A Quasi One-dimensional Method and Results for Steady Annular/stratified Shear and Gravity Driven Condensing Flows

This paper presents an effective quasi one-dimensional (1-D) computational simulation methodology and some important results for steady annular/stratified (or film wise) internal condensing flows of pure vapor. Though the approach is strictly valid for smooth, laminar vapor/laminar condensate flows, it is also approximately valid for laminar condensate and turbulent vapor which are laminar in the near interface region. In-channel and in-tube flows are considered for a range of gravity component values (from 0g to 1g) in the direction of the flow. The 1-D solutions significantly expedite the process of obtaining full two dimensional (2-D) steady/unsteady computational solutions for these flows. For these flows, three sets of results are presented that are consistent with each other and are obtained from: (i) a full 2-D computational fluid dynamics (CFD) based approach, (ii) quasi-1D approach introduced here, and (iii) relevant experimental results involving partially and fully condensing gravity driven flows of FC-72 vapor. The 1-D approach has been implemented for two types of thermal boundary conditions – viz. specifications of temperature or heat flux profiles for the condensing surface. Besides demonstrating and discussing the differences between shear and gravity driven annular flows, the paper also presents a map that distinguishes shear driven, gravity driven, and “mixed” driven flows within the non-dimensional parameter space for these duct flows. With the help of a proper synthesis with reliable experiments, some useful heat transfer correlations are also presented. The paper also demonstrates that μm-scale hydraulic diameter ducts typically experience shear driven flows and provides some important results/discussions for attaining and maintaining annular/stratified flows under these more challenging conditions.