Effects of a Tube Diameter on Single Bubble Condensation in Subcooled Flow*

Bubble condensation that involves an interaction between the bubble and subcooled liquid flow has a significant role in effectively controlling the heat for thermal devices. In the present study, the numerical simulations are performed by using the VOF (Volume of Fluid) multiphase flow model to investigate the effect of the tube diameter on the bubble condensation. As the tube diameter decreases, the condensing bubble persists for a long time, and it disappears at a higher location, indicating that the condensation rate decreases with a decrease of the tube diameter. At a small tube diameter, the heat transfer coefficient of the condensing bubble, which indicates the quantitative parameter of condensation rate, is observed to be smaller than the large tube diameter. Because the subcooled liquid incoming from the inlet does not sufficiently affect the side of the bubble due to the backflow occurring at a narrow gap between the side of the bubble and the tube wall, the heat transfer rate reduces at the small tube diameter.