Modeling and Analysis of a Microfluidic Capillary Valve

Here, a numerical model for analysis of a capillary valve for use in microfluidic devices was presented. Capillary valves are preferred especially in passive microfluidic systems, where the capillary forces dominate the liquid motion, to manipulate the flow. The capillary valve in this work, was formed by the sudden expansion of a rectangular microchannel to an opening, whose depth and width are larger than the height and the width of the channel respectively. Noting that there was no available analytical model to determine the pressure capacity of such valves, a numerical model based on energy minimization was utilized. Free software Surface Evolver was used to solve the model. Dependence of the pressure capacity on the contact angle of the working liquid on the channel material was investigated. It was found that the pressure capacity of the valves would be maximum if the contact angle on all surfaces is 90 degrees. Accordingly, the valves could withstand approximately 2.5 kPa for 100 mu m x 100 mu m channels when the contact angle was 90 degrees. The model was verified by comparing the results with those available in the literature