Parametric Effects of a Heat Transfer System using Supercritical Carbon Dioxide as Working Fluid

This study experimentally explores the parametric effects on the heat transfer efficiency and pressure drop of supercritical CO₂ tested in a horizontal circular heating tube having an inner diameter of 1.0 mm and a length of 170 mm. The experimental results illustrate that the working condition with a longer region after the pseudocritical point will generally deteriorate the heat transfer in the tube. The parametric effect of mass flux can improve the heat transfer efficiency, while the parametric effects of system pressure and inlet fluid temperature can reduce the heat transfer efficiency. The effect of heat flux on the heat transfer efficiency would depend on the outlet flow condition. The optimal heat flux with a highest heat transfer efficiency of about 91.38% occurs in the flow state at tube outlet around the pseudocritical point. Moreover, the measured pressure drops are in the order of several kPa, which could neglect their effects on the local flow properties. The increase of heat flux, inlet fluid temperature and mass flux all tend to enlarge the pressure drop of the heating tube, while the increase of system pressure will lower the tube pressure drop.