Synchronized Observation of Wall Temperature and Bubble Dynamics at the Transition to CHF Condition in Subcooled Flow Boiling

Visual observations of bubbles and wall temperature were carried out to explore the mechanisms to cause departure from nucleate boiling (DNB) in subcooled flow boiling. It was observed that as presumed in the liquid sublayer dryout model, DNB was incepted when the liquid film between the wall and the large bubble was exhausted. At high flow rate and high subcooling condition, however, DNB was triggered immediately after the formation of large bubbles. The situation at DNB in this case would hence be similar to that supposed in the near-wall bubble crowding model since the bubble crowding leads to the formation of large bubbles.