LIQUID FILMS FALLING ON HORIZONTAL PLAIN CYLINDERS: PART 1-EXPERIMENTAL AND NUMERICAL STUDY OF FLOW BEHAVIOR

Abstract

In this paper, an experimental and numerical investigation of liquid film falling over three horizontal plain cylinders is presented. The flow Reynolds number range studied is 50−2000, rendering the flow laminar. Numerical predictions are obtained using FLUENT, a proprietary computational fluid dynamic (CFD) code, for the 2D and 3D configurations of the three cylinders. In the numerical predictions, the mathematical approach is based on the volume of fluid (VOF) method to account for the fluid's two phases, namely, air and water. The primary objective of the present study was to carry out experiments to validate the numerical code. It was found that increasing the Reynolds number resulted in the flow mode changing from droplet, to jet, to sheet mode. The numerical analyses accurately predicted the Reynolds numbers at which these transitions occur. The flow mode is also related to the separation distance between the horizontal cylinders. The flow mode tends to be droplet at large separation, whereas it tends to be jet and sheet modes at small separations. The distances between adjacent columns of droplets and the adjacent jet decrease with increasing Reynolds number and cylinder diameter, a phenomenon also captured by the numerical analyses. No effects of hysteresis were observed on the spacing of the columns of droplets and jets as the Reynolds number was increased and decreased. The frequency at which droplets fell from all of the cylinders increased when the distance between the water feeder and the cylinder increased, and this effect exhibited hysteresis as the flow rate was successively increased and decreased.