IMPULSE TURBINE

1.0 INTRODUCTION

By using turbine we can change one form of energy (kinetic) to other form of energy such as electricity. These can be achieved when turbines develop torque and shaft power from the momentum change of fluids –liquid, vapor or gas, which passes through the turbine. To produce high momentum, a higher velocity of fluid is required therefore differences in pressure at the inlet and outlet of the turbine can be achieved. The turbine then converts the energy supplied by the compressed or heated fluid into works that drives electric generators or t transfer power by using shaft.

2.0 OBJECTIVE

The objectives of this experiment are to analyzed and apply the First Law of Thermodynamics to a simple open system undergoing a steady flow process. These experiment also to ascertain the relation of torque-speed and power-speed characteristics of a simple impulse turbine. Based on the data obtained through this experiment, we then plotted a graph and determine the required information as follows:

2.1 Rotational Speed vs Power.

2.2 Rotational Speed vs Torque.

3.0 THEORY

This requires the application of the First Law of Thermodynamic. A unit mass of fluid pass through into a turbine under steady flow. The pressure, specific enthalpies and velocities at inlet and outlet are as shown. While the unit mass flows, specific heat (q) and specific work (w) take place. By applying the First Law of Thermodynamic in the form of steady flow the equation is as follow:

q = h2-h1 + (v2² -v1²) + w

2

Even though there will be heat transfer during the process, it is normally small enough and can be considered as zero. Since the velocities at the inlet and outlet are usually similar, therefore it can be neglected. As a result the equation can be wrote as follow:

w = h1-h2

Where the enthalpy change for air is:

h1-h2 = Cp (T2 – T1)

4.0 APPARATUS

The apparatus used for this experiment is single stage, axial flow and simple impulse turbine manufactured by P.A Hilton Limited. The turbine rotor is made of steel shaft, which runs in lubricated ball bearings housed in an extension to the nozzle plate. The blade is made from solid brass and has 45 blades of symmetrical shape with tip angle of approximately 40 degrees. A stainless steel shroud ring is shrunk on the blades to minimize tip leakage and to increase strength. The nozzle plate carries 4 equally spaced convergent nozzles which discharge at 20 degrees to the plane of rotation into the blades. A removable thick walled stainless steel sleeve is attached to the nozzle plate with quick release catches and forms a combined guard and exhaust casing for the turbine. The end of this casing is closed by a polycarbonate window, which allows observation of the rotor during operation.

The turbine is mounted centrally in the lower front of a high quality GRP panel for bench top use. All the controls and instruments are grouped conveniently around the turbine and the unit may be operated from one position. Each nozzle is

provided with its own isolating valve so that the number of nozzles in operation may be varied. Compressed air from the local supply passes through a filter/regulator, which reduces the pressure to approximately 65 kPa gauges. This air flows through a throttle valve to manifold and to each of the 4 nozzle isolating valves. After expansions in the turbine, the flow through the exhaust casing to the atmosphere via an air flow meter. A relief valve fitted to the manifold is set to discharge at 100 kPa gauge to prevent the turbine from exceeding its safe speed in the event of a malfunction of the pressure regulator. Others equipment’s criteria are as follows:

4.1 Rotor

3.1.1 Blade circle diameter : 45mm

3.1.2 Blade inlet angle : 40º

3.1.3 Blade outlet angle : 40º

3.1.4 lade height : 4.25mm

4.2 Brake Wheel Effective Radius : 14.5m

4.3 Moments of Inertia of Moving Parts : 30 x 10-6 kgm²

4.4 Assumption : Air to be an ideal gas.

5.0 PROCEDURE

Before the experiment can be conducted it requires a thorough preparation as follows:

5.1 The brake band is ensured to be correctly fitted to the two pulleys and the load cell. The brake band must not be twisted. The load cell has a maximum 10N capacity.

5.2 The exhaust casing must be at its position and locked.

5.3 By using the plastic funnel, 4 drops of oil is put into the small hole on top of the shaft housing.

5.4 The nozzle valves are ensured to be opened

5.5 The electrical supply is switched on.

5.6 The air compressor is turned on and the throttle valve is slowly opened until the inlet pressure is between 30 kPa to 40 kPa gauge. The turbine should run up until 20000 to 30000 RPM (Caution : Never operates the turbine higher than 35000 RPM).

5.7 The throttle valve is slowly opened and the inlet pressure must be between 60 kPa and 65 kPa

6.0 EXPERIMENTAL REPORT:

6.1 Experiment 1

6.1.1 The throttle valve is adjusted to the required inlet pressure which is 30 kPa.

6.1.2 Unscrew the brake adjusting screw until the turbine operates to the speed of approximately 30000 RPM.

6.1.3 The inlet pressure and speed is hold until the inlet and exhaust air temperature are stable.

6.1.4 All instruments are observed and recorded accordingly.

6.2 Results from Experiment 1

No

DESCRIPTION

READING

1

Ambient Temperature

22ºC

2

Inlet Pressure (P1)

30 kPa

3

Number of Nozzles in Operation

4 ea

4

Inlet Temperature (T1)

23.3ºC

5

Exhaust Temperature (T2)

22.9ºC

6

Rotational Speed (n)

35 RPM

7

Brake Band Force (F)

0 N

8

Air Flow Rate (m)

3.2 g/s

6.3 Experiment 2

6.3.1 The throttle valve is adjusted to the required pressure as stipulated in table 2.

6.3.2 The brake adjusting screw is adjusted until the turbine operates to the speed of approximately 30000 RPM. An interval is calculated based on the maximum speed to give 7 readings (inclusive of the max of 30000 RPM and min reading of 0 RPM).

6.3.3 Wait until the condition is stabilized.

6.3.4 Record the brake band and actual speed.

6.3.5 Adjusted the brake screw until the speed has decreased as per value in step 2.

6.3.6 Repeat this process until the turbine RPM reaches 0 and for other inlet pressures as in table 2.

6.4 Results from Experiment 2

6.4.1 30 kPa

Test No

1

2

3

4

5

6

7

Inlet Pressure

P1 (kPa)

30

30

30

30

30

30

30

Rotational Speed

N (x 10³ RPM)

30

25

20

15

10

5

0

Brake Band Force F (N)

0.14

0.27

0.43

0.64

0.85

1.01

1.19

Torque

T (x 10³ Nm)

2.925

6.450

9.525

14.650

19.150

23.525

28.225

Power

P (W)

88.8

158.8

190.2

220.5

192.3

112.6

0

6.4.2 25 kPa

Test No

1

2

3

4

5

6

7

Inlet Pressure

P1 (kPa)

25

25

25

25

25

25

25

Rotational Speed

N (x 10³ RPM)

26

22

17

13

9

4

0

Brake Band Force F (N)

0.15

0.25

0.35

0.45

0.65

0.75

0.95

Torque

T (x 10³ Nm)

2.925

4.525

7.650

10.250

15.125

17.125

23.125

Power

P (W)

75.90

98.90

129.90

131.00

133.10

66.90

0

6.4.3 15 kPa

Test No

1

2

3

4

5

6

7

Inlet Pressure

P1 (kPa)

15

15

15

15

15

15

15

Rotational Speed

N (x 10³ RPM)

22

18

15

11

8

4

0

Brake Band Force F (N)

0.09

0.12

0.18

0.28

0.35

0.43

0.63

Torque

T (x 10³ Nm)

1.900

2.500

3.925

5.950

8.200

9.550

13.650

Power

P (W)

40.10

41.50

57.975

65.550

66.600

39.700

0

7.0 GRAPHICAL INFORMATIONS

The graphical information for this experiment are as follows:

7.1 Rotational Speed vs Torque – 30 kPa

7.2 Rotational Speed vs Power – 30 kPa

7.3 Rotational Speed vs Torque – 25 kPa

7.4 Rotational Speed vs Power – 25 kPa

7.5 Rotational Speed vs Torque – 15 kPa

7.6 Rotational Speed vs Power – 15 kPa

8.0 DISCUSSION

8.1 The objectives of this experiment are to analyzed and apply the First Law of Thermodynamics to a simple open system undergoing a steady flow process has been achieved.

8.2 From this experiment, the relation of torque-speed and power-speed characteristics of a simple impulse turbine can be observed by plotting graphs.

8.3 However the results of this experiment are not as accurate as theoretical. These discrepancies has been predicted and caused by several factors and as follows:

8.3.1 Parallax error. A common error that occurs during any experiment. This error normally happened during taking measurement from equipments or tool. If the eyes of the reader were not properly aligned with the scales, the result will differ and not accurate. This error can be reduced by taking a couple of reading or person and take the average. However this technique may time consuming for the whole process.

8.3.2 Zero Parallax. An error of a measurement from equipment’s or tool’s scale where when it supposed to be zero, but it still giving a reading. This error may occur if the equipments or tools used in the experiment are not calibrated. To reduce this error, before any experiment can be conducted ensure all the precisions equipment had been calibrated as per schedule.

8.3.3 Sensitivity of Equipment. The equipment used in this experiment is very sensitive from its surroundings. The readings will not consistent and will differ if any vibrations occurs around the equipment. To reduce this discrepancy, movement of a person must be limited and controlled.

8.3.4 Responsibilities. Every person must understand the whole procedures and processes. All processes have to be divided to each members involved in the experiment in order to reduce any errors to occur.

9.0 CONCLUSIONS

9.1 Overall it is a successful experiment, where the Torque was found indirectly proportional to the rotational speed.

9.2 From the graph plotted the Power shows that it has a quadratic curve to the rotational speed.

9.3 We can apply the first law Thermodynamic while carried out this experiment 1. The torque and power required also determine from Experiment 2.

REFFERENCES

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