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.
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.
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
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.
