Amplification of surface roughness on polymers utilizing sacrificial micro-particles to enhance heat transfer for quenching in liquid nitrogen

A sacrificial micro-roughening technique for surface modification on polymers was developed to improve quenching under cryogenic conditions over conventional abrasive methods. Sugar particles as novel grit material that enabled significantly augmented pore formation, normal to the surface (Rz up to 118 µm), were sprayed in a time-controlled manner onto an uncured epoxy-based solder mask supported on a printed-circuit-board substrate, to be later dissolved with water; creating micro-cavities characterized on a wide range of surface roughness. The high level of surface modification could lead to prominent quenching performance through Leidenfrost-effect suppression and critical-heat-flux enhancement (max. 400%), reducing quenching time from 3.84 s for an unmodified surface to 1.06 s for an optimally treated surface. The transient heat-transfer profile for three surface models was investigated to identify the underlying principles of quenching enhancement when altering surface properties. High-speed imaging was taken at different stages of the quenching process to provide visual information on the transient patterns of vaporization at the occurrence and transition between (1) the formation of initial vapor film upon the plunge into liquid nitrogen, (2) minimum heat flux if it occurs, and (3) critical heat flux. It is hypothesized that elevated surface area resulting from increased surface roughness could respectively facilitate the destruction of the vapor film at an early time and instigate bubble nucleation at its critical heat flux.