Experimental Investigation of Heat Transfer to Supercritical Pressure R134a in Artificially Roughened Tubes

Abstract The environment in supercritical water-cooled reactors (SCWR) is highly corrosive. With increasing time of operation, an oxide layer grows on the surfaces of the fuel rod cladding, which increases the roughness of their surface. The aim of this study is the investigation of the effect of the roughness due to corrosion on the heat transfer to a fluid at supercritical pressure conditions. The drastic variations in the thermophysical properties of SCW can lead to a deterioration or an enhancement of the heat transfer. The correct prediction of the heat transfer deterioration, which can cause sharp temperature peaks on the fuel rod cladding is a big challenge. Until the current day, most experimental investigations are conducted, using hydraulically smooth heat transfer surfaces. In the present investigation, the effect of the surface roughness is investigated systematically with experiments, using R134a as a working fluid. In the first step, heat transfer experiments are conducted in a hydraulically smooth directly heated tube, covering a wide range of operating conditions. In the second step, the experiments were repeated, using a tube with a rough inner surface. Based on the results from the two test tubes, the effect of the surface roughness on heat transfer is evaluated.