Development Of A New Heat Transfer Correlation For Flow Of Supercritical Steam In Spiral Tubes Under Deteriorated Heat Transfer Regime

Abstract

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 co-efficient of spiral tubes are compared with the same of straight tubes. Over the parameters range considered, the heat transfer co-efficient 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 co-relations are tested for spiral geometry under deteriorated heat transfer regime and it is found that none of those can predict the heat transfer co-efficient accurately. Using the simulation results along with Buckingham p-theorem, a new co-relation for heat transfer co-efficient is proposed for spiral tubes carrying supercritical steam and operating under deteriorated heat transfer regime. The new co-relation can predict the wall temperature and heat transfer co-efficient accurately. The co-relation has an error band of +/-25%.