Prediction of heat transfer to supercritical pressure fluid at rough surface

• Derivation of new correlation, considering the effect of wall roughness on heat transfer at supercritical pressure. • Evaluation of the new correlation with new in-house experimental data. • Evaluation of the new correlation with data from the literature. • Comparison of the new correlation with correlations from the literature. The highly corrosive environment in supercritical water-cooled reactors (SCWR) is a big challenge for the fuel rod cladding materials. Within a refueling cycle, which is aimed to be at least 2 years long, an oxide layer grows on the outer surface of the fuel rod. Thus, roughness on the heat transfer surface is increased over time. To predict the heat transfer to fluids at supercritical pressure conditions is challenging, especially in the vicinity of the pseudocritical point, i.e.., when the fluid close to the wall already exceeds the pseudocritical temperature and the fluid in the core of the subchannels is still sub-critical. In the literature, many correlations exist, taking the variations of the thermophysical properties of the fluid into account. Further, effects such as local laminarization near the wall due to buoyancy or bulk flow acceleration are considered in many correlations. However, the rough wall induces another level of complexity to heat transfer to a fluid under supercritical pressure conditions. This work aims to develop a heat transfer correlation, which can take the effect of the wall roughness on the heat transfer to a fluid under supercritical pressure conditions into account. For this purpose, previously obtained experimental data, which has been obtained in a smooth reference tube and in a test tube, which has been artificially roughed at its inner surface, are available. The experiments have been conducted with the surrogate fluid R134a in the KIT Model Fluid Facility (KIMOF) at the Karlsruhe Institute of Technology (KIT), Germany.