TABLE OF CONTENTS High volume flow of liquids in industrial waste systems, waterworks, and irrigations systems are commonly carried in open channels, which are characterized by low system heads and high volume flow rates. Open channel flow is flow in any channel in which the liquid flows with a free surface. Examples of this are rivers, irrigation ditches, canals, flumes, and other uncovered conduits. Certain closed channels, such as sewers and tunnels when flowing partially full and not under pressure, are also classified as open channels.
In the timed gravimetric method, the entire contents of the flow stream are collected in some type of container for a fixed length of time. The weight of the fluid is then determined and the flow rate is calculated. The timed gravimetric and dilution methods are generally not used for routine industrial flow measurement because they are not suited to provide a continuous record of flow rate. They are more often used for occasional flow rate measurement at a particular time and place, for calibrating some other type of device, or for developing a liquid levelflow rate curve for a particular location.
In the dilution method, the flow rate is measured by determining how much the flowing water dilutes an added tracer solution. Although brine tracers have been used, radioactive and fluorescent dye tracers are more commonly used today. In the velocity-area method, the flow rate is calculated by determining the mean flow velocity across a cross...
