Calibration of Rectangular Notch(Fluid Mechanics)
Experiment
Calibration of Rectangular Notch
- Theory: The notch is hydraulically defined as an opening provided in the side of a tank in such a way so that the top level of the liquid is below the top edge of the opening. Notches are generally used for measuring the flow of liquid in the channels.
In the unit, a centrifugal pump sucks the water from the sump
tank and discharges it into a small flow channel. The notch is fitted at one
end of the channel. The water flowing over the notch falls into the collector.
The water from the collector is then goes to the measuring tank for the
measurement of actual flow.
For a Rectangular Notch, The theoretical discharge is given by
Qth= (2/3) x
√2g xB x H3/2
Where, H= Head over the notch=(Water level – Sill level) in
meter.
B= Crest width of
the notch.
For the given notch, B= 0.20 m
Also, it is given that
Length of the measuring tank (L)= 0.80 m
Width of the measuring tank (B)= 0.60 m
- Apparatus:
Rectangular Notch, adjustable channel, sliding depth gauge, measuring
tank, stop watch .
- Procedure:
1. Fit the required
notch in the flow channel
2. Fill up the water in the sump tank.
3. Close the water supply gate valve to
the channel and fill up the water up to sill level in the channel.
4. Check that the water does not leak from
the sides of the notch.
5. Take down the initial reading of the
crest level (sill level) by the sliding depth gauge.
6. Now start the
valve and open the gate valve slowly so that water starts flowing over the
notch.
7. Let the water
level become stable and then note down the height of water surface at the
upstream side by sliding depth gauge.
8. Close the drain
valve of measuring tank, direct the collector into the measuring tank and
measure the discharge by measuring the rise of water in the indicator scale
attached to the tank in some time ‘t’ measured with a stop watch.
9. Repeat the
process and find out various discharges.
- Observation
Table:
|
SR No |
Sill Level Height (m) |
Water height on upstream side (m) |
Height of water above sill (H) in m |
Rise in water level in the measuring tank(h) in m |
Time taken for rise ‘h’ in the tank(t)in seconds |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
- Calculation:
1. , H= Head over the
notch=(Water level – Sill level) in meter.
2. Actual discharge Qa=0.6x 0.8x h/t m3/sec
3.Theoretical discharge Qth= (2/3) x √2g xB x H3/2,
here B= 0.20 m.
4. Co-efficient of discharge Cd= Qa/ Qth
5. Calculate
the average value of Cd for variable flows.
Post a Comment