The impact of lift and wall lubrication forces on the prediction of subcooled flow boiling

Subcooled flow boiling is widely used as a mode of heat transfer in many industries, especially in Pressurized Water Reactors. Two fluid Eulerian-Eulerian model coupled with RPI boiling model is used to predict the subcooled flow boiling in vertical tubes. When the bubble size is small the lift force tends to push the bubbles towards the wall and wall lubrication force tends to push the bubbles away from the wall. Many researchers have not considered the lift and wall lubrication forces and suggested that predictions are better without lift and wall lubrication. Few have used Tomiyama model for lift and simulated the DEBORA-4 test, the results were not encouraging. But there is no proper study analyzing the impact of various models on subcooled flow boiling. In this paper, various lift and wall lubrication models are compared to have a clear understanding of the role played by the lift and wall lubrication forces. Limitations of the models are discussed in detail. Tolubinsky and Kostanchuk (1970), Cole (1960) and Lemmert and Chawla (1977) models are used for bubble departure diameter, frequency, and nucleation site density respectively. The inclusion of lift and slightly modified wall lubrication forces showed a considerable improvement in the prediction of the vapor fraction profiles. Simulation results are validated with experimental data (DEBORA-4). (author)