Abstract.
A turbine extracts energy from fluid or air flow to gen erate power and converts it into useful work.The blade attached on the shaft will react to the flow so that it it will move and cause rotational energy to the rotor.Francis turbine ma y be designed for a wide ranged heads and flows.Francis turbines widely used in the world b ecause their high efficiency .The ouput power varies from just few kilowatts to one gigawatt covering a head range ran ge from 20 meter to 700 meter.The francis turbine can be used for pumped storage where it will acting as pump during low power demand and then reversed and used to generate power during peak demand. Theory:
This type of hydraulic machine is converting the head energy to mechanical energy.
The input, .Q H . H
P i n
2 g .Q. i . g
2 g The output, .T
P out .( F r )
2 N
T
60 The turbine efficiency, P o P in
1 00%
Flow rate, Q
V t
Figure 1 Francis Turbine Impel Apparatus:
Armfield R16 Francis (Reaction) Turbine
Figure 2 Armfield R16 Francis Turbine
Part
No.
1 2 3 4 5 6 7
Sump Tank Pump assembly Centrifugal pump Suction pipe Valve Delivery pipe Electromagnetic flow meter
Procedure:
1. Check that the sump tank is filled. 2. Check that the valve at the pump discharge is closed and set the guide vanes on the turbine to the closed position. 3. Release any load on the disc brake by unscrewing the handwheel and check that the dial gauge reads zero. Adjust if necessary. 4. Switch on the pump and slowly open the valve at the pump discharge to the fully open position. This valve is to be kept opened throughout the test. 5. Gradually open the guide vanes to approximately mid-position, typically 15o on the indicator, then clamp in position. 6. Allow the speed of turbine to stabilize, then take readings of:e. turbine speed (read on Tachometer, RPM) f.
Inlet head (read on Bourdon gauge, m head) g. Flow rate (read on flow meter, m3/hr h. brake force (read on brake spring balance, kg) 7. Slowly apply load to the disc brake by turning the hand wheel in a clockwise direction until the speed of the turbine reduces by approximately 100RPM. 8. Keeping the speed steady (by re-adjusting the brake load if necessary), repeat the readings in step 6. 9. Repeat steps 7-8 until turbine stalls (0 RPM) 10. On completion if the test:i.
Close the guide vanes
j. Release the load on the brake k. Switch off the pump l.
Close the valve at the pump discharge
Result.
Brake arm radius (r) = 0.25m Turbine
Inlet
Speed, N
Head, H (m)
Flow meter Reading
Volume
Brake
Brake
Brake
Flowrate, Q
Reading
Force, F
Torque, T (Nm) 0
Mechanical Power, PM (W)
Water Power, PW (W)
Turbine Efficiency,%
0
2118.9 0
1269.8
2462.3 51.54
2000
10.8
72.05
0.02
0
0
1800
10
90.50
0.0251
2.6
25.506 6.3765
1600
9.8
98.00
0.02722
4.3
42.183 10.545
1766.83
2616.9 67.52
1400
9.6
100
0.02777
5.0
49.05
1 797.40
2615.3 68.73
1100
9.5
108
0.03
6.2
60.822 15.20
1750.9
2795.9 62.62
1000
9.4
110
0.0305
6.6
64
1675.52
2812.5 59.57
12.26 16
Calculation.
From the data taken,we calculate; flow rate,Q(
Volume
Brake Force,F(N)
Brake Torque,T(Nm)
Mechanical Power,Pm(W)
Water Power,Pw(W)
Turbine Efficiency,µ(%) Example calculation step with turbine speed ,N=1925RPM 1) Volume flow rate,Q(=72.05
2)Brake Force,F(N)=mg =Brake reading x9.81 =2.6x9.81 =25.506 N 3)Brake Torque,T(Nm)=Fxr =25.506x0.25 =6.3765 N/m 4)Mechanical Power=ωXT
=
T
=0.02
=
(
=1269.8 5) Water Power,Pw(W)=pgQH =1000(9.81)(0.02)(10.8) =5297.4 W 6)Turbine Efficiency (Pout/Pin)x100 =1410.9/5297.4 =26.63 % Graph
Torque(Nm) Vs Turbine Speed(N) 2500
2000
1500
1000
500
0 0
1
2
3
Figure 1
4
5
6
7
Mechanical Power(W) Vs Turbine Speed(N) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 0
500
1000
1500
2000
2500
Figure 2
Turbine Efficiency(%) Vs Turbine Speed(N) 80
70
60
50
40
30
20
10
0 0
500
1000
Figure 3
1500
2000
2500
Discussion Based on the graph plotted from our result,Some information had been extract.We can see that the trend for all of the graphs is the same,as it inversely proportional to each other.For the first graph which is the torque against turbine speed,we found out that when the turbine speed increases,the brake torque increase,the b rake torque decreases.This is because we keep increasing the force ,the friction is higher and thus it makes the fluid velocity decrease.
For the second graph which is the mechanical power against turbine speed,we can see that when the turbine speed increases,the mechani cal power decreases as well.The Francis turbine is a reaction turbine,which means that the working fluid changes pressure as it moves through the turbine,giving up the energy .From the pressure formula,we knew that as we increases the load,the pressure increases.As the turbine speed increase,the load also increases and pressure increase.As the turbine speed increasemthe load alos increases and pressure increases.Thus,the mechanical power increases with the pressure increase For the third graph,we cannot get 100% efficiency because the machine is now well calibrated.besides that,this might experience wear since it has been used for a long time,resulting an error in data recorded.
Conclusion In Conclusion, we found that the brake torque, mechanical power and turbine efficiency are all inversely proportional to turbine speed. He nce,in reality we can apply this knowledge by keeping the turbine speed as low as possible but still economical.There are some errors in the experiment which causes inaccurate readings ho wever we still get the correct patterns that suit the predicted results.
