W a s h i n g t a n A unified theory of one-dimensional, adiabatic, separated, two-phase flow is presented. T o describe the flow adequately, four mixture specific volumes are defined. They are based on area, momentum, kinetic energy, and velocity averages. Increasing relative velocity between the phases initially lowers a l l mixture specific volumes except the velocity average. The momentum average specific volume minimizes when the slip ratio equals (V,/Vf)'/Z, while the kinetic energy average specific volume reaches i t s minimum value a t a slip ratio of (Vg/Vf)1'3. Area average specific value does not minimize with slip ratio.Because a higher slip ratio would decrease the entropy of a closed system, ( V g / V f ) 1 / 3 is the maximum slip ratio attainable in two-phase critical flow. Based on the maximum slip ratio and isentropic flow, a new critical flow model was developed and compared with the steam-water critical flow data of four recent investigations. While the predicted flow rates followed well the pressure behavior of the experimental data, they were too low a t high qualities and too high a t low qualities. The average percentage difference between experimental and predicted critical flow rates was -8.5% (three hundred and seventy-six data points).Differences i n the approach to critical flow between a gas and a vapor-liquid stream appear to be caused by the latter's increased frictional and gravitational pressure drops and relative velocity effects.

Reverse osmosis has come of age as a unit operation and is finding increasing usage in water and waste treatment. Large-scale (100–1000 gpm) units are currently operating throughout the world on a wide variety of feed streams. This paper summarizes the status of development of reverse-osmosis processing of municipal and industrial waste streams. Plants are described which process secondary effluent, metal-finishing wastes, and textile dye wastes. Capital and operating costs are also presented for reverse osmosis and compared with those of other desalting methods.

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Reverse osmosis is a continuous, reliable, demineralization and concentration process that requires very little operating attention. The key component is a semipermeable membrane that passes water but retains all suspended matter and most of the dissolved salts and organic substances in water. Reverse osmosis is being applied to high-purity water production, waste-stream concentration for pollution control, water reclamation, and food and pharmaceutical processing. It offers significant advantages over some other desalination techniques.

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