A FINITE-DIFFERENCE COMPUTATIONAL MODEL OF ANNULAR FILM-FLOW BOILING AND 2-PHASE FLOW IN VERTICAL CHANNELS WITH OFFSET STRIP FINS

This paper describes a detailed computational model of annular two-phase flow through offset strip fin heat exchanger geometries. In this model, a modified finite difference scheme is used to compute the velocity and pressure fields throughout the vapor core of the fin matrix. The vapor phase model is iteratively matched to a second finite difference model of the liquid film flowing along the channel walls. Three-dimensional interactions between the liquid film flowing along the prime and secondary surfaces of the matrix are also incorporated into the model. By solving the Navier-Stokes equation in the vapor phase, this model provides, for the first time, detailed local information about the shear stress and static pressure variation along the liquid film. This makes it possible to study the local variation of the heat transfer coefficient and wall shear stress all along the matrix. The model is validated against experimental data for two different offset fin geometries and then used to systematically study the effects of fin and channel geometry on two-phase transport. Special properties of two-phase flow through offset fin matrices discovered using the model are also described and the effects of these properties on the accuracy of previous annular flow models is discussed.