DRYOUT UNDER FLOW OSCILLATION IN A BOILING CHANNEL AT LOW MASS FLUX AND PRESSURE

摘要

Recent advanced technologies in boiler manufacturing bring about highly efficient and compact water-tube boilers for gas firing or oil firing. These boilers have very simple water-circulation system, which often brings about flow instabilities followed by the critical heat flux, CHF, problems. This paper describes such an oscillatory flow CHE, at relatively low mass flux and at low pressure. The CHF is a decreasing function of the amplitude and period of the flow oscillation, and reaches almost 40 % of the steady state value. When the tube wall thickness is thin, the CHF is mainly controlled by the two-phase flow dynamics and is well simulated using a simple lumped-parameter modeling. At very low mass flux, the CHF depends significantly on the flow orientation, and is closely related to the flow pattern transition.