Hydraulic bench, to measure the actual volume flow rate.The coefficient of discharge of an orifice meter is the ratio of the actual discharge to the theoretically-calculated volume flow rate. This is because of frictional losses incurred as the fluid traverses the pipe length. It can be seen that at the contracted section, the pressure magnitude is the least after which the pressure head is restored but to decremented value in comparison to the pressure at the inlet. The figure above shows the graphical trend of pressure variation across the orifice plate. The velocity of fluid at this section shows an instantaneous hike followed by a pressure decrement. The section where the streamlines come the closest possible is termed the vena contracta. Consequently, the streamlines come close to each other. When an orifice meter is installed in a pipe, the cross-section contracts. The actual discharge can be determined by recording the time to fill a known volume of fluid in the volumetric tank. The theoretical discharge through the pipe cross-section can be calculated as H = Pressure difference in the limbs of manometer The manometric fluid in both limbs of the manometer shows a difference in the levels which is noted down. The differential pressure becomes eminent on the limbs of the manometer in the form of a pressure step-down. Consequently, the velocity of fluid shows an instantaneous surge, thereby dropping the fluid pressure at the contracted section. The figure above shows an orifice meter connected in a pipe of diameter D containing a fluid flowing under the influence of pressure forces.ĭue to the presence of the orifice plate, the pipe’s diameter reduces. The differential pressure head is measured using a manometer and the discharge through the pipe cross-section can easily be calculated. Orifices are used to measure the discharge or volumetric rate of flow through tanks, reservoirs, or any fluid receptacle.Įvidently, the flow through an orifice depends upon the diameter and type of orifice as well as the head of fluid present above it.Īn orifice meter or orifice plate is also a discharge measuring device employed in a pipe to create a pressure gradient by altering the pipe cross-section at the point it is installed.
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