The heat transfer from a hot wall to impinging mist droplets in the spheroidal state

Abstract

The heat transfer from a hot metal wall to impinging mist droplets has been studied with a non-stationary method. The heat transfer rate has been determined by differentiation of the cooling curve of a thin metal disc, that was heated to a high temperature, and then cooled by a mist of steam and water droplets flowing perpendicular to it. The droplets were about 60 microns in diameter and had velocities of about 5 m/sec. The experimental results have been compared with a theoretical estimation based upon the assumption that the drops obtain the fully-developed spheroidal state. The estimation was made by extrapolating a theory, confirmed by experiments described in two foregoing articles, which dealt with sessile drops and large impinging drops. For the given experimental conditions the spheroidal state occurred only at the upper limit of the experimental temperature range (400°C). In the latter case the weight loss of the droplets by evaporation during the impact amounted to less than 0·5 per cent.