Experimental Investigation On Heat Transfer Characteristics Of Supercritical Carbon Dioxide In A Wide Temperature Range And Simulation On A Concentrating Radiation Solar Receiver

Supercritical carbon dioxide has excellent physical properties such as high density and low viscosity.The supercritical carbon dioxide Brayton cycle has advantages such as high thermal efficiency,small equipment size and simple system.And when the supercritical carbon dioxide Brayton cycle is applied in the solar thermal power generation system,it has obvious advantages.The heat exchanger and heat receiver of the supercritical carbon dioxide Brayton cycle are the key components of the solar thermal power generation system,involving a wide temperature range(30?700 ?)and a large pressure range(7-20 MPa).In order to master the key data of the related design,it is an urgent need to conduct the heat transfer characteristics of supercritical carbon dioxide in a wide temperature range and to investigate the operating principles of the supercritical carbon dioxide heat receiver under concentrated radiation conditions.A supercritical carbon dioxide heat transfer experimental system is established,where the temperature range of the experiments is 30-500 ?,the pressure range is 7-15 MPa and the mass flow range is 10-?90 kg/h.The heat transfer characteristics of supercritical carbon dioxide in a wide temperature range in a horizontal straight tube are investigated,and the effects of mass flow,pressure,temperature,heat flux,and other factors on the heat transfer characteristics are analyzed.The results show that when the temperature of supercritical carbon dioxide is near the pseudo-critical temperature,the heat transfer coefficient reaches a peak at the pseudo-critical temperature.And the higher the pressure,the slower the change of the heat transfer coefficient,and the smaller the peak value of the heat transfer coefficient.The larger the heat flux,the slower the change of the heat transfer coefficient,the smaller the peak value of the heat transfer coefficient,and the higher the corresponding temperature where the heat transfer coefficient reaches the peak value.When supercritical carbon dioxide is at high temperature,the mass flow is the major factor affecting the heat transfer coefficient,while the pressure and the heat flux have slight effects on the heat transfer coefficient.And the heat transfer coefficient increases slowly as the fluid temperature increases.The semi-empirical heat transfer correlation based on the experimental data is as follow:Wherein,85%of the deviations between the fitted values and the experimental data are within±20%.Therefore,the semi-empirical heat transfer correlation can accurately predict the heat transfer characteristics of supercritical carbon dioxide in the Brayton cycle temperature range,providing important guidelines for related designs.Based on the heat transfer experiments,a supercritical carbon dioxide concentrating radiation solar receiver is designed.Preliminary studies on simulation of the transfer characteristics are conducted by coupled light path analysis,and the effects of mass flow and temperature on the operating characteristics of the solar receiver are investigated.The results show that the receiver reaches 79%optical efficiency and 83%?89%heat receiving efficiency when the receiver aperture is at about 50 mm,providing the foundation for the further optimization of the supercritical carbon dioxide concentrating radiation solar receiver.A supercritical carbon dioxide concentrating radiation solar receiver is designed.Preliminary simulation study is conducted by coupling concentrating radiation,and the effects are investigated on the performance of the solar receiver,including mass flow and temperature.The optical and absorbing efficiencies reach 79%and 83%-89%,respectively,which could be optimized further.