Local liquid film behavior of annular two-phase flow on rod-bundle geometry – II. Modeling and verification

Abstract

Local liquid film behavior of annular flow on rod bundle geometry is vital for accurate prediction of dryout. This paper is the Part II of a two-part study devoting to modelling and prediction of local liquid film behavior of annular flow on rod bundle geometry based on the unique feature of experimental phenomenon in Part I of this work. In this paper, a mechanism model is developed to predict the local liquid film thickness of annular two-phase flow on rod bundle geometry, in which the spatial distribution of gas flow in the cross-section of rod bundle is specified, and the local velocity of liquid film is obtained by employing the triangular relationship that taking into account properly the momentum and mass balances for the liquid film and the gas core. Ordinary differential equation (ODE) for the liquid film thickness is developed according to the Navier-Stokes equations for momentum balance of film flow on a rod to analyze the spatial characteristic of film thickness, in which the droplet entrainment-deposition process and the effect of circumferential shear stress are considered as boundary conditions during mass transfer at the gas-liquid interface. The present model predicts the experimental local liquid film thickness with the maximum relative error of ±10%. Circumferential coherent wave structure is formed by the combination effect of transversal stress gradient in the wave, droplet redeposition and film flow by circumferential shear stress, and the circumferential shear stress reduces the relative importance of the droplet redeposition with respect to the transversal stress gradient making the peripheral distribution of film thickness more uniform.