FLOW MEASURING METERS

 

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FLOW MEASURING METERS

The followings are the most common criterion’s for fluid flow meter.

(i) Differential Pressure Flow meters

(ii) Velocity Flow meters

(iii) Positive Displacement Flow meters

(iv) Mass Flow meters

(v) Open Channel Flow meters

Differential Pressure Flow meters

Pressure drop is created by inserting obstructions in the flow. Then Bernoulli’s Equation is used to calculate the flow velocity and hence the flow rate.

(i) The various differential pressure flowmeters are:

(a) Orifice plate

(b) Nozzle

(c) Venturi tube

(d) Rotameter

(ii) Velocity Flow meters

(a) Pitot Tubes

(b) Calorimetric Flow meter

(c) Turbine Flowmeter

(d)Vortex Flow Meter

(iii) Positive Displacement Flow meter

(a) Reciprocating piston meters are of single piston and multiple-pistons type

(b) Oval-gear meters

(d) Rotary vane meters

(iv) Mass Flow meters

Mass flow meters measure the mass flow rate directly.

(a) Thermal Flow meter

(b)Coriolis Flow meter

(v) Open Channel Flow meters

(a) Weir and V-notches
(b) Sluice Gates

PRACTICAL APPLICATIONS OF  FLOW MEASURING METERS
1. Orifices, Venturimeters, Rotameters and Pitot Tubes

These meters use the Bernoulli Equation to calculate the fluid flow rate using pressure difference through obstructions in the flow. These are used in general applications.

2. Weirs and V-notches

Weirs are used for measuring flow rates in open channels and rivers. These are used with water supply and sewage plants.

3. Sluice Gate
Sluice gates are used for controlling and measuring flow rates in open channels and rivers in connection with the hydro power plants

TURN DOWN RATIO

Turn down ratio (or Rangeability) is the ratio of maximum flow rate to minimum flow rate. This makes the meter of acceptable accuracy.

Orifice plate turn down ratio 3: 1 to 5:1
Orifice meter turn down ratio 4:1

 

COMPARISON BETWEEN ORIFICE/VENTURIMETER AND ROTAMETER

Sr. No. Orifice meter or Venturimeter Rotameters
1. Area of flow is constant     Variable area of flow
2. Cheap Costly
3. No calibration required  Calibration required
4. Can measure flow of any fluid Rotameters for water cannot be used with any other fluid
5.    Can measure the flow with impurities    Cannot measure the flow with

impurities

6. Suitable for any mass flow rates Suitable for only small mass flow rates