Chemical looping can achieve high product selectivity using lattice oxygen in oxygen carriers for partial oxidation of methane. Oxygen carrier La_1−xSr_xFe_0.8Al_0.2O₃ was prepared by sol-gel method for chemical looping dry reforming of methane. The reaction performance of the oxygen carrier doped with different proportions of Sr was tested by thermogravimetric and fixed bed reactor. The experimental results showed that the oxygen capacity of x=0.4 oxygen carrier in La_1−xSr_xFe_0.8Al_0.2O₃ is as high as 1.88 mmol·g⁻¹, with excellent reaction performance and less carbon deposition. The stability of the oxygen carrier La_0.6Sr_0.4Fe_0.8Al_0.2O₃ was further tested for 20 redox cycles. The oxygen carrier maintained excellent redox performance, achieving 61.2% methane conversion, 97.1% CO selectivity, and 1.81 H₂/CO. The material characterization results displayed that the morphology and crystal structure of the oxygen carrier were stable. The results show that La_0.6Sr_0.4Fe_0.8Al_0.2O₃ is an excellent oxygen carrier suitable for chemical looping dry reforming of methane.

The application, screening, evaluation and funding of National Natural Science Foundation of China programs in Engineering Thermophysics and Energy Utilization Discipline in 2024 are summarized and statistically analyzed. The strategic research, funding proposals in the field of energy and power under the carbon peaking and carbon neutrality goals are introduced. The outstanding achievements funded by the discipline in 2024 and future work in 2025 are introduced as well.

Aiming at the problems of low power generation efficiency and water high consumption in the chemical recuperated gas turbine cycle, a chemical reinjection gas turbine cycle is proposed in this study. It is proposed that part of the flue gas in the gas turbine was put back into the reactor, the reaction of methane self-reforming reaction, and realize the efficient transformation of methane conversion rate. The technology features fully realize the effect of improving the quality of gas turbine flue gas waste heat, and improving the circulation work. Through the improvement of the fuel energy conversion process and the optimization of the heat transfer process of the system, the power generation efficiency of the new system is increased by 9.12% compared with that of the chemical heat recovery system at the design point, the performance of the power generation of lower pressure ratio and high gas turbine inlet temperature is better. The economic analysis shows that the economic payback period of the system is 2.3 years, which has good economic benefits. 

Frosting usually has a negative impact on device, when ultrasound is used for frost retardation/defrosting, can realize no downtime defrosting, cooling and heating without interruption during defrosting time. But due to its mechanism is not clear, technical difficulties to pragmatize, failed to get popularization and application. This paper reviews the research progress of ultrasound in the field of frost retardation and defrosting from two aspects of its mechanism and pragmatization. Firstly, the ultrasound characteristics is introduced, including commonly used ultrasound wave types and their propagation, ultrasound effects on frost retardation and defrosting, distribution of equivalent force on the cold surface; then, the growth of frost is inhibited by delaying the generation of liquid droplets, delaying the freezing of droplets, crushing the frozen droplets and suppressing the frost branch growing; based on the frost crystal fracture breaking, defrosting effecting factors and defrosting enhancement methods, ultrasonic defrosting mechanism is summarized; and, from the equipment frost retardation/defrosting effects and its energy consumption comparison, practical difficulties and problems, the ultrasound frost retardation/defrosting practical applications is sorted; Finally, a outlook of the ultrasound used for frost retardation/defrosting in the future is given to provide reference.

Heat pump heating technology can effectively reduce the energy consumption and environmental pollution caused by coal-fired heating. However, the low-temperature adaptability of commonly used heat pump heating systems is poor, making it difficult to meet the heating demand in cold regions. Considering that Stirling heat pump technology has a wide range of available temperature zones, an electrically-driven free-piston Stirling air source heat pump is developed in this paper to investigate its heating performance under different climatic conditions. The experimental results show that the overall coefficient of performance of the Stirling heat pump reaches 2.31, 1.97 and 1.78 for normal, cold and very cold regions, respectively. In addition, the relative Carnot efficiency of the Stirling heat pump gradually increases with rising heat-pumping temperature difference. Its advantage is more obvious at large heat-pumping temperature difference.

Sugar alcohols are gaining attention as highly promising medium-temperature phase change materials (PCMs) due to their superior overall performance. Currently, the evaluation of the comprehensive performance of sugar alcohol composite PCMs optimized for a single objective remains incomplete. In this study, erythritol (Ery) was used as a PCM, combined with expanded graphite (EG) and Al₂O₃ as additives. A ternary composite PCM was prepared using the melt blending method, and its comprehensive performance was assessed. The results showed that the components of the ternary composite PCM exhibited excellent physical compatibility. Among them, the ternary composite PCM with 0.5%(wt) Al₂O₃ / 1.5%(wt) EG/Ery demonstrated the best overall performance. This ternary composite PCM maintained a high melting enthalpy of 312.9 kJ/kg and, compared to Ery, achieved a thermal conductivity of 1.083 W/(m·K), an increase of 54%. In the isothermal cooling test, its supercooling degree was reduced by 9.3°C, in the non-isothermal cooling process, its supercooling degree was reduced by 16.7°C. The pyrolysis temperature increased by 20°C, and the maximum pyrolysis rate temperature increased by 8.3°C, significantly enhancing thermal stability. Additionally, after 40 isothermal cycling tests, its supercooling degree and melting enthalpy remained essentially unchanged, demonstrating excellent cycling stability.

The photovoltaic-thermoelectric hybrid power generation system is a promising solar energy technology. However, traditional series-connected photovoltaic-thermoelectric system faces challenges such as mismatched device operating temperature and high thermal resistance. In this study, a bifacial type photovoltaic-thermoelectric hybrid power generation system with a sandwichlike configuration is proposed. An experimental setup is constructed to investigate the effects of different irradiance levels and cooling water flow rates on the performance of the new system under steady-state indoor conditions. Experimental data shows that the output power of photovoltaic module and thermoelectric device in bifacial type system is superior to that of traditional series system. Moreover, increasing irradiance levels can enhance the system’s power generation capacity but may reduce the photovoltaic power generation efficiency. Additionally, increasing the cooling water flow rate can further enhance the system’s output performance.

To address the problem of battery thermal management failure caused by the limited latent heat of phase change materials (PCMs), this paper proposes a novel composite battery thermal management system. The system utilizes serpentine liquid cooling tubes with fins to recover the latent heat of PCMs. Numerical simulations were employed to study the effects of battery spacing, liquid cooling structural parameters, and coolant flow rates on the thermal management performance of the hybrid system, leading to the determination of optimal parameter values. The results indicate that all three liquid cooling operation modes can consistently maintain the temperature of the battery module below 50°C. Furthermore, by optimizing the operation time of the liquid cooling system, the latent heat of PCMs can be promptly restored, thereby maximizing the utilization of the latent heat of PCMs.

Supercritical CO₂ Brayton cycles, due to their advantages in performance and compactness, hold promising prospects for hypersonic vehicles. However, the unique thermal environment of the aerospace scenario poses challenges to the cycle. In this paper, a model of a supercritical CO₂ Brayton cycle is established and validated. The study investigates the transient response of the Brayton cycle system under two operating conditions: a sudden increase in thermal load and a combined disturbance of thermal load and insufficient cold source. Dynamic simulation results indicate that both a sudden increase in thermal load and insufficient cold source can lead to a decrease in the thermodynamic performance of the cycle. Moreover, the combined disturbance may even result in controller failure, imposing higher demands on component design.

District heating system is one of the important carriers for coordinating renewable energy and traditional energy and realizing flexible consumption of renewable energy. Considering the impact of the uncertainty of renewable energy output and user cluster heat load on the dynamic transportation process of district heating network, it is necessary to quantitatively analyze the uncertain variables on both sides of the source and load and the dynamic characteristics of the heating network. This paper first established a dynamic transportation model of the heating network to solve its heat loss and transmission delay characteristics. Secondly, the Gram-Chalier A algorithm was applied to calculate the probability distribution semi-analytical expression of the thermal power of the source and load nodes of the system, and Bayesian credible inference method was used to calculate the fluctuation interval of node thermal power. This paper selected a secondary heating network in Beijing for model accuracy validation and case analysis. The system has 90 nodes and 109 pipes. The results show that the proposed model and algorithm can effectively quantify the fluctuation interval of nodes’ thermal power.

The exploitation of natural gas hydrate is a major strategic demand of the country, and further improvements in 
production and efficiency are needed before its commercial development. How to realize its efficient exploitation depends on the thermodynamic mechanism of the hydrates. Traditional hydrate thermodynamics studies are limited to phase equilibrium characteristics and lack the consideration of non-equilibrium thermodynamics in the hydrate decomposition process. At the same time, the hydrate decomposition process may be accompanied by icing and melting. The thermodynamic characteristics of hydrate exploitation under complex heat and mass transfer conditions need to be clarified. In this study, a 2 L natural gas hydrate depressurization decomposition experimental system was used to simulate the hydrate reservoirs with different distributions and perform long depressurization (to 1.0 MPa) at a constant exhaust rate of 0.55 L·min−1(normal conditions). The results show that there is a non-equilibrium thermodynamic relationship (T[°]=8533.8/{38.98−ln(1000p[MPa])}−275.25) between the temperature and pressure in the hydrate-bearing area during the depressurization process, which is only controlled by the hydrate decomposition and is not affected by the reservoir temperature gradient. According to the Gibbs phase law, the thermodynamic freedom of phase transition process is 1. As a result, the natural gas hydrate decomposition belongs to the phase transition process, and the quantitative relationship between temperature and pressure is consistent with the thermodynamic theory. When the hydrates depressurize to about 2.1∼2.3 MPa, instantaneous icing occurs in the reservoir, leading to a sudden increase in temperature and accelerating the hydrate decomposition. Due to the constant exhaust rate, the accumulated gas increases the pressure up to 2.36 MPa. It is found that the temperature and pressure of hydrate-bearing reservoir still satisfy the non-equilibrium thermodynamic phase diagram of hydrates before and after icing. This study illustrates the thermodynamic mechanism of phase transition in the presence of heat and mass transfer in the natural gas hydrate decomposition process, which can provide a more practical theoretical basis for the process of exploitation site monitoring.

In accordance with international environmental protection conventions, some high GWP HFCs refrigerants are facing obsolescence and destruction. Therefore, it is necessary to develop energy-saving, high-efficiency destruction way. In this paper, the performance differences of various catalysts in the photothermal catalytic degradation of R134a was compared based on existing technical route. Furthermore, the effects of material properties on the reaction rate, such as morphology, band structure and photoelectric properties, were obtained through characterization of catalysts. Based on the law of the effects, anatase TiO₂ was selected for modification. The modified catalyst achieved a degradation rate of over 98% within 30 minutes, with the reaction rate increasing by 3.8 times.

In this paper, a flow calorimeter was developed for the measurement of isobaric specific heat capacity (c_p) at low temperature. The calorimeter was composed of four parts: thermostatic bath, flow system, calorimeter and data acquisition system. The calorimeter can measure the c_p in the temperature range of 115 ∼ 340 K, and the pressure can reach 8 MPa. The uncertainty of temperature, pressure and heat capacity were 11 mK, 0.02 MPa and 0.9%, respectively. The c_p data of propane, isobutane, ethane and ethane + propane binary mixtures at low temperature were measured. The measured data showed a good agreement with the calculated values of high-precision Helmholtz equation of state. The average absolute relative deviations of propane, isobutane, ethane and ethane + propane was 0.26%, 0.32%, 0.31% and 0.38%, respectively, which verified the reliability of the device.

In order to study the adsorption characteristics of materials with different pore sizes and microporous filling process, the pore adsorption during silicon-N2 adsorption was investigated using a combination of experimental and theoretical methods. The thermodynamic analysis of the adsorption isotherms of the nonporous materials was used to obtain the true Zeta adsorption isothermal constants of the materials, and it was found that the entropy of adsorption in the range of low pressure ratios first increased sharply and then decreased, and then began to increase again after reaching a pole. The molar latent heat is negative in this range, indicating the instability of the adsorbent at this time, from which the unstable interval determines the pressure ratio range of the microporous filling process. The pressure ratio and the corresponding cluster size at the beginning of the pore filling process of mesoporous silica materials were determined using the Zeta isothermal constant of the corresponding system. The cluster molecules were analyzed in relation to the pore size, and the scaling factor decreased with the increase of the pore size, and a physical model was proposed for the earlier merging of clusters at the adsorption sites due to the wall bending of the pores to start the pore filling process.

Entransy analytical model of heat transfer process in stacked porous medium is built, and a new utilization efficiency of Entransy is proposed, meanwhile wave function and field function characteristics of Entransy are found. Based on the model, coupling the cooling curve, surface temperature of cooling products in porous medium, internal temperature gradient, convective heat transfer coefficient along quick freezer, entransy dissipation rate during cooling process are predicted for the first time. Mesoscale characteristics of coupled heat transfer for conduction, convection and radiation in heat transfer process in porous medium have been found. Results show that, volume scale of internal heat transfer core and temperature gradient control heat flux and convective heat transfer coefficient on surface, and wavy characteristics of internal temperature difference decreasing rate affect tendency of heat flux convective heat transfer coefficient. Temperature change trend can be predicted accurately based on along heat transfer coefficient. Porous medium can enhance heat transfer, and scaling factor of heat transfer coefficient without and within porous medium is about 0.6, meanwhile radiation and convection have field synergy characteristics.

In this paper, a new solar photovoltaic/thermal system with parabolic trough concentrator and indium tin oxide/ethylene glycol nano-fluid beam splitting is proposed. Indium tin oxide/ethylene glycol nano-fluid is prepared and tested. The results show that the absorptivity and transmittance of the indium tin oxide nano-fluid are 30.9% and 69.1% in the full wavelength range. The optical behavior of the photovoltaic/thermal system is studied and the overall optical efficiency of the system is 89.38%. When the sun tracking error is less than 0.2 ̊, the photovoltaic/thermal system can have an overall optical efficiency which is greater than 84.14%. The operation performance analysis reveal that the photoelectric efficiency of the photovoltaic subsystem is 29.1%, and the overall photoelectric conversion and thermal efficiencies of the photovoltaic/thermal system are 19.1% and 19%. The thermal efficiency of the system can be improved by increasing the inlet indium tin oxide nano-fluid velocity, or by reducing the inlet indium tin oxide nano-fluid temperature and external convectional heat transfer coefficient.

Energy storage is the key technique to establish the new-type power system and achieve the dual carbon goal, and the compressed air energy storage is a highly promising option for largescale long-term energy storage. In this study, an afterburning-type compressed air energy storage system integrated with molten salt thermal storage was proposed, and thermodynamic models of the proposed system were developed. Then, influences of key parameters on system performance under different power loads were evaluated. The analysis results show that the four operation modes of the system can meet four power load demands, i.e., the high power load demand, the medium-high power load demand, the medium-low power load demand, and the low power load demand. Among them, the output power corresponding to high power load demand is 1573.93 kW, and the output power corresponding to low power load demand is 350.15 kW. The roundtrip efficiency of operation mode with low power load is the highest of 69.87%.

A thermo-economic model was used to analyze the thermodynamic and economic characteristics of a geothermal ORC system. The evaporation and condensation temperatures of typical hydrofluoroolefins (HFOs) working fluids including R1224yd(Z), R1233zd(E) and R1336mzz(Z) were optimized to obtain the maximum net power. The thermo-economic characteristics were analyzed and compared with the traditional working fluids R601, R601a and R245fa. The results show that the evaporation and condensation parameters of R1224yd(Z) and R245fa are close under the optimal conditions. When the geothermal water inlet temperature is lower than 130°C, the net output power of R1336mzz(Z) is the maximum among the selected fluids, which is 1.47%∼1.89% more than that of R1233zd(E); but the heat exchanger area increases by more than 17%. When the geothermal water inlet temperature is higher than 130°C, the net output power of R245fa is the maximum, and the power generation cost is reduced by 15.5%∼16.8% compared with R1336mzz(Z).

As the core power component of the supercritical carbon dioxide (SCO₂) Brayton cycle, accurate analysis of the aerodynamic thermodynamic performance and loss characteristics of the compressor under near-critical conditions is crucial for the efficient operation of the cycle. The compressor is prone to condensation when working near the critical point, and the condensation process is non-equilibrium. In this paper, an SCO₂ non-equilibrium condensation model based on the Euler-Euler source term is established and compared with the equilibrium condensation model to evaluate the impact of the non-equilibrium condensation process on the aero-thermodynamic performance of the SCO₂ centrifugal compressor. The results show that the non-equilibrium condensation model is more accurate in predicting efficiency, and non-equilibrium condensation will cause the compressor to enchance the inlet flowrate and enter near-surge conditions faster.

The International Maritime Organization (IMO) and port States have increasingly stringent requirements for ship energy efficiency, and the improvement of ship energy efficiency based on waste heat recovery is one of the most effective ways to meet this challenge. TEG-ORC combined cycle is a new method to realize the utilization of multiple waste heat steps in ships, but the effect of bottom cycle ratio on the performance of combined cycle system has not been studied in detail. The theoretical model is optimized and the influence of variable bottom cycle ratio on the performance of the main parameters of the combined cycle system is studied experimentally. The experimental results show that under the conditions of ORC bottom cycle working medium R245fa, working medium mass flow rate m = 0.079 kg/s and evaporation pressure P = 0.7 MPa, with the gradual increase of bottom cycle ratio, the system output power and flue gas waste heat utilization rate of the main engine increase, and the cost of combined power generation decreases. When the bottom cycle ratio of TEG/ORC is 0.885, the flue gas waste heat utilization rate of the main engine is 85.07%, the total output power of the system is 688.4 W, the thermal efficiency of the system is 7.07%, and the power generation cost of the combined cycle system is 3.338 CNY/kWh.

Ammonia has recently received much attention as a novel clean energy with broad application prospects. The paper focuses on the extinction limits of dimethyl ether/ammonia mixtures cool and hot diffusion flames by an atmospheric counterflow burner. The low and high temperature chemical kinetics of dimethyl ether/ammonia are analyzed. The results show that the extinction limits of dimethyl ether/ammonia mixtures cool and hot diffusion flames decrease with the increase of the ammonia blend ratios. For dimethyl ether/ammonia cool flames, the low temperature reactivity of dimethyl ether is inhibited mainly through three aspects: ammonia and dimethyl ether vie OH, DME + NO ⇐⇒ R + HNO and RO₂ + NO ⇐⇒ RO + NO₂. For dimethyl ether/ammonia diffusion hot flame, the high temperature reactivity of dimethyl ether is improved by the reaction of OH, H and O radicals generated by ammonia with dimethyl ether and the reaction of HCCO + NO ⇐⇒ HCNO + CO and HCCO + NO ⇐⇒ HCN + CO₂. Moreover, this research shows that the main oxynitrides in dimethyl ether/ammonia cold flame and hot flame are NO₂ and NO respectively.

In this paper, CFD numerical simulation and orthogonal experimental design are used to study the cavitation characteristics and optimise the anti-cavitation performance of the self-developed hydrodynamic suspension micro-pump. Through numerical simulation to get the cavitation characteristic curve of the micro-pump and the cavitation flow characteristics of different cavitation number analysis, selected impeller inlet diameter, vane thickness, suction chamber diameter, volute height of the base circle of the four factors for orthogonal test optimisation, the results show that the suction chamber diameter of the comprehensive performance of the micro-pump has a more significant impact. Simulation found that the increase of suction chamber diameter can make the vertical section of the vortex area significantly reduced; experiments measured after the optimisation of the prototype head increased by 5.20%, the critical cavitation number reduced by 59.6%.

Zinc-bromine redox flow battery (ZBFB) is one of the most promising candidates for large-scale energy storage due to its high energy density, low cost, and long cycle life. However, numerical simulation studies on ZBFB are limited, and the effects of operational conditions on battery performance and related energy storage mechanisms remain unclear. Herein, a 2D transient model of ZBFB is developed to reveal the effects of current density, compressed electrode thickness, and electrode active area on battery performance. The results show that the battery overpotential increases with increasing current density; compressing the electrode thickness decreases the battery ohmic loss but increases the concentration polarization; and increasing the electrode active area increases the battery ohmic loss and concentration polarization, causing a decrease in the battery energy efficiency. This work provides an insight into the effect of operational and structure parameters on ZBFB performance, which is useful for high performance ZBFB design.

Although carbon capture technology has received widespread attention recently, there is still a lack of efficient carbon capture materials. Herein, we synthesized various deep eutectic solvents (DES) and compared the differences in sorption capacity from multiple perspectives. The sorption capacity of DES based on ethanolamine (MEA) can reach 4.39 mmol/g at 20°C and 0.24 MPa, while DES consisted by acetic acid (AcOH) can only reach 0.85 mmol/g under the same conditions. This is mainly due to the chemical reaction between MEA and CO₂ to generate aminoformate monoethanolamide, while AcOH is only the physical dissolution of CO₂ molecules. The sorption capacity of DES increases with the enhancement of CO₂ partial pressure and decreases with the raise of temperature. Especially, the sorption capacity of AcOH-TPAC-7 attenuates by 40.2% at 25°C and 0.24 MPa compared to 20°C and 0.24 MPa. The sorption capacity of AcOH-TPAC-7 increases with the improvement of water content, while MEA-TPAC-7 manifests the opposite trend.

The coal-supercritical water fluidized bed (SCWFB) reactor is a large-scale clean energy equipment that operates in a multi-phase environment with coupled heat and mass transfer and chemical reactions. Studies on the SCWFB reactor have generated a significant amount of multidimensional, transient flow fields data through experimental and numerical simulations. This paper presents a data-driven 3D multi-phase flow fields spatio-temporal prediction model, 3DReactorNet, which uses deep learning technology to learn the complex multiphase flow fields inside the SCWFB reactor. The obtained unstructured multi-phase flow fields simulation data is processed by spatial interpolation to achieve fast and accurate prediction of the spatio-temporal evolution of the 3D multiphase flow fields inside the reactor under unknown operating conditions. In this paper, the confidence level of the prediction results of the 3DReactorNet was measured using the MC Dropout method. The test results indicate that the prediction results of the 3DReactorNet are highly consistent with the CFD simulation results. Additionally, the prediction speed is much faster than CFD simulation, which is beneficial for efficient reactor design and optimization.

In this paper, the electrothermal characteristics and failure mechanism of lithium-ion batteries during external short circuit were analyzed, and the performance of batteries without thermal runaway in subsequent use and the potential thermal runaway risk were explored. The results indicated that the temperature and voltage changes of the battery during external short circuits were related to the internal resistance which changes with SOC and short-circuit current. Further external short-circuit batteries were accompanied by phenomena such as electrolyte evaporation, lithium metal deposition, electrode particle rupture, and membrane closure, which affect the internal Li⁺ transport process. The battery without Thermal runaway was tested in the cycle. The battery capacity was recovered in the cycle, and the polarization internal resistance was reduced to the initial level, but the ohmic internal resistance was higher than the initial value. The potential risk of Thermal runaway inside such batteries was analyzed through the secondary short circuit.

In this paper, a finless micro-bare-tube heat exchanger with tube bundle diameter varying gradually in the range of 0.4 ∼ 1.0 mm is proposed. The air-side friction and heat transfer performance of micro-bare-tube heat exchangers with bundle diameters varying gradually were studied by CFD simulation. By using the relevant empirical formula and NSGA-II algorithm, the multiobjective optimization of the dynamic friction factor f and heat transfer performance factor j was carried out, and the optimal structural parameters of the micro-bare-tube heat exchanger with varied pipe diameter were determined. When the longitudinal tube wall spacing is 0.214 mm, the transverse tube wall spacing is 1.127 mm, and the tube bundle diameter is 0.876 mm, 0.746 mm, 0.697 mm and 0.550 mm from outside to inside, the heat transfer performance factor j reaches the maximum value of 0.04169, and the flow friction factor f reaches the minimum value of 0.01270. Compared with the equal-diameter finless micro-bare-tube heat exchanger, the new structure not only reduces the pressure drop, improves the heat transfer efficiency, but also saves the amount of metal manufacturing materials and refrigerant charge.

Manifold microchannels have lower pressure drop and higher heat transfer efficiencies than traditional microchannels, and combining the manifold microchannel heat transfer method with the boiling heat transfer method will further enhance the heat transfer performance of the device. In this study, high thermal conductivity diamond was used as the microchannel substrate, and computational fluid dynamics was utilized to investigate how the flow and boiling heat transfer performance of the device is affected by the outlet/inlet width ratio of the manifold microchannel and the ratio of the manifold size to the total size of the microchannel. The findings indicate that the device’s integrated heat transfer performance will be enhanced by a manifold microchannel outlet/inlet ratio larger than 1; the greater outlet/inlet ratio, the easier the bubbles in the microchannels break up and detach, and the better heat transfer performance.

In hydrogen liquefaction systems, the continuous catalytic conversion of ortho-para hydrogen is recognized as a key technology for achieving low energy consumption. The conversion heat of ortho-para hydrogen, which exhibits temperature dependence, is observed to vary significantly along the course of the heat exchanger, influencing the cooling process of hydrogen gas flow. This study investigates continuous conversion cryogenic hydrogen plate-fin heat exchangers, employing theoretical analysis and the development of a dynamic simulation model to explore the heat exchange and catalytic matching characteristics of such exchangers. Optimal cold fluid flow rates in various temperature zones have been determined. When helium is used as a cold fluid, optimal cold-to-hot mass flow rate ratios of 3.5 in the 80∼60 K range and 4.7 in the 60∼40 K range are identified. The dynamic simulation elucidates the heat transfer-catalytic matching relationship between normal hydrogen conversion and the cooling fluid in hydrogen heat exchangers, offering insights for the design and optimization of hydrogen liquefaction processes. These findings contribute to enhancing process efficiency, reducing energy consumption, and promoting sustainable development in the
hydrogen energy sector.

Transpiration cooling in two-dimensional porous plate under hypersonic flow has been numerically investigated. The numerical model considers the complex interaction between the hypersonic mainstream region and porous medium region. The simulations are performed at Mach number 6.47. The liquid water is adopted as the coolant. The effects of the injection rates, the particle diameter, porosity and properties of porous material on transpiration cooling performance are analyzed. The simulation results show that the average cooling efficiency of porous plate increases from 0.41 to 0.87 when the injection rate varies from 0.0159% to 0.0795%. It also can be found that the effects of particle diameter and porosity of porous plate on transpiration cooling efficiency are marginal. The influence of particle diameter on transpiration cooling efficiency becomes weaker at higher injection rate. Such as, the temperature profiles of porous plate for different particle diameters are almost the same when the injection rate is 0.0795%. Furthermore, the thermal conductivity of porous material has marginal effect on the averaged cooling efficiency of porous plate; however, the greater temperature difference between the two ends in the porous plate can be obtained at a smaller thermal conductivity.

Porous media combustion can improve the burning rate and flame stability, achieve stable flame in ultra-lean/rich conditions, and expand the flammability limit. Based on the assumption of homogeneous porous media, a combustion model considering multiple porous media morphological features is established, and the combustion characteristics in porous media with different structural and material parameters are calculated. The results show that five parameters, namely, porosity, mean pore diameter, tortuosity, material thermal conductivity and emissivity, affect the combustion state in porous media by influencing the gas-solid heat transfer, thermal conductivity and radiation processes. Due to the effect of radiation, the pore structure has a more significant effect on the combustion rate compared to the material parameters, smaller pore diameter and higher tortuosity will improve the gas-solid heat transfer process and enhance the burning rate, while overly intense gas-solid heat transfer will enhance the radiative heat loss, and lead to combustion instability and quenching in porous media. The trend of the cell structure and porous material influence on the porous media combustion characteristics obtained from the model calculations is consistent with the experimental results.

Gallium nitride (GaN) is a typical wide-bandgap semiconductor with a critical role in a wide range of electronic applications. Ballistic thermal transport at nanoscale hotspots will greatly reduce the performance of a device when its characteristic length reaches the nanometer scale, due to heat dissipation. In this work, we developed a tip-enhanced Raman thermometry approach to study ballistic thermal transport within the range of 10 nm in GaN, simultaneously achieving laser heating and measuring the local temperature. The Raman results showed that the temperature increase from an Au-coated tip-focused hotspot was up to two times higher (40 K) than that in a bare tip-focused region (20 K). To further investigate the possible mechanisms behind this temperature difference, we performed electromagnetic simulations to generate a highly focused heating field, and observed a highly localized optical penetration, within a range of 10 nm. The phonon mean free path (MFP) of the GaN substrate could thus be determined by comparing the numerical simulation results with the experimentally measured temperature increase which was in good agreement with the average MFP weighted by the mode-specific thermal conductivity, as calculated from first-principles simulations. Our results demonstrate that the phonon MFP of a material can be rapidly predicted through a combination of experiments and simulations, which can find wide application in the thermal management of GaN-based electronics.

In order to clarify the characteristics of different zooming strategies, and develop the algorithm of gas turbine hybrid-dimensional simulation for multistage compressor with high pressure ratio. For a split-shaft gas turbine and its 17-stage compressor, the hybrid-dimensional simulation models that coupled zero-dimensional engine model and compressor through-flow model were developed based on the De-coupled approach, conventional iterative coupled approach, fully coupled approach, and the improved iterative coupled approach proposed in this paper respectively. The variations of different zooming strategies were compared and analyzed, the results indicate that the De-coupled approach, iterative coupled approach and fully coupled approach can basically achieve the same simulation accuracy, the maximum relative error between simulation result and experimental data is less than 10%. Moreover, the De-coupled approach tends to converge easily, its simulation accuracy and efficiency are affected by factors such as the quality of characteristic map. Although the conventional iterative coupled approach exhibits high simulation efficiency, its robustness is difficult to guarantee in the zooming of multistage compressor with high pressure ratio. The fully coupled approach has relatively low simulation efficiency and high requirements for both the solving algorithm and the initial value of iterative variables. Meanwhile, the improved iterative coupled approach effectively utilizes the wide pressure ratio range of the 17-stage compressor, exhibiting both high robustness and high simulation efficiency, the effect is optimal.

To reduce the instability and uncertainty of current linear methods for combustion kinetic model reduction, a new nonlinear method based on artificial intelligence algorithm is proposed to simplify chemical models. This method is applied to reduce the USC-Mech II and JetSurF 2.0 mechanisms, so that the reduced mechanisms can accurately predict the ignition delay time of ethylene and n-decane respectively. The results show that the new reduction method based on particle swarm optimization (PSO) can obtain more compact reduced models. The 22-species ethylene mechanism and the 45-species n-decane combustion mechanism are obtained, which are more compact than those obtained by other reduction methods under similar operating conditions. 

Efficient utilization of waste heat is a crucial approach to achieving energy conservation and emission reduction. In recent years, the highly efficient heat pump technology has been widely applied in industrial waste heat recovery due to its excellent energy utilization efficiency. However, the narrow operating temperature range of compression and absorption heat pumps makes it challenging to meet the ”large temperature rise” heat exchange requirements in industrial waste heat recovery at higher heating temperatures. Firstly, this paper analyzes the circulating principle of the new high-temperature coupled heat pump. Secondly, it establishes a thermodynamic steady-state mathematical model for the coupled heat pump. According to calculations under the design conditions of a chemical waste heat project, when the waste heat inlet temperature is 90°C, the coupled heat pump can produce hot water at 115°C with a COP of 2.33. The effects of compressed circulation condensing temperature, medium temperature waste outlet temperature, and cooling water outlet temperature on the performance of the coupled heat pump cycle are analyzed. Compared with conventional technology, this new high-temperature coupled heat pump can efficiently transfer”large temperature difference” under higher heating temperatures and demonstrates good technical economy potential for market application.

To achieve carbon peak and neutrality targets, a new type power system is being constructed in China, and the operational flexibility of coal-fired power plants should be enhanced. The integration of steam energy storage system is an effective way to enhance the frequency regulation capability of coal-fired power plants. Dynamic models of steam accumulator and steam turbine thermal system were developed in this study, and the dynamic characteristics of the steam accumulator and turbine thermal system were studied during the charging and discharging processes of the steam accumulator. Moreover, the energy efficiency and frequency regulation capability of the steam accumulator were evaluated. Results show that the steam accumulator has a fast response speed to support the frequency regulation of coal-fired power plants, and the equivalent round-trip efficiency is 46.62% when the steam accumulator is charged at 30% THA condition and discharged at 100% THA condition.

With the development and increased integration of electronic devices, the internal heat issues have become increasingly severe. During thermal cycling, the mismatch in thermal expansion coefficients of materials can generate significant thermal stress, leading to a series of thermal reliability problems. Regulating the thermal expansion coefficients of materials is crucial for improving the thermal issues in electronic devices. In this work, molecular dynamics simulation was used to investigate the thermal expansion coefficient of Cu/Graphene composites. It shows that the introduction of graphene effectively reduces the thermal expansion coefficient of the Cu-based material, and the randomly distributed doping exhibits isotropy. The Cu/Graphene nanocomposite with oriented doping exhibits anisotropy, which is attributed to the close arrangement and strong bonding forces between graphene layers, effectively limiting the expansion of the copper matrix. Compared to the In-plane direction, the Through-plane direction has a lower thermal expansion coefficient and elastic modulus.

In order to investigate the unsteady flow mechanism in the tip region of the axial compressor, a numerical simulation study was carried out to investigate the unsteady evolutionary characteristics of the tip leakage flow field. It was discovered that the dominant frequency of the unsteady flow at the blade tip region was 1863.3 Hz, and the tip leakage vortex formed at the leading edge of the suction surface broke down in one oscillation phase and formed a new vortex structure. Due to the combined effect of the differential pressure between the suction surface and the pressure surface and the leading edge excitation shock wave, the vortex structure gradually moved to the leading edge of the adjacent blades, and during this cross-cycle evolution, the vortex structure appeared to be maintained for about 1/9th of a cycle. In the subsequent cycle, the vortex structure formed by the tip leakage vortex breakdown dissipated while interacting with the broken vortex to form a blockage region in the passage. Along with the influence of the excitation shock wave, this blockage region exacerbated the generation of the “leading edge overflow”phenomenon. It was also hypothesized that the tip leakage vortex breakdown due to vortex wave interference was the key factor in the flow unsteadiness. After the tip leakage vortex broke down, a new vortex structure was formed at the leading edge of the adjacent blade, and a series of evolutionary processes occurred over time, which was the main cause of the unsteady flow in the blade tip region. 

The wind turbine is affected by the harsh environment, and the blade surface is prone to damage. Aiming at the problems of small damage size and variable shape and style, this paper proposes a lightweight wind turbine blade surface damage detection algorithm based on improved YOLOv5. According to the characteristics that the basic network is sensitive to the deviation of small target position detection, the two loss measurement methods of NWD and IOU are combined. At the same time, in order to reduce network complexity and improve network performance, multidimensional dynamic convolution ODConv is integrated into the YOLOv5 model backbone network. The experimental results show that the computational complexity of the improved network is reduced by 45%, and the average accuracy of the algorithm is improved by 8.3%, which can better identify the surface damage of wind turbine blades.

In response to the high-stability low-temperature environment requirements for the primary thermodynamic temperature measurement of superfluid helium to liquid helium temperature range, this paper adopts a two-stage GM cryocooler pre-cooled closed 4He Joule-Thomson cooling method, and builds a 2∼5 K cryostat. The lowest temperature of the core component can reach 1.5 K, satisfying the requirement of the lowest operating temperature. Direct current and alternating current temperature control experiments were conducted in the 2∼5 K range. The results show that alternating current temperature control has advantages in the 2∼5 K temperature range. Temperature control stability better than 40 μK in the 2∼5 K temperature range has been realized. Typical results are 25.5 μK@2 K, 31.6 μK@3 K, 16.2 μK@4 K and 20.7 μK@5 K. This study provides a prerequisite for further upgrade and optimization of the cryostat and high-accuracy primary measurement of thermodynamic temperatures in the 2∼5 K temperature range.