Gearless Wankel-like pump/mixer: Design challenges and prospects

This review covers the authors' attempt to simulate, design and prototype a novel gearless Lau-Wan fluid pump that can also act as a mixer. The gearless pump has a fluid chamber which features a single-lobed limacon (planar) geometry, based on the geometric model used in defining the Wankel rotor and chamber. The simulation study predicts that the mechanical efficiency of the pump varies linearly with the head coefficient; within the onset of internal leakage, the capacity coefficient is not sensitive to pump efficiency. Although the valveless positive displacement pump results in a low efficiency (less than 30%) — pump flow-rate decreasing appreciably at the onset of an internal leakage — the flow field reveals threedimensional vortices even in the laminar regime, including Taylor-like counter-rotating vortex pairs, indicating that these pumps may be exploited for microfluidic mixing applications. The preliminary design and prototyping stage involved considerations for the fluid chamber, rotor, drive shaft, the motor and the flow circuit. This led to three main designs, namely the single-stage (single-tier rotor) pump/mixer, the N- stage pump/mixer (where we have investigated the case of N = 2) and the single-stage (two-tier rotor) pump/mixer. Key challenges and prospects of these prototypes are discussed. Given that the planar geometry design described is the minimum required to keep a clean tank bottom during mixing, such a rotary pump/mixer may find applications in biofuel processing, e.g. biodiesel.