Measurement of coalescence frequency in an agitated tank

Abstract

AbstractA new method for measuring the frequency of coalescence of drops in an agitated tank is proposed. It makes use of the fact that the rate of establishment of a new steady state mean drop size following a reduction in agitation intensity is related to the coalescence frequency in the tank. This method allows independent examination of the effects of drop size and impeller speed on coalescence frequency, and has the advantage that, since the measurement is not dependent upon the addition of external substances, high degrees of purity can be maintained and the effect of trace additions to the dispersion observed. The results provide some support for the assumption of an inverse proportionality between coalescence frequency and drop size. For constant drop size, coalescence frequency was found to depend on impeller speed raised to the power of 1.3 to 1.65 and the volume fraction of dispersed phase to the power of 0.6. The magnitude of density difference between the phases and the operating temperature were found to affect coalescence frequency, although it is suspected that these two effects are interrelated. The addition of small quantities of simple electrolytes to the continuous phase was found to cause a marked reduction in coalescence frequency.