Danny Blanchard Phil Ligrani 1 e-mail: ligrani@mech.utah.edu Bruce Gale Department of Mechanical Engineering, University of Utah, 50 South Central Campus Drive, Rm. 2110, Salt Lake City, UT 84112 Miniature Single-Disk Viscous Pump „Single-DVP…, Performance Characterization The development and testing of a rotating single-disk viscous pump are described. This pump consists of a 10.16 mm diameter spinning disk, and a pump chamber, which are separated by a small gap that forms the fluid passage. The walls of the pump chamber form a C-shaped channel with an inner radius of 1.19 mm, an outer radius of 2.38 mm, and a depth of 40, 73, 117, or 246 m. Fluid inlet and outlet ports are located at the ends of the C-shaped channel. Experimental flow rate and pressure rise data are obtained for rotational speeds from 100 to 5000 rpm, fluid chamber heights from 40 to 246 m, flow rates from 0 to 4.75 ml/min, pressure rises from 0 to 31.1 kPa, and fluid viscosities from 1 to 62 mPa s. An analytical expression for the net flow rate and pressure rise, as depen- dent on the fluid chamber geometry, disk rotational speed, and fluid viscosity, is derived and found to agree with the experimental data. The flow rate and pressure rise of the pump vary nearly linearly with rotational speed. The volumetric flow rate does not change significantly with changes in fluid viscosity for the same rotational speed and pumping circuit. Advantages of the disk pumps include simplicity, ease of manufacture, ability to produce continuous flow with a flow rate that does not vary significantly in time, and ability to pump biological samples without significant alteration or destruction of cells, protein suspension, or other delicate matter. DOI: 10.1115/1.2175167 Introduction There is a need to circulate or move fluid through macroscale and/or microscale channels in many applications, including mi- crosensors, separation devices, drug delivery systems, electronics cooling, and other small-scale and microscale fluidic devices. Many different micropumps are proposed to meet this need, gen- erally to fulfill specific applications 1. These include membrane pumps 2–8both without check valves 2–5 and with check valves 6–8, electrohydrodynamic pumps 9–11, electrokinetic pumps 12,13, viscous pumps 14,15, rotary pumps 16,17, peristaltic pumps 4,18–20, ultrasonic pumps 21,22, and several other types of pumps 23–26. Many of these micropumps are fabricated using microfabrication technology. Nonmechanical pumps like the electrohydrodynamic and electrokinetic pumps do not have moving parts, which increases reliability. However, such devices are generally limited by low flow rate and pressure rise capabilities, the applications of the pump, the working fluids that can be pumped, and high supply voltage requirements 1. Me- chanical pumps like rotary pumps, peristaltic pumps, and mem- brane pumps have a wide variety of possible working fluids and applications. However, such mechanical micropumps are believed to be feasible only when they are greater than a certain size 1, due to the large viscous forces in the fluid at small pump geom- etries. At very small scales, the viscous forces are significant, and result in large pressure drops over small lengths for fluid flow through a channel 27. One motivation of the present effort is to employ these large viscous forces to produce a millimeter-scale pump with an easily adjusted, constant flow rate. Many variations of macroscale viscous pumps have been pro- posed 28–34. Most of these pumps have a linear relationship between flow rate and pressure rise for a range of operating pa- rameters and pump geometries. Viscous pumps are ideal for ap- plications where high pressure rises, and low to moderate flow rates are required 34. Uses of different viscous pumps at micros- cales are described by Sen et al. 15, and Kilani et al. 14. Sen et al. 15 presents a pump that employs a shaft whose axis is per- pendicular to the flow direction, and is positioned eccentrically in a channel. The difference in viscous shear between the shaft and the two channel walls produces a net pumping effect. Numerical simulations are performed by Sharatchandra et al. 35 to deter- mine the optimal configuration. This pump is easy to fabricate, but has limited flow rates and pressure rise capabilities. Kilani et al. 14 describes a spiral pump that uses one spinning disk rotating over a single spiral channel to produce a pumping effect. Results from a macroscale version of this pump are consistent with an analytical expression for flow rate and pressure rise 14. A small- scale version of this pump may be complex to fabricate. A new viscous micropump is presented, called the single-disk viscous pump single-DVP, to achieve easily controlled flow rates and pressure rises while maintaining simplicity and ease of manufacturing. An analytical equation is presented, based on the Navier-Stokes equations, which relates pressure rise and flow rate to the pump geometry, rotational speed and working fluid proper- ties. The predicted performance of the pump from the analytical equation is compared to experimental data. The disk pump is unique because it uses viscous stress to produce a pumping effect by employing one disk and a C-shaped channel 36. Figure 1 shows external and internal views of the single-DVP. The spin- ning of the disk causes a net movement of fluid due to the viscous stresses imposed on the fluid from the spinning disk. As the fluid passage height becomes smaller, the Reynolds number decreases, and the viscous forces become more significant than inertial forces. Thus, one assumption employed in the flow analysis is that the inertial or advection terms in the Navier-Stokes equations are insignificant compared to the diffusion of momentum terms. Fol- lowing this analysis, the development, fabrication, and testing of the disk pump is discussed. The flow rate and pressure rise for various rotational speeds are measured experimentally and com- pared to analytical expressions for the flow rate and pressure rise. Based on such results, advantages of this micropump compared to other micropumps are identified and discussed, and include a wide range of possible flow rates, simplicity, planar structure, well con- 1 Corresponding author. Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 21, 2005; final manu- script received September 29, 2005. Review conducted by Joseph Katz. 602 / Vol. 128, MAY 2006 Copyright © 2006 by ASME Transactions of the ASME