Measurement of Film Thickness for Continuous Fluid Flow Within a Spinning Cone

Abstract

This paper reports experimental measurements of film thickness for continuous fluid flow within a spinning cone. The results are compared to analytical theory for thin film flow and found to be in good agreement. Spinning cones are used in various industrial process machines, including spinning cone distillation columns, centrifugal film evaporators and continuous centrifugal filters. In each case a fluid is fed continuously into the centre of a conical vessel which spins about a vertical axis with the cone apex pointing downwards. The fluid acquires the angular velocity of the cone and migrates up the internal wall of the cone under centrifugal force. Knowledge of the film thickness and flow velocity is often important in order to understand other performance parameters of the process such as evaporation or filtration rates. This paper aims to aid the design of new process machines by providing a mathematical model for film thickness that is validated by experimental results. Experiments have been conducted in which the angle of cone, angular velocity and input flow rate were all varied. Film thickness measurements were obtained via a novel optical method based on photographing the displacement of a projected grid on the surface of the flow within the cone. The method has the advantages of not disturbing the flow in any way and can provide thickness measurements over the whole cone depth. Measurements are also made insensitive to any transients by use of relatively long photographic exposures. Measurements are compared to analytical theory for axisymmetric, steady state, free-surface laminar flow of a Newtonian fluid in a spinning cone. The theory assumes the flow is thin but takes account of gravity. The theoretical model is found to be in good agreement with the experimental results.