Consideration on Nusselt numbers of liquid metals under low Peclet number conditions

The Nusselt number of liquid metal in the low Peclet number region is discussed in the present paper. Old data measured by Johnson et al. (1953b) are investigated carefully from the stand point of instrumentation of the test section because their Nu numbers are extremely lower than the theoretically deduced Nu number under the low Peclet number conditions. Seven selected experimental conditions are simulated by the FLUENT code. The laminar flow model and transition k-kl-ω model are used to simulate corresponding experimental conditions. Calculated outlet fluid temperatures are compared with the measured results in order to confirm the consistency of the input energy. Other calculated results are compared to investigate the deficiencies in the data processing. As a result, it is a most likely cause that the temperature difference used to deduce the heat transfer coefficient is overestimated in the experiment. This is possibly caused by the estimation of the wall temperature without taking into account thermal resistances due to contacts and the simple estimation of the fluid temperature. The low Nu numbers based on the measured result should be corrected and it is clarified that the re-evaluated values by CFD simulations show similar trend as measured data by Skupinski et al. (1965) and by Ampleyev et al. (1969). All other data which show the lower Nu numbers by Subbotin (1974) in the low Peclet number region, and Stromquist (1953), and Johnson et al. (1953a) in the high Peclet number region should be investigated again.