Heat Transfer Measurements of Supercritical Carbon Dioxide in a Horizontal Circular Straight Tube

Abstract

Supercritical fluids have been drawing attention to many researchers as heat transfer media for power plant cycles, for refrigeration and heat pump applications. The exceptional heat transfer characteristics of supercritical fluids are key parameters for those applications. Above critical pressure, especially, in pseudocritical region, small temperature and pressure variations can lead to significant changes in the thermo-physical properties of the fluids. The large variation of thermo-physical properties of the fluid in the near critical point can cause a different thermo-fluid behavior and an enhanced convection heat transfer characteristics in this region. This allows enormous potential for energy transfer, but also alters the turbulent flow due to changes in the turbulent shear stress, brought about by acceleration and buoyancy effects. These effects are not fully understood and require further research to be able to predict the dynamic behaviors for further design applications. A supercritical CO2 testing loop has been built at Texas A&M University at Qatar to perform detailed heat transfer and pressure drop measurements to investigate the thermo-physical and dynamic characteristics of supercritical fluid flows. As an initial test, the total heat transfer coefficient of the tube has been measured at the supercritical conditions and the results are compared with that of a sub-cooled fluid and discussed here.