NOZZLE PERFORMANCE

1.0 INTRODUCTION

2.0 OBJECTIVE

The objective of this experiment is to study relationship (at constant inlet pressure) between:

2.1 Air mass flow rate

2.2 Nozzle efficiency and back pressure for various nozzle profile.

3.0 APPARATUS

The Apparatus used in the experiment is Nozzle performance test unit (F791).

4.0 THEORY

Pressure ratio, (ratio of outlet and inlet absolute pressure).

Nozzle efficiency, actual KE at nozzle exit =

Isentropic KE at nozzle exit

Finding the actual velocity;

Air jet

Note that the air has no axial velocity when it leaves the impact head.

Force, F

From Newton’s Second Law, the force exerted (in axial direction) is equal to the rate of change of momentum (in the same direction).

Thus,

To find isentropic velocity,

Energy balance equation between (1) and (2):

……….(1)

q=0 (adiabatic process), w=0 (no work transfer), negligible for gas and small different in height. negligible compared to

Equation (1) become for perfect gas

…………………… (2)

Note that,

=

………………… (3)

Substitute equation (3) into (2)

Finding theoretical air mass flow rate:

And for perfect gas, P=

5.0 PROCEDURE

The procedure for this experiment are as follows:

5.1 The air inlet control valve was close and the chamber pressure control valve was open. Before proceeding further, ensure that the contacts were clean, that the battery was in good condition and that the impact head was fitted to the end of the cantilever. Also, check that the micrometer dial has been correctly zeroed and that a cantilever load/deflection graph is available.

5.2 Unscrew all the knurled nut at the top right hand end of the chamber, withdraw the nozzle mounting sleeve and assemble nozzle no. 1 into the unit.

5.3 The diverter handle was turned to upward position.

5.4 With the chamber pressure control valve fully open, the inlet control valve was adjusted to give a constant air inlet pressure of 600 kPa gage.

5.5 The micrometer adjustment screw was rotated until the voltmeter and the lamp indicates that the contact is just made. (Greatest sensitivity is obtained if the screw is adjusted so that the voltmeter indicates about 0.5V).

5.6 The pressure, temperatures, air mass flow rate and dial reading have been recorded.

5.7 The chamber pressure was increase to about 100kPa gage and repeat the above step.

5.8 Making sure that the inlet pressure remains constant, the test at other chamber pressure was repeated.

5.9 The whole test was repeated with other nozzles.

6.0 SAMPLE OF CALCULATION

To find we have to interpolate the graph of calibration of cantilever to find weight, (N). For instance, for experiment 1, the second dial reading is 48. So,

Thus, W= 2.1

As we know that

In this experiment, we use air as the perfect gas, thus the value of, R= 287 and the temperature we convert it into Kelvin, thus T= 293K.

Thus substitute it into formulae,

= 488

When we get both velocities, we can calculate the efficiency of the nozzle by using this formula,

=

To find the theoretical air mass flow rate, we will apply this formula;

With value of

A=

=

Thus,

=

7.0 RESULT

Experiment 1: Nozzle no. 1

Atmospheric pressure: 100.7 kPa

1.

2.

3.

4.

5.

6.

7.

kPa (gauge)

600

600

600

600

600

600

600

, ()

23.6

23.6

23.6

23.6

23.6

23.6

23.7

, kPa (gauge)

0

100

200

300

400

500

575

24.5

24.5

24.5

24.5

24.5

24.5

24.5

Cantilever deflection

55.2

48.6

41.8

35.3

24.2

13.2

3.4

Air mass flow rate,

5.2

5.2

5.2

5.1

4.5

3.6

1.7

Pressure ratio,r (P2/P1)

0

0.17

0.33

0.5

0.67

0.83

0.96

V2a (ms-1)

462.4

413.2

363

314.2

221.5

171.4

66.7

V2s (ms-1)

769.8

488

403.7

328.5

254.9

176.6

0

Efficiency (%)

37.2

72.3

77.8

91.5

75.2

96.3

0

Experiment 2: Nozzle no. 2

Atmospheric pressure: 100.7 kPa

1.

2.

3.

4.

5.

6.

7.

kPa (gauge)

600

600

600

600

600

600

600

, ()

22.5

22.5

22.5

22.3

22.2

22.2

22.3

, kPa (gauge)

0

100

200

300

400

500

600

22

22

21.8

21.8

21.8

21.8

22

Cantilever deflection

52.3

49.2

39.6

31.5

26.7

15.4

2.3

Air mass flow rate,

5.4

5.3

5.2

5.1

5.0

4.2

1.4

Pressure ratio,r (P2/P1)

0

0.17

0.33

0.5

0.67

0.83

1

V2a (ms-1)

442.5

395.8

328.2

273.2

221.4

165.3

70.4

V2s (ms-1)

773.9

486.2

402.1

329.7

253.2

172.5

0

Efficiency (%)

33.7

69.8

62.6

62.7

76.4

82.1

0

Experiment 3: Nozzle no. 3

Atmospheric pressure: 100.7 kPa

1.

2.

3.

4.

5.

6.

7.

(gauge)

600

600

600

600

600

600

600

, ()

22.2

22.3

22.2

22.1

22.1

22.1

22

(gauge)

0

100

200

300

400

500

600

22

22

21.8

21.8

21.6

21.8

22

Cantilever deflection

53

45

40

32

25

17

4

Air mass flow rate,

5.1

5.1

5.2

5

5.2

4.5

1.6

Pressure ratio,r (P2/P1)

0

0.17

0.39

0.5

0.72

0.92

1

V2a (ms-1)

496.2

398.2

330.9

264

194.3

153.8

176.6

V2s (ms-1)

777.5

489.8

405.7

328.9

258

177

0

Efficiency (%)

41.2

65.6

64.9

66.2

58.4

78.2

0

Calibration of cantilever:

Weight, (N)

Dial reading

0

0

0.5

11.0

1.0

22.0

1.5

33.5

2.0

45.0

2.5

55.5

3.0

66.0

3.5

76.5

4.0

87.5

8.0 GRAPHICAL INFORMATIONS

By plotting the graph of calibration of cantilever, we will get the as shown below:

When we plot graphs for 3 experiments, we get graphs like below:

Experiment nozzle 1

Experiment nozzle 2

experiment nozzle 3

9.0 DISCUSSION

9.1 We can conclude that we do not have to correct the value of air mass flow rate because the value of flow meter correction, k=1. That’s mean we can use the original value of air mass flow rate that we get.

9.2 The value of theoretical air mass flow rate is greater than that we get. During taking the reading, the scale is change. It always moves. Thus, quite difficult to us to get the actual value.

9.3 The value of air mass flow rate will decrease when pressure ratio near to one. Besides, from the graph of efficiency Vs pressure ratio, the efficiency become zero when pressure equal to one. That’s mean, when inlet pressure and chamber pressure are same, the efficiency will become zero.

10.0 CONCLUSION

10.1 When the pressure ratio equal to one, the value of efficiency is zero

10.2 The value of air mass flow rate will decrease when pressure ratio near to one.

REFFERENCES

Thermodynamics an Engineering Approach – Fifth Edition, Yunos A. Cengel and Michael A. Boles