential for various engineering applications, and their performance is enriched by surface modification. The proposed system enriches the heat exchanger’s performance by adapting a peened stainless steel (SS) surface blasted with copper, grinding, sand, and iron. The influences peened SS surface modified with a copper blast, grinding, sandblast, and iron blast on the surface morphology of shell and tube heat exchanger surface (STHE) is analyzed via tungsten heated cathode electron gun featured scanning electron microscope and observed coarse grain surface. The SS surface featured STHE performance is experimentally evaluated by different flow rates (30, 60, 90, and 120 L/min) underwater fluid medium functioned by the temperature ranges of 25–75°C and its results are compared with computational fluid dynamic (CFD)/heat transfer research (HTRI) analyzed results. The 60 L/min flow rate was spotted as an optimum value for both shell and tube side reasons. The STHE is operated with a 60 L/min flow rate under the different peened surfaces and evaluated its Stanton number, Nusselt number, logarithmic mean temperature difference (LMTD), overall heat transfer coefficient, number of transfer units (NTU), effectiveness, and exergy efficiency. The iron blasted SS peened surface was observed to have better SHTE performance like Stanton number (0.0012), Nusselt number (2180), reduced LMTD of 31°C, improved overall heat transfer co-efficient of 2400 W/(m2∙K), better NTU of 0.5532, good effectiveness value of 0.451 62, and hiked exergy efficiency of 10% respectively.
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Journal of Thermal Science. 2025, 34(1): 62-76. https://doi.org/10.1007/s11630-024-2046-5A comprehensive numerical model is developed to simulate the growth of microalgae under light/dark cycling conditions. The purpose of this study is to predict the growth rate of Chlorella vulgaris cultivated in photobioreactors (PBRs) in order to improve the light conditions for microalgae and enhance the photosynthetic efficiency. Computational fluid dynamics (CFD) is used to simulate its internal hydrodynamic behaviors. The Lagrangian method is employed to track the movement of microalgae cells. The radiative transfer equation (RTE) is used to obtain light intensity distribution. The combination of light radiation field and microalgae cell motions is used to construct the light history and they are integrated into the model of the photosynthetic units (PSU) to calculate the microalgae growth rate. The numerical results demonstrate that enhanced light/dark cycling frequency with ordered mixing can promote efficient microalgae cultivation. The effect of the vortex flow field generated by the baffles in an air-lift PBR is analyzed for increasing microalgae growth rate. When using the 1:1 baffle spacing, the biomass production of microalgae is increased by 41.8% compared to the original PBR.
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Journal of Thermal Science. 2025, 34(1): 77-91. https://doi.org/10.1007/s11630-024-2005-1Throughflow design has the advantages of less time consumption and large optimization space, and thus is the corner stone of advanced design system of multi-stage axial-flow compressors. The majority of relevant studies were limited to the throughflow inverse designs, and quite few works have been till now devoted to the throughflow optimal designs. In this work, an automatic and rapid throughflow-based optimal design method is proposed for axial-flow compressors in which a throughflow inverse design solver is embedded in optimal genetic algorithm to improve the design efficiency of axial-flow compressor. Two types of design parameters in the throughflow inverse design of axial-flow compressors, i.e., swirl and shroud curve, are simultaneously used to optimize both the blade shape and flow path. The proposed method is validated by the redesign optimization of the benchmark axial-flow compressor NASA Stage 35, and the CFD predictions show that the throughflow-based optimization leads to 1.18% efficiency benefit at design condition. The proposed method is then utilized to the two-dimensional throughflow optimal design of a large-scale 6.5-stage axial-flow industrial compressor. The optimal design results are confirmed by CFD predictions, indicating that the proposed method can effectively improve the design adiabatic efficiency of the compressors by 1.09% within a few minutes on desk-top computer. Two throughflow design implications are also obtained for advanced axial-flow industrial compressors. This work could enhance the capability of throughflow design method and has engineering application value to explore the throughflow optimization space of multi-stage axial-flow compressors.
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Journal of Thermal Science. 2025, 34(1): 92-109. https://doi.org/10.1007/s11630-024-1970-8Low-Reynolds-number effect is an important factor affecting the performance of compressors and other main components of high-altitude long-endurance unmanned aerial vehicles. To improve the flow condition and reduce flow loss under the condition of high altitude and low Reynolds number (Re), this paper proposes an optimization process based on a surrogate model, which combines the class-shape transformation method (CST), the Latin hypercube sampling (LHS) method, the light gradient-boosting machine algorithm (LightGBM), and a genetic algorithm (GA) to optimize a high-subsonic compressor profile. The surrogate model is verified to be accurate and can be used in the optimization process. The accuracy of the GA is higher than the other algorithms under common test functions. The optimization results are verified by numerical simulation, and the flow differences before and after optimization are compared, especially the flow within the boundary layer. By changing the blade shape, the optimization process adjusts the loading distribution to delay the transition of the optimized blade on the suction surface, which changes the turbulent reattachment in the laminar separation bubble (LSB) into laminar reattachment. Therefore, the mixing loss induced by the turbulent reattachment of the LSB and the wake loss of turbulent separation at the trailing edge are significantly reduced, and the performance of the compressor profile is finally improved. In addition, turbulent separation of the optimized profile is delayed reducing the range of the wake region on the suction surface. By this optimization process, the reduction of total pressure loss coefficient at Re of 2.5×105, 3.5×105, and 4.5×105 are 16.32%, 20.76%, and 22.16%, respectively.
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Journal of Thermal Science. 2025, 34(1): 110-128. https://doi.org/10.1007/s11630-024-2077-yThe influence of partitioned profiling design based on a large-pitch highly loaded cascade is studied by numerical simulation. The partitioned profile is mainly composed of a pressure-side convex structure near the leading edge and a suction-side convex structure at the midstream and downstream sides of the passage. The influence of the change in the vertex axial position and peak value of the B-line on the secondary flow control is analyzed. In this paper, air (ideal gas) is selected as the flow media. The average static pressure at the outlet and the average total temperature at the inlet are kept constant. SST γ-θ is used as the turbulence model. The results show that the pressure-side convex structure suppresses the spanwise and pitchwise migration of the inlet flow by adjusting the static pressure distribution of the flow field, so the development of the pressure-side leg of the horseshoe vortex is effectively limited. The suction-side convex structure adjusts the static pressure distribution of the flow field and increases the included angle between the cross-flow and suction surface, so the accumulation of low-momentum fluid, the development of a corner vortex and the flow separation at the trailing edge of the suction-side surface are all suppressed near the endwall-suction corner. Consequently, the energy loss coefficient of the large-pitch highly loaded cascade is decreased from 0.0564 to 0.0485, representing a 25% reduction in secondary flow losses.
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Journal of Thermal Science. 2025, 34(1): 129-144. https://doi.org/10.1007/s11630-024-2066-1A new passive control approach, utilizing bionic slanting riblets, is employed to mitigate the flow close to the blade endwall in a linear cascade, and its effectiveness and mechanism in controlling corner separation are investigated through numerical simulations. The slanting riblets are positioned at the endwall upstream of the cascade channel, and the influence of riblet height, yaw angle and relative position on the control of corner separation is investigated. The findings indicate that the application of slanting riblets can efficiently counteract corner separation across the stable operational range. Specifically, the introduction of riblets with a height of merely 0.1 times the boundary layer thickness results in a significant reduction in total pressure loss by up to 14.53%, while simultaneously enhancing the static pressure coefficient by 21.74%. Flow analysis reveals that minute vortices produced within the riblet channels tend to coalesce, forming a potent large-scale vortex near the boundary layer’s base downstream. This phenomenon results in reduced additional losses compared to conventional vortex generators. Additionally, the induced vortex promotes enhanced mixing between the mainstream flow and boundary layer, inhibiting the lateral displacement of low-energy fluids within the endwall boundary layer. Consequently, this delays the onset of separation vortex formation and eliminates vortex rings in the corner region, ultimately enhancing the aerodynamic efficiency of the cascade.
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Journal of Thermal Science. 2025, 34(1): 145-158. https://doi.org/10.1007/s11630-024-2074-1The characteristics of wind turbine wakes are influenced by multiple factors, including the atmospheric boundary layer (ABL) wind and wind turbine operating conditions (e.g., tip speed ratio and yaw angle). In this study, two types of ABL winds with different velocity gradients and turbulence intensities are generated in a wind tunnel through configurations of spires, baffles, and various numbers of roughness elements. A wind turbine with a rotor diameter of 0.8 m and a hub height of 0.6 m is tested under varying tip speed ratios, yaw angles, and ABL wind conditions. The results indicate that the streamwise velocity deficit in the near-wake region becomes more pronounced with an increase in the tip speed ratio, while the far-wake velocity deficit remains largely unaffected by changes in the tip speed ratio. As the yaw angle increases, the wake deflection becomes more prominent and the wake narrows; the offset of the wake center at various downstream positions grows linearly, reaching a maximum value of approximately half the rotor diameter. Furthermore, the turbulence level and influence range in the wake region are reduced when the turbine is yawed. Under ABL wind conditions, high turbulence intensity in the incoming flow accelerates wake recovery, and the Reynolds stress at different lateral positions tends to become consistent with increasing longitudinal distance. Additionally, turbulence has a significant impact on the meandering characteristics of the wind turbine wake, with greater fluctuations in the wake center observed under higher turbulence intensities. Overall, this study provides insights that could inform the optimal operation of wind farms.
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Journal of Thermal Science. 2025, 34(1): 159-175. https://doi.org/10.1007/s11630-024-1994-0The supercritical carbon dioxide (sCO2) Brayton cycle system has become an emerging and highly promising method of thermal power conversion due to its efficiency advantage, system compactness, and excellent adaptability of the heat sources. For the low carbon sCO2 Brayton cycle testbed with cycle output power approaching 3 MW, a relatively detailed dynamic simulation model of the entire system is constructed to explore the dynamic response characteristics of the system with different startup strategies and different buffer tank volumes during the startup process. The simulation results indicate that the smaller the volume of the buffer tank, the more rapid and obvious the parameter fluctuation in the buffer tank during the startup. Assuming the allowable relative deviation limit of density is 5%, then the ratio of the buffer tank volume to the volume of the entire closed loop should not be lower than 36.80%. The strategy of simultaneous temperature and speed increase during turbine bypass start can effectively reduce the fluctuation of compressor inlet parameters and reach the steady-state more quickly. This paper provides the recommended matching table for the opening of the turbine bypass valve (TBV) and the main regulating valve (MGV) to reduce the parameter fluctuation during the bypass switching. The effectiveness of the proposed turbine bypass and bypass switching startup strategy is verified by simulation, which may be used as a reference for test bench’s future debugging and operation.
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Journal of Thermal Science. 2025, 34(1): 176-187. https://doi.org/10.1007/s11630-024-2072-3The seemingly useless reeds are prepared as thermal insulation materials, which not only meet the requirements of environmental sustainability but also enhance the added value of reeds, creating new economic benefits. The hydrophobicity of raw biomass surfaces leads to problems such as weak bonding strength and non-dense structure in the formed materials, as well as issues related to the residual insect infestations on the surface. In this study, reed straw was used as the raw material, and foamed geopolymer was used as the binder to prepare building insulation materials based reed. To improve the interfacial adhesion performance between reed straw and foamed geopolymer, a thermochemical modification method-thermal carbonization, was proposed. In this study, the mechanical properties and hydraulic properties of the studied materials with different degrees of surface thermal modification were tested, especially the fire resistance performance, and weathering resistance performance rarely found in published literature. When the surface thermal modification condition of reed straw was 250°C (30 min), the comprehensive performance of reed-based building insulation materials was the best, when the studied material density was 321.3 kg/m3; the compressive strength was 0.59 MPa; the thermal conductivity was 0.101 W/(m∙K); the pH was 11.27; the moisture absorption rate was 25.1%, and the compressive strength loss rate in wet-dry cycles was 18.5%. In addition, it had excellent fire resistance performance and weathering resistance performance. This new material can be widely used to improve the thermal insulation of traditional buildings and as sandwich filler in prefabricated buildings, such as preparing insulating walls.
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Journal of Thermal Science. 2025, 34(1): 188-205. https://doi.org/10.1007/s11630-024-2043-8During data center operation, it generates a significant volume of low-grade waste heat. To recover waste heat, a coupled system including solar collector, double effect absorption refrigeration and organic Rankine cycle is proposed. The system performance is analyzed in detail. For the organic Rankine cycle, five organic working fluids (R245fa, R245ca, R123, R11, and R113) are selected. R245fa, R113 and R245ca obtain the maximum net power output, thermal efficiency and exergy efficiency, respectively. In the double effect absorption refrigeration system, the evaporation temperature, condensation temperature, and generation pressure affect the COP and exergy efficiency. When the generator pressure is unchanged, the COP increases with increasing evaporation temperature and decreasing condensation temperature. When the COP reaches 1.3, the COP slightly decreases as the evaporation temperature or condensation temperature changes. Similarly, the exergy efficiency of refrigeration systems exhibits the same trend as the COP, and the exergy efficiency maximum value appears at approximately 0.32. A new performance indicator, rPUE, was defined to evaluate the data center power utilization efficiency. The flow distribution ratio and heat source temperature were optimized with multi-objective optimization. When the mass flow distribution rate is 0.6 and the heat source temperature is 441.5 K, rPUE and the total unit production costs of the system obtain the optimal solution.
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Journal of Thermal Science. 2025, 34(1): 206-222. https://doi.org/10.1007/s11630-024-2059-0Syngas produced from the gasification of organic feedstocks from biomass is one of the clean and sustainable sources of energy. The advantages of simple access and renewability of biomass energy can meet the energy needs of temporary power supply. This study presents a biomass power-generation system for vehicular applications. Using biomass and a free-piston Stirling engine generator (FPSEG) as the primary material and prime mover, respectively, biomass energy is converted into electricity by combusting the syngas to heat the FPSEG. Matching and key parameter design for biomass gasification and thermoelectric conversion systems within a power generation system were performed. A porous medium area was constructed using Si-C foam ceramics to obtain an energy-conversion experimental platform. The effects of bed height, porosity, porous-region diameter, and air-intake conditions on the power-generation performance were investigated, and optimisations were performed for the thermoelectric conversion system. The rate of increase during FPSEG power generation first increased and then decreased with increasing bed height, peaking at a bed height of 40 mm. An increasing porous-region diameter accelerated FPSEG power generation, whereas porosity changes in the porous media did not significantly affect the rate of change during FPSEG power generation. With increasing air intake, the rate of increase during power generation first increased and then decreased. The maximum change rate and the highest thermoelectric conversion efficiency of the power-generation system occurred at 9.5 m3/h and 6.5 m3/h (~45.1%) air intakes, respectively. Optimising the thermal inertia and combustion structure of the thermoelectric conversion system significantly increased the power-generation rate of the system, with 1.8 W/s being observed at a 9.7 m3/h air intake.
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Journal of Thermal Science. 2025, 34(1): 223-241. https://doi.org/10.1007/s11630-024-2064-3Metal foam promotes the heat transfer of phase change materials (PCMs) in the penalty of reducing the energy storage density of the composite PCMs. In this work, the effects of constant porosity (0.96, 0.94, 0.92, or 0.90) and pore density (PPI) of metal foam on heat transfer of composite PCMs are studied. Melting rate could be enhanced by employing with low porosity copper foam. Furthermore, aiming to the right bottom phase changing “dead region”, a regionalized enhancement strategy of cascaded metal foams is introduced. The dynamic melting performances of all the composite PCMs are comprehensively analyzed. The results reveal that the cascaded configuration is beneficial for optimization. Details show that the horizontal strategy enhances melting performance: a maximum of 17.98% reduction in total melting time could be reached when the rear part porosity is 90%. The energy storage density rate could be raised by 5.48%. Besides, the vertical strategy performs with a better average temperature uniformity of 0.441 and brings a lower temperature in the heated wall. To sum up, the regionalized enhancement of copper foam provides better performance in the phase change process. It shows significant potential for solar heat storage and thermal protection.
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Journal of Thermal Science. 2025, 34(1): 242-253. https://doi.org/10.1007/s11630-024-2079-9The particle packed bed energy storage system has advantages such as low costs and wide temperature ranges, which can be combined with solar thermal power generation systems to solve the inherent volatility and discontinuity of renewable energy. Developing new materials with low costs and excellent storage performances is one of the eternal research hotspots in the field of energy storage. This paper innovatively uses sintered ore particles as energy storage material and studies the effect of particle size on the airflow resistance characteristics, energy storage characteristics, and thermocline evolution characteristics of the packed bed through thermal energy storage experiments. The results indicate that for the particles in the macro scale, the smaller the particle, the lower the absolute permeability of the bed and the greater the airflow resistance. The packed bed with smaller particles has a larger specific surface area, larger bulk mass, and smaller bed voidage. Therefore, the packed beds with smaller particles have better thermocline characteristics, less irreversible loss, and can achieve higher thermal efficiency and higher exergy efficiency in the heat storage cycle. The cycle thermal efficiency in packed beds with 25–40 mm, 16–25 mm, and 10–16 mm particles is 53.58%, 56.27%, and 57.60%, respectively, and the cycle exergy efficiency is 61.81%, 69.25%, and 74.13%, respectively. Moreover, this paper also studies the effect of discharging airflow rates on thermal storage performance. The experimental results indicate that suitable discharging strategies should be selected based on different heat demands.
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Journal of Thermal Science. 2025, 34(1): 254-267. https://doi.org/10.1007/s11630-024-2012-2In this study, a triple spark ignition scheme was first designed on a three-cylinder 1.5-L dedicated hybrid engine (DHE). On this basis, the effect of different ignition modes on engine combustion and emission characteristics was studied, especially under high dilution condition. The results tested at 2000 r/min and 0.8 MPa BMEP (brake mean effective pressure) show that with highly increased in-cylinder flow intensity, using only passive prechamber (PPC) has a lower lean limit than that with single central spark plug (CSP), thereby leading to slightly higher minimum fuel consumption and nitrogen oxides (NOx) emissions. Adding side spark plugs (SSP) based on PPC can result in improved capability of lean limit extension and engine performance than CSP. However, the improvement level is lower than that with triple spark plugs (TSP). As the excess air ratio λ increases, the advantage of PPC and PPC with SSP in improving the combustion phasing compared with CSP gradually weakens. Correspondingly, the increasing tendency of their ignition delay and combustion duration is more obvious. The added SSP based on PPC can effectively shorten the ignition delay of leaner mixture, but the combustion duration can be only slightly improved. As a result, under extremely lean condition, the advantage of PPC and PPC with SSP in terms of combustion characteristics over CSP becomes much smaller. In contrast, the TSP ignition can achieve much shorter ignition delay and combustion duration simultaneously under this condition. Due to the highest available dilution level, the TSP ignition achieves the lowest raw NOx emissions. Moreover, it can also reduce the raw carbon monoxide (CO) and hydrocarbons (HC) emissions compared to CSP due to a more thorough combustion of the end gas mixture. Based on the excellent performance of TSP, the highest engine brake thermal efficiency (BTE) was further explored. The results show that with normal RON 92 fuel, the engine finally achieved 43.69% and 45.02% BTE under stochiometric mode with exhaust gas recirculation (EGR) and lean-burn mode respectively. When using RON 100 fuel, the highest BTE was further increased to 45.63% under lean-burn mode.
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Journal of Thermal Science. 2025, 34(1): 268-282. https://doi.org/10.1007/s11630-024-2065-2In this study, focusing on the geometry characteristics of spherical expanding flame, the turbulent premixed flames of natural gas/air mixtures were investigated in a fan-stirred turbulent combustor. The effects of initial temperature (T=300–400 K), initial pressure (P=0.1–0.3 MPa), turbulence intensity (u′=1.0–2.7 m/s), oxygen volumetric percentage (φ(O2)=15%–21%) and carbon dioxide volumetric percentage (φ(CO2)=0–20%) were delved into. The flame profile under the Cartesian coordinate system was derived from the schlieren images taken by the high-speed camera. Besides, from both macroscopic and microscopic perspectives, the influence of experimental conditions on the flame geometry characteristics was explored through flame front extraction, wavelet decomposition and network topology. The results demonstrate that for significant flame wrinkling, changes in species concentrations and turbulence intensity have more pronounced effects on the flame wrinkling ratio. The wrinkling of the flame front maintains a certain degree of similarity, as evidenced by the locally concentrated distribution of the angles of the maximum fluctuation radius. The disturbance energy under large-scale (D6–D8) disturbances exhibits relatively high values with a similar trend, exerting a significant impact on the geometry characteristics of the flame front. The peaks of correlation degree are scattered either with the decomposition scale or the development of flame radius, indicating no linear correlation between different detail components. Furthermore, the probability distribution of node degrees in key wrinkled regions exhibits different trends with that of large-scale wrinkling and disturbance energy, especially with changes in initial pressure. This occurs because the number of key wrinkles varies based on the perturbation’s strength or the region’s span. Consequently, an increase in the fluctuation frequency of the flame’s local radius may not necessarily lead to an increase in the number of key folded regions.
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Journal of Thermal Science. 2025, 34(1): 283-302. https://doi.org/10.1007/s11630-024-2055-4This study investigates the effect of aluminium oxide nanoparticlesaddition to biodiesel blends made from dairy milk scum on performance and combustion characteristics of the diesel engine. The dispersion of Al2O3 nanoparticles in B20 blends at different concentrations was done with the help of ultrasonicator. Good number of blends were prepared for the analysis. Advanced Machine learning algorithms (Random Forest (RF) and CatBoost) was used for the prediction. The results show that in comparison to biodiesel blends without nanoparticles, the kinematic viscosity and density is higher for fuel blends with nanoparticles. But these Fuel blends have higher calorific values. These blends exhibited reduced Brake Specific Fuel Consumption (BSFC) of 2.85% than the blends without nano particles (Dairy Scum Methyl Ester Biodiesel 20%+Neat Diesel 80% (in volume), DSMEB20), 57.14% less CO, 40.8% less hydrocarbon, and increased NOx emissions compared to conventional diesel, contributing to the development of environmentally friendly and renewable biofuel blends with nanoparticles. DSME B20NP30 is the optimal blend for performance and emission characteristics. The study concludes with findings on enhanced Brake Thermal Efficiency (BTE) of 26.29% in 3×10–5 (in volume) Al2O3 nanoparticle-blended DSME B20 and other DSME B20 fuel blends, emphasizing the importance of optimal nanoparticle concentration. The correlation matrix shows how engine load, efficiency measures (BTE, BSFC), and emissions (CO, CO2, NOx, Smoke) are connected in complex ways. The results help us understand the complicated dynamics of engine performance and emission characteristics better. Taylor’s diagram for BTE and BSFC shows that CatBoost-based BTE models perform superior to RF-based models during the training as well as testing phase. Similar results were obtained for CO and CO2 emission results.
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Journal of Thermal Science. 2025, 34(1): 303-322. https://doi.org/10.1007/s11630-024-2057-2The asymmetry of the multi-orifice spray will cause uneven heat load of the marine diesel engine, thereby affecting its working performance and service life. Therefore, an in-depth understanding of the spray and flame characteristics of multi-orifice nozzles will guide the optimization of the nozzle structure, needle design and diesel atomization and combustion process. For this reason, four groups of dual-orifice nozzles with different hole diameters (0.1–0.55 mm) and mass flow rates covering the typical marine medium-speed diesel injections are designed and customized, and the constant volume chamber (CVC) with high temperature and pressure is used to simulate the actual in-cylinder working conditions of the diesel engine for the spray visualization experiment. To study the asymmetry of the fuel sprays discharged from a diesel injector, the multi-orifice nozzle is simplified as a dual-orifice nozzle in this study. Combined with X-ray Computed Tomography (CT) imaging technology, the influences of the nozzle internal structure on the spray and flame asymmetry are studied in the constructed supercritical environment. It is found that the asymmetry of the inlet angle and the equivalent length-diameter ratio is positively correlated with the inconsistency of the dual sprays. With an increase in the injection pressure and nozzle diameter, the asymmetry of the dual spray becomes more pronounced, resulting in greater disparities in the ignition delay times and ignition positions of the two sprays. Moreover, the increase in nozzle diameter also leads to combustion instability, resulting in a flame with a serrated appearance. With the increase of ambient temperature, the proportion of liquid phase in the jet decreases and the relative density of spray front decreases.
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Journal of Thermal Science. 2025, 34(1): 323-336. https://doi.org/10.1007/s11630-025-2092-7A 3D simulation using Computational Particle Fluid Dynamics (CPFD) methods was used to calculate coal combustion in a 75 t/h industrial-scale circulating fluidized bed (CFB) boiler. Combustion characteristics, gas-solid flow characteristics, and gaseous pollutant emissions of CFB boilers from combustion ignition to stable operation were systematically evaluated in this study. Results show that the temperature distribution is relatively uniform throughout the boiler. As the combustion process unfolds within the boiler, the gas composition curve strikingly portrays the inverse correlation between CO2 and O2 concentrations. As the combustion reaction progresses, it becomes evident that the concentration of CO2 progressively increases, while the concentration of O2 concurrently decreases. This inverse relationship underscores the fundamental combustion reaction, where carbon-based fuels react with oxygen to produce carbon dioxide and release energy. Furthermore, a comprehensive analysis has revealed that, from ignition to stable combustion, both nitric oxide (NO) and sulfur dioxide (SO2) emissions exhibit a declining trend. This reduction in pollutant generation is attributed to the improvement in combustion efficiency. More complete combustion leads to lower levels of unburned hydrocarbons, which are prone to NO formation. Similarly, the sulfur content in the fuel is more efficiently oxidized to sulfur trioxide (SO3) or bound in sulfates, reducing SO2 emissions. At steady state in the simulation, the SO2 mass flow rate varies significantly with the furnace height, gradually increasing from 0.07 kg·s–1 at 4 m at the bottom of the furnace to a peak of 0.078 kg·s–1 at 8 m in the center, and then decreasing to 0.06 kg·s–1 at 20 m at the top of the furnace.
