Critical Heat Flux in Forced Convective Subcooled Boiling with Multiple Impinging Jets. Effect of Subcooling.

Abstract

Critical heat flux during forced convective subcooled boiling on a rectangular heated surface of 40 or 60 mm in length and 7 mm in width, which is supplied with subcooled liquids through a small round jet which impinges at the center of the surface has been studied experimentally employing three different liquids (water, R113, and R22) at pressures from 1 to 25 bar under high subcooling condition up to 115 K. A flow model based on observation of the change in the flow aspect with increasing heat flux shows that the flow state can be divided into two regions : first, a subcooled region including weak boiling where the liquid is kept subcooled ; and second, a saturated region where the liquid is kept at the saturation temperature and most of the liquid splashes out as droplets. A criterion is proposed that the CHF in the saturated region can be determined from the existing equation for the CHF for the saturated liquid, while for the same heat flux in the subcooled region, the equation can be derived from a simple heat balance under the assumption that the subcooled liquid is heated to the saturation temperature at the leading edge of the saturation region. By eliminating the length of the subcooled region from the two equations and after revising them slightly, a generalized correlation can be derived, which yields about 82% of the CHF data with an accuracy of ±20%.