Net flow generation in closed-loop valveless pumping

Net flow generation in valveless pumping, met in many physiological applications and recently in micropumping devices, constitutes an open fluid dynamics issue due to the complex interaction between the fluid medium and the flexible walls of the pump. In the context of the present experimental work, the conditions of the net flow generation are examined in a closed-loop horizontal valveless pump, which consists of a rigid and an elastic tube of equal diameters and lengths, and a pincher that forces the liquid within the tube to oscillate at Reynolds and Womersley numbers up to 7800 and 48, respectively. Pinching off as well as at the mid-length of the pump flexible tube, net flow is generated at certain pinching frequencies for which details are presented based on simultaneous recording of the pressure at the two tube junctions, the flow rate and the displacement of the pincher. Pinching off the mid-length of the pump at low pinching frequencies, net flow rate is practically null due to the almost identical pressure waveforms at the tube junctions, which vary in phase with the pincher motion. However, close to the first natural frequency of the hydraulic loop, the reflection of the pressure waves at the tube junctions combined with their increased phase difference cause high axial pressure gradients, which when they increase simultaneously with the squeezing of the tube, net flow rate maximization occurs. Pinching at the flexible tube mid-length area, nonzero net flow rates can also be generated, the sign of which changes when the pincher mid-point crosses the tube mid-length without being nullified.