To enhance the recovery of low-grade compression heat in supercritical carbon dioxide (S-CO2) energy storage systems, a novel system integrating a three-stage non-uniform compression and expansion cycle with heat pumps is proposed by this study. A multi-stage optimization strategy is developed based on steady-state thermodynamic modeling to identify the optimal design configuration and maximum theoretical efficiency. The Pareto-optimal front is identified by the NSGA-II algorithm, followed by the selection of final solutions via the TOPSIS method, and a final refinement guided by the ratio allocation model. The round-trip efficiency (RTE) is shown to be improved from 68.7% to 73.0% as the third-stage expansion ratio is increased from 1.5 to 3.0. A configuration with a decreasing compression ratio and an increasing expansion ratio is identified as the optimal setup among the nine modes, through which a maximum RTE of 73.6% and a peak turbine output of 4.2 MW are obtained. The inlet temperature of the first-stage compressor (Tcom1) is revealed by sensitivity analysis to be the most influential parameter on both RTE and net output power, with sensitivity factors of 1.3 and 2.9, respectively. By implementing the multi-stage optimization strategy, these performance metrics are further enhanced, culminating in a maximum RTE of 77.48% and a peak net power output of 4.68 MW.

High-pressure die casting (HPDC) is extensively utilized in the automotive industry because it can efficiently manufacture complex components. But the components produced can suffer from porosity defects that deteriorate the subsequent mechanical properties of the castings. To address this problem, the highly integrated die casting (HIDC) process was developed and tested to significantly suppress porosity defects. However, the mechanism of defect formation and the evolution law of flow and solidification of the HIDC process have not been fully elucidated. A refined three-dimensional model with dynamic mesh was developed to simulate the entire transient HIDC process of ADC12 aluminum alloy. The model encompasses low-pressure filling, depressurization, high-pressure injection, and solidification. Experimental data were used to define the inlet velocity and piston position curves as initial conditions. Additionally, the influence of liquid fraction on the wall heat transfer coefficient was considered. The simulation results agree well with the experimental data in terms of porosity area and defect distributions. The evolution of defect formation and solidification fraction in the HIDC process was demonstrated. In addition, the effects of filling percentage and slow injection speed were discussed. It was found that a filling percentage of 60% is the optimal value for balancing gas inclusions and stratified solidification defects, which is in good agreement with the experimental results. Increasing the slow injection speed from 0.09 m/s to 0.16 m/s mitigated gas entrapment caused by melt backflow. Consequently, the predicted porosity decreased from 7.2% to 0.29%.

Addressing the issues of poor thermal conductivity in traditional Kelvin structure-based heat sinks and the suppression of natural convection in the TPMS structure-based heat sinks. The Half Primitive structure proposed in this study is designed to investigate and validate the effects of enhancing thermal conduction across thermally contacting interfaces and promoting heat transfer induced by internal natural convection. Numerical simulations based on the sensible heat capacity method are conducted to analyze the thermal behavior. The numerical model has been validated, and the simulation results are in good agreement with the test results. The effects of heat transfer properties, including temperature, average heat transfer coefficient (havg), and Grashof number are discussed. The analysis results indicate that the enhancement of thermal conduction across thermally contacting interfaces and the promotion of internal natural convection significantly improve the thermal performance of the PCM-based heat sink. After enhancing the thermal conduction at the bottom, the Half Primitive structure reduced the base temperature difference between the Kelvin structure and the primitive structure by 73 % at 650 s. Following the enhancement of internal natural convection, taking the average base temperature difference between pure conduction and convection heat transfer scenarios as an example, the average temperature difference of the Half Primitive structure is 8.64 % higher than that of the Primitive structure. Moreover, the havg of the Half Primitive structure is 36.3 % higher than that of the Kelvin structure, and the difference in havg between the Half Primitive and Primitive structures narrows to approximately 4.8 %.

Lattice structures based on triple periodic very small surfaces (TPMS) have been widely studied in the field of heat transfer due to their complex geometries that offer the advantage of increasing the heat exchange area and enhancing convection phenomena. However, the influence of specific structural parameters of a particular TPMS structure type on the overall flow and heat transfer characteristics remains understudied. In order to investigate the relationship between the structural parameters and the heat transfer and flow properties to meet the thermal design requirements, this paper designs a heat exchanger based on a Gyriod-type TPMS structure according to the actual working conditions of fuel/lubricating oil heat exchanger in an aero-engine. Numerical simulations are carried out using the SST K-omega turbulence model, and the relationships between the three design parameters (uniform lattice size l, unidirectional lattice size l(single), and hot/cold fluid porosity ratio epsilon(h)/epsilon(c)) and the key characteristics, such as the flow resistance and convective heat transfer coefficient, are calculated. Among them, the structural parameters l and l(single) are mainly used to improve the heat transfer effect by changing the heat transfer area of the heat exchanger, and the parameter epsilon(h)/epsilon(c) can largely improve the convective heat transfer coefficient and optimize the flow state by changing the distribution of the cold and hot fluid channels. In the studied range of structural parameters, the convective heat transfer coefficients of cold and hot fluids of the epsilon(h)/epsilon(c) = 2 model under the same working condition are 34 % and 26 % higher than those of the 10 mm model, and the average synergistic angle of the cold fluid surface on the XY center plane is 77.55 degrees.

Concentrated photovoltaic-thermoelectric systems have received extensive research attention as a means of enhancing the utilization rate of solar energy. However, the expedited progress of these systems has been hindered by a myriad of challenges, such as the additional power consumption required for active cooling and the inadequate cooling rates of conventional passive cooling techniques. To overcome these limitations, a novel concentrated photovoltaic-thermoelectric system integrating thermosyphon cooling has been developed and subjected to a comprehensive analysis, encompassing its start-up performance, pipe resistance characteristics, and power generation performance have been analyzed. The results reveal that the buoyancy generated by the thermosyphon is 8.22 N, which effectively drives the speed of cooling water circulation to 0.011 m/s. The startup time of the thermosyphon effect lengthens gradually with a decrease in inclination angle of heat sink, while the cooling temperature at the final stable state remains relatively consistent. Remarkably, at 240 kW/m(2), the concentrated photovoltaic cell exhibits a remarkable heat dissipation power density of 15.26 W/cm(2). Meanwhile, the optimal output voltage of concentrated photovoltaic is 1.907 V, at which the concentrated photovoltaic output power is 1.774 W. The optimal output voltage of thermoelectric is 0.528 V, at which the thermoelectric output power is 0.054 W. The results provide guidance for designing high-performance cooling systems for concentrated photovoltaic-thermoelectric systems.

During the operational process of electronic components, excessive heat generation results in significant temperature elevation. This elevated temperature poses a significant risk to their service life. Regarding the issue of efficient thermal management of electronic devices in enclosed spaces experiencing high heat flow, a thermal management scheme for electronic equipment using TPMS and a PCM-based heat sink is proposed. The apparent heat capacity method is employed to simulate the melting process of the PCM-based heat sink. The effects of structural parameters w1, w3, and C of TPMS structures on the heat transfer characteristics (including base temperature, liquid fraction, average cell temperature, and average heat transfer coefficient) of the PCM-based heat sink during the melting process are discussed. A temperature testing platform is established. Experimental research is performed to investigate the effect of TPMS structures with two different printing prototypes (Sample 1, and Sample 2) on the heat sink during the intermittent cycle. The results indicate that increasing the parameters C and w1 significantly improves the average heat transfer coefficient (HTC) of the heat sink. When C increases from 0.3 to 0.7, the average HTC increases from 307 W/(m2 & sdot;K) to 358 W/(m2 & sdot;K). When w1 increases from 1 to 3, the average HTC increases from 284.5 W/(m2 & sdot;K) to 321.3 W/(m2 & sdot;K). Sample 1, possessing superior thermal conductivity, exhibits better heat transfer performance. When the temperature achieves a stable periodic variation, the base temperature of Sample 1 stabilizes within the range of 310 K-340 K. And Sample 2 stabilizes within the range of 315 K-350 K.

Compressed energy storage systems play a crucial role in the widespread adoption of renewable energy, effectively addressing the unpredictability and intermittency of renewable energy. Among these systems, compressed supercritical carbon dioxide systems represent a novel category within the realm of energy storage solutions. To enhance the utilization of low-quality compression heat, this study introduces an approach involving staggered correspondence between compression heat and regenerative heat utilization. Building upon this concept, a coupled heat pump-type energy storage system is developed without needing an external heat source. A nonuniform compression and expansion ratio optimization strategy is presented, based on the staggered heat utilization method. This method considers the utilization of compression heat in graded stages. On this basis, from the thermodynamic parameter perspective of the stage design, compression and expansion ratio, the thermodynamic characteristics are analyzed using round-trip and thermal efficiency as key metrics. Results indicate that optimal compression and expansion ratios should prioritize first-stage compression and second-stage expansion. Notably, implementing a first-stage compression ratio of 4.5 and a first-stage expansion ratio of 1.5 respectively enhances round-trip efficiency by 10.2 % relative to the initial design conditions (69.0 %) and the maximum efficiency up to 80.1 %.

The setting machine exhaust gas contains a large number of fiber particles and micro oil droplets, which are adhesive and flammable. This leads to difficulties in waste heat recovery of the exhaust gas. In this article, numerical and experimental studies of a non-uniform plate heat exchanger with dimples/protrusions for waste heat recovery of setting machines are carried out. Based on the three-dimensional fluid-thermal-structural coupling method, the regenerative process between gas and air are investigated numerically with low Reynolds number turbulence model. The effect of the structural parameters (protrusions diameters, protrusions spacing and plate spacing) and operation parameters (air inlet temperature, gas and air flow rate) on the heat transfer performance are discussed. The multi-objective optimization of the plate regenerator is conducted by Box-Behnken Design and Nondominated Sorting Genetic Algorithm II to maximize the thermal performance coefficient and minimize entransy dissipation number. It is found that when D1, H1 S1, D2, H2, S2 are 9 mm, 7 mm, 161 mm, 9 mm, 8 mm and 153 mm respectively, the heat exchanger has the best heat transfer performance. Compared with the original model, the heat transfer rate of the optimized heat exchanger is increased by 3.9%, the thermal performance coefficient of the air side and flue gas side is increased by 5.7% and 5.9% respectively, and the entransy dissipation number is reduced by 24.6%.

A model of a NUAA-PTRE pre-cooled air turbine engine was established. The design point parameters of the engine were optimized, including the pressure ratio, air flow rate of the compressor, efficiency, throat area, and efficiency of the turbine. The air flow rate at the engine operating point was 142.73 kg/s. High performance of the key components under a wide range of working conditions was realized after optimization. To achieve the indicators of the overall scheme, adaptability studies of key components were conducted. A three-stage variable geometry design was applied to the inlet. The pre-cooler was optimized with a power-to-weight ratio of over 100 kW/kg and a compactness of 278 m2/m3. The built-in rocket gas generator and dual-component injector were developed, and the combustion and heat transfer processes were simulated. The overall optimization design of the NUAA-PTRE and the adaptive design of the components were completed, and high performance of the engine in a wide range of flight conditions at Ma 0~5 and altitude 0~25 km was achieved.

Thermal management of equipment in confined spaces is of great importance for the safe operation of equipment. Solid-liquid phase change materials (PCM) can be applied to the thermal management of intermittent electronic equipment because of their large isothermal latent heat absorption capacity. In this paper, experimental and numerical research on the thermal performance of an intermittent rectangular cavity plate fin PCM-based heat sink is carried out, which can be applied to heat dissipation in narrow spaces with high heat flow. The optimal PCM-based heat sink structure is obtained by numerical simulation based on the Taguchi method, and the enthalpy method is used to model the phase change process. Temperature testing and visualization experiments are used to visually present the PCM-based heat sink's internal temperature distribution and validate the numerical model. The effects of fin structure parameters, heating power, cooling air speed and number of intermittent cycles on thermal performance (base temperature, liquid fraction and operating time) are analyzed for different structured PCM-based heat sinks. The results show that the PCM-based heat sink with 8 fins, 15 mm fin height and 2 mm fin thickness has the longest stage C at the critical base temperature of 348 K and reaches the maximum operating time of 1193 s during the charging cycle. The natural convection in stage C of the charging cycle plays a crucial role in prolonging the operating time. Meanwhile, increasing the number of intermittent cycles can result in longer operating time and lower critical base temperature. As the number of intermittent cycles increases from 1 to 8, the temperature difference between the maximum and minimum temperature of the base during the whole cycle is reduced from 48 K to 25 K, and the temperature fluctuations gradually decrease.

Herein the multi-objective optimization of an axial cyclone separator is performed to enhance the overall performance with different velocities. And the separation efficiency and pressure drop are expected as the objective functions. In this paper, the difference value between internal and external blade outlet angles is regarded as one of the parameters to optimize. The regression expressions, which are obtained by Box-Behnken Design and the two-fluid model, are used in Nondominated Sorting Genetic Algorithm II to maximize separation efficiency and minimize pressure drop. It is found that the separation efficiency has a peak value with the rise of inlet velocity, and the response degrees of the internal angle, difference of the two angles, and blade number is disparate at different velocities. The pressure drops of the optimal axial cyclone tubes are smaller than the initial ones, but the separation efficiency is almost the same. Meanwhile, the accuracies of the optimization and numerical results are verified by the experiments. For the samples in 3, 5, and 7 m/s, pressure drop can be reduced by 24.1%, 22.7%, and 34.3% respectively. The simulation results indicate that the radial pressure difference and swirl number have been reduced. Besides, the optimal designs have more stable and even near wall particle distribution after multi-objective optimization.

In recent years, renewable energy, particularly solar energy and wind energy, has demonstrated robust growth worldwide. However, the intermittent nature of these energy sources causes significant challenges for the security and reliability of grid, which limits the penetration growth in power market. To enable a higher penetration of renewable energy sources and satisfy the demand for peak shaving and valley filling of the grid, one possibility is to couple them with energy storage systems. In this study, two supercritical compressed carbon dioxide energy storage systems coupled with concentrating solar thermal storage are proposed. One is a simple compression cycle, and the other is a split compression cycle. Both thermodynamic and economic performance have been investigated numerically. The effects of energy storage pressure, heating temperature, thermal oil mass flow rate and split ratio are discussed. The results indicate that under the designed condition, there exists a maximum energy storage efficiency for the simple cycle when the heating temperature is lower than 538.15K. Continuing to increase heating temperature, the efficiency first increases from 64% to 73.9% rapidly as the total pressure ratio rises from 3 to 5. However, the improvement of it will be limited after the pressure ratio exceeds 5. Besides, if the thermal oil mass flow rate rises, the efficiency also has a maximum value, which appears between 150kg/s and 160kg/s. Finally, for the split cycle, there exists an optimal value. And the optimal condition can promote the Dynamic Payback Period and Levelized Cost of Energy to fall about 2 years and 6.1% compared to the simple cycle.

In order to solve the heating problem of electronic devices, an optimal configuration of rectangular cavity straight fin phase change material (PCM) based heat sink is determined to extend the safe operating time in the charging process. With PCM-based heat sink as the object of research, a three-dimensional and transient melting model is constructed. The effects of fin number, height and thickness on phase change heat transfer process and natural convection are explored in depth, and the optimal configuration parameters of PCM-based heat sink are obtained. The results show that the configuration of 8 fins,15 mm in height and 2 mm in thickness is adopted as the optimal heat sink structure, with the longest safe operating time-1170 seconds. In the stable period of phase transition, the base temperature remains unchanged and the natural convection disturbance is strong. The short and dense fin arrangement can prolong the safe operating time of safety limit temperature 343K better.

The influences of the internal and external outlet angles on separation performance and flow field are compared and analyzed. Two arc functions are employed for controlling the internal and external angles. The separation process in the cyclone tube is calculated by using two-fluid model based on the Eulerian-Eulerian method. The results show that the structure with the internal outlet angle smaller than the external one is more beneficial to the separation performance. It is found that the small internal angle can help increase the swirl number,while the small external angle can help increase the friction coefficient. Several groups of numerical simulations are conducted for the air intake unit of the gas turbine in practice. When the internal outlet angle is 35° and the external outlet angle is 40°, the blade has sufficient cyclone strength and the separation rate of particles with diameters of 10—100 μm is between 70％—98％. The small blade angle is more conducive to the separation of fine particles,leading to violent collision of large particles on the outer wall and reduction of separation efficiency. In addition,reducing the external angle is conducive to the discharge of large particles.

Abstract The axial cyclone separator has simple structure, operates to reducing dust concentration in grain storehouses, and features low production cost, and convenient installation. Aiming to obtain the separation characteristics of an axial flow guide separator, the particle wall collision and the performance of multi-tubes were simulated with Fluent. The renormalization group (RNG) k − ε model was used to study the turbulent modeling and the user define function (UDF) was used to calculate the particle-wall collision. The simulation and experimental results were compared to verify the computation model. The results showed that the basic feature of the flow pattern remains stable and the separation efficiency of 800 kg/m3 particles is higher than 2650 kg/m3 particles when the inlet velocity increases from 2 to 5 m/s. When the inlet velocity was 5 m/s, the normal velocity restitution ratio had a significant effect on the efficiency, the separation efficiency of 167 μm particles changed from 76.74 to 97.93% and a smaller normal velocity restitution ratio had a higher the efficiency. In comparison, the efficiency remained unchanged when changing the tangential velocity restitution ratio. Furthermore, the effects of three target wall materials on the separation efficiency were investigated. And the simulated efficiency the of 296 μm particle of 2024 aluminum, 410 stainless steel and Ga1–4V titanium were 82.15, 79.52 and 77.53% respectively. Besides, effects of tube diameter on performances of cyclone separator were discussed and high intense collisions between particles and walls may occur in a small diameter of cyclone tube, causing deteriorated separation performance. Moreover, with the addition of the dust chamber, the efficiency of cyclone used in combination is slightly improved since the vortex in the exhaust pipe has been finely changed.

真空保温技术广泛应用于LNG的储藏和运输领域,利用真空层进行隔热是一种有效的保温手段.模拟研究了带有聚四氟乙烯支撑环的三维输送管道的散热过程,讨论了真空层压力、环境温度、对流换热系数对散热性能的影响规律,并与热阻分析结果进行了对比验证.结果表明:随着真空层压力从0.001 kPa升至5.33 kPa,换热量从83.82 W升至124.72 W,0.001 kPa到2 kPa段的换热量升高的最快.随着外界温度从268.15 K升至298.15 K,换热量从97.54 W升至120.56 W,并且呈线性增长趋势.随着外界对流换热系数从5 W/(m2·K)增至25 W/(m2·K),换热量从112.1 W增至127.8 W.管间区域的空气在上方形成一个温度为290 K左右的高温区,下方形成一个温度为80 K左右的低温区,两区域之间形成环流,环流中部的空气流动速率最快为0.26 m/s.

基于欧拉方法,考虑温度对热物性的影响,耦合相间换热和界面浓度模型,模拟鼓泡塔内气体和熔融盐的换热行为.模拟分析熔融盐温升速率、体积换热系数和塔内熔融盐温度分布的规律,结果表明熔融盐温升速率和体积换热系数随表观气速的增加而增加,随初始液面高度的增加而减小,中心处熔融盐温度沿轴向高度增加逐渐减小,熔融盐温度径向分布随液位高度的增加逐渐趋于均匀.

Supercritical Carbon Dioxide (S-CO2) Brayton cycles and Concentrating Solar Power (CSP) plants are gaining increasing attention due to environment pollution problems and their higher efficiencies. At present, there is a lack of researches on the dynamic thermal analysis of CSP plants based on S-CO2 Brayton cycle, which needs to be resolved urgently. Therefore, a one-dimensional dynamic model of the printed circuit heat exchanger (PCHE) is developed, which is incorporated into transient model of the solar tower power plant. And the Modified Euler or Fully-implicit Runge-Kutta Method is used to complete the dynamic solution. The results indicate that the pressure ratio equaling to 3.5 and the zigzag PCHE regenerator with a diameter of 2 mm will be the best choice for our designed power plant to achieve the balance between larger net output work and power efficiency improvement, which provides the reasonable design parameter for more complicated three-dimensional transient models. By taking the binary nitrate working temperature limitation and common influences of temperature and pressure on S-CO2 thermophysical properties into consideration, as the direct normal irradiance (DNI) decreases, the S-CO2 heat transfer coefficient will increase. When DNI value changes between 780 W/m(2) and 970 W/m(2), the cold side S-CO2 outlet temperature of PCHE regenerator and S-CO2 Brayton cycle power efficiency will produce 114.65 K and 8% fluctuation in no more than 15 minutes.

随着工业生产和社会经济的迅猛发展,电能的消耗量急速增加,与此同时化石能源却越来越少,塔式太阳能热发电的潜力逐渐显现.建立了以熔融盐为传热介质、超临界CO2分流再热式布雷顿循环为动力循环的塔式太阳能热发电系统模型.深入分析了分流系数及压比、回热度及压差和腔式太阳能集热器的温度对系统循环热效率的影响.结果表明:不同压比存在不同的最优分流系数,使S-CO2循环效率最大;随着回热度的提升,对系统性能的提升效果越来越明显;存在最优集热器温度,使整体太阳能热发电系统效率最大.