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.

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.

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.

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.

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.

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.

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.

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.

During the energy release phase of the compressed air energy storage (CAES) system, the air pressure in the storage device gradually decreases. When it falls below a certain threshold, the unit cannot maintain the rated total output power. To address this issue, the study proposes the applications of bypass systems in the CAES system expanders. In this paper, three types of bypass systems are designed for the expander unit of a CAES system: single-stage bypass systems (3 configurations), two-stage bypass systems (3 configurations), and three-stage bypass system (1 configuration), with a total of 7 configurations. By adjusting the openings of the main and bypass valves, the total inlet and outlet pressures of certain turbines are modified, thereby changing their mass flow rates and output powers to achieve the rated total output power. The results show that 5 configurations can achieve the desired performance. The three-stage bypass system enables the lowest terminal air pressure in the storage device, expanding the sliding pressure operation range of the unit. The optimal configuration is the two-stage bypass system that independently controls T1 and T2, which achieves the longest power generation duration and the highest energy density, representing a 71.25% improvement compared to the original unit. Therefore, adopting the bypass control methods can extend the power generation duration and increase the energy density of the CAES system.

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%.

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.

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.

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.

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.

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.

This work proposes a LNG cold energy recovery-freezing desalination-thermal storage coupling system, where the LNG cold energy drives an organic Rankine cycle to generate power. Simultaneously, seawater is subjected to cryogenic centrifugal desalination, and the desalinated ice produced is stored as a thermal storage medium. The thermodynamic and economic analyses of the system are conducted. The results show that the daily freshwater production of the system is 119.66 t, with a net output power of 52.10 kW. The investment payback period is 3.23 years, and the desalination cost is 0.48 USD·t⁻¹, significantly lower than the cost of traditional reverse osmosis desalination.

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%.

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.

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.

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 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.

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.

Supplying industrial steam can achieve combined heat and power generation, and it is an effective way to enhance the energy efficiency and economic performances of coal-fired power generation units. However, the high extraction temperature entering the industrial steam pipeline limits the operational flexibility, when the combined heat and power unit operates under low power load condition. To address this issue, a parameter sliding operation strategy by reducing the reheat steam temperature was proposed in this study. Then, the system performance analysis model under variable operating conditions was developed, and the flexibility and energy consumption characteristics of the system were analyzed with a 330 MW combined heat and power unit as the reference case. The results show that the maximum peak shaving capacity of the unit increases by about 14% with the operation mode of reheat steam temperature sliding, and the coal consumption rate of the unit can be reduced after the temperature of the reheated steam is reduced to a certain extent. Under typical heating conditions, the annual operating income of the operation mode of reheat steam temperature sliding is about 788400 CNY.

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 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. 

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.

Poly (vinylidene fluoride) (PVDF) is widely used in many fields, such as thermal interface materials and membrane distillation membranes; therefore, modeling its thermal conductivity is of great importance. In this study, equilibrium molecular dynamics simulations were used to calculate the thermal conductivity of PVDF at different degrees of polymerization and temperatures. The results revealed that as the temperature and degree of polymerization increase, the overall thermal conductivity of PVDF increases. Moreover, at certain temperatures, λ_C and λ_B were found to be linearly related to the reciprocal of the molecular gyration radius and macroscopic density, respectively. Additionally, when the molecular gyration radius of PVDF is large, λ_NB shows an approximately linear relationship with the gyration radius. Finally, correlations for predicting λ_C, λ_B, λ_NB, and the overall thermal conductivity of the material were proposed based on extensive numerical results. The findings of this study have significant implications for the development and design of PVDF materials.

Continuous rotating detonation engine is one application of detonation-based propulsion, with the characteristics of simple structure, high combustion efficiency, stable thrust, and diverse application forms, which has received significant attention in recent years. Low-reactivity fuels are difficult to achieve efficient rotating detonation combustion, due to their poor chemical reactivity and large detonation cell size. To achieve the engineering application of continuous rotating detonation engine, it is necessary to break through this core key technology. This review article provides an overview of the latest progress in continuous rotating detonation of low-reactivity fuels. The combustion organization mechanism of continuous rotating detonation powered by low-reactivity fuels is discussed from three aspects: improving chemical reactivity, optimizing combustor configuration, and ramjet-based rotating detonation. This will provide reference and guidance for the development of subsequent continuous rotating detonation engines.

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.

The effect of convergent nozzle on the operation characteristics of rotating detonation engine with cavity is investigated. The cross-correlation algorithm is applied to identify the propagation mode of detonation wave, and the stability parameters of detonation wave propagation are defined according to the loop delay of the auto-correlation. The total pressure at the combustor outlet is calculated by the average static pressure and Mach number, and then the total pressure recovery coefficient is obtained. With the decrease of nozzle outlet area, the lower boundary of detonable equivalent ratio will decrease. The stability of detonation wave propagation is less affected by the nozzle. The reduction of the nozzle outlet area is beneficial to increasing the velocity of detonation wave and the total pressure recovery coefficient of rotating detonation engine.

In this study, the process of CO₂ removal by a hollow fiber membrane contactor (HFMC) is investigated numerically. In the HFMC, the absorbent solution (potassium lysine solution) flows through the fiber bundle, while the air flows on the shell side. The hollow fiber membrane contactor consists of staggered cylindrical fiber tubes with equal longitudinal and horizontal pitches. This study investigates the flow and mass transfer process of air and absorbing liquid inside the HFMC systematically by computational fluid dynamics methodology. After experimental validation, the model is used to calculate the friction factors and Sherwood numbers for various operating conditions on the shell side. Besides, the new correlations for predicting friction factor and Sherwood number are proposed as reference to the designs of membrane modules. This work is crucial for simplifying performance evaluation and scale-up design for the membrane module. 

In this study, the oxidation kinetics of Cu₂O was investigated using the micro-kinetics rate equation theory based on first principles. Firstly, the reaction paths and energy barriers of Cu₂O oxidation are obtained using DFT calculations based on first principles; secondly, the reaction rate constants are calculated using the results of DFT calculations to establish the surface reaction rate equations; finally, a kinetic model describing the oxidation process of Cu₂O is established by considering the surface reaction and the diffusion of the bulk phase. The model is validated using experimental data of Cu₂O oxidation in the literature. The results show that the model predictions are in good agreement with the experimental results.

Microchannel heat sinks are highly favored in the thermal management of high-performance electronic devices due to their superior heat dissipation capabilities. To effectively enhance the heat dissipation performance of staggered ribbed microchannel heat sinks, this paper addresses the multi-objective optimization problem for such heat sinks by combining the Non-dominated Sorting Genetic Algorithm II (NSGA-II) with response surface methodology. The optimization is carried out under the conditions of minimizing both the pressure drop across the microchannel inlets and outlets and the maximum temperature difference on the heat exchange surface. The Box-Behnken experimental design method is employed, with the rib incidence angle, rib spacing, and rib height as design variables, and the pressure drop and maximum temperature difference on the heat exchange surface as objective functions, to conduct a numerical simulation study on the flow and heat transfer performance of the heat sink. To reduce the pressure drop and improve temperature uniformity, NSGA-II is used to optimize the geometric parameters of the microchannel heat sink. Compared to the original design, the Pareto optimal solution obtained using NSGA-II resulted in a 34.922% reduction in the maximum temperature difference on the heat exchange surface, with almost no change in the pressure drop, and an overall improvement in heat transfer performance by 9.415% under the same pumping power.

The three-fluid heat exchanger features a compact structure, enabling concurrent direct heat exchange among three distinct fluid, thereby presenting significant potential for diverse applications. However, a notable limitation is the scarcity of experimental data. This study established an experimental platform for performance testing of a three-fluid heat exchanger utilizing parallel flat tubes and conducted experimental tests to evaluate its heat transfer efficiency. The results show that the heat transfer performance of the three-fluid heat exchanger is primarily influenced by the refrigerant, air, and water flow rates, as well as the temperature differentials between them. When the refrigerant experiences superheating at the evaporator outlet, enhancing the refrigerant flow rate can notably enhance the heat transfer efficiency. However, once the dryness fraction falls below 1, further increasing the flow rate leads to minimal change in heat transfer performance. In the interaction between the refrigerant and water, an increment in the refrigerant flow rate from 15.6 kg/h to 40.5 kg/h results in a gradual rise in heat transfer capacity from 817.3 W to a plateau around 1100 W. The heat transfer capacity escalates linearly with the temperature difference between any two mediums. With the elevation of air temperature from 23.9°C to 30.0°C, the total heat transfer capacity increases from 1037.6 W to 1307.4 W, with the heat transfer efficiency bolstered by higher air speed and water flow rates.

The compressor is the core component of an air conditioner, and its vibration characteristics play a key role in improving the reliability of the compressor. In order to clarify the effect of the fixing method of air conditioner external pipeline on the compressor’s vibration characteristics, this paper carried out some experimental research on it. Two variable factors, including the location of the constraints and the number of constraints on the air conditioner external pipeline, were taken into account; the vibration acceleration in different directions at each test point of the compressor was recorded during the test at an operating frequency of 30 Hz∼90 Hz. The results of the test show that a moderate increase in the distance between the restraining position and the outdoor unit can lead to a better realization of compressor vibration reduction; Increasing the number of constraints achieves little vibration reduction in the axial direction at the compressor position, but will increases the radial vibration acceleration at the motor position considerably.

If the liquid water generated in the proton exchange membrane fuel cell (PEMFC) cannot be discharged in time, it will cause “water flooding”, thus hindering the mass transfer of reactant gas and leading to the degradation of cell performance. Flow field configuration is one of the decisive factors influencing the transport properties of reactants and products. In this study, the overall performance of 108 cm² large-scale PEMFCs with conventional parallel flow field configuration and modified parallel flow field configuration with divergent design are comparatively analyzed by a three-dimensional two-phase PEMFC numerical model. It is found that the modified parallel flow field configuration enhances the liquid water discharge performance and has a more uniform current density and oxygen distribution, thus enhancing the overall performance of the PEMFC. Compared with the conventional parallel flow field, the power density, current density uniformity, and temperature uniformity of the optimal modified parallel flow field design are improved by 2.31%, 15.31%, and 8.82%, respectively. In addition, a comprehensive evaluation by the entropy weighting method reveals that the optimal modified parallel flow field design improves the comprehensive evaluation index from 0.057 to 0.309.

Supercritical water gasification technology can realize the resource utilization of biomass waste. Formation and evolution of the pore structure of particles in supercritical water are different from that of the conventional state due to the unique physical properties of supercritical water. While pore structure affects the flow, heat transfer and chemical reaction of particles in supercritical water obviously, it is crucial to investigate the pore structure evolution. In this paper, biomass gasification experiment is carried out in the batch reactor first to obtain solid particles. Then the pore structure properties of the obtained solid particles are comprehensively characterized. The influence of different operating conditions on the formation and evolution of pore structure is obtained by analyzing the pore structure properties of the particles. It is found that the pore volume of biochar is about 57 times higher than that of raw material, and the specific surface area is enlarged about 86 times. 

Carnot battery is an emerging energy storage technology characterized by low cost and independence from geographical constraints. The use of latent heat thermal energy storage in Carnot battery results in high energy density, offering broad application prospects. This paper constructs a Carnot battery system based on a packed bed latent heat storage and establishes its dynamic model. The analysis includes the impact of heat transfer fluid flow rate and organic working fluid mass flow rate on system performance. A functional relationship for the mass flow rates of the heat transfer fluid and organic working fluid has been established at a design power of 1000 kW. Subsequently, using the NSGA-II algorithm for multi-objective optimization with roundtrip efficiency and energy density as optimization objectives. After balancing using the LINMAP method, the roundtrip efficiency and energy density obtained were 62.74% and 12.96 kWh/m³.