Electrohydrodynamic Pumping in Microsystems
The electrical manipulation of fluids in microsystems has many existing and potential applications. This chapter reviews five different ways of electrohydrodynamic actuation in microdevices. First, we describe the basic equations of Electrohydrodynamics i
- PDF / 994,365 Bytes
- 49 Pages / 439.37 x 666.142 pts Page_size
- 7 Downloads / 230 Views
∗
Departamento de Electr´ onica y Electromagnetismo, Universidad de Sevilla, 41012-Sevilla, Spain Abstract The electrical manipulation of fluids in microsystems has many existing and potential applications. This chapter reviews five different ways of electrohydrodynamic actuation in microdevices. First, we describe the basic equations of Electrohydrodynamics in the microscale, providing some basic concepts of electrical conduction in liquids. We also deal with some basic fluid-mechanical aspects that are common for micropumps. Then, five different electrohydrodynamic micropumps are studied and compared: from those that employ forces in the liquid bulk to those that employ forces in the electrical double layer.
1
Introduction
Microfluidics deals with the pumping, control and manipulation of microlitre to pico-litre volumes of fluids. The typical length of the system ranges from 100 nm to 1 mm. In our case, we are going to deal with liquids in microsystems: sub-continuum effects that are important for gases in microfluidics (or, in general, in nanofluidics) are not important here. The continuum assumption of fluid mechanics is a good approximation in our case since the Knudsen number (molecular mean free path length divided by typical length) is much smaller than one. Liquid manipulation can be subdivided loosely into: digital microfluidics where the liquid is divided into droplets (e.g. electrowetting) and continuous microfluidics where the liquid is transported inside conduits. In this chapter, we deal with continuous microfluidics. ∗
This work has been supported by the Spanish Government Ministry MEC (contract FIS2006-03645) and the Regional Government Junta de Andaluc´ıa (contract P09-FQM4584).
A. Ramos (ed.), Electrokinetics and Electrohydrodynamics in Microsystems © CISM, Udine 2011
128
Antonio Ramos
Possible applications of microfluidics are (Stone et al., 2004; Laser and Santiago, 2004): dispensing therapeutic agents into the body; cooling of microelectronic devices; handling of liquids in space exploration, where miniaturization is required; micropropulsion for small satellites, as another potential application of microfluidics in space; handling of liquids for the Labon-a-chip technology, i.e. micro-devices for chemical or biological analysis of chip-format. Microfluidic transport can sometimes be achieved by passive mechanisms such as surface tension or gravity. Other applications employ macroscale pumps: syringe pumps, pressure/vacuum chambers and valves. However, many applications would benefit from an on-chip active micropump. According to Laser and Santiago (2004), there are two categories of micropumps: (a) displacement pumps, which exert pressure forces on the working fluid by one or more moving boundaries and (b) dynamic micropumps, which exert forces directly on the liquid, without moving parts. The piezoelectric or the electro-wetting micropumps are examples of displacement pumps. Most of electrohydrodynamic (EHD) micropumps are dynamic pumps: they use electric forces directly on the liquid. The piezo-actua
Data Loading...
