Numerical Simulation Of Boiling Heat Transfer In The Receiver Evaporator Section Of Solar Power Tower Plant

In recent years, solar thermal power technology has been a research hotspot in the area of renewable energy throughout the world as the rapid increase in energy demand. The solar receiver is a critically important energy conversion unit to convert solar energy to thermal energy. Only the semi-circumference facing the heliostat field receives heat flux, while the other semi-circumference depart from the heliostat field is adiabatic. What’s more, the heat transfer of boiling flow in the pipe with the water-vapor as the working fluid is especially complex. So the understanding of the heat transfer characteristics in it is significant and important. This paper develops the water-vapor tube numerical model under the uneven heat flux boundary with semi-circumference heated and the other semi-circumference adiabatic to modeling the three-dimensional and unsteady water-vapor two-phase flow through ANSYS FLUENT. The numerical simulation results show the flow characteristics of the two-phase flow and represent the evolution of the flow patter and the velocity field of the fluid. On the other hand, the simulation results show the thermal characteristics of the fluid and the tube wall. The fluid continuously absorbs radiation heat along the axial direction and the temperature gradually increases to 373 K. At the same time, the temperature profile of the tube wall is extremely uneven both along the axial direction and along the circumference direction, which corresponds well to the incident heat flux of the heated wall. The maximum temperature and the maximum temperature difference all appear on the cross-section at Z=1000 mm with the maximum heat flux. Furthermore, the Nu number is closely related to the flow patter and the maximum Nu value is at the bubble flow. What’s more, this paper analyzes the temperature gradient distribution and obtains the maximum temperature gradient in the three directions:axial, radial and circumferential. All the results will provide references for comprehensive understanding about the overall thermal performance of the tube in the solar receiver.Generally, the heliostat field in the solar thermal power tower plant used the multi-aiming point strategy to reduce the non-uniformity of radiation heat flux on the receiver to prevent the overheating. In this paper, a single tube used in solar thermal power tower cylinder receiver was studied theoretically. The heat flux on the tube using the multi-aiming point strategy with multiple concentrated points was achieved by the Gaussian function with multiple maximum values. Then the thermal parameters characteristic were analyzed by numerical simulation. The results show that each aiming point has the optimal position making the lowest non-uniformity of the radiation heat flux on the tube when the number of the aiming point is constant. What’s more, the radiation heat flux on the tube is more and more uniform and the maximum wall temperature decreases with the number on the aiming point increasing, while the maximum absolute temperature gradient increases. As a consequence, the thermal parameters must be considered comprehensively according to the multi-aiming point strategy to choose the optimal number of the aiming point and their optimal positions.