Critical heat flux triggering mechanism on micro-structured surfaces: Coalesced bubble departure frequency and liquid furnishing capability

Abstract

This study presents a new critical heat flux (CHF) triggering mechanism for explaining the CHF enhancements of micro-structured surfaces. Differentiating the existing vapor recoil mechanism and hydrodynamic instability theory, this model focuses on the phenomenological observations of the boiling phenomena in which a number of small bubbles are generated, which then merge and coalesce into a large bubble. According to this model, the CHF phenomenon is governed by the frequency of the coalesced bubble departure and the liquid furnishing capability into a thin liquid–vapor layer (macrolayer). The microstructures on the surface change the evaporative mass flow rate owing to the liquid–vapor interface deformation near the triple contact line of the macrolayer, leading to a change in the coalesced bubble departure frequency. The liquid flow resistance, which increased owing to the microstructures, can affect the liquid volume flow rate available for evaporation in the macrolayer; thus, it directly alters the CHF behavior. The liquid flow resistance induced by the microstructures could contribute to the relative deterioration of the CHF value at the surface. The CHF can be directly modeled by means of the summation of the mean velocity of liquid flowing into the macrolayer due to the pressure potential induced from capillary and disjoining pressure effects, as well as the coalesced bubble departure frequency.