Visualization experiments of the two-phase flow inside a hemispherical gap

Experiments have been carried out in order to visualize the behaviour of a two-phase flow inside a hemispherical narrow gap. The test facility consists of a hemispherical heater and a pyrex-glass bell-jar-shaped vessel. The transparent pyrex-glass vessel was intended to make a 1 mm gap between the heater and itself but the gap size was not uniform because of manufacturing difficulties. The incoming water and escaping steam flowed in counter-directions through separated flow paths. As the heater power increased, the escaping steam velocity increased and finally reached the counter-current flow limit(CCFL). The CCFL occurred at the location where the top-end gap size is smaller compared to the other part. Just below the top-end where the CCFL occurred, the heater surface was found to be locally dried out. (C) 1998 Elsevier Science Ltd.