This presentation summarizes the rotameter, a variable area flow meter used to measure fluid flow. It discusses the history and invention of the rotameter, its working principle, construction including a tapered glass tube and float, measurement process using a calibrated scale, derivation of its formula, advantages like low cost and linear scale, and common uses for low-cost flow measurement where high accuracy is not required. The presentation concludes with a note about flexibility being important when working with fluid mechanics concepts.

2. Presented By:
Momina Noor (M12-PG01)
Mahnoor Butt (M12-CE16)
Sabahat Tahir (M12-CE12)
Farah Naeem (M12-CE55)

3. Objective:
The purpose of this presentation is
to develop a better understanding
of rotameter, its working and its
use on domestic and industrial
scale.

4. Contents:
 History
 Rotameter
 Working Principle
 Construction
 Working
 Derivation & Graph
 Advantages & Disadvantages
 Uses

5. History:
 The history of variable-area meters dates to 1908
when they were invented by German engineer Karl
Kueppers in Aachen, Germany.
 Felix Meyer recognized the commercial potential
of Kueppers’ invention, and in 1909 founded
“Deutsche Rotawerke” in Aachen.
 Kueppers invented the special shape for the inside
of the glass tube that realized a symmetrical flow
scale.

6. Rotameter-Variable area meter
 What is rotameter ?
A device used to measure fluid
flow, in which a float rises in a
tapered vertical tube to a height
dependent on the rate of flow
through the tube.

7. Working Principle:
 It is a variable area meter
which works on the
principle of upthurst force
exerted by fluid and force of
gravity.

8. Construction:
 Graduated tapered metering
glass tube.
 Float

9. Tapered tube:
 Safety-shielded glass tube are
in general use for measuring
both liquids and gases.
 Metal tubes are used where
opaque liquids are used or
temperature or pressure
requirement is quite high.
 Plastic tubes are also used in
some rotameter designs due to
their lower cost and high
impact strength.

10. Float:
 Floats may be constructed of metals of various
densities from lead to aluminum or from glass or
plastic.
 Stainless-steel floats are common ones.
 Float shapes and proportions are also varied for
different applications.
 For small flows floats are spherical in shape.

11. Different floats:

12. Working:
 Fluid enters the tapered tube, some
of the fluid strikes directly the float.
Some of the fluid passes from sides.
 Two forces are acting in this case:
 Upthurst Force (Buoyancy)
 Weight of the float
 Annular space increases due to
increase in area of the tube.
When equilibrium is established the
float comes to rest.

13. Measurement of flowrate:
 The flowrate is measured
directly from calibrated scale.
 The reading is noted
generally from ending point
of cap of the float.

14. Formula:
 The pressure difference over the float −ΔP, is given by:
 
f ρ ρ g
A
P f 
  
f
V
 If area of the annulus between the float and tube is A2
and the cross-sectional area of the tube is A1, then
equation for orifice will become:
 
2
 
A
2
1
2
2
1








A
P
G C A D


15. Formula:
 Substituting the value of −ΔP :
 









 



 



2
A
2
1
2
1
2
A
A
gV
G C A
f
f f
D
  

16. Graph:

17. Range, Repeatability & Accuracy
Wide rangeability 5:1 – 12:1
 High repeatability 0.5 – 1 %
 Low accuracy 2 – 3 %

18. Advantages:
 No external power or fuel.
 Manufactured of cheap materials.
 Since the area of the flow passage increases
as the float moves up the tube, the scale is
approximately linear.

19. Disadvantages:
 Impact of gravity.
 Accuracy of rotameter.
 Uncertainty of the measurement.

20. Conclusion:
Rotameter is used:
 To measure the flow of gases and air at low flowrates.
When cost is the main consideration.
 When high accuracy is not required.

21. "You mustn't be too rigid when
doing Fluid mechanics."

22. THANK YOU ...

23. Question Answer Session