Studies of natural convection in molten salt around vertical tubes

Abstract

Experiments with laser velocity measurements will be performed in a vessel which is presently being built at Seaborg. The purpose is to study natural convection for the application of a molten salt nuclear reactor. This presentation is a summary of thermohydraulic calculations made in preparation for those experiments. After the completion of the experiments, they can be used to benchmark the simulation methods for the aforementioned reactors as well as e.g., heat exchangers.

Non-stationary phenomena such as flow stability and evolution of velocity and temperature fields are difficult to predict using generic CFD, particularly in the transitional regime between laminar and turbulent flow, which is expected to occur in this configuration. The Rayleigh number in the presented case is of the order of 109, and the flow is still laminar with speeds of a few centimeters per second. It is non-stationary though, so the simulations using ANSYS/Fluent are time-resolved.

The results from the CFD support the estimates made with Rayleigh number formulas. They also show that the thermal boundary layer is less than one millimeter thick, and the zone of buoyant flow is about four millimeters thick, which is important for the choice and tuning of the measurement methods.