PREDICTION METHODS FOR THE NUMBER DENSITY OF NUCLEATION SITES

摘要

The paper summarizes investigations on the distribution and activation of nuclei on technical heater surfaces in boiling heat transfer. The governing physical phenomena are described. The most familiar prediction methods for the active nucleation site density are evaluated according to the considered effects and obtained accuracy. Based on the analysis of decisive physical effects affecting the nucleation process, a modeling strategy is suggested that is based on first principals. This strategy integrates the nucleation process in the whole nucleate boiling process. It includes available models for bubble growth and departure. Special attention is paid to the entrapment of gas on a real heater surface and the influence of microscale heat and mass transfer phenomena, e.g., adhesion of liquid on the wall, on the nucleation process. As input parameters the suggested model needs only the topography of the heater surface, the wetting characteristics, and the thermophysical properties. Due to the need of further investigations, some ideas for future research topics are presented.