Experimental study of bubble flow behavior during flow instability under uniform and non-uniform transverse heat distribution

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces non-uniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction. (C) 2020 Korean Nuclear Society, Published by Elsevier Korea LLC.