Modeling and observation of fine gas compression in a confined narrow tube by electrowetting-on-dielectric

Capillarity describes liquid flowing against gravity in an open narrow tube with certain wettability and is well described by the Young–Laplace equation. However, the modeling of the gas compression in a confined narrow tube due to capillary action with variable wettability is yet to be established. Thus, this study observes and models the relation between the gas pressure increment in a confined narrow tube and water contact angle (CA) variation induced by electrowetting-on-dielectric (EWOD). An increment of 1.64 Pa/°CA was obtained for a confined tube with a 3 mm diameter, which well matched the measured result (1.48 Pa/°CA). Fine gas compression can be achieved by varying the voltage input. The gas compression process was determined to be an adiabatic process with a ∼10% conversion efficiency (CA varying from 110° to 65°). The concept and modeling of this EWOD-based gas compression process will pave the way for fine gas compressors in microfluidic applications.