An orifice plate is a device that is used for the measurement of flow rate for reducing pressure or for the restricting flow. An orifice plate is a thin plate with a hole in it, which is usually placed in a pipe. When a fluid (either liquid or gaseous) passes through the orifice, its pressure builds up slightly upstream of the orifice. But as the fluid is forced to converge to pass through the hole, the velocity increases & the fluid pressure decreases.
Orifice Plate is the heart of the Orifice Meter. It restricts the flow & develops the differential pressure which is proportional to square of flow rate. The flow measuring accuracy entirely depends upon the quality of Orifice plate and its installation. Working …show more content…
This pressure that is dropped is measured using a pressure sensor that measures the difference in fluid pressure & when calibrated this pressure drop becomes a measure flow rate. The flow rate is given by,
Qa = (Cd.A2/√(1-(A2/A1)^2))*(√(2(P1-P2)/P))
Where, Qa = Flow rate
Cd = Discharge coefficient
A1 = Cross-sectional area of the pipe
A2 = Cross-sectional area of the orifice
P1, P2 = Static pressures Uses: Orifice plates are most commonly used to measure the flow rates in pipes when the fluid is single-phase (rather than being a mixture of gases & liquids or liquids & solids), the flow rate is continuous instead of pulsating, the fluid occupies the entire pipe (precluding silt or trapped gas), the flow profile is even & well-developed & the fluid & flow rate meet certain other conditions. Small diameter orifice plate is used for gases because gases are compressible & large diameter plate is used for liquid because liquids are incompressible. The concentric orifice plate is used for measuring flow rates of pure fluids. The eccentric as well as segmental orifice plates are used for the measurement of the flow rates of fluids that contains suspended materials like solids, oil mixed with water & wet …show more content…
TARGET FLOWMETER: Definition:
Target flowmeters are also known as drag force flowmeters. Target meters sense & measure forces caused by liquid impacting on a target or drag-disk or a “target” suspended in the liquid stream.
The target surface is positioned at a right angle to the fluid flow. A direct indication of the liquid flow rate is achieved by measuring the force exerted in the target. Usually, the meter consists only of a hinged & swinging plate that moves outward, along with the liquid stream.
In such type of cases, the device serves as a flow indicator. The force exerted by the flow on the target is proportional to the pressure that is dropped across the target. Bernoulli’s equation says,
“The pressure drop across the target is proportional to the square of the flow rate.”
Advantages: They do not possess any moving parts to wear out, such as bearings which can cause failures. They possess high reliability where life tests have been made to 20,000,000 cycles. Range or fluid changes attained by simply changing targets. It has low initial set up