What’s the Orifice Plate?
What’s the Orifice Plate?

خانه What’s the Orifice Plate?

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What’s the Orifice Plate?

What’s the Orifice Plate?

It is the most popular and common means of measuring current. It is based on the fact that the pressure difference created along the device by a plate located in the process line is measured to determine the flow rate.

There are three common types of Orifice Plate: Concentric, Eccentric, and Segmental. Oriflate Plate is also the center of the simplest and cheapest headmeter.

When the orifice plate is installed on a flow line, the surface through which the plates are installed is reduced by the flow of fluid in the path in the area where the plates are installed, which reduces the pressure in the dimension and Before the plates, this pressure difference depends on the rate of flow.

The orifice plate compresses the fluid flow along its path in order to produce a pressure drop similar to the function of elementary devices; The result is that the fluid pressure at the beginning of the flow is greater than the flow pressure at the end of the flow. The pressure drop is proportional to the square of the fluid velocity.

The main advantage of this device is the lack of moving parts and its low price (especially that it does not increase with the size of the pipe) and they measure well clean currents. The measurement accuracy of this device depends on how it is installed, the ratio of the pipe surface and the properties of the fluid and should be installed in straight pipes.

By installing the orifice plate on the constant pressure pipe, the current increases with a slight increase, and also with its rapid decrease, the current passing through the orifice decreases. This part is called vena contracts. While the flow velocity is at a maximum, on the other side of this part the constant pressure compensates for the slow and low flow.

Eccentric and segmental orifices are used to overcome problems with fluids containing solid particles (suspensions).

For different sizes of orifice plates, there is a direct relationship between the flow through the orifice plate and the pressure drop due to the flow passing through the orifice plate.

In an orifice plate, the constant pressure in the direction of flow is always significantly less than the pressure in the opposite direction of flow. Also, some of the pressure energy is converted into sound and heat, which is in the form of friction and turbulence in the orifice plate.

We now examine what happens at points 1 and 2 in the figure below.

At point 1, the fluid is disturbed by the orifice plate, at which point the flow velocity is equal to V1 and the cross section is A1. At point 2, the fluid has the highest possible velocity V2 and the cross section of A2, where A2 is less than A1. Point 2 is called the Vena Contract. Vena Contract is the point at which the cross section reaches the minimum and the maximum speed.

Bernoulli’s Theorem

Applying Bernoulli’s law to the above form we will have:

E1 = E2 = potential energy + kinetic energy + compressive energy

The parameters in the above expression are:

E1 = Energy before orifice …………. ………. …… .. Energy before orifice

V1 = Velocity upstream of the orifice …………… Velocity before orifice

P1 = Pressure before orifice …………………… ..… Pressure before orifice

Z1 = Elevation before orifice ………………… ..… .. Elevation before orifice

Rho1 = Fluid density …………………………. ……….… .. …… Fluid density

And

E2 = Energy before orifice …………. ………. …… .. Energy after orifice

V2 = Velocity upstream of the orifice …………… Velocity after orifice

P2 = Pressure before orifice …………………… ..… Pressure before orifice

Z2 = Elevation before orifice ………………… ..… .. Elevation before orifice

Rho2 = Fluid density …………………………. ……….… .. سی Fluid density

Which is for fluid. Rho1 = Rho2 and for horizontal tube Z1 = Z2

Q = V * A, which by placing in the above relation and also that the flow through both cross sections is the same, we reach the following relation:

According to the obtained relation, we see that fluid flow has a direct relationship with the square root of the pressure difference.

Why do Orifis always equip the plates with a tab?

Orifice Plates are equipped with an Orifice Tab for the following reasons:

1- Indicates the presence of orifice in pipelines.

2. The diameter of the hole is engraved on it.

3- The material of Orifis plate is engraved on it.

5- Orifis plate tag is engraved on it.

6. The entrance of Orifis Plate is marked on it.

Author: persian / Date: 2017-10-26
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