Simulation of complex liquids in micropump Haifa El-Sadi * , Nabil Esmail Department of Mechanical Engineering and Industrial Engineering, Concordia University, Montreal, Que., Canada H3G 1M8 Received 30 November 2004; received in revised form 1 March 2005; accepted 1 April 2005 Available online 2 June 2005 Abstract Complex liquids can be encountered in many applications of microdevices. In the present study, the performance of microscrew pump using complex liquid is investigated numerically. The microscrew pump operation depends on the surface sweep forces. It consists of a screw placed inside a microchannel. When the screw rotates, a net force is transferred to the fluid due to differential pressure on the depth of the thread and pressure gradient along the screw axis, thus causing the fluid to displace. Three-dimensional complex liquid simulations of micropump were performed. The effect of screw pitch, thread, Reynolds number and pump load on the micropump performance has been studied. The simulations of complex liquids indicate that the highest bulk velocity is achieved with high thread depth at low Reynolds number. However, effective pumping is accomplished at low Reynolds number, high pressure load and high thread depths. q 2005 Elsevier Ltd. All rights reserved. Keywords: Pitch; Microscrew; Surface sweep forces; Complex liquid; Thread 1. Introduction The field of MEMS is a rapidly emerging technology, in which new potential applications are continuously being developed. On the other hand, precise control of micro- fluidics flow in microelectromechanical system (MEMS) devices, such as micropump [1], heat sink [2], heat exchanger [3], and intravenous drug delivery systems [4–6], require a fundamental understanding of the inter- actions between microfluidics and microchannel. Micro- pumps are between the most developed of all MEMS devices, and have been executed into the mainstream [7,8]. Micropumps are imperative components for distributing fluid and samples in microanalysis system. In general, pumps can be divided into two major categories: (1) displacement pumps, which apply pressure forces on the working fluid through moving boundaries; and (2) dynamic pumps, which constantly add energy to the fluid in a way that increases its momentum (e.g. Centrifugal pumps) or its pressure (e.g. Electroosmotic) [17]. Pumps and micropumps classification is illustrated in Fig. 1 [17]. Positive displacement pumping is the most widespread method used in micropumps. On the other hand, the actuation of the reciprocating diaphragm can be achieved by different principles such as piezoelectric, pneumatic, electrostatic, etc. [9,10]. However, various pumping ideas were proposed to overcome the valve problem correlated with positive displacement pumps. The simulations for the novel viscous pump carried out are based on this principle at high Reynolds number (Newtonian) [11]. Predicting the dependence of fluid motion in open channel through the rotational cylinder and the fluid properties is still an issue receiving considerable attention in the literature. Previous studies showed numerical simulation of two- and three- dimensional viscous fluid (Newtonian) and the influence of the dynamic parameters, width and other geometric [12,13]. However, many fluids demonstrate a more complicated relationship between the observed shear stress and the rate of strain as non-Newtonian fluid or complex liquids. Therefore, much attention is given to the flow of non- Newtonian liquids in Microgeometries. Previous studies showed the effect of micropump on the behavior of fluid flow system [14]. Many studies of high viscous liquids using macroscrew pump were performed by Cooper [18]. He was dealing with Microelectronics Journal 36 (2005) 657–666 www.elsevier.com/locate/mejo 0026-2692/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2005.04.037 * Corresponding author. Tel.: C1 514 848 2424x8793; fax: C1 514 848 4509. E-mail address: el_sadi@me.concordia.ca (H. El-Sadi).