Investigation of forced liquid flows in open capillary channels

Abstract

We investigate a forced flow through an open capillary channel consisting of two parallel plates under microgravity condition. The aim of the experiments is to determine the maximal volume flux that can be withdrawn from the channel. The theoretical approach with a one-dimensional Bernoulli equation leads to a non-linear ordinary differential equation for the radius of curvature along the free surface of the channel. Both laminar and entrance pressure losses are taken into account as well as the flow conditions before the inlet of the channel. Several experiments with different channels and fluid properties were performed in the Bremen drop tower. The theory shows good agreement with the experimental data for a wide range of the non-dimensional parameters Ohnesorge number, gap ratio and channel length. The knowledge of the maximum volume flux is necessary to prevent gas ingestion at the channel outlet which is un-desired for applications in surface tension tanks.