An assessment of heat-transfer correlations for turbulent water flow through a pipe at Prandtl numbers of 6.0 and 11.6

An experimental investigation assessed the accuracy of existing heat-transfer correlations for turbulent flow of water in smooth tubes at Prandtl numbers (Pr) of 6.0 and 11.6. The best correlations were selected for use in designing ocean thermal energy conversion (OTEC) heat exchangers. Two shell-and-tube heat exchangers, a plain-tube evaporator and a plain-tube condenser, were tested to obtain data for water at Pr = 6.0 (800 F) and Pr = 11.6 (400 F), respectively. From measured values of the overall heat-transfer coefficients, the water-side coefficients were determined by the Wilson plot method. The results were used as a data base for evaluating seven widely used heat-transfer correlations. Overall, the best correlations were found to be Petukhov-Popov and Sleicher-Rouse, both of which agree within + or - 5% with the experimental data over the entire Reynolds number range. The Dittus-Boelter and Sieder-Tate correlations, popular with heat-transfer engineers, underpredict the data by 5% to 15% and thus are considered too conservative. Predictions from the Kays correlation compare favorably with the data at Pr = 6.0 but are slightly high (nonconservative) at Pr = 11.6. The Eagle Ferguson correlation is acceptable at Pr = 6.0 but a little too conservative at Pr = 11.6.