7. As you take the measurements plot a graph of head drop across the meter against flowrate, Q.
8. Explore the behaviour of the pitot-static tube (8) as it is slid along the pipe.
Results
Table 1. Values for maximum flow
Tapping 1 2 3 4 5 6 7 8
Diameter (m) 0.026 0.023 0.022 0.018 0.018 0.026 0.026 0.026
Area A (mm2) 530.9 422.7 374.6 265.9 261.1 530.9 530.9 530.9
Piezometer Level (m) 0.274 0.266 0.224 0.182 0.050 0.250 0.247 0.245
Volume collected (m3) 0.005
Time for collection (s) 12.04
Discharge Q (m3/s) 4.153E-4
.
Table 2.
0.00093
Table 3.
Volume collected (m3) Time for collection (s) Discharge Q (m3/s) h1 (m) h5 (m) H6 (m) (h1 – h5) (m) CD
0.005 12.04 0.000415 0.274 0.050 0.250 0.224 0.943 22.73
0.005 13.00 0.000385 0.270 0.070 0.249 0.200 0.925 21.05
0.005 13.72 0.000364 0.268 0.090 0.250 0.178 0.929 19.94
0.005 14.56 0.000343 0.264 0.110 0.248 0.154 0.941 18.79
0.005 15.97 0.000313 0.262 0.130 0.249 0.132 0.927 17.13
0.005 17.06 0.000293 0.258 0.150 0.248 0.108 0.959 16.04
0.005 19.19 0.000261 0.256 0.170 0.248 0.086 0.955 14.26
0.005 25.12 0.000199 0.254 0.190 0.249 0.064 0.846 10.89
0.005 31.81 0.000157 0.252 0.210 0.251 0.042 0.825 8.60
0.005 49.75 0.000101 0.250 0.230 0.250 0.020 0.764 5.50
Discussions
The measured pressure distribution of the flow through the venturi meter is shown in Figure 2. (Since I forgot to record the position of the Piezometer, I used their numbers instead.) It can be seen, that the pressure is minimum at the throat section, this is due to the increase in velocity as the diameter decreases across the length of the tube. So therefore, the diameter of the tube is inversely proportional to the velocity, while proportional to the pressure of the fluid flowing through the tube. It is noticed that the curve for the measured pressure does not return to zero as the ideal one this is due to losses during the flow.
Figure 2. Pressure distribution along the pipe
Figure 3 plots the relationship between the flow Q and the (h1-h5)1/2. It can be shown that the linear correlation is fine and this proves the correctness of Eq.(3) in general.
Figure 3: Relationship between the flow rate and (h1-h5)1/2.
Figure 4: Change of CD as Q increases.
For all the cases measured, the CD is lower than 1. The coefficient of CD is not constant as the flow changes, as shown in Figure 4. The coefficient becomes better when the flow rate increases and reaches a plateau afte a certain flow rate of about 0.00025 m3/s. Since the coefficient is mainly resulted from the energy loss in the pipe. We know th
