Heat Transfer to Supercritical Pressure Carbon Dioxide Flowing Upward Small Circular Tube

A supercritical fluid is any substance at a temperature and pressure above its critical point. For this reason the occurrence of the critical heat flux due to the liquid-gas phase transition can be avoided. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density. These particular characteristics have already been practiced in the fossil fuel boilers to raise the thermal efficiency since 1950s. The use of supercritical fluids is recently being extended to nuclear power systems, and printed circuit heat exchangers, just to name a few. Supercritical fluids tend to contribute to compact and simple design of thermodynamic cycle and cost reduction when it comes to power conversion systems. The Pressure Applied CO2 Operation (PACO) apparatus is an experimental loop concerned with thermofluid characteristics of supercritical carbon dioxide (S-CO2) being considered as working fluid for power conversion in the Loop Energy Exchanger Integral System (LEXIS) for a fusion reactor as well as a Generation IV nuclear energy system. S-CO2 has such advantages as high density, easy accessibility, low price and no toxicity compared against other fluids. One of the most salient characteristics is its low critical point, which renders change from CO2 to S-CO2 easier than other gases. These benefits lead S-CO2 to be used in power stations in lieu of water or helium. PACO is home to a small vertical circular tube test section housing upward flow of S-CO2 as part of LEXIS.