Mass Transfer from Evaporating 1-Hexanol Drop by Using Two Experimental Technique

We measured the rate of evaporation of 1-hexanol drop suspended either from a quartz capillary or from a thermocouple in a stream of hot dry air flowing in a vertical wind tunnel. In the measurement with the capillary the mass flux from the drop was counterbalanced by the liquid supplied into the drop through the capillary. In the experiments with drop suspended from thermocouple the rate of mass transfer was deter­mined from the variation of droplet diameter with time. The maximum temperature in bulk at which the evaporation from thermocouple could be conducted was T_∞ = 339 K with drop temperature T_O = 331 K. In the case of capillary the maximum temperature in bulk was T_∞ = 499 K with drop temperature T_O = 375 K. At these conditions the mass flux from the drop suspended from capillary was about 25 times higher than those for the drop on thermocouple. In calculations of Sherwood fl.umber the experimentally determined mass transfer was related to the mass transfer from a stationary drop at nonisothermal conditions. It was found that in the range Re = 20÷55, where both techniques overlapped, the results from capillary measurements were for about 6% higher than those obtained from thermocouple. It might be caused both by the difference in the flow field inside and around the drop and the measurement of the temperature. For Re < 3 the experimental data from thermocouple were correlated by the expression: Sh = 2.00 + 0.192 (Re^1/2 Sc^1/3)² and for Re > 3 by the expression Sh = 1.54 + 0.620 (Re^1/2 Sc^1/3). Both results are in very good agreement with previous authors.