Semi-mechanistic prediction of spatial variation of local critical heat flux along a slightly inclined downward-facing surface

Abstract

A semi-mechanistic critical heat flux (CHF) model has been developed based on own experimental data. It is the first model, which can predict a spatial variation of the local CHF along a 10 degrees inclined flat surface facing downward. To model the slug flow within the two-phase boundary layer, the present work modified several fundamental variables of the original Cheung and Haddad's model and they are critical void fraction, shear stress, and newly introduced momentum loss terms responsible for pressure drop via drag force exerted on the vapor slug and acceleration of the entrained liquid to the boundary layer flow. The present model predicted that the local CHF varied spatially along the heater surface, and the CHF variation could be divided into two regions. The first region is the buoyancy dominant region, in which the local CHF increases rapidly along the heater surface from the beginning point. In the second region called momentum loss dominant region, the local CHF gradually decreases as the position is down further. Interestingly, the current model showed that the very upstream region over the inclined heater surface is mostly susceptible to occurrence of boiling crisis, whose results could be supported by the Sulatskii et al.'s work.