A simplified multi-mode wall condensation model for pure substances

Abstract

Condensation is an important phenomenon in industries such as the nuclear and refrigeration sectors. The motivation for the development of a pure-component wall condensation model was the estimation of the amplitude of a condensation-induced hydraulic shock (CIHS) during the hot gas defrost in industrial ammonia refrigeration systems. In such a scenario, condensation occurs both homogeneously in the bulk of the fluid via interfacial and dispersed-phase condensation and heterogeneously on wall surfaces. Within the heterogeneous wall condensation, several modes of condensation have been identified, such as the dropwise and film condensation modes. A mathematical wall condensation model that blends the dropwise and film condensation modes was successfully developed and calibrated to a validated theoretical model for water. Through demonstrative CFD simulations, the dropwise condensation mode was shown to be a high heat transfer mode with the potential to completely condense an inlet stream of vapor. The area fraction covered by droplets was found to be between 7–11$\text{\%}$, whereas heat flux through the droplet, was three orders of magnitude greater than the convective heat transfer. The current study presents the first closed-form wall condensation model for pure substances available for CFD codes that accounts for the high heat-flux dropwise condensation mode. This model can be implemented into both CFD and reduced-order codes and applied to a variety of transient multiphase flow problems in several industry sectors including safety-relevant cases.