Hydrodynamic and thermal entrance lengths for laminar forced convection of molten salt with internal heat source

Abstract

Fluids with internal heat sources exhibit distinct heat transfer characteristics from those without. Using the correlations developed for the latter to predict the hydrodynamic and thermal entrance lengths of molten salt with internal heat source may result in non-negligible errors. Thus, these entrance lengths for laminar molten salt with internal heat source are evaluated using Fluent, with the influences of mass flow rate, inlet temperature, volumetric power density and tube diameter discussed. Results indicate that as the Reynolds number and tube diameter increase, both entrance lengths increase. In contrast, increasing inlet temperature and volumetric power density only increase the hydrodynamic entrance length, while the thermal entrance length remains unchanged. Unlike fluids without internal heat sources, the outlet-to-inlet viscosity ratio exerts an important influence on the hydrodynamic entrance length, rendering existing correlations developed for fluids without internal heat sources invalid. However, part of the thermal entrance length correlations remains accurate within an acceptable tolerance range. Finally, new hydrodynamic and thermal entrance length correlations for laminar molten salt with internal heat source are proposed, with the maximum relative deviations of 9.45% and 1.71% from the numerical results, respectively.