Frosting modes and anti-frosting mechanism of organic solvents in micro-tube precoolers

Frost formation on pre-coolers induced by low-temperature cryogens during the intake air pre-cooling process poses a substantial threat to the safe and reliable operation of pre-cooled engines. In response to the unclear mechanisms of frost formation and anti-frosting under current micro-scale and ultra-low wall temperature conditions, this paper takes a micro-tube pre-cooler module with a characteristic scale of 0.9 mm as the research object. By constructing an ultra-low temperature wall condition ranging from −120 °C to −140 °C, the frost formation patterns of the pre-cooler, as well as the anti-frosting effects and intrinsic mechanisms of organic solvents, are systematically investigated via experimental methods. Key results indicate that the frost layer evolves through three distinct stages, namely initiation, propagation, and stabilization, exhibiting a front-end aggregation characteristic wherein the first three tube rows contribute to the majority of total frost accumulation. Non-uniform liquid nitrogen flow distribution across the capillary bundle, combined with the impinging shear effect of the incoming flow Reynolds number ( Re ) on the frost layer, gives rise to two polarized cycles: “high flow rate, increased frost accumulation, stable flow resistance” and “low flow rate, reduced frost accumulation, elevated flow resistance”. After the initiation of frosting, the wall cooling rate is 30%–50% higher than that in the non-frosted stage, accompanied by a 5–50 °C outlet temperature rebound induced by the collapse and regeneration of the frost layer. Anhydrous methanol, anhydrous ethanol, and their mixture with a 1:1 mass ratio all exert effective inhibition on frost growth, among which the mixed solvent exhibits the optimal anti-frosting performance. Specifically, at 500 8 s, the pressure loss coefficient of the mixed solvent is 71.9% lower, and its heat transfer capacity is 173.8% higher, compared with those under pure frosting conditions. In detail, methanol modulates the wall temperature to adjust the heat transfer distribution; ethanol sustains the tube bundle wall temperature above 0 °C by increasing the condensate thermal resistance; while the mixture capitalizes on the synergistic effects of the two solvents by establishing a more uniform temperature field. This study offers crucial technical support for the dynamic anti-frosting control of precoolers in hypersonic engines.