Natural Convection Heat Transfer in Thermally Stratified Liquid Metal

Abstract

Natural convection tests were conducted using Pb-Bi alloy, with the view to evaluating the effects brought by thermal stratification in liquid metal on the natural convection heat transfer along an immersed vertical metal surface. The vertical metal surface was represented by a stainless steel plate 300 mm high, placed in a cylindrical vessel 400 mm in diameter filled with molten Pb-Bi. The experiment was performed with the heat flux of the plate surface maintained constant and uniform. The temperature distribution through the liquid metal filling the vessel was controlled by regulating a flow of air blown onto the vessel surface; temperature measurements were made by means of a traversing thermocouple.

For the case of unstratified bulk fluid, the values obtained for heat transfer rate agreed well with corresponding data given by Sheriff for Na. With increasing degree of stratification, the thickness of the boundary layer decreased in keeping. The resulting increase of heat transfer rate indicated a definite dependence on the stratification parameter; this dependence was determined and expressed in terms of nondimensionalized boundary layer equations. Calculation of heat transfer rate based on numerical method yielded values agreeing fairly well with the experimentally determined data, but that based in integral approximation proved to give underestimated values.

KEYWORDS:

• boundary layers
• comparative evaluations
• experimental data
• heat flux
• heating
• heat transfer
• integral approximation
• intermediate plenum
• liquid metals
• natural convection
• numerical calculation
• thermal stratification