Studies in drop formation

Abstract

An exhaustive survey of literature has indicated that no investigation has been carried out on drop formation in non?Newtonian fluids. Further, it is noted that little attention has been paid to the problem of drop formation from multi?orifices. An attempt has been made in the present investigation to tackle these industrially important problems. Formation of drops from single nozzles submerged in power?law fluids is studied. Data are collected over a wide range of variables. The effect of power?law parameters, nozzle diameter, flow rate etc. on the drop size is found. A model based on a two?stage mechanism is proposed to explain the results. The model predicts the drop volumes satisfactorily. It is found that consideration of non?Newtonian behaviour is important at low and medium flow rates and its importance decreases with increasing flow rate. Drop formation from multi?orifices submerged in Newtonian as well as power?law fluids is investigated. For a wide range of continuous?phase properties, the drop?volume data are collected. By introducing a correction for the drag force, the model for single nozzles is extended to explain the results obtained. A condition for coalescence at the distributor is derived. In the absence of coalescence between the forming drops the model is shown to predict the drop volumes satisfactorily. It is found that the models for single nozzles can confidently be used to predict the drop sizes in liquid–liquid contactors employing sieve plates. The equations for drop formation in power? law fluids from single submerged nozzles are extended for some other important non?Newtonian fluids such as the fluids following the Ellis, the Bingham and the viscoelastic models. This has been done by considering the appropriate viscous drag forces. The influence of the Ellis parameters and the Bingham parameters on drop size is discussed.