Predicting the liquid film dryout in flow boiling
Accurate prediction of critical heat flux is one of the most crucial problems in the industrial systems using boiling heat transfer. The dryout of liquid film in annular regime is the most common mechanism for triggering the sudden deterioration of heat transfer rate in flow boiling. In annular regime, the flowrate of liquid film decreases due to the droplet entrainment and vaporization; while, the deposition of droplets in vapor core leads to the increase in film flowrate. In order to predict the heat flux at the onset of liquid film dryout, correlations have been proposed for the deposition rate, the entrainment rate, the vapor quality and entrainment fraction at the transition to annular flow, and the film flowrate at the sudden deterioration of heat transfer rate. Validity of the new set of correlations has been tested against the wide range of available critical heat flux data.
Expected flow patterns in an uniformly heated tube