MIDDLE EAST TECHNICAL UNIVERSITY
DEPARTMENT OF AEROSPACE ENGINEERING
AE 547 EXPERIMENTAL AERODYNAMICS
LABORATORY PROCEDURE
VENTURI METER (H5)
ANIL GÜÇLÜ
TABLE OF CONTENT
1.
INTRODUCTION ...................................................................................................................... 3
2.
VENTURI METER TEST SETUP INFORMATION ......................................................... 3
a.
Venturi Meter Apparatus..................................................................................................... 3
b.
Volumetric Hydraulic Bench .............................................................................................. 4
3.
INSTALLATION AND ASSEMBLY...................................................................................... 6
4.
THEORETICAL INFORMATION ......................................................................................... 7
5.
EXPERIMENTS ......................................................................................................................... 9
a.
Discharge Rate Calculations ............................................................................................... 9
b.
Pressure Calculations ........................................................................................................ 11
2
1. INTRODUCTION
Venturi meters have been used to measure the volume flow along a pipe for
many years. The fluid flowing in the pipe passes through a section which is called
as “throat”. The throat has a smaller cross sectional area than other parts of the
pipe. Assuming that the volume flow speed is constant, the velocity of the fluid
through the throat is higher than the other sides of the pipe. There is a relation of
the velocity of the flow and the pressure at the walls. As the velocity increases,
the pressure falls proportional to the velocity. So, the flow rate can be calculated
with the measured pressure and pipe parameters.
2. VENTURI METER TEST SETUP INFORMATION
Venturi meter test setup composed of two main parts, which are Venturi meter
apparatus and volumetric hydraulic bench. Detailed information about these
components is given in this chapter.
a. Venturi Meter Apparatus
With using venture meter, which is procured from TecQuipment Company, it is
possible to see and measure the complete static head distribution along a
horizontal venture tube, Figure 1.
Figure 1 – Venturi Meter (H5)
The Venturi meter has three main holes. These holes can be named as fluid inlet,
outlet, and air valve. As seen from Figure 1, fluid is supplied from the inlet (from
3
supply) and goes out to the measurement tank from the outlet. Flow velocity is
adjusted with a control valve. The order of measured pressure can be changed
with changing the air pressure in the manometer. Air valve hole is used to
change and set the air pressure of the manometers. Technical details of the
Venturi meter can be seen in Table 1.
Table 1 – Technical Detail of Venturi Meter
Item
Details
Dimensions and Weight
720 mm high x 650 mm wide x 300
mm front to back, 15 kg
Nominal Venturi Dimensions
Inlet pipe diameter 26 mm
Throat diameter 16 mm
Water Manometers
11 off 0 to 40 mm water
The Venturi tube has two heads. One of them is placed at the cross-sectional area
at the upstream section; another one is at the throat section. With the help of
eleven manometers, pressure distribution along the meter can be observed. The
ideal pressure distribution and the measured pressure distribution can be
compared. Coefficients of the discharge for the meter parameter can be
identified with using the outcomes of the experiments.
b. Volumetric Hydraulic Bench
The Volumetric Hydraulic Bench has a mobile water source and a water level
indicator. There is a water pool inside the bench. The water is generally is
colored as blue. With the water pump, which is placed inside of the bench, the
water is pumped from the reservoir, to another test apparatus. It is important
that the pump should not be worked when there is not enough water on the
reservoir. The water, which goes out of the test apparatus, which is placed, on
the bench, goes to the pool again. There are some test apparatus, which is
recommended, however the bench can be used for any other suitable test
apparatus. The volumetric hydraulic bench can be seen in Figure 2.
4
Figure 2 – H1D Volumetric Hydraulic Bench
There is a valve, which controls the flow of water to an outlet pipe that passes
through a hole and connects to another test apparatus. Inside of the volumetric
hydraulic test bench can be seen in Figure 3.
Figure 3 – The Drain Valve
There are also some holes on the volumetric tank to prevent forgetting the drain
the tank. Inside of the bench can be seen in Figure 4.
Figure 4 – Inside of the Hydraulic Bench
There is an On/Off switch, a fill level indicator, the stack pipe and a flow control
valve mounted to the bench, which is shown in Figure 5.
5
Figure 5 – Tools of the Bench
Technical details of the hydraulic test bench are shown in Table 2.
Table 2 – Technical Details of the Hydraulic Test Bench
Item
Details
Dimensions and weight
Net: 1200 mm long x 760 mm wide x
1100 mm high and 80 kg
Sump tank capacity
Approximately 160 Liters
Volumetric tank capacity
35 Liters
Maximum accurate measuring rate
2 L/sec
Pump
60L/min
Electrical supply
220 to 240 VAC 50Hz 1A
or 110 to 120 VAC 60Hz 2A
or 220 VAC 60Hz 2.5A
Circuit protection
Thermal overload and under voltage
sensor built into on/off switch.
3. INSTALLATION AND ASSEMBLY
For measuring the flow rate with Venturi meter test bench, it has to be mounted
on the hydraulic test bench. After the Venturi meter is placed on the hydraulic
test bench, test can be operated after the below steps are followed. Steps 1-5 are
related with the hydraulic test bench and 6-14 is related with the Venturi meter
apparatus.
6
1.
2.
3.
4.
Lift the Drain Valve from its hole in the Volumetric Tank.
Pour clean water into Volumetric Tank.
Connect the electrical supply.
Press the ON button of the on/off switch to start the pump and check the
leaks.
5. Switch off the pumps.
6. Put the apparatus on the top of the Hydraulic Bench.
7. Connect the bench supply hose to the inlet of the Venturi meter.
8. Connect the outlet of the Venturi meter to the plastic tube.
9. Set both apparatus flow control and bench supply valve to approximately
one third fully open positions.
10. Check that the air valve on the other manifold is tightly closed.
11. Switch on the bench supply and allow water to flow. To clear air from the
manometer tubes, you may tilt the apparatus.
12. Shut the apparatus flow control valve. Air now will be trapped in the
upper parts of the manometer tubing and manifold.
13. Open air valve just enough to allow water to rise approximately halfway
up the manometer scale.
14. Watch the values on the manometers and note it down.
15. You will record 3 data sets while turning the valve.
4. THEORETICAL INFORMATION
There are some notations which are used during the theoretical calculations.
Table 3 – Notation
Symbol
Meaning
Units
u, u1, u2 and un
Velocity of flow
m.s-1
D
Diameter of the pipe
m
h, h1, h2 and hn
Head
m of water
Δh
Head Differential (h1-h2)
m of water
Q
Volume flow or discharge
m3.s-1
a, a1 and a2
Cross-sectional areas
m2
C
Flow Coefficient
-
G
Acceleration due to gravity
9.81m.s-2
The relation among the velocity at the throat (u2), the volume flow, and the cross
sectional area is the given in equation 1.
𝑄
𝑢2 = 𝑎
2
(1)
7
Figure 6 – Ideal Conditions in a Venturimeter
For an ideal venturimeter, Bernoulli’s theorem states that;
𝑢12
𝑢2
𝑢2
+ ℎ1 = 2𝑔2 + ℎ2 = 2𝑔𝑛 + ℎ𝑛
2𝑔
(2)
Constant flow along the pipe can be found as;
𝑄 = 𝑢1 𝑎1 = 𝑢2 𝑎2 = 𝑢𝑛 𝑎𝑛
(3)
Substituting the equation 2 from equation 3 yields;
𝑢22
𝑎
2
𝑢2
( 2 ) + ℎ1 = 2𝑔2 + ℎ2
2𝑔 𝑎
1
(4)
After solving the equations for u2 leads;
2𝑔(ℎ1 −ℎ2 )
𝑢2 = √
𝑎 2
1−( 2 )
(5)
𝑎1
Lastly, the discharge rate (volume flow) can be found as;
2𝑔(ℎ1 −ℎ2 )
𝑄 = 𝑎2 √
𝑎 2
1−( 2 )
(6)
𝑎1
Ideal dimensionless pressure can be obtained from;
𝑎
2
𝑎
2
(𝑎2 ) − (𝑎2 )
1
𝑛
(7)
8
5. EXPERIMENTS
After the experiment setup is prepared for test, the pressure tap values on the
venturi meter manometers are observed and recorded with rotating the valve.
Then, you must have ten different data sets at different flow rates. According to
the data set, you will do some calculations about discharge rate and the pressure.
a. Discharge Rate Calculations
During the experiment, write down the heights of the manometer bars in the
cells in Table 4.
Note: Q1 flow rate is zero which means there is no flow (valve is closed), Q 3 is
the fastest flow rate among Q1-Q3.
Table 4 – Experimental Data Sets
Tapping
Heads (h) (mm)
Q1
Q2
Q3
A (Upstream) (h1)
B
C
D (Throat) (h2)
E
F
G
H
J
K
L
9
Draw the heights of the manometers in the following plot at different discharge rates (Q1-Q3).
60
Manometer Heights (mm)
50
40
Q1
30
Q2
Q3
20
10
0
A
B
C
D
E
F
G
Venturi Meter Sections
H
Figure 7 –Measured Data vs. Venturi Meter Sections
J
K
L
According to the heights data at 3 different discharge rates, calculate the each discharge rate Q1-Q3 and write down in Error! Reference
source not found..
Table 5 – Discharge Rate Values ( x 10-4 m3/s)
Q1
Q2
Q3
b. Pressure Calculations
In pressure calculations, you will calculate and compare the ideal and actual dimensionless pressure values.
For ideal case, the venturi shape parameters will be used (Figure 8).
Figure 8 – Venturi Meter Parameters
11
Fill the Table 6 with your calculations.
Table 6 – Ideal Pressure Distribution
Throat Area (a2) / Upstream Area (a1) = (a2/a1)2 =
Tapping
Distance
along
Venturi (mm)
A (Upstream)(a1)
Diameter (m)
Area (m2)
Throat Area/Area (a2/an)
0
(a2/an)2
Ideal Dimensionless Pressure
𝒂𝟐 𝟐
𝒂𝟐 𝟐
( ) −( )
𝒂𝟏
𝒂𝒏
0
B(a3)
C(a4)
D(Throat)(a2)
1
E(a5)
F(a6)
G(a7)
H(a8)
J(a9)
K(a10)
L(a11)
12
The actual pressures will be calculated in Table 7. As stated before, there are ten measurement data sets. Fill the actual pressure
distribution table, Table 7, according to the flow rate, Q3 which you calculated before.
Table 7 – Actual Pressure Distribution
Flow Q3 =
𝒖𝟐𝟐
=
𝟐𝒈
Tapping
Distance along Venturi (mm)
A (Upstream)(h1)
0
hn (m)
hn-h1 (m)
Actual Dimensionless Pressure
0
0
𝒉𝒏 − 𝒉𝟏
(𝒖𝟐𝟐 /𝟐𝒈)
B(h3)
C(h4)
D(Throat)(h2)
E(h5)
F(h6)
G(h7)
H(h8)
J(h9)
K(h10)
L(h11)
13
Calculate the pressure values at each section of flow discharge rates Q1-3 (x 10-4 m3/s) are given in Table 8.
Table 8 – Actual Pressure Distribution for all Qs
Tapping
Q1
Q2
Q3
A(Upstream)(h1)
B(h3)
C(h4)
D(Throat)(h2)
E(h5)
F(h6)
G(h7)
H(h8)
J(h9)
K(h10)
L(h11)
14
After calculating the actual pressure values, compare with the ideal pressure values. The data graph of the pressure values are given in
Figure 9.
1.2
Dimensionless Pressure
1
0.8
Ideal
0.6
Q1
Q2
Q3
0.4
0.2
0
A
B
C
D
E
F
G
Distance along venturi (mm)
H
J
K
L
Figure 9 – Pressure Distribution Results
15