Characteristics of critical heat flux under rolling condition for flow boiling in vertical tube

Abstract

This paper presents the characteristics of the critical heat flux (CHF) for the boiling of R-134a in vertical tube under rolling motion in a marine reactor. It is important to predict CHF of marine reactor under rolling motion in order to consider the safety margin of the reactor. MArine Reactor Moving Simulator (MARMS) test was conducted to measure the CHF of R-134a flowing upward in a uniformly heated vertical tube under rolling motion. A CHF loop mounted on rolling equipment, which can periodically roll from side to side through rotating by motor and mechanical power transmission gear. The CHF tests were performed in a 9.5mm I.D. test section with heated length of 1m. Mass flux ranges from 285kg/m2s to 1300kg/m2s, inlet subcoolings from 3 to 38°C and outlet pressures from 1.3 to 2.4bar, respectively. Amplitudes of rolling range from 15° to 40° and period from 6 to 12s. Fluid-to-fluid (FTF) scaling was applied to convert the test matrix of MARMS from water to R-134a equivalent conditions. CHF ratios (ratio of the CHF under rolling condition to the stationary CHF) as mass flux and pressure in rolling motion are quite different from those of other existing transient CHF experiments. For the mass fluxes below 500kg/m2s (region of relative low mass flux) at 13, 16bar, CHF ratios seem smaller than unit but in region (region of relative high mass flux) where mass fluxes are above 500kg/m2s, it was found that the ratios increased. Moreover, rolling CHFs tend to enhance compare with stationary CHFs in the entire mass flux region at 24bar. To understand the CHF mechanism under rolling motion, considering the flow regime in this study using a new approach was analyzed.