Xiaoping Yang

Microscale gas flow attracts significant research interest in recent years since it is concerned with a wide range of engineering applications. It is noted that the Navier–Stokes equations-based scheme and the standard lattice Boltzmann method both encounter a great challenge in the simulation of such flows. The newly developed discrete unified gas kinetic scheme (DUGKS) has been demonstrated to be capable of modeling microflows, but presently it is mainly limited to the problems with straight boundaries. In this study, the ghost-cell (GC) immersed boundary method is introduced to the DUGKS for handling curved boundaries. The most attractive feature of the GC method is to set a ghost point inside the solid domain, at which the information is unknown and will be extrapolated linearly from the corresponding wall and image nodes. As for the two latter points, the distribution functions are first evaluated by the inverse distance weighted (IDW) method and then should be corrected according to the impenetrability condition and Maxwellian diffuse-scattering rule. Three typical test cases, including the plane Poiseuille flow, cylindrical Couette flow and flow through porous media are simulated to validate the present IDW-GC-DUGKS. The results demonstrate the accuracy and feasibility of the method for the gaseous microflows.

S-CO2 (supercritical carbon dioxide) is used as working fluid for power system cycle. This paper presents thermodynamic performance analysis results on S-CO2 Brayton cycle. Based on the assumptions of the relevant initial parameters, the mathematical models of compressor, turbine, recuperator and heater are constructed, and the thermal efficiency of regenerative Brayton cycle and recompression Brayton cycle are calculated and analyzed. The results reveal that the efficiency of the recompression cycle is higher than that of the simple regenerative cycle. The effects of inlet temperature, inlet pressure of the main compressor and inlet temperature, inlet pressure of the turbine on the thermodynamic performance of the recompression cycle are studied, and the influencing mechanism is explained. The results show that the cycle efficiency decreases with the increase of the inlet temperature of the main compressor; there exists an optimum inlet pressure in the main compressor to maximize the cycle efficiency; and the cycle efficiency of the system increases with the increase of the inlet temperature and pressure of the turbine. When the inlet temperature of the turbine exceeds 600 ℃, the thermal efficiency of the cycle can reach more than 50%.

A packed bed is a good heat-storage method because of its simple structure, low cost, and good heat-transfer performance. Packed beds generally have a thermocline temperature distribution. This study analyzes a molten-salt thermocline storage system packed with a sensible heat material based on simulation and experimental research. The relationships between heat transfer and the characteristic parameters of the filling material, charging time, and initial conditions are obtained. Investigation results show that the thickness of the thermocline layer reduces with the increase in volume heat capacity but increases with time. The equivalent diameter of particles almost has zero effect on the thermocline thickness, and porosity has an indirect impact on the thickness of the thermocline layer but influences the movement speed of the thermocline. The maximum temperature difference between the fluid and solid decreases, but the range of temperature differences increases with time.

During the process of car movement, the air will cause some resistance to the car, and the resistance will increase rapidly when the speed increases. The aerodynamic characteristics of the car will...

Thermal energy storage is considered as an important subsystem for solar thermal power stations. Investigations into thermocline storage tanks have mainly focused on numerical simulations because conducting high-temperature experiments is difficult. In this paper, an experimental study of the heat transfer characteristics of a molten salt thermocline storage tank was conducted by using high-temperature molten salt as the heat transfer fluid and ceramic particle as the filler material. This experimental study can verify the effectiveness of numerical simulation results and provide reference for engineering design. Temperature distribution and thermal storage capacity during the charging process were obtained. A temperature gradient was observed during the charging process. The temperature change tendency showed that thermocline thickness increased continuously with charging time. The slope of the thermal storage capacity decreased gradually with the increase in time. The low-cost filler material can replace the expensive molten salt to achieve thermal storage purposes and help to maintain the ideal gravity flow or piston flow of molten salt fluid.