Utilizing 70◦C low-grade heat sources discharged by low-temperature proton exchange membrane fuel cells for the efficient supply of cooling capacity is the key to enhance the efficiency of combined cooling and power systems. In this paper, a hybrid adsorption refrigeration system using solid desiccant cooling system is designed and experimentally studied to recover 70^◦C low grade heat and realize efficient cooling and dehumidification. Results show that the hybrid system can be operated effectively under a heat source temperature of 70^◦C. Increasing inlet air temperature or relative humidity can facilitate the system performance promotion. The cooling capacity and COP are up to 3.95 kW and 0.539, respectively. Using such hybrid system to exploit 70^◦C low-grade heat sources can significantly improve the overall efficacy of proton exchange membrane fuel cells, reaching 67.3%.

A finite time thermodynamic (FTT) model of HI decomposition membrane reactor under different sweep modes is established. The sweep flow rate, reaction inlet pressure, permeable membrane thickness and reactor length are taken as decision variables, and the multi-objective optimization is carried out to maximize HI conversion rate, H₂ recovery rate and total entropy generation rate. It is found that the HI conversion rate and H₂ recovery rate are consistent to some extent within a given range of decision variables, but they cannot reach the optimum with the total entropy generation rate at the same time. Compared with the co-current sweep mode, the target values of Pareto front have higher HI conversion and H₂ recovery in the countercurrent sweep mode. Different decision methods are used to select the optimal solution. TOPSIS decision point in cocurrent mode and LINMAP decision point in counter-current mode had smaller deviation factors and could be used as the optimal solution for reactor parameter design.

Based on the quantum law of corresponding states and considering the structural differences between hydrogen isomers, a mathematical model was developed for predicting the transport parameters of low-temperature orthohydrogen and parahydrogen. The results were examined and analyzed, and it was found that the quantum correspondence state principle method could predict the viscosity and thermal conductivity of orthohydrogen and parahydrogen in the temperature range of 20∼100 K and pressure range of 0.01∼10 MPa with good accuracy. The pressure has a significant impact on the prediction accuracy of the model, and the prediction error of the correspondence state principle is basically controlled within 6% when the ambient pressure is less than 1 MPa. Further correction of the physical constants in the model is expected to improve the prediction accuracy of the correspondence state principle.

The optimal cogeneration share coefficient can guide the capacity configuration of cogeneration units and maximize the economic benefits of cogeneration. In this paper, a method for determining the techno-economic optimal cogeneration share coefficient considering the energy consumption characteristics of variable load conditions is proposed, the off-design working condition analysis model of cogeneration system is developed, and the variable load energy consumption characteristics of the case unit are calculated. The techno-economic cogeneration share coefficient is optimized. The results show that the optimal techno-economic heating coefficients are 0.750 and 0.702 respectively when considering and ignoring the energy consumption characteristics of variable load conditions, and the corresponding annual cost saving relative error without considering characteristics of variable load conditions reaches 22.0%. More accurate techno-economic benefits of cogeneration will be obtained by considering the energy consumption characteristics of variable load conditions.

Based on the adaptive demand of the defrosting control method, the degradation of heating capacity (DHC) method was developed in this work to identify the frosty state, and the defrosting effect was evaluated adopting a fully connected neural network (FNN) classification model. Results indicated that in the monitoring case of the ASHP system, the proposed DHC method can effectively identify the frosty state, and the defrosting effect recognition accuracy achieved 91.3% for the trained FNN classification model in the testing data set. Compared with the original defrosting control method, the defrosting frequency, heating loss and power consumption were respectively reduced by 66.3%, 1775 MJ and 1829 MJ, and the SCOP was increased by 8.6% throughout the heating season. The promising results in this work will provide an innovative approach for the implementation and optimization of the defrosting control strategy of the ASHP system in practical operation.

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.

Based on a quasi-steady-state simulation model, a method to optimize the cooling-down rate of an auto-cascade refrigeration system operating with a rectifying column and multi-component mixed refrigerant is proposed in the paper. Targeted on the maximum cooling capacity, the optimal suction pressure-evaporating temperature curve for a specified mixed refrigerant concentration can be obtained, which can be matched by the sectional suction pressure adjustment in the practical applications to reduce the overall cooling-down time, and the concentration of mixed refrigerant can be optimized to further improve the cooling-down rate based on this way. The fastest overall cooling-down time is achieved using the R50/R1150/R290/R600a as the mixed refrigerant (0.35/0.25/0.15/0.25 by mole) and corresponding shifting parameters (including two shifting temperatures −20°C and −105°C) and three shifting suction pressure 700 kPa, 600 kPa and 550 kPa) for the sectional suction pressure adjustment, when the air temperature in the test chamber is dropped from 20°C to −100°C. Calculation results also show that the optimal concentrations are different for different evaporating temperatures, and the cooling-down rate can be improved further if the concentration of the mixed refrigerant can be adjusted during the cooling-down process. The optimization methods used in this paper can also provide references for researches on cooling-down processes of other refrigeration systems using multi-component mixed refrigerants.

The common bulkhead tank is one of the most efficient forms for cryogenic propellants, and the non-loss storage technology in the common bulkhead tank is the key issue. A cold shield model designed for the common bulkhead and zero boil-off storage is built based on the liquid oxygen/liquid methane common bulkhead and zero boil-off storage experiment system. The coefficient of temperature variation that considers the location variation characteristic and time variation characteristic of the temperature during the transient heat transfer and flow process is proposed. Compared with the nonuniformity coefficient, the coefficient of temperature variation is more suitable to evaluate the thermal uniformity of the cold shield. The results show that the cold shield with coiler performs an excellent thermal uniformity, the maximum coefficient of temperature variation of the cold shield is 3.85%.

This paper proposes control strategy based on Model Predictive Control (MPC) algorithm for the secondary cooling system of train battery. The study focuses on designing MPC and Proportion Integration (PI) control strategies for the battery secondary cooling system, and compares their control effects on the battery cooling rate. Under the battery charging and discharging conditions of 20 A and 30 A, the MPC control strategy achieves stable battery temperature in 37 s and 63 s, respectively, while the PI control strategy achieves stable battery temperature in 280 s and 500 s, respectively. The results show that compared with the PI control strategy, the MPC control strategy can significantly accelerate the battery cooling rate, and the control system has better robustness and adaptability.

Petal-shaped rod assembly has attracted extensive attention at home and abroad due to its excellent heat transfer performance. In order to obtain flow characteristics of petal-shaped rod assembly under natural circulation flow conditions, multi-scale coupling simulations were carried out on a natural circulation system with 3×3 petal-shaped rod assembly. Firstly, based on one-dimensional user program and STAR-CCM+, a one-dimensional and three-dimensional coupled numerical model of natural circulation system was constructed, and the model was verified by combining experimental results. Then, the effects of heating power and height difference on natural circulation capacity and resistance coefficient of the petal-shaped rod assembly were analyzed emphatically. The results showed that the systemic exhaust power and the height difference between the cold and heat sources satisfies a power function distribution. By introducing a viscosity correction factor and a structural influence factor, a general expression form for the resistance coefficient of petal shaped fuel assembly under wide Re number ranges, different pitches, heating, and cold conditions was obtained. Its reliability was verified based on simulation and open experimental data. 

A three-dimensional mathematical model of steam condensation flow in a smooth tube based on Euler’s liquid film model was established by using ANSYS FLUENT software. The simulated pipe is 500 mm in length and 38 mm in diameter. Under simulated conditions, the saturation temperature of inlet steam is 70°C, the total heat transfer temperature difference is 5°C and 7°C, and the inlet steam speed is 14∼20 m/s. The simulation results show that the liquid film thickness increases with the increase of the flow distance at the bottom of the pipe, and the liquid film thickness increases first and then becomes stable at the top of the pipe. The larger steam inlet velocity produces higher liquid film thickness. The liquid film flow velocity increases with the increase of the flow distance at the bottom of the pipe, and the liquid film flow velocity increases first and then slowly decreases at the top of the pipe. A larger steam inlet velocity produces a higher liquid film flow velocity.

The Brayton cycle is characterized by high efficiency and compactness, making it suitable for use in nuclear reactor thermal-electric conversion systems. In the present work, a system simulation model was built based on EBSILON software for four open Brayton cycle configurations: simple cycle, simple regenerative cycle, reheat regenerative cycle, and intercooled reheat cycle, and key parameters were analyzed. The cycle parameters were optimized with the objectives of cycle efficiency and power density, and compared with the closed Brayton cycle. The results revealed that among the four configurations, the reheating and recuperative cycle achieved the highest cycle efficiency at 25.44%, while the simple recuperative cycle demonstrated the highest power density, reaching 171.13 kW·m⁻³. Improving the open cycle into the closed Brayton cycle increased the maximum cycle efficiency by 12.56 percentage points and the maximum power density by 11.87 kW·m⁻³.

In order to meet the cooling requirements of dual temperature zones, a single compressor is used to drive 80 K and 40 K dual temperature zone cold fingers. Moreover, the dual cold fingers adopt the active phase shifter to adjust the phase difference distribution in the cold fingers. The refrigerator can achieve high-efficiency cooling in dual temperature zones with lightweight. This paper is based on the dual cooling temperature zones pulse tube refrigerator with active phase shifters. Numerical computational analyses and experimental verification studies were carried out from the characteristics of the acoustic power distribution into dual cold fingers, phase difference at the regenerator cold ends, and cooling capacity variations. The study results show that by actively adjusting the phase difference of the phase shifter piston when the ambient temperature changes, the refrigerator can maintain high-efficiency cooling and achieve active environment temperature adaptation.

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.

The safe operation of high-power electronic chips highly requires high-efficiency heat dissipation techniques. Flow boiling heat transfer has received widespread attention due to the high heat transfer coefficient. To accurately simulate the complex two-phase process of flow boiling in a microchannel, a phase change model based on the volume of fluid (VOF) method with phase interface temperature correction is proposed in this paper. The flow boiling heat transfer process in a single microchannel with a single microcolumn is simulated to investigate the effects of heat flux and inlet subcooling by analyzing the evolution of two-phase flow process and temperature field. The results show that due to the local vapor coverage, there is a turning point of thermal resistance for flow boiling in microchannel under different working conditions, and high heat flux corresponds to higher bubble growth rate and nucleation area. A high subcooling will delay the turning point, but the overall thermal resistance will increase.

In order to reduce the energy and water consumption of the cooling system in data center (DC), a DC cooling scheme coupled with radiative sky cooling (RSC) was proposed on the basis of mechanical cooling and direct air-side economizer, the corresponding system configuration and operation strategy were designed, and the mathematical model was established. A modular container DC in Xi’an coupled with the proposed scheme was simulated, and the energy and water saving effects as well as the environmental economic benefits were evaluated. In addition, the regional adaptability of the cooling scheme in 10 typical cities in China was analyzed. The results showed that, the energy saving and emission reduction rate of the proposed coupled cooling scheme (CM) can be attained 55% compared with the mechanical cooling (MCM), and increased by 5.2% compared with the outdoor air humidification scheme (OAHM). Meanwhile, the water consumption is reduced by 18.7%. Additionally, compared with MCM, the energy saving and emission reduction rate of CM in the studied 10 cities is between 42.9% and 78.1%, better energy saving and water saving benefits can be obtained.

Constructing a high-efficiency refrigeration cycle is essential for developing efficient refrigeration systems and achieving energy savings and emission reductions in the refrigeration industry. The traditional approaches to constructing refrigeration cycles are often based on expert experience, resulting in subjective and suboptimal cycle structure. This paper proposes an automatic method for constructing a refrigeration cycle with an ejector based on graph theory and heat exchanger separation. The mathematical description of the ejector structure and cycle configuration are determined, and an algorithm for constructing a refrigeration cycle with an ejector is established. The proposed method is applied to construct a refrigeration cycle with an ejector and two-phase recuperator used for freezing. The constructed cycle improves the energy efficiency ratio by 23% compared to the classical refrigeration cycle with an ejector for recovering expansion work.

A method of gas turbine overall performance evaluation was developed based on A 300 MW Class gas turbine, the effect of combustor exit OTDF&RTDF、turbine blade material and blade cooling mass flow are also added to this performance model. The accuracy of the method has been assessed by two different gas turbines, L20A and M701F3, where sufficient data can be reasonably derived from the open literature, the difference of gas turbine exit temperature are in 3^◦C. Some key parameters such as pressure ratio, compressor efficiency, combustor loss and temperature distribution, turbine stages, turbine efficiency, allowable metal temperature of turbine blade material and cooling mass flow were researched, and found that the effects of compressor pressure ratio, combustor temperature distribution, turbine stages and efficiency, blade material and cooling mass flow are quite big, and turbine stages have the biggest effect to gas turbine exit temperature. These parameters should be carefully considered in a new GT design to have the best GT exit temperature.

The water and thermal management strategies in the proton exchange membrane fuel cell stack are closely related to the structure and size of the stack. Computer-aided design simulation tools can be included in the development process. A two-dimensional model of the rapid prototyping stack based on COMSOL software is developed in the present study. In the model, the components of the entire are considered. The interactions among the transport processes of air, water, heat, and electricity within the membrane electrode assembly, bipolar plates, and cooling water channels are computed. A pair of inlet and outlet headers are added to the model to realistically simulate the gas flow distribution of the entire stack. The geometric dimensions and the number of unit cells in the model are parameterized, which can be quickly modeled and simulated according to the design requirements. A preliminary design scheme for the stack can be provided before more detailed 3D simulations are carried out. A 2D fuel cell stack model with 10 unit cells connected in series is presented as an example. This model solves a complete set of mass, momentum, composition, and temperature conservation equations for heat transfer in gas flow channels, porous media, electrode coupling surfaces, and solid fluids. With the U-shaped configuration, the oxygen velocity, mass fraction and current density distribution characteristics of the electrode coupling surface of the battery stack are analyzed. Based on the stack model, the effects of parameters such as voltage,PEM conductivity, and air intake velocity on the stack moisture distribution are studied. The simulation results show that high voltage operation, larger conductivity of the proton exchange membrane, and larger air flow rate will improve the stack performance. By optimizing the existing model structure, a more uniform distribution of water and gas in the stack is obtained, providing a reference for the further fuel cell stack design.

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.

The application, screening, evaluation and funding of National Natural Science Foundation of China programs in Engineering Thermophysics and Energy Utilization Discipline in 2023 are summarized and statistically analyzed. The strategic research, funding proposals in the field of energy conversion and utilization under the carbon peaking and carbon neutrality goals are introduced. The outstanding achievements funded by the discipline in 2023 and future work in 2024 are introduced as well.

The key to performing efficient adjoint-based design optimization is accurate sensitivity information. First, based on the in-house Reynolds-Averaged Navier-Stokes (RANS) flow solver, the discrete adjoint solver is developed using the source code transformation automatic differentiation tool-Tapenade. Second, the effect of both flow and adjoint solvers’ residual convergence levels, constant eddy viscosity assumption, and four different sensitivity evaluation methods on adjoint sensitivity accuracy is mainly studied. Then, the experiences of computing efficient and accurate adjoint sensitivity information are summarized, which provide the basis for performing efficient adjoint-based design optimization. Finally, the adjoint-based turbomachinery aerodynamic design optimization of the transonic compressor rotor-NASA Rotor 67 is performed. Moreover, the commercial software-NUMECA is used to further verify the effectiveness and reliability of the optimization results.

When the distance between solid walls is only a few nanometers, the self-diffusion coefficient of fluid is reduced by 1∼2 orders of magnitude due to the nanoconfinement effect, and the effects of pore size, temperature and pressure are significant and complex. It is of great significance to analyze the diffusion mechanism and law of nanoconfined fluid and establish a concise correlation formula. In this study, a wide range of fluid self-diffusion coefficient data in nanopores were obtained through careful calculation and analysis based on molecular dynamics simulation. The mechanism and law of the adsorption effect on fluid diffusion were analyzed, and a novel dimensionless diffusion coefficient, which can simply describe the fluid diffusion behavior, was proposed, and the corresponding correlation formula was established with Knudsen number, which has strong applicability.

Integrating direct air carbon capture (DAC) with renewable integrated energy systems (IES) provides an effective pathway to regional carbon neutrality. The reasonable configuration approach is a prerequisite for the stable, flexible, economic and zero-carbon operation of the overall system. Conventional configuration approaches cannot reflect the dynamic CO₂ mass transfer characteristics and energy consumption differences of DAC adsorption and desorption, resulting in suboptimal or infeasible configurations. To this end, this paper constructs the configuration-oriented DAC models to reflect its dynamic operation characteristics. Based on this, a DAC-IES configuration scheme is established with the annual total costs including investment costs, operation and maintenance costs, renewable curtailment penalties, and negative-carbon environmental benefits as the objective function to obtain the optimal capacity and collaborative operation strategy of each equipment, revealing the flexible operation mechanism of DAC under the background of intermittent fluctuation energy supply. The case study validates the effectiveness and superiority of the proposed configuration method. The analysis also indicates that the flexible operation of DAC systems enables better coordination with renewable energy and more cost-effective carbon capture. 

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 the field of active thermal utilization of nuclear energy, high temperature heat pipes (HTHPs) need to have a large length and ensure superior temperature uniformity. However, the existing research focuses on theoretical prediction of the performance and preparation of the HTHP with a relatively short length. In this paper, the HTHP with the length-diameter ratio of 67 is first prepared, the frozen start-up characteristic is theoretically analyzed, and the frozen start-up and steady heat transfer performance are experimentally studied, and a heating method that could give full play to the excellent heat transfer performance of the HTHP with a large length-diameter ratio is proposed. The HTHP with the length-diameter ratio of 200 is further prepared, and its heat transfer performance is qualitatively verified. The frozen start-up process is investigated by quantitative experiments, and the heat transfer law in the laryngeal region of the super-long HTHP is found.

In order to reduce the influence of alcohol-amine carbon capture system on thermal economy of coal-fired power plants, a carbon capture system was built based on rate model through ASPEN PLUS software, and built a novel carbon capture system integrating rich liquid split process, lean vapor compression process and steam superheat utilization. The results show that when the liquid-rich split ratio is 0.1 and the flash tank pressure is 0.16 MPa, the energy consumption of the novel carbon capture system is the lowest (3.09 GJ/t (CO₂)), which is 20.77% lower than that of the conventional carbon capture system. Among them, the utilization of steam superheat reduces the energy consumption of the system by 11.54%. In addition, EBSILON software was used to build the sub-critical unit thermal system coupled with the carbon capture system. The results showed that when the unit load is 127.55 MW and CO₂ capture capacity is 500000 tons/year, the boiler heat load of the novel carbon capture unit decreased by 1.87% and the coal consumption for power generation decreased by 7.22 g/kWh. It can be seen that the optimization measures adopted in this study can not only reduce the reboiler duty of the carbon capture system, but also greatly improve the thermal economy of the subcritical carbon capture unit.

To meet the urgent need of efficiency improvement of micro gas turbines, a highperformance microchannel recuperator suitable for additive manufacturing processing is designed. Based on the basic theory of counter flow heat exchanger and the characteristics of metal additive manufacturing, a modular wavy plate microchannel heat exchanger is designed. The stainless-steel prototype is processed by laser selective melting technology, and tested experimentally. The heat exchanger unit contents 52 microchannels with height of 0.7 mm. The compactness of the prototype reaches more than 1700 m²/m³. The experimental results show that average Nu number increases by 88.9% compared with the traditional flat primary surface heat exchanger under the condition of relative pressure loss less than 2%, and the key performance parameters proves the advancement of this heat exchanger among the existing compact heat exchangers.

Sugar alcohols, as high-performance medium-temperature phase change thermal storage materials, have attracted significant attention, and their thermal stability is an important material property parameter that restricts their practical use. This study focuses on erythritol and comprehensively evaluates its thermal stability using three indicators: mass loss, melting point change, and melting enthalpy decay. Additionally, a kinetic model for assessing its thermal stability is established. The results show that the primary gaseous products of heated erythritol include various small molecules, while the solid products mainly consist of the formation of C=O bonds. A comparison of thermal stability characterization parameters such as mass loss, melting point, and melting enthalpy reveals that the melting enthalpy of erythritol decreases by 10.2% in the air atmosphere at 145°C for 48 h, which is significantly higher than the changes observed in the other two indicators. Therefore, melting enthalpy decay is chosen as the evaluation indicator for erythritol’s thermal stability. In a nitrogen (N₂) atmosphere, the activation energy of the melting enthalpy decay model is determined to be 80.0 kJ·mol⁻¹, with a logarithmic pre-exponential factor of 15.14 h−1. Based on the model, further analysis indicates that the half-life of erythritol’s melting enthalpy at temperatures ranging from 120 to 140°C is between 2401 to 7851 h.

A novel built-middle photovoltaic Trombe wall with vertical fins was proposed in this study. Based on the first and second laws of thermodynamics, the effects of fins spacing and height on the performance were numerically investigated, and the performance was compared with that of the built-middle photovoltaic Trombe wall without fins. The results show that the thermal efficiency can be effectively improved within a certain range of fins spacing and fin height. Decreasing the fins spacing and increasing the fins height can enhance the electrical efficiency. By introducing the overall exergy efficiency, it is found that the obtained electrical energy dominates the overall exergy efficiency compared to thermal energy. There exists the optimal fins spacing to maximize the overall exergy efficiency under higher fins, and increasing fins height can enhance the overall exergy efficiency of the system. The finned-built-middle photovoltaic Trombe wall has the overall exergy efficiency of 12.74% at 15.625 mm of fins spacing and 45 mm of fins height, which is an improvement of 11.29% compared to the system without fins, and has a great potential for application.

In modern warfare, infrared stealth of military objectives plays an important role in improving their survival and breakout capabilities. In this paper, aiming at the multispectral infrared stealth, i.e., narrow-band high absorption at the active detection wavelength of near-infrared laser (1.54 μm), low emission in the two atmospheric window bands and taking into account the radiative heat dissipation requirements in the non-atmospheric window bands, we combine the rigorous coupled-wave analysis and deep learning methods to reversely design the Ge/Ag/Ge multilayer film circular hole metasurface structure. By analyzing the potential physical mechanisms and the emission and absorption characteristics at different angles for the optimized structure parameters, the multi-band synergistic stealth is achieved.

The problem of oxygen carrier (OC) sintering and agglomeration in long-term chemical looping combustion (CLC) limits its industrialization progress. In the paper, a kind of Cu-based oxygen carrier was prepared by the fluidized bed crystallization granulation method, and studied by long-term redox cyclic tests on a fluidized bed thermogravimetric analyzer (FB-TGA). The reactive activity measurement was conducted on the OC particles before and after the redox cycles. The results show that the reactivity of the OC particle remains stable after 24 h redox cycles, and there were no obvious sintering and agglomeration. The morphology characterization was carried out on the OC particles before and after the redox cycles. The BET of OC particles is up to 40 m²/g, resulting in better reaction activity. In addition, the main component in the OC particles was transformed from CuAl₂O₄ into Al₂O₃ and CuO after 24 h redox cycles. The Cu-based OC particles exhibit a smooth spherical structure after the redox cycles, and still maintain porous. The active Cu element is highly dispersed on the particle surface. 

Based on the chemical reaction mechanism of diesel fuel with PODE, the TRF-PODE chemical kinetics model was constructed and verified, the ignition and combustion characteristics of PODE/diesel fuel were studied by numerical simulation at high altitude. The results show that the addition of PODE increases the instantaneous heat release rate and decreases the corresponding time of the highest point of ignition temperature under the condition of low pressure at high altitude. The maximum ignition promotion rate occurs in the region of negative temperature coefficient (NTC), which is increased with higher PODE blending ratio. PODE increases the formation of OH· and promotes the pre-oxidation of nC₇H₁₆ in the low temperature oxidation at high altitude. As a result, the highest mole fraction of hydroxyl group in the reaction increases obviously with the decrease of pressure, which leads to the decrease of reaction rate. Under high temperature, the oxygen of PODE itself increases the formation of OH· in the reaction, leading to a reduction of the proportion of O₂ participating in the formation of OH·. Therefore, more O₂ could oxidize the small molecules in the reaction, promote the formation of free ions, and enhance the reaction activity, which is beneficial to improve the combustion characteristics of diesel engines at high altitude.

In the design process of modern turbine blades, the geometric parameters along the radial distribution need to be constantly adjusted, and the design cycle is long. In order to solve this problem, this paper constructs a one-dimensional design method of three-dimensional blade: the blade flow channel is divided into several sub-flow channels along the radial direction, and each sub-flow channel is designed in one dimension to obtain its optimal speed ratio and geometric angle. Then, the one-dimensional design results of each sub-flow channel are superimposed along the radial direction to construct a three-dimensional blade. Using the boundary conditions of the last stage of an F-class gas turbine, the blade is redesigned by this method, and the parameters such as the static blade outlet pressure and the backward angle in the numerical simulation results are used as additional constraints for fine design. The results show that compared with the original design, the optimized turbine has a slight increase in the loss in some areas of the rotor, the flow rate is reduced by 0.26%, but the outlet kinetic energy loss is significantly reduced. At the same time, the wheel efficiency is increased by 1.7%, the total-to-total efficiency is increased by 0.37%, and the shaft work is increased by 1.47%.

In order to explore the advantage mechanism and flow rate adjustment limit of the variable tandem stator compared with the conventional stator, the variable-angle performance of a two-stage fan under the condition of the conventional stators and the variable tandem stators is analyzed by numerical simulation. The results show that the flow angle at the exit of the stator determines the flow rate of the rotor components in next stage, the flow rate of the stator components can be increased by opening the front blades of the tandem stator, and the overall flow rate of the fan is limited by the flow rate of the stator components. For the intermediate stage, adjusting the conventional stator will cause the change of the inlet and outlet geometric angles to be unmatched. After changing to tandem stator, adjusting the appropriate front blade angle will greatly reduce the stator loss and increase the flow capacity under the same outlet geometric angle. For the exit stage, the tandem stator can adjust the front blade of the series to achieve higher flow capacity and less loss on the premise of ensuring the flow direction of the fan outlet. Compared with the conventional scheme, the efficiency of the tandem scheme is increased by 10%. 

By employing the digital particle image velocimetry method, the electric-field-controlled deformation and rotation characteristics of a droplet in a shear flow field are experimentally studied. The electrohydrodynamic mechanisms of the droplet deformation are revealed and the effects of the electric field and shear flow field on the droplet deformation are summarized. It found that the droplet deformation can be controlled by altering the strengths of the shear flow field and electric field, and the physical parameters of the fluids. when the conductivity ratio of the droplet to the continuous fluid R is larger than the permittivity ratio S, the viscous force cooperates with the electric force and the surface charge convection effect to promote droplet deformation. when R<S, the electric force and the shear flow force promote the droplet deformation, while the surface charge convection effect reduces it. Besides, a vortex inside the droplet is formed by the shear flow. The vortex intensity is enhanced and reduced by the electric field when R>S and R<S,

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).

The combination of spray flash and mixing evaporation (FME) was one of the most effective way to process wastewater with high aqueous salt concentration. In this paper, aqueous NaCl solution was selected as working fluid, a comprehensive calculation model for flow field of FME, including movement, evaporation and crystallization of droplets was set up on basis of previous experimental results. Numerical simulation was carried out with initial diameter of droplets between 20 and 200 μm, initial temperature between 100 and 120^◦C, initial mass fraction 0.26, initial speed 20 m·s⁻¹, and air speed of 15 m·s⁻¹, air temperature between 100∼300^◦C, and spray angle between 0 and 90◦ Results suggested that, during the increasing of spray angle from 0 to 90^◦ the main location of crystallization moved from the spray axis to the top of spray plume, making crystal easier to be separated. Besides, with the increasing of spray angle, superheat or air temperature, the average mass fraction of crystallization increased, but the average particle size and crystallization distance decreased. In order to measure the effect of crystallization within a given distance, complete crystallization efficiency was defined as the ratio of the mass flow rate of crystal salt of droplets to the mass flow rate of dissolved salt at inlet. Results suggested that this efficiency could be improved by increasing spray angle or air temperature. A semi-empirical formula for complete crystallization efficiency was proposed, and the main error between its calculated value and the simulated value was in ±35%. Above conclusion could provide technical support for design and operation of industrial desalination system.

Based on the technique of “solving regionally and couping at the interfaces”, this paper proposed a coupled model to numerically investigate the transient heat and speices transport during the phase change transpiring cooling process using the water as the working fluid. The results indicated that maldistribution of coolant would occur due to the unsteady and nonuniform heat flux from the supersonic mainstream, and the maldistribution of coolant would inherently exacerbate during the applications. After 30 s of the transpiration cooling, with the coolant flow being squeezed to the downstream, the peak flow rate exceeds the inlet flow rate by the factor of 9.1, and the area of low flow rate region filled by evaporated coolant occupied over 76% of all. The increase flow rate would induce a liquid film at the interface, which could reduce the thermal insulating properties, thus the surface heatflux on the porous region filled with the liquid phase coolant (about 0.15 MW·m⁻²) would be higher than the region filled with evaporated coolant (about 0.11 MW·m⁻²). However, the cooling capacity of gaseous fluid is relatively low, and the temperature of porous strucure filled by gasous coolant would rapidly increase. Therefore, regulating the inlet coolant flow would be nescessary to mitigate the effects of local coolant evaporation.