The determination of superheated layer thickness and wall superheat in vertical tube natural circulation reboiler

The characteristics of incipient boiling for vertical thermosiphon reboiler are studied in detail. The liquid film adjacent to the heating surface, the superheated layers thickness, δ*, must attain a threshold value so that the critical bubble nuclei with radius rc can further grow to the point of detachment. Thus, the relation between δ* and rc at the threshold of post-critical growth is of primary importance in determining the onset of nucleate boiling. In the present study a semi-empirical equation for wall superheat is proposed which includes the effect of submergence for the experimental data available in the literature. The data for water and organic fluids having wide range of thermophysical properties were correlated with a single correlation having mean absolute deviation of 14.73%. The value of δ*/rc for each fluid and unified value have also been also proposed.