Study of natural convection in confined media with thermal stratification

The intermediate plenum in a pool-type LMFBR is a stagnant layer of the coolant formed at the boundary between the hot and cold plena with a large temperature difference. Its function is to protect the major structures around the plenum separator structure from thermal loading. The objectives of the present study are to get the natural convection heat transfer correlation and to establish the analytical method for the prediction of the temperature profile in the intermediate plenum, which is characterized by a thermal stratification. Natural convection heat transfer tests, using lead-bismuth alloy, conducted to evaluate the effect of thermal stratification on the liquid metal heat transfer rates. The enhancement of heat transfer rate by bulk fluid stratification is calculated for thermally stratified sodium. Effects of heat flow from the side walls are evaluated on the heat transfer and temperature distribution in confined media with a high degree of thermal stratification. Following stationary tests, transient tests simulating a reactor trip, in water and liquid metal were conducted for the prupose of obtaining basic idea which regards to the transient temperature profile after sudden cooling of a top roof of the intermediate plenum. A practical method is proposed to obtain a stable solution of natural convection at high Grash of number in thermally stratified fluid. From the present study, the analytical methods have been established for the prediction of the temperature profile in the intermediate plenum of a pool-type LMFBR. (author)