Separate factors’ effects on CHF for flow boiling in an inclined rectangular channel under low mass flux

Abstract

Flow boiling under natural circulation is a reliable method of safety strategy for a thermal dissipation system, especially in the nuclear power system, however, the CHF is the safety limit. Thus the CHF prediction is paramount important for such systems. In order to well understand CHF mechanism and develop the theoretical models, separate factors’ (heater surface orientation, mass flux and inlet quality) effects on CHF for flow boiling under low mass flux and low pressure are investigated both experimentally and theoretically in this study. A rectangular channel with the cross section of 17 mm × 10 mm is used as the flow channel and the main heater with stainless steel surface has the size of 17 mm × 17 mm. The flow boiling experiments were tested for deionized water under the atmosphere pressure at the outlet. The CHF values for flow boiling were obtained under various surface orientation of 15–90°(0° is completely downward), mass flux of 110–288 kg/m2s and inlet quality of 0.003–0.036. The separate factors’ effects on the CHF were analyzed. It is concluded that the CHF increases with the increase of the mass flux, inlet quality and heater surface orientation, however it is not linear. A CHF model based on the sublayer dry out model is proposed. The developed model well predicts the CHF variation trend with each separate parameters (orientation, mass flux and inlet quality). And more than 90% predicted results have the error within ±15%.