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Lab
Hydraulics CE-331
Experiment No.1 & 2
Orifice and free jet flow
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EXPERIMENT 1
Objective
The objective is to determine the coefficient of velocity (Cv).
Method
By measurements of the trajectory of a jet issuing from an orifice in the
side of reservoir under steady flow conditions (constant head).
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Equipment
• Hydraulics bench which allows us to measure flow by timed volume
collection.
• Orifice and jet apparatus.
Technical data
• Diameter of small orifice
• Diameter of large orifice
3 mm = 0.003 m
6 mm = 0.006 m
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Theory
Consider a tank containing a liquid and with an orifice at its side wall at a
depth H below the free surface
Vena contracta
The cross section
where the contraction
is greatest or where
the area of the jet is
minimum is called
vena contracta.
The ratio of area jet Aj at vena contracta to area of orifice Ao is symbolised
by coefficient of contraction. Cc = Aj / Ao
If we apply the Bernoulli’s equation between two the two points 1 at the
free surface and point 2 at the vena contracta:
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Theory - Trajectory method
The actual velocity (Va) can be determined by measuring the position of a point
on the trajectory of a free jet, down stream of the vena contracta.
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Procedure
• Make sure that the reservoir is positioned across the channel on top of
the hydraulic bench, and level the reservoir by the adjustable feet on
the base.
•
Measure and record the diameter of the orifice.
• Turn on the pump and open the valve gradually, as the water level
rises in the reservoir, adjust the bench valve to give water level 2 to 3
mm above the overflow level. This gives a constant head and produces
steady flow through the orifice.
• Position the over flow tube to give high head. Note the value of the
head.
• Determine trajectory of the jet using the needles mounded on the
vertical backboard to follow the profile of the jet.
• Attach a sheet of paper to the back-board.
• Mark the location of the top of each needle on the paper.
• Measure the horizontal (x) and vertical (y) distances from the orifice.
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Taking a set of result
•
•
•
•
•
•
•
Orifice diameter
Head
Horizontal distance
Vertical distance
(yh)^0.5
Slope of X vs (yh)^0.5
Cv = (average slope/2)
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Experimental Data
Orifice diameter, Do (m)
6 /1000
Head , H (m)
265/1000
X, (m)
0
0.05
0.1
0.15
0.2
0.25
0.3
Orifice diameter, Do (m)
6 /1000
Head , H (m)
350/1000
X, (m)
0
0.05
0.1
0.15
0.2
0.25
0.3
Y, (m)
Y, (m)
(YH)^0.5
Orifice diameter, Do (m)
3 /1000
Head , H (m)
265/1000
X, (m)
0
0.05
0.1
0.15
0.2
0.25
0.3
Y, (m)
(YH)^0.5
(YH)^0.5
Orifice diameter, Do (m)
3 /1000
Head , H (m)
350/1000
X, (m)
0
0.05
0.1
0.15
0.2
0.25
0.3
Y, (m)
(YH)^0.5
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Analysis
1 –Plot X vs. (YH)^0.5 and determine the slop of the graph.
Cv = average slop /2
Cv = X / ((2) (YH)^0.5)
Report writing
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Lab
Hydraulics CE-331
Experiment No.2
Orifice and free jet flow
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Experiment No.2
Objective:
The objective is to determine the coefficient of discharge (Cd) and
coefficient of contraction (Cc), of two small orifices.
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Procedures:
• Measure the flow rate using a measuring cylinder for a specific time (5
second).
• Note the reservoir head value.
• Repeat this procedure for different heads, by adjusting the level of
overflow pipe.
Experimental Data
Orifice daimter, Do (m)
Head , H (m)
volume (m3)
time (s)
Qa (m3/s)
Qth
H^0.5
Analysis
1 – Plot Qa vs. (H)^0.5 and determine the slop of the graph.
Cd = slope/(A(2.g)^0.5)
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