Transient performance of flow over a rotating object placed eccentrically inside a microchannel?numerical study

Abstract

Industrial applications today are demanding the implementation of microelectromechanical systems (MEMS) into their products. These are mechanical devices that are able to perform work, and yet have characteristic lengths less than 1 mm. As a result, the Reynolds number is typically low, which indicates the dominance of viscous forces. When a cylinder is placed eccentrically inside a microchannel, where the rotor axis is perpendicular to the channel axis, a net force is transferred to the fluid as a result of the unequal shear stresses on the upper and lower surfaces of the rotor. Consequently, this causes the surrounding fluid in the channel to displace towards the microchannel outlet. The present numerical investigation is a comparative study of transient flow behavior in a microchannel with rotating cylinders with different cross-sectional geometries. The effects of channel height, eccentricity, Reynolds number, and pump load were studied, as well as the development of their respective streamlines and pressure contours. The steady state results were compared with existing numerical and experimental results, and the comparisons showed very good agreement. Keywords Rectangle cylinder flow AE Square cylinder flow AE Transient microfluidics List of symbols C D cylinder drag coefficient C L cylinder lift coefficient C M cylinder moment coefficient d diagonal length of rotor (m) F L lift force on cylinder per unit length (N/m) F D drag force on cylinder per unit length (N/m) h channel height (m) L perimeter of rotor (m) M moment on cylinder (N m) _ m mass flow rate (kg/s) P in inlet pressure (Pa) P out outlet pressure (Pa) P* non-dimensional pressure DP channel pressure rise (Pa) DP* non-dimensional pressure rise Q non-dimensional volume flow rate Re Reynolds number R normal distribution ratio S curve length (m) S non-dimensional channel height t time (s) t* non-dimensional time Dt time step size (s) " u average velocity inside microchannel (m/s) u* non-dimensional average velocity U cylinder surface velocity (m/s) V fluid velocity vector (m/s) y c distance from channel axis to cylinder center (m)Greek letters a body forces per unit mass (m/s 2 ) e rotor eccentricity l fluid dynamic viscosity (Pa s) m fluid kinematic viscosity (m 2 /s) h angle sweep over surface, =s/L (rad) q fluid density (kg/m 3 ) s fluid shear stress (Pa) s* non-dimensional fluid shear stress x rotor angular velocity 1 Introduction

Numerical Study of the Laminar Flow Past a Rotating Square Cylinder at Low Spinning Rates

“…These rotors could become noncircular as a result of these imperfections in manufacturing. Also, future micropumps may not even utilize rotors with circular cross sections, as is the case for the cellular motor-based micropump, which is currently in development for future use as a novel drug delivery system, and which utilizes a capsule-shaped rotor [6]. Accordingly, there is serious need to study the fluid dynamic transport around a spinning square which is yet to be reported in the contemporary literatures.…”

“…However, similar studies on rotating square cylinder are almost unavailable. Few studies are available for the flow past a square cylinder with an angle of incidence [18,19] and few demonstrate the performances of various rotating objects placed inside a microchannel [6] or within a square [20] and/or circular enclosures [21]. Accordingly, we aim here to numerically investigate the fluid dynamic transport around a rotating square cylinder in a free 1 stream.…”

Lubrication analysis of the viscous micro/nano pump with slip

“…The simplicity in the design of the viscous pump is its major attractive feature for MEMS, NEMS and LOC applications. The viscous pump consists of a transverse-axial rotor (usually cylindrical, but not always as in the numerical study of Phutthavong and Hassan (2004)) eccentrically placed in a channel, so that the viscous resistance between the small and large gaps between the cylinder and the channel walls generate a net flow along the channel. The advantages of such a viscous pump extend beyond MEMS, NEMS and LOC devices, as they may be utilized for medical or biological purposes since they are capable of pumping very small flowrates of fluid, which is necessary in applications such as drug delivery.…”

Design and development of a new portable roof gutter for electricity production

“…The design of the rotating gutter is illustrated in the block diagram where the structure of the rotating tube is represented as a spherical turbine in which the division of the spherical turbine into slides affects the rotation significantly [22,23].…”