ICONE19-43858 An improved critical heat flux prediction model for subcooled and low quality flow boiling under motion condition based on microscopic mechanism

Abstract

The motion of the flow channel will create a new acceleration field other than gravitational acceleration field for the fluid flow in the heated channel. In order to investigate the influence of this new arisen acceleration field on the occurrence of critical heat flux in subcooled flow boiling, an improved model under motion condition based on microscopic mechanism of bubble dynamics is developed. The proposed CHF model is on the basis of liquid sublayer dryout mechanism which has been well investigated by the previous researchers. New forces due to the flow channel motion will make the intermittent vapor blankets in the near wall region behave in a different way. In the present model, the thickness of the liquid sublayer is calculated based on the balance of the forces exerted on the vapor blanket such as evaporation force, lift force, radial buoyancy force in the normal direction of the heated wall (this force arises from the radial acceleration due to the motion of the flow channel), wall lubrication force, and Marangoni force. And the balance of drag force, and buoyancy force in the flow direction (this force is dependent on both the gravitational acceleration and the axial acceleration due to the motion of the flow channel) is taken into account to determine the relative velocity of the vapor blanket, (U_B-U_<BL>). The parametric trends of CHF in terms of mass flow rate, inlet subcooling and pressure, and the effects of accelerations (due to the motion of the flow channel) in both the flow direction and the normal direction of the heated wall are studied qualitatively and quantitatively. Comparisons of the prediction results and experimental data for subcooled-flow-boiling water under both static and motion conditions show good precision and accuracy.