Development of a New Heat Transfer Correlation for Flow of Supercritical Steam in Spiral Tubes Under Deteriorated Heat Transfer Regime

Heat transfer to supercritical steam flowing inside spiral tube under deteriorated heat transfer regime is investigated in this work using three-dimensional numerical simulations. The numerical solver is first validated with experimental results and subsequently multiple simulation cases are formulated with spiral tube by varying the flow and thermal conditions. The wall temperature and heat transfer coefficient of spiral tubes are compared with the same of straight tubes. Over the parameters range considered, the heat transfer coefficient is improved by 88% when straight tube is replaced with spiral tube, for similar flow and thermal conditions. Most significantly, the deteriorated heat transfer regime, which is otherwise witnessed in straight tubes is completely avoided by using spiral tubes, for the similar flow conditions. Tangential velocity, which arise due to centrifugal force is the primary reason of enhanced heat transfer in spiral tubes. Three standard heat transfer correlations are tested for spiral geometry under deteriorated heat transfer regime and it is found that none of those can predict the heat transfer coefficient accurately. Using the simulation results along with Buckingham p-theorem, a new correlation for heat transfer coefficient is proposed for spiral tubes carrying supercritical steam and operating under deteriorated heat transfer regime. The new correlation can predict the wall temperature and heat transfer coefficient accurately. The correlation has an error band of +/- 25%.