Numerical investigation of the thermal creep flow in a microchannel with dual heterogeneous ratchet surfaces

Persistent efforts in optimizing Knudsen pump designs are driven by the goal of enhancing their performance and expanding their application scope. This study employs the discrete unified gas kinetic scheme to investigate the influence of key geometric and thermodynamic parameters on the thermal creep flow and pumping performance of a novel double-ratchet Knudsen pump. The pump features periodic ratchet structures on both the low-temperature top and high-temperature bottom walls, each comprising curved diffuse-reflection segments connected by vertical specular-reflection segments. Simulations reveal that a directional gas flow is generated by the thermal creep effect, with the maximum velocity localized near the ratchet protrusions. The wall angle θ enhances pumping performance by intensifying this thermal edge flow, whereas an increased channel width ratio B/L weakens it. Increasing B/L from 0.1 to 0.7 leads to a 59% increase in the mass flow rate. Optimal performance is achieved at zero wall displacement (l/L = 0) and a Knudsen number of 0.1, with mass flow rate increasing linearly with the temperature difference ΔT. Notably, flow reversal and complex vortex structures emerge at Kn ≥ 5. The mass flow rate of the proposed pump exhibits a 200% enhancement over that of a typical double-ratchet pump. These findings elucidate the underlying mechanisms in double-ratchet pumps, providing valuable insights for the design and optimization of high-performance Knudsen pumps.