REWETTING AND TRANSIENT HEAT TRANSFER ON THE HEATED HORIZONTAL TUBE SURFACE DURING THE AIR-ATOMIZED SPRAY COOLING

The purpose of this study is to investigate the cooling and rewetting of a heated horizontal tube surface with an air-atomized water spray impingement. Rewetting and transient heat transfer are crucial in nuclear reactor safety during a postulated accident, such as cooling of hot calandria tubes (CT) during the large-break loss of coolant accident (LOCA). The rewetting velocity in the circumferential direction and the rate of cooling of the heated tube surface were determined as a function of nozzle operating parameters. To estimate the local spray impingement density on the tube surface, an in-house mechanical patternator was designed and developed. To record the flow state during cooling, a high-speed video camera was used. The rewetting velocity on the tube surface was determined using the outcome of thermocouples mounted on the heated tube wall and an imaging system used to record the video picture during the runs. The two techniques of calculating rewetting velocity are compared. The highest heat flux removed from the tube surface was estimated as 3.7 MW/m², and the maximum rewetting velocity was found to be 5.58 mm/s. An excellent agreement regarding rewetting velocity has been reported utilizing thermocouples and a high-speed camera.