Abstract:
Micropump is the fundamental component of a microfluidic device and has been the subject of a number of researches for the last few decades. This type of pump can control and transfer small amount of fluid usually less than 15 μL/min. The length scale of the pump is of the order of 100 μm or less which significantly facilitates its possible applications in a number of miniature technologies such as microelectromechanical systems (MEMS), biomedical engineering, robotics, space explorations and so on. In the present study, a viscous force based pumping device is investigated. The proposed viscous pump consists of two counter rotating cylinders (rotors) which are placed symmetrically at vertical position inside a narrow channel. When the cylinders (rotors) rotate, the viscous pump could generate a net flow against an externally imposed pressure gradient.
To model the flow field around the viscous micropump, the Navier-Stokes equations have been numerically solved using Finite Volume Method (FVM). Flow has been considered to be incompressible, three dimensional (3D) and laminar. The PISO (Pressure-Implicit with Splitting of Operators) algorithm was used for the pressure-velocity coupling which ensures rapid rate of convergence without any significant loss of accuracy. Glycerine has taken as the working fluid with constant flow and thermal properties. The numerical results have been validated with available experimental data for the case of a single rotor micropump.
Results of the proposed dual rotor micropump have been reported in the form of non-dimensional flow quantities such as dimensionless average velocity, driving power and efficiency. To study the effect of geometric parameters, several pump configurations were considered with various channel height, wall clearance and channel width. The optimum size of wall clearance was determined which plays a significant role on the flow dynamics inside micropump as well as on the pump performance. For dimensionless channel heights of 2.1, 2.3, 2.5, 2.7 and 3.0, the optimum dimensionless wall clearance was found to be 0.01, 0.02, 0.05, 0.075 and 0.10 respectively, for a particular flow condition. It was also found that channel width has significant role on the performance of pump until the channel width is less or equal to 20 times the cylinder diameter. Moreover, computations have been carried out for the cases with non-Newtonian fluids (relevant to biomedical application) with power law model under different operating condition. It was observed that the performance of the proposed micropump improves in case of non-Newtonian fluids. In addition to steady flows, a number of unsteady computations have been carried out to investigate the initial transient flow dynamics of micropump operation for the cases of Newtonian and non-Newtonian fluids.
