Table Exp 5.docx

Experimental Procedure: 1. Make sure that the apparatus is set up correctly. 2. Check that the gauge reading of pressure is zero to avoid errors . This can be fixed by releasing the air bubbles at the back of the gauge. 3. Close the valve of the flow control and start opening the pump until you reach 25 L/min for a flow and let it settle . 4. Measure and Record the ambient atmospheric pressure (Pa). Then measure the temperature of water by a thermometer. 5. Gradually open the flow control valve wait for the bubbles to stop and start taking the readings. 6. Use flow control valve to increase the flow from 25 L/min to 45 L/min and take the readings for Upstream(P1) and Throat pressure(P2). 7. As we increase the flow rate the cavitation starts to show as a white vapor . 8. Close the Pump. 9. Use the continuity equation (Q=A1V1) to calculate the inlet flow velocity (v1) for each flow rate. 10. Complete the extra column p1 + pa. 11. Plot a chart p1 + pa against ρv12/2 . 12. Calculate the gradient of your chart, this will be k2. Find the intercept of the chart, this will be approximate vapor pressure pv.

Useful data:     

Water Temperature = 23oC Water Density, ρ = 1000 kg/m3 Atmospheric Pressure, Pa = 101325 Pa Venturi Inlet Area, A1 = 2.1 × 10−4 m2 Venturi Inlet Area, A2 = 0.36 × 10−4 m2

  

10 L/min = 0.0001667 m3/s 1 bar = 100000 Pa v1 = Q/A

Sample Calculations: Convert Q from L/min to m3/s (Q=25 L/min ) 10 L/min = 0.0001667 m3/s 0.0001667 𝑚3/𝑠  25 𝐿/𝑚𝑖𝑛 10 L/min



𝑄=



v1 = 𝑨

= 4.1675  10−4 m3/s

𝑸

=

4.1675  10−4 2.1 ×10−4

= 1.9857 m/s

Convert P1 from bar to Pa 1 bar = 100000 Pa 

P1(Pa)= 100000  0.1 = 10000 Pa



𝜌𝑣 2



P2(Pa)= 100000  -0.66 = -66000 Pa



V2 = 𝑨

2

2

=

1000 (1.9857) 2

= 1971.50

𝑸

=

4.1675  10−4 0.36 ×10−4

= 11.58 m/s

Complete table:

Flow Reading

Upstream Pressure

Q

P1

Upstream Flow Velocity

L/min

3

m /s

bar

Pa

P1 + Pa Pa

25

4.17× 10−4

0.10

10000

111325

27.5

4.58× 10−4

0.15

15000

116325

30

5.00 × 10−4 5.42× 10−4

0.35

35000

136325

0.6

60000

161325

5.83× 10

−4

0.85

85000

186325

6.25× 10

−4

32.5 35 37.5 40 42.5 45

1.1

110000

211325

6.67× 10−4

1.37

135000

236325

7.08×

10−4

1.7

170000

271325

7.50×

10−4

200000

301325

2 o

o

Water Temperature ( C) = 23 C Water Density, ρ (kg/m3) = 1000 Atmospheric Pressure, Pa (Pa) = 101325 Pa

v1 m/s 1.9857 2.1809 2.3809

Throat Pressure ρv12/2 1971.50 2378.16 2834.34

P2 bar -0.66 -0.88 -0.88

Pa -66000 -88000 -88000

Flow Velocity at Throat v2 m/s 11.58 12.72 13.89

-86000 2.5809 3330.52 -0.86 15.06 -84000 2.7762 3853.64 -0.84 16.19 -82000 2.9762 4428.88 -0.82 17.36 -80000 3.1762 5044.12 -0.80 18.53 -78000 3.3714 5683.17 -0.78 19.67 -76000 3.5714 6377.45 -0.76 20.83 2 −4 Venturi Inlet Area, A1 (m ) = 2.1 × 10 Venturi Inlet Area, A2 (m2) = 0.36 × 10−4