Local heat transfer coefficient measurements using thermal camera for upward flow of Freon 22 in a vertical tube at supercritical conditions and development of correlations

This paper presents experimental results obtained towards characterizing heat transfer behaviour in supercritical fluids employing R22 as a simulant fluid. It is well known that two regimes exist in supercritical heat transfer, viz., heat transfer enhanced regime and heat transfer deteriorated regime and very limited data exist in the heat transfer deteriorated regime. The use of thermal camera has resulted in obtaining high resolution wall temperature data leading to the identification of the bulk enthalpy at which the peak wall temperature occurs. The results bring out the effect of inlet temperature very precisely, on which not much information is available in the literature. Finally the work identifies a criterion for the onset of heat transfer deterioration and correlations to predict the complete heat transfer behaviour exhibited by supercritical fluids. These correlations are shown to predict satisfactorily with a large number of experimental data available in the literature.