Unsteady laminar forced convection heat transfer due to rapid decrease in flow rate of liquid sodium in a concentric annulus

Experiments have been made of unsteady forced convection heat transfer from a heated surface of 52 mm in length on an inner cylinder of 7.6 mm in diameter to liquid sodium flowing in a vertically orientated concentric annulus with 14.3 mm inside diameter. With constant heat flux of 1.0 x 106 W/m2, liquid sodium flow rate was reduced ramp-wise within about 25 seconds from an initial equilibrium state, Pe=72, to Pe=6.4 and from Pe=141 to 11.5 where Pe denotes the Peclet number. A theoretical model capable of describing the effect of heat conduction in the inner and outer walls of an annulus as well as in liquid sodium was developed. The numerical results obtained by the model agree with the experimental results for the two different flow transient conditions. (author)