CIVL 4046 Fluid Mechanics
Experiment Number 5
Objective: Determination of the coefficient of discharge for (a) Venturi Tube and (b)
Orifice plate.
Equipment setup:
Flowmeter Demonstration Apparatus (Armfield)
Theory
(a) Venturi Tube
(b) Orifice Meter
Fig. 1
u n2
u
u
Bernoulli’s equation:
 h1 
 h2 
 hn
2g
2g
2g
where, u1 and u 2 are the velocities at sections 1 and 2.
2
1
2
2
(1)
Equation of continuity: u1a1  u 2 a 2  u n a n  Q , where Q is the discharge. Where
and are the cross-sectional areas at section 1 and 2, respectively.
Substituting the value of u1 in Eq. (1) and rearranging, we get
u2 
2 g (h1  h2 )
2
and Q  a 2 u 2  a 2
2 g (h1  h2 )
2
a 
a 
1   2 
1   2 
 a1 
 a1 
In practice, there is some loss of energy between sections 1 and 2, therefore,
Q  C d a2
2 g (h1  h2 )
(2)
2
 a2 
1  
 a1 
Qactual  C d Qtheoretical
where
is called the coefficient of discharge and usually ranges from 0.92 to 0.99.
The discharge equation for orifice meter is the same as Eq.(2).
1
CIVL 4046 Fluid Mechanics
Results and Calculations:
(a) Venturi Tube Data
Diameter of the pipe at section 1:
Diameter of the pipe at section 2:
Table 1. Measurements and Calculations for Venturi Tube
Volume
Time
Qactual
h1  h2 Qtheoretical
3
(L)
(s)
(m /s)
(m3/s)
(m)
Cd
(b) Orifice Meter Data
Diameter of the pipe at section 1:
Diameter of the orifice at section 2:
Table 2. Measurements and Calculations for Orifice Meter
Volume
Time
Qactual
h1  h2 Qtheoretical
(L)
(s)
(m3/s)
(m3/s)
(m)
Cd
Format for the report
The following sections must be included in the laboratory report
Objective, Equipment setup, Theory
Readings and calculations
Graphs for both the devices (Qactual versus Qtheoretical and Cd vs Qactual)
Comments on the results
2