A preliminary experimental investigation on characteristics of natural convection based on solar thermal collection using supercritical carbon dioxide

SUMMARY In this paper, an experimental work is carried out to investigate the characteristics of solar thermal collection using supercritical CO 2 . This solar thermal conversion is based on supercritical CO 2 natural convection, which is much easily induced because a small change in temperature can result in large change in density close to the critical point. In addition, its critical temperature is 31.1°C and low enough to be easily reached in the low‐temperature solar thermal conversion system. The obtained results show that the supercritical CO 2 flow rate is smooth curve and not affected by the sudden variation of the solar radiation. The solar thermal conversion operation process can be divided into three periods: starting‐up, transition, and stable period. When the system reaches the stable period, the CO 2 flow rate will keep at a high value even if the solar radiation stays at a low level. It is also found that the smaller local solar radiation variation is, the better ability of keeping the flow rate near the peak level the supercritical CO 2 fluid owns. It is also found that a small pressure difference can drive a supercritical CO 2 flow with high flow rate. Furthermore, high solar thermal conversion efficiency is found at a high mass flow rate and under operation pressure near the critical point. Copyright © 2012 John Wiley & Sons, Ltd.