Experimental Study on the Mechanism of Transition Boiling Heat Transfer : 2nd Report, The Relation between the Behavior of Growing Vapor Bubble and the Mechanism of Heat Transfer

Abstract

A semi-empirical theory of transition boiling heat transfer for small horizontal heating surface is presented based on the measurements of hydrodynamic behavior of vapor bubbles in the nucleate and transition boiling regions. In nucleate boiling the growth rate and the rising velocity of vapor bubbles have been found to be roughly constant. Thus the inertial force acting on it is supposed to exert an influence similar to the drag force acting on a freely rising bubble. In transition boiling, on the other hand, the rising velocity of a bubble was slower than that of a nucleate boiling bubble. The above-mentioned difference in the behavior of a growing vapor bubble was attributed to the change of forces acting on it. The relationship between the dry area on the heating surface and diameter of a bubble in the transition boiling region was derived theoretically from the force balance on the growing vapor bubble by making some appropriate assumptions. The heat flux calculated by the present theory, in which the coexistence of nucleate boiling at the solid-liquid contact part and film boiling at the dry part of heating surface was assumed, agreed reasonably well with the measured value.