Orifice meter :Working

Flowmeter is the devices that measure the flow rate of the fluid. They are installed in any process vessels in order to measure the process flow data like volumetric flow rates, velocities etc.

They are designed in such a way that it can measure and calibrated to get parameters at an exact specific time at a specific location.

Today we are going to discuss various flow meters and their classification and also there working principals.

In last blog post we had discussed briefly about venturi meter . If you missed that blog , you can go through it by click below link.

Flow meter working:Venturi meter

Orifice meter.

The venturi meter has certain practical drawbacks for ordinary plant practice. The venturi meter is expensive and it occupies considerable space and it's ratio of throat diameter cannot be changed once it is fabricated. And also maximum measurable flow rate is fixed.

The orifice meter overcomes these above limitation but it too have some drawbacks.

One thing common in both is that both can use manometers system.And the principle of orifice meter and venturi meter are identical.i.e the reduction in cross sectional area of flowing stream in passing through the orifice increases the velocity head which decrease the pressure head and this pressure reduction can be measures using manometer or other digital measuring devices.

Above image shows an orifice meter.

Orifice is simply a plate drilled and machined according to the requirement , mounted between two flanges which is then fitted to pipe in which fluid flows. Pipes is drilled to provides pressure taps at before and after orifice plate and these pressure taps are connected to manometers. These pressure taps location can be arbitrarily chosen and coefficient of the meter will depends upon the position of the taps.

Credit : Mecholic

Bernoulli's equation provides basis for the correlation between pressure head and velocity head.

Here in orifice meter , due to several sharpness in orifice plate , fluid stream separates and form free flowing jet called VENA CONTRACTA.

This is because of a sharp change in the cross section area of the device whereas in venturi meter the change in cross-section area was not sharp but it gradually decreases stage by stage I.e converging followed by throat followed by diverging.

Due to this fluid stream separation certain mechanical energy loss take place.Hence power consumption in orifice meter is comparatively large then venturi meter.

Talking about coefficients , orifice coefficient are much lower and variable due to there different size and shape of opening where's in venturi meter the cross section area was fixed.