EXPERIMENTALLY DETERMINED TURBULENT PRANDTL NUMBERS IN LIQUID-SODIUM AT LOW REYNOLDS-NUMBERS

Turbulent Prandtl numbers have been deduced from measurements of mean velocity and mean temperature distributions and their half value radii for a liquid sodium jet discharging into essentially still fluid. Results obtained indicate a velocity dependence and are similar to those reported in the literature for pipe flows. The velocity dependence, which is assumed to be due to transition to an inertial-conductive flow regime where turbulent diffusion of heat inherent in the turbulent Prandtl number no longer exists, becomes pronounced at low velocities. Combination of the new jet flow and existing pipe flow data for liquid sodium leads to a simple functional relationship between turbulent Prandtl number and eddy diffusivity of heat which may be readily solved for epsilon(H) once epsilon(M) is known. The combined results show that, for liquid sodium, significant increases in turbulent Prandtl number occur when flow conditions lead to epsilon(H)/alpha < 2.5, that is, when epsilon(M)/nu < 2/Pr.