Thermal Characteristics in Supercritical CO2 Along Heating Tube

The system using CO2 as a refrigerant such as heat pump or Rankine cycle, depends greatly on the phase state and physical properties of CO2. In the present study, as a basic research on CO2 in the supercritical state, an experiment using a plane heating tube has been conducted, where two peaks of the local heat transfer coefficient are confirmed along the tube length. It is thought that the Prandtl number and the Reynolds number influence each peak. It is still unknown, however, how the carbon dioxide in the supercritical state flows internally. In the present study, thermal flow characteristics of supercritical state CO2 by reproducing internal flow with numerical calculation is also conducted. From both experiment and numerical verification, it is revealed that the local heat transfer along the pipe length is greatly affected by the changes of CO2 properties at (or after) the pseudo-critical state. Keywords: Solar Rankine System, CO2, Supercritical Fluid, Solar Energy, Numerical Analysis