Volumetric Flow Rate

Control Volume

Conservation of Mass

Thermodynamics Heat Transfer and Fluid Flow Volume 3 of 3
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Fluid Flow CONTINUITY EQUATION Volumetric Flow Rate The volumetric flow rate ( ) of a system is a measure of the volume of fluid passing a point in V the system per unit time. The volumetric flow rate can be calculated as the product of the cross- sectional area (A) for flow and the average flow velocity (v). (3-1) V A v If area is measured in square feet and velocity in feet per second, Equation 3-1 results in volumetric flow rate measured in cubic feet per second. Other common units for volumetric flow rate include gallons per minute, cubic centimeters per second, liters per minute, and gallons per hour. Example: A pipe with an inner diameter of 4 inches contains water that flows at an average velocity of 14 feet per second. Calculate the volumetric flow rate of water in the pipe. Solution: Use Equation 3-1 and substitute for the area. V (p r²) v V (3.14) ( 2 12 ft)² (14 ft sec ) V 1.22 ft³ sec Mass Flow Rate The mass flow rate of a system is a measure of the mass of fluid passing a point in the ( m) system per unit time. The mass flow rate is related to the volumetric flow rate as shown in Equation 3-2 where r is the density of the fluid. (3-2) m r V If the volumetric flow rate is in cubic feet per second and the density is in pounds-mass per cubic foot, Equation 3-2 results in mass flow rate measured in pounds-mass per second. Other common units for measurement of mass flow rate include kilograms per second and pounds-mass per hour. Rev. 0 Page 9 HT-03

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