The dryout of a thin heated liquid film

The breakdown of a thin liquid film in the annular two-phase cocurrent downward flow under heating was studied theoretically and experimentally. Three different models were developed to predict the breakdown condition. Comparison of the experimental data with the small perturbation theory shows that an empirical value of amplification factor of about 6, corresponding to a contact angle of approximately 80 deg is required for film breakup. Based on this value the small perturbation theory was found to agree with data satisfactorily. For the rivulet model and dry-patch model, the data can also be fitted by choosing a large contact angle. An explanation was given to account for the effect of heating, as well as the surface roughness and contamination.