Theoretical prediction on post dryout heat transfer in bilaterally heated narrow annuli

A non-equilibrium mechanistic model was developed for predicting the heat transfer in the region of the post-dryout dispersed flow which is generated in the narrow annuli heated bilaterally. For that purpose, 11 heat transfer processes were taken into account based on the analysis of the heat exchange processes occurring among droplets, vapor and annular tube-walls heated from both sides. The experiments were also carried out using the annular tube with gaps of 1.0 mm, 1.5mm and 2.0 mm, under the condition of low mass flow, low pressure and high quality. We could find out that the present model predicts the wall temperature and the vapor superheat accurately. And also it was shown that the forced convection between the heated wall and superheated vapor dominates the overall heat transfer, although the heat transfer by droplets contacting directly with the wall and evaporated in the interface between droplet and the superheated vapor is not neglected. The radiation heat transfer would be neglected because of its small contribution (less than 0.11%) to the total heat transfer. (authors)