1University of Maribor, Faculty of Mechanical Engineering, Institute for Power, Process and Environmental Engineering, Maribor 2000, Slovenia. E-mail:
2University of Maribor, Faculty of Mechanical Engineering, Institute for Power, Process and Environmental Engineering, Maribor 2000, Slovenia.
Presented investigation treats convective effects of ebullition cycle in a partial nucleate boiling regime. During the ebullition cycle the bubble induces considerable flows of liquid phase in its vicinity. To quantify these flows the partial nucleate boiling on single nucleation site has been investigated experimentally using PIV technique.
After inception the bubble interface passes through five different stages. These stages are: hemispherical expansion, vertical elongation, base shrinking, bubble departure and rising. Liquid phase movement induced by rising bubble is well-known as a drift flow phenomenon. Rising bubble convection during the waiting time has been recognized as the most important stage of ebullition cycle for the heat transfer assessment.
Unsteady velocity distribution of drift flow in close vicinity of the boiling surface has been analyzed using flow field data acquired by PIV. Vertical and radial velocity distributions caused by rising bubbles grouped in three different morphological groups are presented graphically along marked surface parallel with boiling plate. At the end the governing heat transfer mechanisms in the bubble influence area are treated briefly.
heat transfer, two-phase fluids, nucleate boiling, artificial nucleation sites, vapor bubbles, drift flow, PIV experimental method
