A comprehensive critical heat flux mechanism model applicable to narrow rectangular channels

Abstract

Critical heat flux (CHF) is an essential consideration for the economy and safety of the equipment operation. To understand the CHF triggering mechanism and two-phase evolution characteristics from nucleation boiling until the occurrence of boiling crisis in narrow rectangular channels, a series of CHF visualization experiments were carried out at different gap sizes (1–5 mm), with pressures ranging from 1 to 4 MPa, inlet subcooling ranging from 65 to 120 K, and mass flux ranging from 350 to 2000 kg/(m²·s). Based on the visualization results and energy balance analysis, a comprehensive CHF mechanism model capable of predicting DNB type boiling crisis, Dryout type boiling crisis, and PM (premature) type boiling crisis is proposed. Comparison of the presented CHF mechanism model with the CHF experimental values in one side heated narrow rectangular channels showed that the MRE and RMSE of DNB type boiling crisis are 15.2 % and 21.3 %, of Dryout type boiling crisis are 10.1 % and 12.7 %, and of PM type boiling crisis are 11.8 % and 13.8 %, respectively. The MRE and RMSE of CHF values in double sides heated narrow rectangular channel are about 13.6 % and 15.7 %, respectively, and of non-uniform heated narrow rectangular channel are about 15.9 % and 19.1 %, respectively.