Mechanisms and Characteristics of Trace Water Vapor Frosting on a Cryogenic Surface from the Perspective of Initial Nucleation

Abstract

Under some extreme conditions of ultra-low water vapor content and ultra-low temperature, trace water vapor frosting can also bring significant hazards. Elucidating the mechanisms and characteristics of trace water frosting is a prerequisite for developing effective anti-frosting or defrosting methods. Owing to the importance of the initial nucleation for the subsequent frosting, in this work, guided by nucleation physics, the nucleation mechanism and characteristics of trace water vapor were investigated. The critical nucleation parameters, the critical nucleation transition conditions and the preferred nucleation phase diagram for condensation or desublimation were obtained. Finally, parametric and sensitivity analyses of the nucleation mass transfer rate were carried out to fully elucidate the peculiarities of trace water frosting. The results show that desublimation nucleation requires a larger critical supersaturation or subcooling, but has a smaller critical nucleation radius and nucleation mass transfer rate. Under trace water conditions, the nucleation type is only desublimation nucleation, and there is no transition from condensation to desublimation. The sensitivity of nucleation mass transfer rate to the surface temperature or surface contact angle is more significant under extremely low water content conditions (<1 ppmv), so the working conditions and surface parameters can be adjusted appropriately to control the nucleation process characteristics and thus the subsequent frost layer characteristics. The results of this work not only provide a guideline for revealing the nucleation mechanisms of trace water vapor frosting, but also indicate the specificity of the trace substance phase change process.

Keywords: cryogenic frosting, trace water vapor, initial stage, nucleation mechanism, condensation or desublimation