Backpressure-induced Transport Degradation and Wall-adhesion Mechanisms in a Ferrofluid Pump

Ferrofluid pumps exhibit significant potential in chip cooling, precision transport, and microfluidic systems owing to their non-contact actuation, self-sealing capability, and controllable microscale transport characteristics. However, existing studies have mainly focused on flow-rate characteristics under zero-backpressure conditions, while the interfacial evolution, dynamic sealing degradation and wall-friction mechanisms of ferrofluids under backpressure remain poorly understood. This study systematically investigated the maximum pressure-bearing capability, flow evolution, and wall-adhesion behavior of ferrofluid pumps under different backpressure conditions, revealing the mechanisms of backpressure-induced interfacial instability and backflow formation. The results show that, at low rotational speeds, ferrofluids maintain a stable slug-like structure and achieve near-ideal positive-displacement transport. As the rotational speed increases, the response of the ferrofluid to the external rotating magnetic field gradually lags behind, degrading the dynamic sealing performance and forming leakage channels under backpressure. Furthermore, backpressure not only suppresses the net flow rate by enhancing the reverse pressure gradient, but also alters the wall adhesion and liquid-film evolution of ferrofluids. Ferrofluids with different concentrations exhibit distinct interfacial response characteristics: low-concentration ferrofluids tend to generate free magnetic-liquid residues and severe wall adhesion, whereas high-concentration ferrofluids produce significant wall deposition due to high viscosity and intensified wall shear effects. Intermediate concentrations yield a relative balance between cohesion and fluidity. In addition, moderate backpressure enhances interfacial confinement of the liquid slug, whereas excessively low or high backpressure induces interfacial instability, exhibiting pronounced nonlinear characteristics. These results provide new physical insights for the design of high-backpressure ferrofluid micropumps and magnetically driven microfluidic systems.