FLOW VISUALIZATION STUDY OF POSTCRITICAL HEAT-FLUX IN INVERTED FLOW

A visual study of film boiling was carried out to determine the flow r egime transition in the post-CHF region for a transient bottom reflood ing of a hot transparent test section. The effect of test liquid subco oling and inlet velocity on flow transition as well as on the quench f ront propagation was investigated. The respective ranges for liquid ve locity and subcooling were 1.8-26.8 cm/s, and 20-45-degrees-C, respect ively. The test liquid was Freon 113 which was introduced into the bot tom of the quartz test section whose walls were maintained well above the film boiling temperature of the test liquid, via a transparent hea t transfer fluid. The flow regimes observed down stream of the upward moving quench front were the rough wavy, the agitated, and the dispers ed droplet/ligaments in agreement with a steady state, two-phase core injection study carried on recently by one of the authors. A correlati on for the flow regime transition between the inverted annular and the dispersed droplet/ligament flow patterns was developed. The correlati on showed a marked dependence on the void fraction at the CHF location and hence on the flow regime encountered in the pre-CHF region.