Numerical investigation on heat transfer to supercritical CO2 in rolling motion

The numerical calculations with and without rolling motions are conducted to investigate the effect of rolling motion on flow and heat transfer of supercritical CO2 in a vertical double-pipe heat exchanger. The purpose is to provide the detailed information on heat transfer behaviors for better understanding the abnormal heat transfer mechanism of supercritical fluid in rolling motion. It concludes that the effect of rolling motion on the supercritical CO2 is much more notable than that on conventional single-phase fluid. The rolling motion can cause the periodic oscillation of the local heat transfer coefficients and suppress the whole heat transfer deterioration. As supercritical CO2 temperature or mass flux increases, the influences of rolling motion and flow direction on the heat transfer decrease markedly. The secondary flow induced by the rolling motion for upward flow is stronger than that for downward flow, and the influence of rolling motion on the left and right sides of the tube is more obvious than on other locations. The heat transfer deterioration phenomenon weakens gradually as the rolling period decreasing or rolling amplitude increasing. It is important to note that the rolling motion may bring about the large wall temperature oscillation and the wall peak temperature increment to influence the safety of high-pressure pipeline.