This PPT contains Process Design Of three major flow meters used in industries i.e Venturi Meter, Orifice Meter, & Rota Meter

1. PROCESS EQUIPMENT & DESIGN
Topic: Differenet types of Flowmeters
•Venturi Meter
•Orifice Meter
•Rotameter

2. VENTURI METER
 The venturi meter has a converging conical inlet, a cylindrical throat and a
diverging recovery cone. It has no projections into the fluid, no sharp corners
and no sudden changes in contour. The following figure shows the venturi
meter with uniform cylindrical section before converging entrance, a throat
and divergent outlet.
 The converging inlet section decreases the area of the fluid stream, causing
the velocity to increase and the pressure to decrease. The low pressure is
measured in the center of the cylindrical throat as the pressure will be at its
lowest value, where neither the pressure nor the velocity will be changing. As
the fluid enters the diverging section the pressure is recovered lowering the
velocity of the fluid.

3.  The major disadvantages of this type of flow detection are the high initial
costs for installation and difficulty in installation and inspection.

4.  The Venturi effect is the reduction in fluid pressure that results when a fluid
flows through a constricted section of pipe. The fluid velocity must increase
through the constriction to satisfy the equation of continuity, while its pressure
must decrease due to conservation of energy: the gain in kinetic energy is
balanced by a drop in pressure or a pressure gradient force. An equation for the
drop in pressure due to Venturi effect may be derived from a combination of
Bernoulli’s principle and the equation of continuity.
 The equation for venturi meter is obtained by applying Bernoulli equation and
equation of continuity assuming an incompressible flow of fluids through
manometer tubes. If V1 and V2 are the average upstream and downstream
velocities and ρ is the density of the fluid, then using Bernoulli’s equation we get,

5. 

6. where D1 and D2 are diameter of pipe and throat in meters respectively.
Eliminating V1 from equation (1) and equation (2) we get,
V2 =
1
𝛼2−𝛼1 𝛽4
2𝑔 𝑐(𝑃1−𝑃2)
𝜌
-----------(3)
where β is the ratio of the diameter of throat to that of diameter of pipe.
If we assume a small friction lose between two pressure taps, the above
equation (3) can be
corrected by introducing empirical factor Cv and written as;
V2 =
𝐂𝐯
𝟏−𝜷 𝟒
𝟐𝒈 𝒄(𝑷 𝟏−𝑷 𝟐)
𝝆
------------(4)

7. Now, 𝑚 = ρV2AT
Putting this value in (4);
𝒎 = Cv AT
𝟐𝒈 𝒄(𝑷 𝟏−𝑷 𝟐)𝝆
𝟏−𝜷 𝟒 -----------(5)
where,
ṁ=mass flowrate of fluid, kg/s
AT=area of Throat = (π/4)d0
2, m2
P1,P2= pressure at upstream and downstream static pressure taps, Pa
gc = 1
ρ = density of fluid, kg/m3

8. 

9. ORIFICE METER
 Orifice meter is a type of flowmeter and a device basically used for
measuring the flowrate.
 It is a widely used flowmeter in chemical industry, compared to
Venturimeter and Rotameter.
 Orifice meter consists of a sharp or square edged orifice plate which is
mounted between two flanges at the flanged joint.
 This is shown in the figure.
 When the fluid flows through the orifice it forms free flowing jet, this free
flowing jet contracts and then expands.
 Minimum flow area achieved by free flowing jet is known as Vena
Contracta.

11. Process Design of Orificemeter
Mass flowrate through orifice is given by,
ṁ = 𝑪 𝟎 𝒀𝑨 𝟎
𝟐𝒈 𝒄 𝝆(𝒑 𝟏 − 𝒑 𝟐)
𝟏 − 𝜷 𝟒
where,
ṁ=mass flowrate of fluid, kg/s
A0=area of orifice=(π/4)d0
2, m
P1,P2= pressure at upstream and downstream static pressure taps, Pa

12. Ρ = density of fluid, kg/m3
C0 = coefficient of orifice
= f(Re0, β, location of taps)
where,
Re0 =
𝑑0 𝑢0 𝜌
𝜇
=
4ṁ
𝜋𝑑0 𝜇
where,
u0 = velocity of fluid through orifice, m/s
µ = viscosity of fluid, kg/(m.s)
𝛽 =
𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑜𝑟𝑖𝑓𝑖𝑐𝑒
𝑖𝑛𝑠𝑖𝑑𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑝𝑖𝑝𝑒

13. Y = expansion factor
= 1 for liduids
= 1- [((1-r)/k)(0.41 + 0.35 β4)] for gases
where,
r = p2/p1, ratio of downstream to upstream pressure
k = Cp/Cv, specific heat ratio

14. Locations of Pressure Taps
Corner Taps – static holes are made in upstream & downstream flange.
Flange Taps– static holes are made at distance 25.4 mm on both upstream &
downstream side.
Radius Taps – static holes are made at a distance one pipe diameter on
upstream side and half pipe diameter on downstream side.
Vena Contracta Taps – upstream side hole is half to two times pipe diameter
from plate and downstream tap is located at the position of minimum
pressure.

15. Taps – static holes are located at 2.5 times pipe diameter upstream side
and 8 times pipe diameter on downstream side.

16. For Re0> 30000,
C0 = between 0.595 to 0.62 for vena contracta taps
C0 = between 0.595 to 0.8 for radius taps
C0 = 0.62 for corner taps
Relation between discharge co-efficient C0, β and ReD is given by Stolz
equation
C0 = 0.5959 + 0.0312 β2.1 – 0.184 β8 + 0.0029 β2.5 (106/ReD)0.75 + 0.09 L1β4 (1 –
β4)-1 – 0.0337 L2β3
where,
L1 = l1/D and L2 = l2/d0

17. where,
d0 = diameter of orifice
β = d0/D
l1 = distance of upstream tapping from the upstream face of orifice plate,
mm
l2 = distance of downstream tapping from the downstream face of orifice
plate, mm

18. ROTAMETER
 A Rotameter is a device that measures the flow rate of liquid or gas in a closed
tube. It belongs to a class of meters called variable area meters, which
measure flow rate by allowing the cross-sectional area the fluid travels
through, to vary, causing a measurable effect.
 Rotameters are a particular kind of flow meter, based on the variable
area principle. They provide a simple, precise and economical means of
indicating flow rates in fluid systems. This variable area principle consists of
three basic elements: A uniformly tapered flow tube, a float, and a
measurement scale.

20. Implementation
 A Rotameter consists of a tapered tube, typically made of glass with a 'float',
made either of anodized aluminium or a ceramic, actually a shaped weight,
inside that is pushed up by the drag force of the flow and pulled down by
gravity. The drag force for a given fluid and float cross section is a function of
flow speed squared only, see drag equation.
 A higher volumetric flow rate through a given area increases flow speed and
drag force, so the float will be pushed upwards. However, as the inside of the
Rotameter is cone shaped (widens), the area around the float through which
the medium flows increases, the flow speed and drag force decrease until
there is mechanical equilibrium with the float's weight.

21.  Floats are made in many different shapes, with spheres and ellipsoids
being the most common. The float may be diagonally grooved and partially
coloured so that it rotates axially as the fluid passes.

22. Equation of Rotameter:
qm = CDA2
 qm = mass flow rate
 CD = Coefficient of rota meter = 0.75 approx
 Vf = volume of float
 Af = area of float

23. 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.
 Clear glass is used which is highly resistant to thermal shock and chemical
action.

24. Disadvantages
 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.
 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.

25.  Since the float must be read through the flowing medium, some fluids may
obscure the reading. A transducer may be required for electronically
measuring the position of the float.
 Rotameters are not easily adapted for reading by machine; although
magnetic floats that drive a follower outside the tube are available.
 Rotameters are not generally manufactured in sizes greater than 6
inches/150 mm, but bypass designs are sometimes used on very large
pipes.