The present capability to understand and predict two-phase transport for annular flow in complex fin-matrix passages is clearly limited by the current lack of information regarding the shedding, entrainment and deposition mechanisms in such flows. These studies address this problem specifically by examining the manner in which liquid is shed from fin structures and the way in which the liquid breaks-up into droplets and is dispersed into the core flow. Microprobe instrumentation is being developed to obtain quantitative information about local droplet density and size distribution downstream of fin structures, and this instrumentation will also augment the general capabilities of researchers working on multiphase flow transport. Detailed quantitative measurements of the entrainment downstream of fin-type structures and lateral transport of liquid between fins and prime surface areas, as well as in situ measurements in vaporizing and condensing flows in fin matrix passages are being made. These experiments include simultaneous measurement of entrainment characteristics and overall heat transfer for convective vaporization and condensation of pure coolants and binary mixtures over wide ranges of flow conditions. The final stage of the study will use data obtained in the experiments to assess and improve existing models of shedding, deposition and lateral film transport. These improved models will be incorporated into improved computational schemes for predicting the overall transport to evaluate the impact of these mechanisms on heat and mass transfer in the matrix. The information regarding liquid transport mechanisms obtained in the proposed research will serve to enhance the capabilities for predicting two-phase transport in compact evaporators and condensers, cooling towers, and other equipment in which the flow passages are complex and/or contain interrupted surfaces.
