The process of adiabatic evaporation in a free falling liquid column was investigated theoretically and experimentally.A model for the vacuum evaporation on the surface of vapor-liquid flow was built with an adiabatic evaporation experiment at temperature of 20—55℃

evaporation pressure of 2—15 kPa

and Reynolds number 1500—5000.A criterion equation for the heat transfer in the system was obtained.The analysis result showed that excessive superheat (ΔTsup>11℃)would cause entrainment to decrease the separation efficiency.The evaporation efficiency could reach 63.2%—6.5% with the length-diameter ratio from 43.5 to 87.Higher length-diameter ratio caused a breakup of the liquid column

and the enhancement of the evaporation efficiency was not significant.Based on the evaporation model

the evaporation process of free falling liquid column could be analyzed effectively with process simulation

which provides a reference for its industrial design.