Bubble Dynamics of a Single Condensing Vapor Bubble from Vertically Heated Wall in Subcooled Pool Boiling System: Experimental Measurements and CFD Simulations

Bubble dynamics of a single condensing vapor bubble in a subcooled pool boiling system with a centrally heated cylindrical tank has been studied in the Rayleigh number range 7 . 9 × 1 0 1 2 < R a < 1 . 8 8 × 1 0 1 3 . The heat source in the system is steam condensing inside a vertical tube. The tube was placed in the center of the tank (300？mm i.d., 300？mm height) which is well filled with water. Experimental investigation has been carried out with High Speed Camera while Computational Fluid Dynamics (CFD) investigation has been performed using Volume of Fluid (VOF) method. The heat source has been modeled using simple heat balance. The rise behavior of condensing bubbles (change in size during rise and path tracking) was studied and the CFD model was validated both quantitatively and qualitatively. 1. Introduction Pool boiling is a complex nonlinear dynamic process. The microscopic aspects of boiling process, for example, embryo nucleation and surface roughness determine its nature largely. The microscopic effects eventually exhibit in a macroscopic behavior. Further, boiling is a highly stochastic process and the precise prediction of the location and time of the generation, collapse, coalescence is difficult with the present status of knowledge. The condensation of bubbles in subcooled boiling systems is extremely important for studying the hydrodynamics during subcooled pool boiling. The simple reason for this is that condensation changes the shape and size of the bubbles. When a bubble is formed at the interstitial site in the case of nucleate boiling the bubble grows to a certain diameter and then departs from the interstitial site. As the bubble departs from the nucleation site, it tends to slide along the hot surface and detaches from the surface. The bubble then does not necessarily follow a straight path but moves near or away from the wall. In addition to experimental investigations, Computational Fluid Dynamics (CFD) is useful to obtain better understanding of bubble dynamics. Experimental investigations on dynamics of single vapor bubbles condensing in a subcooled boiling liquid have been carried out by Voloshko and Vurgaft [1] and an analytical model was developed. The authors found the relation between the dynamics of vapor bubble during condensation and intensity of heat exchange at vapor bubble interface. Bubble dynamics of vapor bubbles in subcooled liquids have been investigated (both experimentally and numerically) by researchers [2–9]. Numerical investigations using volume of fluid (VOF) method have been recently carried out by