What is Orifice Plate Flow Meter ?
An Orifice Plate Flow Meter is the name given to a form of flow meter that is used for the measurement of the flow rate of Gas or Liquid, particularly steam, with the help of the principle of Differential Pressure Measurement. It is used primarily for strong applications, given that it is very cheap to buy and reputed for its durable construction. This type of meter is used commonly in steam, gas and clean liquid services. It can be availed for pipes of all sizes, although it is very economical for measuring flows in larger pipes. Many organizations also approve the use of this meter for custody transfer of gases and liquids. Find out how this meter works.
Orifice Meter – What is the Basic Working Principle?
It comprises of an Orifice plate that is its basic element. The bore of the plate can be made in numerous configurations, to deal with different types of flow measurement tasks. The flowing conditions have to be assessed to determine which the most appropriate configuration is for each type of measurement job.
Once this Orifice plate is put in a line, there is development of a differential pressure across the Orifice plate. It is a linear drop in pressure, which is directly proportional to the flow rate of the gas or liquid. Once there is placement of an orifice plate in a pipe that transports the fluid – the flow rate of which has to be measured – the orifice plate results in a drop in pressure that varies with the rate of flow. This reduction in pressure is measured with a differential pressure sensor. When it is adjusted finely, the drop in pressure can help measure the flow rate.
What Is Its Working Mechanism?
Once the fluid comes closer to the orifice, there is a slight rise in pressure and then an abrupt drop as the orifice gets passed by. It goes on dropping until it reaches the “vena contracta”. Gradually, it rises until at around 5 – 8 diameters in the downstream direction an optimal point of pressure is reached. The orifice pressure will be lower at this point as compared to the upstream pressure of the orifice.
As the fluid moves through the orifice, the drop in pressure is due to the higher velocity of the gas that passes through the orifice’ narrowed section. When there is reduction in velocity as the fluid gets out of the orifice, there is a rise in pressure and it finally goes back to its actual level. All the loss of pressure does not get recovered due to losses of turbulence and friction in the stream.
The drop in pressure across the orifice rises when there is an increase in the flow rate. No differential is there when no flow is there. The differential pressure happens to be directly proportional to the velocity square. Thus, it stands to reason that in case the other factors stay constant, the square of the flow rate can be directly proportional to the differential.