Two-phase flow patterns and frictional pressure gradients in a small, horizontal, rectangular channel.

摘要

Two-phase flow patterns and frictional pressure gradients in flow in small, rectangular channels are being studies as part of a larger research program addressing phase-change heat transfer of pure refrigerants and refrigerant mixtures in plate-fin heat exchangers. Small rectangular flow channels were selected as representative of plain fin geometries. The particular channel reported herein has dimensions of 19.05 (times) 3.18 mm. Adiabatic flows of air/water mixtures, with the flow channel horizontal and the channel exit at near-atmospheric conditions, were utilized in the experiments. Analysis and interpretation of the pressure data relative to observed flow pattern transitions led to an objective method for determining the plug/bubble-to-slug flow transition. This method, together with visual observations, supplemented with photographic data, was used to develop a flow pattern man. A comparison of existing flow pattern maps for circular pipes, capillary tubes, and larger rectangular channels led to the conclusion that, while qualitative agreement exists, these maps are not generally applicable on a quantitative basis to the subject small rectangular channel. Two state-of-the-art correlations for frictional pressure gradient were evaluated, with particular emphasis on the practically important ranges of total mass quality and mass flux, from the standpoint of plate-fin heat exchangers designed as evaporators. Neither correlation was in good agreement over the entire range of interest. A modified, semiempirical correlation was developed to predict, with satisfactory accuracy for design purposes, the measured data of these experiments. 60 refs., 44 figs., 2 tabs.