Abstract
An experimental study of the effect of ventilation on the rate of evaporation of millimeter sized water drops failing at terminal velocity in air has been carried out in a wind tunnel where drops were suspended freely in the tunnel air stream. It was found that for drops in the size range 1150 µm≤a0≤2500 µm, the mean ventilation coefficient f̄vf̄h could be expressed as f=(0.78±0.02)+(0.308±0.010)X, where X=N&frac13Sc,v N½Re. Previously, we showed that this relation holds for drops in the size range 60 µm≤a0≤400 µm. Taken together, our present and previous data suggest that with reasonable accuracy f̄=0.78+0.308X, for 1.4≤X≤51.4 (60 µm≤a0≤2500 µm). For 0≤X≤1.4 (0≤a≤60 µm), one may use our previous result f=1.00+0.108 X2. To illustrate how the present data may be applied, we computed the distance which is required for a water drop to travel from cloud base through a NACA Standard Atmosphere of various relative humidities, in order to reach the earth's surface with a given size.
