Study on Effects of Orientation on Wall Boiling Heat Flux Partitioning

There have been a number of efforts into development of two-phase thermal hydraulics code, especially, to investigate the boiling heat transfer phenomena with high-resolution. Several models for wall heat flux partitioning have been proposed. However, all the models were developed based on a horizontal wall and thus the effect of wall orientation were not considered even though the boiling heat transfer mechanisms could be strongly distorted by the effects of the wall orientation , for example, bubble sliding and merging. In this study, the high-resolution wall boiling heat flux partitioning experiments were conducted to simultaneously gather the data of liquid-vapor phase, temperature and heat flux distributions on the wall and the bubble dynamics during saturated nucleate boiling. The focus of the study exists on the effect of wall orientation on the heat flux partitioning. In this study, the heat flux partitioning model was compared and validated with the experimental data of liquid-vapor phase, temperature and heat flux distributions on the wall and the bubble shape for nucleate boiling of saturated water at wall superheat of 7.5 .deg. C with various wall orientation of 0 .deg. C (horizontal), 30 .deg. C, 60 .deg. C, 90 .deg. C (vertical). - The magnitude of the total wall heat flux was inconsistent between experiment and correlation. The heat flux prediction error larger than 50% was found for all the data from the various orientations. In addition, the prediction error increases as the boiling wall inclines from the horizontal to vertical