Design of Dilution Junctions for Water Quality Control

Abstract

A method for extending the available water supply in a region is discussed. Using dilution (mixing) junctions, brackish water is mixed with higher quality water, thus producing the required water quality. For good results, the process should be controlled automatically. Typically, the controlled variables are salinity, outlet flow, water level or outlet pressure. Mixing junctions are classified, possible configurations discussed, and the most promising analyzed in detail. Steadystate equations are derived, and a microcomputer program simulating steady‐state operation is presented. This program helps to determine various design constants of the junction. For a dynamic study, a hybrid computer simulation was made, with dynamics of instrumentation simulated on an analog computer. A conclusion of this simulation is that equal‐percentage rather than linear‐control valves should be used. A cost analysis showed that lowest cost is achieved using a self‐actuated pressure or flow regulator, and single‐speed floating control for salinity. A circuit implementing single‐speed floating control, using a conventional control valve and two small solenoid valves, is described and tested by hybrid simulation.