Numerical Characterization of the Performance of Fluid Pumps Based on a Wankel Geometry

The performance of fluid pumps based on Wankel-type geometry, taking the shape of a double-lobed lima？on, is characterized. To the authors’ knowledge, this is the first time such an attempt has been made. To this end, numerous simulations for three different pump sizes were carried out and the results were understood in terms of the usual scaling coefficients. The results show that such pumps operate as low efficiency (<30%) valveless positive displacements pumps, with pump flow-rate noticeably falling at the onset of internal leakage. Also, for such pumps, the mechanical efficiency varies linearly with the head coefficient, and, within the onset of internal leakage, the capacity coefficient holds steady even across pump efficiency. Simulation of the flow field reveals a structure rich in three-dimensional vortices even in the laminar regime, including Taylor-like counterrotating vortex pairs, pointing towards the utility of these pumps in microfluidic applications. Given the planar geometry of such pumps, their applications as microreactors and micromixers are recommended. 1. Introduction The present study is part of a larger effort aimed at exploring applications of fluid pumps based on Wankel-type geometry and is focused on the performance characterization of the simplest of such pumps. Such Wankel-type pumps are essentially rotary positive displacement pumps, which operate by having an inner rotor orbit inside a chamber. The rotor path, determined by the chamber profile, creates a trapped fluid volume which is displaced through the chamber. In contrast to rotodynamic pumps, the trapped fluid is continually compressed to a high pressure without being imparted high kinetic energies. As a positive displacement pump, it has characteristics similar to the reciprocating positive displacement pump and, hence, would generate the same flow at a given speed (RPM) regardless of the discharge pressure, that is, a flat H-Q curve. However, a rotary pump is more susceptible to internal flow leakages especially at high pump heads, leading to a significant reduction in efficiency. The advantages of rotary pumps are that, as well as being able to deliver a flow that is less pulsatile compared with reciprocating piston pumps, they are more compact in design and capable of valveless operation. There are a number of rotary pump types that have been well established and have found industrial application, such as the Gear Pump, Lobe Pump, Sliding-Vane Pump, Screw Pump, and Progressive-Cavity Pump [1], but so far, to the authors’ knowledge, the Wankel-type design for fluid