Circulation in liquid drops: (A heat-transfer study)

Abstract

The process of material and heat transfer to and from liquid drops moving through another continuous fluid has been examined. Continuous phase heat-transfer coefficients have been measured for the system mercury-aqueous glycerol solutions in which the mercury constituted the disperse phase. These data are in good agreement with those previously reported for solid spheres up to a Reynolds number of about 200, at which point drop oscillation commences. The resistance to heat transfer of the disperse phase, expressed as an effective thermal diffusivity, has also been measured, for the system bromobenzene-aqueous glycerol solutions. These results were found to be in general agreement with much reported work and with the mathematical model of K ronig and B rink which applies to liquid drops undergoing internal circulation. Some observations concerning the rigid, circulating, and oscillating behaviour of drops are made. The conclusion is reached on both experimental and theoretical grounds that circulation within a liquid drop results in an effective mass or thermal diffusivity of 2·25 times the molecular value. This result applies for the whole régime of circulation which exists between rigid sphere and oscillating behaviour. The onset of drop oscillation results in a considerable increase in this factor. Some effective diffusivities are reported for the oscillating régime which has not however been sufficiently studied to enable firm conclusions to be drawn. Drag coefficients for falling liquid drops in the above-mentioned systems are also reported and reveal the limitations of recent correlations in this field.