Study on the effect of multiple bubbles hydrodynamics on pool boiling heat transfer

Abstract

In order to clarify the effect of the hydrodynamics of multiple bubbles on the pool boiling heat transfer process, artificial nucleation sites are manufactured on the substrate surface to generate isolated bubble or multiple bubbles. Then, thermodynamic, bubble dynamics and liquid velocity vector field are investigated, through experiment and Computational Fluid Dynamics (CFD) simulation. The interface capturing and energy equations with phase change model are implemented into the simulation, and a combination of thermal parameter measurements, charge coupled device (CCD) camera and particle image velocimetry (PIV) is adopted in the experiment. The results indicate that vapor temperature inside the bubble is significantly higher and the returning liquid around bubble has larger velocity. It will be seen from this that the bubble is an excellent heat carrier and convection flow promoter in pool boiling. Thus, the liquid temperature at the bubble passage is higher. The coalescence of adjacent bubbles can increase bubble diameter rapidly and reduce departure time, and this effect can be intensified through increasing heat flux or wall superheat. The vortices generated during bubble rise can enhance not only the boiling heat transfer performance but also the temperature uniformity. The correlations for nucleation site density and liquid temperature are proposed.