Enhancement of heat transfer in disperse flow and downstream of blockages in rod bundles

Results of experiments conducted to study the effect of a discontinuous phase and blockages in rod bundles on heat transfer are presented. The test section consists of a 4-rod bundle with the rod diameter and pitch of typical PWR fuel elements housed in a plexiglass tube. The rod bundle is 184 cm tall and is heated electrically. The blockages are of sleeve type and they block 60% of the inner flow channel area while leaving a virtually infinite flow bypass region. In the experiments the discontinuous phase is simulated with 30 and 100 μM spherical glass particles entrained in air. The mass flow rate ratio of particles to air was varied from 0 to about 4 or the volume fraction of particles to air was varied from 0 to about 2 . 10-3. The results indicate significant enhancement in heat transfer in the presence of particles. The enchancement is also appreciable downstream of blockages. However the relative enhancement under two phase flow conditions is smaller than that for the single phase. (orig.)