Heat transfer and flow visualization in natural convection in rapidly spinning systems

Steady and transient free convection in liquid contained in a rotating annular reservoir having two radial baffles and a small heat source mounted on the outer cylinder wall is investigated experimentally, using electrolysis of thymol-blue/HC1 solution by a Pt wire to visualize the flow. The heater is turned on either after solid-body rotation is established or just as the reservoir is impulsively accelerated to a higher rotational velocity. The results are presented in photographs and graphs and discussed in detail. It is found that weak buoyant plumes with radial trajectories relative to the spinning container generate axially invariant two-dimensional motions even when the heat source is much shorter than the cylinder. Spin-up simultaneous with the application of heat is shown to enhance the heat-transfer coefficient over a short time period. The applicability of these findings to the design of airborne superconducting generators with rotating liquid-He baths is indicated.