Abstract:
In the present study, the critical heat flux（CHF） experiments in vertical narrow tube with power step are conducted to verify the CHF predictions by non-uniform heating CHF model.The boiling crisis position, CHF, qN,CHF, and average heat flux, qN,AVE, predicted by non-uniform heating CHF model, show a reasonable agreement with the CHF experimental results. The CHFs for different power steps are calculated using this non-uniform heating CHF model to analyze the effects of power step ratio, Rh, power step length, Lh, and the power step position on the boiling crisis: The qN,CHF approximately linearly increases with an increase of Rh. While the qN,AVE decreases with the increasing Rh. As Lh increases, qN,CHF decreases significantly and qN,AVE approaches to CHF under uniform heating condition, qU,CHF. When the position of the power step moves to the upstream, the boiling crisis position will depart from the end of power step. As boiling crisis is trigged at the outlet of tube, the qN,CHF and qN,AVE are both approximately equal to qU,CHF.
