BUBBLE BEHAVIOR AND BUBBLE GROWTH MODEL OF HIGHLY SUBCOOLED FLOW BOILING IN A VERTICAL RECTANGULAR CHANNEL

In the paper, a visual investigation was carried out to study the bubble behavior phenomena with upward subcooled flow boiling in a narrow channel, with a gap of 2 mm. It was found that the bubbles grew up rapidly at different nucleation sites and then condensed subsequently with high bulk subcooling, under system pressures of 0.1 MPa and 0.3 MPa. Under a system pressure of 0.6 MPa and 7.0 MPa, bubbles were generated continuously at different nucleation sites and slid along the heating surface during the growing process. Based on the experimental study, a bubble growth model was proposed with consideration of the bubble behavior and the local thermal condition near the heating wall; the parameters of the proposed model considered the effect of wall superheating and the degree of bulk subcooling, and the Reynolds number Re considered the bulk velocity; these considerations were used to modify the Zuber model. Then the proposed bubble growth model was used to predict the bubble growing process.