The document describes rotameters, which are variable area flow meters that contain a float within a tapered glass tube. As flow rate increases, the float rises within the tube. The document discusses rotameter construction, working principles, modifications to components like floats and tubes, formulas and calculations used, flow rate determination graphs, and advantages and disadvantages of rotameters. It also provides an example problem calculating flow rate based on given float position and properties.

1. ROTAMETERS

2. PRESENTED BY
• IBRAHEEM SALEEM SAYYED [SP12-BEC-022]
• MEHER ALI [SP12-BEC-028]
• MUHAMMAD ALI RAZA [SP12-BEC-038]
• SAFDAR ABBASS [SP12-BEC-072]

3. AN INTRODUCTION
▪ Various flow measuring devices:
– Vortex meter
– Piston flow meter
– Paddle wheel meter
– PD meters
– Magnetic meters
– Ultrasonic meters.
– Variable area meters (ROTAMETERS)

4. AN INTRODUCTION
▪ The first variable area meter with rotating float was invented by Karl
Kueppers in Aachen in 1908.
▪ Felix Meyer found the first industrial company "Deutsche Rotawerke
GmbH" in Aachen recognizing the fundamental importance of this
invention.
▪ Kueppers invented the special shape for the inside of the glass tube
that realized a symmetrical flow scale. They improved this invention
with new shapes of the float and of the glass tube.

5. AN INTRODUCTION
▪ In orifice, nozzle or venturi the variation of flow rate through a
constant area generates a variable pressure drop, which is related to
flow rate.
▪ Another class of meters, called area meters, consists of devices in
which the pressure drop is constant, or nearly so, and the area
through which the fluid flows varies with the flow rate.
▪ This area is related, through proper calibrations to the flow rate.
▪ The most important area meter is the rotameter.

6. CONSTRUCTION & WORKING
▪ A rotameter consists essentially of a graduated tapered
metering glass tube mounted vertically in a frame with the
large end up.
▪ Inside the tube is the float which is an indicating element, the
greater the flow rate, the higher the float rides in the tube.
▪ The fluid flows up through the tube and suspends freely a float
(which actually doesn’t float but is completely submerged in
the fluid).
▪ The entire fluid stream flows through the annular space
between the float and tube wall.

7. MODIFICATIONS IN COMPONENTS
▪ 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.

8. MODIFICATIONS IN COMPONENTS
▪ Metal tubes are used where opaque liquids are used or temperature or
pressure requirement is quite high.
▪ Since float is invisible in metal tube means are to be provided for either
indicating or transmitting meter reading.
▪ The task is accomplished by using a rod called extension, to the top or
bottom of the float and using the extension as an armature.
▪ The extension is used enclosed in a fluid tight tube mounted on one of the
fittings.
▪ The tube is surrounded by external induction coils, the length of extension
exposed to coils varies with the position of float.
▪ This in turn changes the inductance of coil, and the variation is measured
electrically to operate a control valve or to give recorder a reading.

9. FORMULAE,CALCULATIONS AND GRAPHS

10. FORMULAE,CALCULATIONS AND GRAPHS

11. FORMULAE,CALCULATIONS AND GRAPHS
▪ The coefficient CD depends on the shape of the float and the
Reynolds number (based on the velocity in the annulus and the mean
hydraulic diameter of the annulus) for the flow through the annular
space of area A2.
▪ In general, floats which give the most nearly constant coefficient are
of such a shape that they set up eddy currents and give low values of
CD.
▪ The variation in CD largely arises from differences in viscous drag of
fluid on the float, and if turbulence is artificially increased, the drag
force rises quickly to a limiting but high value.

12. FORMULAE,CALCULATIONS AND GRAPHS

13. FORMULAE,CALCULATIONS AND GRAPHS
▪ As seen in Figure earlier, float A does not promote turbulence and
the coefficient rises slowly to a high value of 0.98.
▪ Float C promotes turbulence and CD rises quickly but only to a low
value of 0.60.
▪ The constant coefficient for float C arises from turbulence
promotion, and for this reason the coefficient is also substantially
independent of the fluid viscosity.

14. FORMULAE,CALCULATIONS AND GRAPHS

15. ADVANTAGES
• A rotameter requires no external power or fuel, it uses only the
inherent properties of the fluid, along with gravity, to measure
flow rate.
• A rotameter is also a relatively simple device that can be mass
manufactured out of cheap materials, allowing for its
widespread use.
• Since the area of the flow passage increases as the float moves
up the tube, the scale is approximately linear.

16. DISADVANTAGES
• Due to its use of gravity, a rotameter must always be vertically
oriented and right way up, with the fluid flowing upward.
• Due to its reliance on the ability of the fluid or gas to displace
the float, graduations on a given rotameter will only be accurate
for a given substance at a given temperature. The main property
of importance is the density of the fluid; however, viscosity may
also be significant. Floats are ideally designed to be insensitive
to viscosity; however, this is seldom verifiable from
manufacturers' specifications. Either separate rotameters for
different densities and viscosities may be used, or multiple
scales on the same rotameter can be used.

17. DISADVANTAGES
• Due to the direct flow indication the resolution is relatively poor compared
to other measurement principles. Readout uncertainty gets worse near the
bottom of the scale. Oscillations of the float and parallax may further
increase the uncertainty of the measurement.
• Rotameters normally require the use of glass (or other transparent material),
otherwise the user cannot see the float. This limits their use in many
industries to benign fluids, such as water.
• Rotameters are not easily adapted for reading by machine; although
magnetic floats that drive a follower outside the tube are available.
• Usually rotameters aren't made in very large sizes (more than 4 inches/100
mm), but bypass designs are sometimes used on very large pipes.
• Clear glass is used which is highly resistant to thermal shock and chemical
action.

18. SAMPLE PROBLEM
▪ A rotameter tube is 0.3 m long with an internal diameter of 25 mm at
the top and 20 mm at the bottom. The diameter of the float is 20
mm, its density is 4800 kg/m3 and its volume is 6.0 cm3. If the
coefficient of discharge is 0.7 , what is the flowrate of water (density
1000 kg/m3) when the float is halfway up the tube?