International Journal on Interactive Design and Manufacturing (IJIDeM) https://doi.org/10.1007/s12008-018-0494-4 ORIGINAL PAPER The numerical study of the effect of design parameters on EWOD actuation in microchannels of rectangular cross section Sajad Pooyan 1 · Mohammad Passandideh-Fard 1 Received: 30 May 2018 / Accepted: 6 June 2018 © Springer-Verlag France SAS, part of Springer Nature 2018 Abstract Electrowetting on Dielectric (EWOD) method is widely used to actuate microdroplets sandwiched between parallel plates in microfluidic chips. However, utilization of this method to transport liquid plugs in conduits has not been comprehensively studied to date. In this paper, the EWOD actuation of a liquid plug confined in a microchannel of rectangular cross section is numerically studied using OpenFoam. The effect of various parameters including electrowetting dimensionless number (η), contact angle hysteresis (CAH), dynamic viscosity and surface tension coefficient on transport velocity is investigated by employing an interactive simulation approach. The transport velocity can be considered a gauge to evaluate the actuation efficiency. The results show that, increasing η has a greater impact on velocity for larger values of CAH. In addition, it is shown that the average velocity increases linearly by increasing the surface tension coefficient. An inverse relationship between velocity and dynamic viscosity is also observed. These trends are in accordance with the theoretical model developed for a similar case in the literature. To estimate the maximum possible gap size between electrodes (MPGS), non-actuated distance travelled before the liquid plug comes to stop is evaluated. The results show that by decreasing the values of η, the effect of changing CAH on MPGS becomes more substantial. Keywords EWOD · Microchannel · Liquid plug · InterFoam · Simulation 1 Introduction Microfluidics is a technology in which small quantities of flu- ids (in the range of microliter to picoliter) are transported and manipulated through channels of micrometer scale integrated in a microfluidic chip. The motivation for the application of microfluidics is the need to manipulate tiny amounts of samples/reagents or fabricate portable test devices involv- ing liquid processing. As examples, chemical microreactors, devices to detect a biologic entity in a small amount of sam- ple or point-of-care medical test devices. Today, microfluidic devices, which are also commonly referred to as Labs-on-a- Chip (LOC), are of high importance to many biotechnology, chemistry and engineering applications due to their superior B Mohammad Passandideh-Fard mpfard@um.ac.ir Sajad Pooyan sajad.pooyan@mail.um.ac.ir 1 Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran characteristics such as low material and energy consumption, low response times and high accuracy. One newly emerging subcategory of microfluidics is “droplet microfluidics”, also called droplet-based microflu- idics. Working with tiny quantities of liquid, which form a microdroplet or a liquid plug in a microchannel, instead of continuous flows, dramatically decreases the amount of required samples/reagents and enables these devices to per- form complicated fluidic operations more efficiently. One of the most innovative and successful methods to actuate and manipulate microdroplets in droplet-based sys- tems is Electrowetting on dielectric (EWOD). In this method, applying an electric field near the line of contact of a droplet and a solid surface, exerts an electrostatic force to the droplet free surface and propels the droplet in the direction of the force. The electric field is generated by electrifying a metal- lic plate, called electrode, covered with a thin dielectric layer, underneath the droplet meniscus. The consequent effect of the electrostatic force exerted on the free surface is decreas- ing the contact angle in the portion of the contact line located on the electrode. If the static equilibrium contact angle is θ 0 , contact angle after applying the electric potential, θ v , will 123