HEAT-TRANSFER CORRELATIONS FOR AN IMMERSED FINNED HEAT-EXCHANGER COIL TRANSFERRING HEAT FROM A HOT-WATER STORE

Natural-convection heat transfers, to a finned-tube heat-exchanger coil immersed in a hot-water store, have been investigated Cold water was passed through the pipe of the heat-exchanger in order to extract heat rapidly from the hot water in the store. Natural convection currents in the stored water were created by buoyancy forces, which were induced by the temperature gradients that developed as a result of the heat-extraction process. A heat-transfer correlation in terms of Nusselt and Rayleigh numbers has been deduced in order to predict the natural convection heat-transfer coefficient on the outside surface of the heat exchanger. This correlation, which is valid for heat entering the fins, to within an accuracy of better than 4%, is: Nu = 0.280 Ra0.293 for 100 < Ra < 1500