Parshall flume by ali hossain rafi

Parshall Flume..
It is an important topic in Hydraulic .. In irrigation purpose, Waste Water treatment, Aeration, Industrial water Treatment plant, etc , It is used..

1. Welcome To MY
Presentation
BY AlI HOSSAIN RAFI
Pabna University Of ScIENCE & tECHNOLOGY

2. Objects of Parshall Flume:

To know about flume and Parshall flume
To know about components
To know about design
To know the way of installation
To know about working principle
To measure the theoretical discharge for free flow
and submerged flow condition
To know the way of maintenance
To know the applications
To know advantages and limitations

3. Types of Flumes:

Flumes are classified into following types :
Submerged Venturi Flume
Free flow Venturi Flume
Parshall Flume
Cut-throat Flume

Flumes:
Flumes are specially shaped, engineering structures
that are used to measure the flow of water in open
channels.

Ref: Article 15.13 (Hydraulics & Fluid Mechanics by P.N. Modi & Seth)

4. Parshall Flumes:
It is open channel flow metering
device that was developed to measure
the flow of surface water and
irrigation flows.

It is the modified version of
Venturi Flumes.
Used especially for flows containing
suspended solids.

Fig: Parshall Flume
Parshall flumes have been classified into three main
groups.
1. Very small - 25.4 mm to 76.2 mm.
2.Small 152.40 mm to 2438.4 mm.
3.Large 3048 mm to 15240 mm.

Classification of Parshall flumes:
Ref: Article 15.13 part (c) (Hydraulics & Fluid Mechanics by P.N. Modi & Seth)

5. Components of Parshall Flume:

A Parshall Flume contains three sections:
1.Converging section
2.Throat section
3.Diverging section
Fig: Components of Parshall Flume

6. Design of parshall flume:
Flat in upstream section
Slopes downward in the throat section
Rises in the downstream section
Ending with a hydraulic jump
The floor of the Parshall flume is designed as:

Fig: Design of Parshall flume
Ref: Article Fig15.17 (Hydraulics & Fluid Mechanics by P.N. Modi & Seth)

7. Way of installations:
Parshall flume with elevated
support legs installation.
Parshall flume with packed
earth installation.
Parshall flume with
concrete installation in a
concrete channel.

8. Working principle:
1. Single point measurement:
The single primary point of
measurement denoted as H
a. H
a is the
upstream of throat at a specific location-
2/3 of the sidewall length.
2. Submerged flow:
A secondary point of
measurement H
b is measured at
downstream. The ratio of downstream
to upstream levels H
b/H
a
is known as
submergence ratio.
3. Determining the flow rate:
By using submergence ration,
we can measure the flow rate through a
parshall flume.
The overall procedure can be explained in three steps-

Fig: Working principle
Ref: https://www.openchannelflow.com/blog/how-a-parshall-flume-works

9. Measurement of discharge through parshall flume:
Working formula for theoretical discharge is expressed by:

Q=K??????
??????
??????


Q= free flow (ft
3
/s)
K= discharge constant.
H
a
= depth at the point of measurement in ft.
n= discharge exponent.
The value of 'K' and 'n' depend on the throat width:

Throat width Equation
3'' Q=0.992 H
a
1 .547

6'' Q=2.06 H
a
1 .58

9'' Q=3.07 H
a
1 .53

10. For measurement of discharge with Parshall flumes,
two measurement conditions are required-
Fig: Discharge with Parshall flume
Discharge
through Parshall
flume
Free flow
condition
Submerged flow
condition

11. Free-flow occurs in a flume when:
The rate of flow with the throat is not affected by the
downstream flow.
Insufficient backwater to reduce the discharge through
the flume.
A hydraulic jump should be visible.
Fig: Free flow condition

12. Working formula for free flow condition can
be express as:

Q
th=KH
1.547



Where,
K(a constant depending upon the unit)=0.992
Q
th
= Theoretical discharge in ft
3
/sec.
H = Upstream depth from the invert datum in ft
Ref: Eq
n
:13.61(Hydraulics & Fluid Mechanics by P.N. Modi & Seth)

13. The surface downstream is high enough to reduce
flow through a flume.
Flow depth increase & cause a backwater effect.
Requires the measurement of both an upstream level
(H
a) and a downstream level (H
b).
Submersed-flow occurs in a flume when:
Fig: Submerged flow condition

14. Working formula for submerged flow
condition can be express as:

Q
th=KH
1.321

Where,
K(a constant depending upon the unit)= 6.35
Q
th
= Theoretical discharge in ft
3
/sec.
H = Upstream depth from the invert datum in ft


Co-efficient of discharge = Q
a / Q
th
Ref: Eq
n
:13.61(Hydraulics & Fluid Mechanics by P.N. Modi & Seth)

15. How to Maintain a Parshall Flume:
Maintenance
Inspection
Channel
Inspection
Flow
Inspection
Flume
Inspection

16. 1. Channel Inspection:
The upstream channel banks should be clear of vegetation or
debris.
In downstream channel to make sure that scouring is not
occurring.


2. Flow Inspection:
Turbulence, poor velocity profile, or surging should not be
present.
 The Froude (Fr) number should, ideally, be 0.5.


3.Flume Inspection
Flow surface are to be kept clean of algal growth.
Galvanized flume should be checked for corrosion.
Ref: https://parshallflumes.com/pages/how-to-maintain-your-parshall-flume

17. Application of Parshall flume:
Measure creek flows in
rocky soil in California
Irregation purpose
Sewage treatment plant

18. Waste water treatment
Mine Discharge in Mexico
Make water quality and
stage measurements

19. Measuring flow at a Dam
on the Colorado River
Gaging station to measure
stream flows
Industrial discharge
monitoring

20. Parshall flume Venturi flume
1.It is a self cleaning device 1.It is not a self cleaning
device
2.Cosidering upward slope in
throat and downward slope in
diverging cone.
2.No consideration of slope at
any section
3.The length of throat section
is comparatively higher for
better developing the flow.
3.Shorter length of throat
section.
Difference between Parshall flume and Venturi flume

Ref: https://www.openchannelflow.com/blog/difference-between-a-parshall-
flume-and-venturi-flume

21. Advantages of Parshall flume:
Relatively low head loss.
Many sizes are commonly available.
Its operation is independent of approaching
velocity.
Being a self-cleaning device.
Suitable for portable & permanent installation.
Can continue to measure flow when submerged.
Ref: https://www.openchannelflow.com/blog/advantages-of-parshall-flumes

22. Limitations of Parshall flume:
Large in size.
More difficult to install in very flat channel.
Creates more upstream head than other flumes.
Takes extra cost and time to flume installation
projects.
Aren’t amenable to fluid flow analysis
Ref: https://www.openchannelflow.com/blog/disadvantages-of-parshall-flumes

23. Conclusion:
One of the biggest drawbacks of the Parshall
flume is also one of its benefits, an Hourglass shape.
It is very important with respect to the condition of
Bangladesh as a agricultural and heavy rainfall
country.

24. ThanKS TO ALL