Characteristics of cooling heat transffer and pressure drop of carbon dioxide in smooth and micro-fin tubes at a supercritical pressure

Experimental study for gas cooler at a supercritical pressure was conducted to investigate the heat transfer and pressure drop characteristics for almost pure CO2 and CO2 oil mixtures. A smooth copper tube and a micro-fin copper tube are used as the inner tube of double-pipe counter-flow heat exchanger. In the case of almost pure CO2, it is confirmed that the local heat transfer coefficient of the micro-fin tube is higher than these of the smooth tube, and the values of pressure drop for micro-fin tube are higher than those of smooth tube. In the case of the CO2 oil mixtures, the local heat transfer coefficient decrease with the increase of oil concentration for the micro-fin tubes. It is concluded that amount of oil concentration has much effect to deteriorate the heat transfer performance.