A venturi meter measures fluid flow rate using a Herschel venturi tube. Bernoulli’s principle is used to calculate flow rate by measuring pressure before and after the venturi. The tube design reduces head pressure degradation. The formula considers pipe radius, fluid compressibility, and other variables to obtain an accurate flow rate.
A venturi meter, or venturi flow meter, is a device used to measure the speed, or flow rate, of fluid flowing through a pipeline. The venturi restricts the flow using a Herschel venturi tube. As the liquid flows through the pipe, the device measures the pressure of the liquid before it enters the venturi tube and as it exits the confined area. These measurements are then compared to calculate the volumetric flow rate of the fluid. The flowmeter is commonly used in plumbing applications to determine the flow of fluids such as water, liquid propane, and oil.
For this procedure, the venturi is typically a long tube with conical-shaped entry and exit points. The entry point is usually a thirty degree cone narrowing to a five degree cone at the exit. Venturi results in less head pressure degradation due to the tube design.
The venturi can accurately measure the flow using Bernoulli’s principle. Bernoulli stated that the velocity of the liquid increases in direct proportion to the decrease in pressure. As liquid is forced through a constricted pipe, it begins to move at a faster rate because most of the pressure is held behind the constriction.
A common example of Bernoulli’s principle in action can be found in the nozzle of a garden hose. When the nozzle is fully open, the water flows slowly and usually falls a short distance from the nozzle. When the nozzle is rotated to the closed position, it restricts the flow of water and increases its speed. The pressure held behind the nozzle increases, and the velocity can carry water great distances.
The Venturi meter accurately calculates the volume flow rate of a fluid using a complex formula. This calculation considers the radius of the pipe, whether or not the liquid being measured is compressible, and the total volume of fluid present. Various coefficients are added to compensate for fluid viscosity, changes in venturi cone angles, and other variables. When these numbers are calculated, together with the pressure measurements taken by the venturi, an accurate description of the liquid flow rate can be obtained.
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