Mass transfer in drops under conditions that promote oscillation and internal circulation

Abstract Single drops supported on hypodermic tubing have been studied in a wind tunnel to determine the effect of drop oscillation on mass transfer. The systems studied for the case where internal resistance controls consisted of absorption of sulfur dioxide gas by drops of glycerine, propylene glycol, and ethylene glycol. The results may be expressed in terms of effective diffusivity. No significant effect was noted in glycerine, whereas the glycols gave effective diffusivity values two to eight times greater than theoretically calculated values of molecular diffusivities. Frequencies, amplitudes, and internal circulation velocities in the drops were studied by cinematography. The effect of oscillation on external mass transfer coefficients was studied by sublimation of naphthalene spheres in air. In the cases where the vibrational velocity was less than the stream velocity, no effect was noted; this is in agreement with heat transfer studies. A technique has been developed for studying the effect of internal circulation on effective diffusivity by the use of forced circulation through a drop suspended on hypodermic tubing. A pseudofilm thickness is determined as a function of circulation velocity and presents a means of predicting effective diffusivities for the systems studied. This technique has been demonstrated, giving results in fair agreement with the correlation of Garner and Lane.