| Solar thermal power generation technology is a relatively clean power generation method.The factors such as weather,season and night day affect the heat transfer of the working fluid in the collector and the thermal efficiency of the collector.In particular,it has an effect on the radiation intensity of the solar radiation to the collector.The heat flux received by the collector is uneven in the axial and circumferential directions of the collector tube,resulting in the extremely uneven temperature distribution of the heat transfer medium in the tube.The liquid metal Na has a wide temperature range and excellent heat transfer performance,and has the potential to improve the efficiency of the tower heat collection system as a heat transfer medium.It is suitable for the application of the tower type photothermal system.In this paper,a solar cylindrical collector with solar energy is used as the research object.The CFD and MATLAB software are used to simulate the flow and heat transfer characteristics of the heat collector.The main research contents include:(1)First,the physical essence of the flow and heat transfer of the external circular tube collector is analyzed.It is considered that the essence is the coupling of heat transfer in the tube and the heat conduction problem of the tube wall.The mathematical model and physical model of the problem are given.The k-epsilon turbulence model and the standard wall function method applied to the near wall are theoretically analyzed in the numerical simulation.(2)Secondly,based on Fluent software,the temperature distribution of heat pipe and liquid sodium and molten salt in the tube under uniform heat flux is analyzed.The outlet temperature of medium at different flow rates is compared.The outlet temperature distribution of the collector tube is simulated when the inlet speed of liquid Na and molten salt is 2 m/s,the inlet temperature is 600 K,and the heat flux(0.1-0.7 MW/m~2).The velocity distribution of molten Na and molten salt in the tube is compared.It is concluded that the convective heat transfer coefficient of liquid Na is 2~8 times higher than that of molten salt medium,and liquid Na is easier to achieve full development in the pipe.(3)Finally,the heat transfer characteristics of liquid sodium in a single tube under the boundary condition are simulated and analyzed.The temperature field and velocity field of the heat collector are studied in the transverse and longitudinal directions.The temperature distribution of the whole collector is calculated through MATLAB programming.The factors affecting the heat transfer characteristics of liquid sodium in the heat collector:inlet temperature(500-700 K),inlet velocity(1-10 m/s)and heat flux density(0.1-0.7 MW/m~2)were analyzed.It is concluded that the inlet temperature and heat flux have little effect on the heat transfer characteristics of liquid sodium in the collector tube,and the inlet velocity has great influence on the heat transfer of the inlet section and the full development section of the collector tube.When the liquid sodium is used as a heat transfer medium,the difference between the average temperature of the wall of the collector tube and the average temperature of the tube is 0.18~0.40 K,which is only 0.08~0.37 times of molten salt.The liquid Na has more advantages in improving the heat transfer and heat transfer efficiency of the collector tube,and also provides theoretical guidance for the application of liquid sodium to the tower type photothermal power generation project.The research provides a numerical basis and theoretical guidance for the optimal design of tower solar collector... |
PDF Full Text Request