Research on the backpressure and backflow of a ferrofluid linear pump

Fluid transportation is a critical element in the performance of fluid machinery devices. This paper proposes a ferrofluid linear pump in response to the demand for fluid control without mechanical moving parts inside tubes. The pump includes two rectangular permanent magnets, ferrofluid, tubes, four one-way valves, and a linear actuator. The ferrofluid is bound in the tube by a strong gradient magnetic field generated by two rectangular permanent magnets, forming a liquid plunger. Under the cooperation of four one-way valves on and off, the reciprocating motion of the permanent magnet makes the ferrofluid plunger drive fluid to flow directionally. The maximum backpressure of the ferrofluid plunger under static and dynamic conditions is thoroughly analyzed by theory and experiments. Experiments of the interface profile and backpressure are consistent with the theoretical results in the static condition. The maximum backpressure reaches 8.3kPa in the static condition when the volume of the ferrofluid plunger is 19ul. However, the dynamic test under a reciprocating speed of 10mm/s~50mm/s has a significant backflow phenomenon, and the theory for calculating the backpressure is no longer applicable. The mechanism of the backflow is explored. There is a layer of water film between the ferrofluid plunger and the tube wall. With the increase of the backpressure and reciprocating speed, the thickness of the water film and the velocity gradient may enlarge, which increases the backflow and reduces the volume flow rate. Ultimately, failure occurs when the backpressure exceeds the sealing threshold during the ferrofluid plunger reciprocating process. The critical pressure difference for the pump failure fluctuates around 7.4kPa.