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Rate in Fluid Systems 3.2 Volume Flow Rate Change in volume per unit time Volume flow rate = change in volume/time interval volume is in m3, cm3, ft3, in3, liters or gallons volume flow rate is in m3/s, ft3/min, liters/h Mass Flow Rate Mass of fluid moved per unit time Mass flow rate = change in mass/time interval Mass flow rates are in slugs/s and kg/s Measuring Fluid Rates Easiest method is to collect fluid and measure the amount of fluid collected over a time interval Average flow rate—volume or mass of fluid collected divided by the time interval Flowmeters measure indirectly and do not significantly interrupt the flow. (They measure pressure or velocity.) Measuring Fluid Rates Volume flow rate = cross-sectional area x fluid speed Mass flow rate = fluid density x crosssectional area x fluid speed Processes that Use Rates of Fluids Bottling machine City water supply system Air compressor to tool Conversion factors to know: 1 gal = 231 in3 1 gal = 0.1337 ft3 1 gal = 3.785 x 10-3 m3