Post-Critical Heat Flux Swirl Flow Heat Transfer with Two Refrigerants and Water

Abstract

Boiling heat transfer in the post-critical heat flux (post-CHF) regime was studied experimentally under steady-state swirl flow conditions with low superheat temperatures of the heated surface. Experiments were performed with the vertical flow of refrigerant-113 (R-113) in a tube with an i.d. 7.75 mm and with a heated length of 3.66 m over the mass flux range of 375-535 kg/m 2 s at a pressure of 0.184 MPa. The use of R-113 as the boiling fluid significantly extended the property ranges of available post-CHF swirl-flow data. The swirl flow was generated in the refrigerant tube by the use of four twisted metal tapes with tape-twist ratios ranging from 2.5 to 9.2. Liquid heating produced the low-wall superheat (below 50°C) in the post-CHF region, that was stable at steady state, and that was typical of the operation of many heat exchangers. Superheated vapor measured at the test section exit in most tests ensured that the entire post-CHF region was included. R-113 data were compared with data for water and refrigerant-12. A form of an existing correlation for post-CHF swirl flow heat transfer was generalized, resulting in good predictions of both magnitudes and trends of the data of all three fluids.