Francis Turbine Laboratory Report k3up

PERFORMANCE TEST OF FRANCIS TURBINE Michael Adrian Vallecera Ygnacio 1 Abstract: The Francis turbine is a reaction turbine where water changes pressure as it moves through the turbine, transferring its energy. A watertight casement is needed to contain the water flow. Generally, such turbines are suitable for sites such as dams where they are located between the high pressure water source and the low pressure water exit. The inlet of a Francis turbine is spiral shaped. Guide vanes direct the water tangentially to the turbine runner. Francis turbines can be designed for a wide range of heads and flows and along with their high efficiency makes them one of the most widely used turbines in the world. The objective of the experiment is to some data that were gathered from previous groups in their experiment on the performance of a Francis Turbine. The Francis Turbine set-up located in the USC-TC Mechanical Engineering Hydraulic Laboratory is used. Author keywords: Verification, Hydraulic Turbine, Francis Turbine, Guide Vane Angle

Introduction Humans have used the power of flowing water for thousands of years. Early civilizations used wooden paddle wheels to grind corn and wheat to flour. The word Hydro comes from the Greek word for water. Hydropower traditionally represents the energy generated by damming a river and using turbine systems to generate electrical power. However, there are several other ways we can generate energy using the power of water. Ocean waves, tidal currents and ocean water temperature differences can all be harnessed to generate energy. (Gatte & Kadhim 2012) More than 70 percent of the earth is covered by water. The United States is one of the worlds top producers of hydropower (see chart). As much as 12 percent of the electrical energy generated in the U.S. is currently derived from hydropower systems. Parts of the Pacific Northwest generate as much as 70 percent of their electricity using hydroelectric sources. More than half the renewable energy generated in the United States comes from hydroelectric dams. Hydroelectric power is currently the least expensive source of electrical power and is much cleaner than power generated using fossil fuels. (Gatte & Kadhim 2012)

Student, Dept. Mechanical Engineering, Univ. of San Carlos, Cebu City 6000, Philippines, E-mail: [email protected]

Figure 1 The amount of hydro electric energy of different countries (Courtesy of Gatte & Kadhim)

Generating energy from the power of water represents large amounts of clean, renewable energy. 71 percent of the earth’s surface is covered by water. The world’s hydro power potential amounts to 20 billion Mega Watt hours per year and only 30 percent of this has been developed so far. The Main requirement for hydro-electric power plant is the availability of water in huge quantity at sufficient head and this requirement can be met by constructing a dam across a river. A storage reservoir is formed by constructing a dam across Krishna River. Near the bottom of the dam, there is a water intake. Trash Racks of meters long are provided at the water intake to prevent the ingress of floating and other materials to the turbine. (B.Sandhya Rani & Ramesh, Dr.A., 2015). The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, MA. It is an inward-flow reaction turbine that combines

radial and axial flow concepts. Francis turbines are the most common water turbine in use today. They operate in a head range of ten meters to several hundred meters and are primarily used for electrical power production. The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. A casement is needed to contain the water flow. The turbine is located between the highpressure water source and the low-pressure water exit, usually at the base of a dam.

pump. Priming operation of the centrifugal pump is thus needed and necessary before starting the actual experiment. The axial pump is used to serve as an auxiliary equipment, and this was used to prime the centrifugal pump. The priming cap was opened to release the air trapped inside the impeller blade housing. When there is formation of bubbles in the priming cup meaning there is still air inside the housing. After there are no longer bubbles coming from the housing, priming is done and the priming cup is closed. The centrifugal pump is then started.

Experimental Methods Apparatus The experiment set-up is located in the Mechanical Engineering Hydraulics Laboratory of USC-TC. In figure 2 below, the equipment, valves and pipe connections can be clearly seen and followed. The experimental set-up consists of an axial pump, centrifugal pump, by, Francis turbine, and the Prony brake. Figure 3 Priming Cup (Courtesy of Masbad et al. 2015)

Starting the Centrifugal Pump In starting the centrifugal pump, the gate valve is opened as fast as possible by the time the switch of the centrifugal pump is pressed to the on position. If the centrifugal pump is not properly primed, the centrifugal pump would not be able to pump water (Vlachopoulos 2016). Figure 2 Experimental Set-up of the Francis Turbine (Courtesy of Boschi and Park) Priming Operation of the Centrifugal Pump Cavitation is the formation of water vapour and air bubbles on the water surface due to the reduction of pressure. Cavitation is defined as the process of formation of the vapor phase of a liquid when it is subjected to reduced pressures at constant ambient temperature. (Eisenberg 1968). These cavitations may occur in the blades of the centrifugal pump. With cavitation present, this might cause damage to the

Starting the Francis Turbine After turning on the centrifugal pump, water will now flow through the piping system towards the Francis turbine as shown in Fig. 2. A valve on the turbine setup is opened to allow running water to enter the turbine. This valve provides and regulates the flow of cooling water for the brake shoe of the prony brake. This will prevent the brake from heating up.

Experimental Data Gathering

The parameters being gathered in the verification experiment are the vane setting, speed, torque, and the rectangular weir and the triangular weir. These parameters affect the performance of the turbine. The vane angle setting was adjusted to various setting from 10 to 40. A weight of 1 kg was put on the plate on the lever arm of the prony brake. This serves as the initial load applied to the turbine. From vane setting at 10, the speed of the turbine, the weir from the pelton turbine set-up, weir for the Francis and Kaplan set-up, inlet and outlet pressure of the Francis turbine were obtained. The weir of the Pelton Turbine set-up is included because this was operated simultaneously with the experiment. The operation of the Pelton Turbine in the laboratory affects the flow of water to the Francis Turbine.

Calculations of Parameters

The flow of the water is calculated from the equation: 5

8 θ Q= C d √ 2 g tan ⁡ h 2 15 2

()

(3)

Where: Q – flow rate Cd - coefficient of discharge = 0.5779048 g - gravity θ - angle of the weir H - height of the water level on the weir.

The velocity is then determined from the equation:

V=

The torque applied on the prony brake is calculated from the equation:

T =Fr

Q A

(4) Where: V – velocity of water

(1)

Q – flow rate

Where: T – Torque applied

A – area of the exit pipe

F – Weights applied on the prony brake r – Length of the lever arm

From the Bernoulli’s Equation, the total head can be computed.

The shaft power produced by the turbine was determined using data obtained from the prony brake, and the speed reading in rpm from the tachometer gage in the Francis Turbine experimental set-up. The shaft or output power was calculated using the equation:

2

P V HT= + +z γ 2g (5) Where: P - pressure head V - velocity head γ - specific weight

Pbrake=2 πTN (2)

g - gravitational acceleration z - initial head.

Where: Pbrake – Shaft power produced by the turbine T – Torque applied on the proy brake N – Speed of the turbine

The water power or the input power was determined using the equation:

Q (¿¿ Total)(H Total )(6) Pwater =( γ )¿

2500

Output Shaf Power (W)

Where:

VANE ANGLE vs SHAFT POWER

Pwater - water power

γ

- specific weight of water

QTotal

- total volume flow rate of the

water

H Total - the total head of the water. The efficiency of the Francis turbine is obtained after having the Water Power or the Hydraulic Power and the Brake power or the Mechanical Power. The efficiency is obtained from the equation:

¿ Where:

Pm Pw

(7)

= turbine efficiency

Pm−brake ∨mechanical power Pw – water or hydraulic power

Results and Discussions The data below is taken from another group performing the experiment on the Francis Turbine. This will serve as the reference of our verification. The group will be that of Lasa, Ling and Ragaza.

2000 1500

Tri a l 1 Tri a l 2 Tri a l 3

1000 500 0

5

10 15 20 25 30 35 40 45 50

Vane Angle

Figure 4 Vane Angle VS Shaft Power (Courtesy of Lasa et al 2016)

The graph on the vane angle against the shaft power courtesy of Lasa’s group shows the trend of the shaft power as the vane angle changes. The trend is the same for the three trials. As the vane angle setting increases, the shaft power also increases.

The table below shows the computed values from the gathered data. These values are the mechanical power, hydraulic power and the efficiency of the Francis turbine at different vane setting starting from 10 to 40 degrees at 10-degree interval. Table.1 Vane Setting, (degrees)

Mechanical Power, (KW)

Hydraulic power, (KW)

Efficiency, (%)

10

0.8917

3.36

26.54

20

2.9196

4.12

70.86

30

4.0288

5.22

77.18

40

5.5228

5.92

93.3

Figure 5 shows the graph for the hydraulic and mechanical power at different vane setting.

Power (Kw)

7 6 5 4 3 2 1 0 10

Mechanical power 20 25 30 Hydraulic 35 40 power Vane Setting, 

15

Figure 5 Vane Angle Setting VS Shaft Power

Figure 6 shows plots the output power against the efficiency. From the figure, it can be observed that as the output power increases, the efficiency also increases. However, this is not always the case. From the figure below it can be seen that the efficiency does not always increase together with the increase of output power. There comes a point where the efficiency will decrease again. The highest point where the highest efficiency is located is the optimum output power of the turbine.

As seen in Figure 5, the mechanical power increases as the vane angle setting also increases. Comparing with the data obtained from Lasa’s group, a similar trend can be observed in both of our data. The hydraulic power as resembles the same trend with the mechanical power. The hydraulic power also increases as the vane angle setting increases. From table 1 under the efficiency column, it can be observed that the efficiency increases as the vane angle increases. Looking back to Figure 5, it can be seen that the distance between the Mechanical and Hydraulic power trend line decreases, the efficiency increases. A close distance between the trend line of the mechanical and hydraulic power would be desirable.

The efficiency of the Francis turbine is defined by how much of the energy available from the water input to the turbine, can be converted into shaft power. 100

Efficiency, %

80 60 40 20 0

0

1

2

3

4

5

Output power, (KW) Figure 6 Efficiency VS Output Power

6

Figure 7 Efficiency VS Output Power (Courtesy of Faria, et al. 2010)

Conclusion From the performed experiment on performance test of Francis Turbine using the Francis Turbine experimental set-up in the mechanical engineering hydraulics laboratory, the efficiency of the turbine at different vane angle setting were obtained. The data obtained from Lasa’s group were compared to that of this experiment. Both data shows similar trend line on the efficiency of the turbine as the vane angle setting is changed. From the experiment, the vane angle setting at which the Francis turbine operates at the highest efficiency was at the 40 degrees. Adjusting the vane setting with a given head and flow would help in optimizing the efficiency of the Francis Turbine.

Notations:

QT – Volume flow rate for the triangular weir hT

– Head reading for the triangular weir

QR – Volume flow rate for the rectangular weir h R – Head reading for the rectangular weir

L – Length of the rectangular weir QTotal – Total volume flow rate of the fluid

v – Flow velocity of the fluid A

– Cross – sectional area of the pipe system

Pbrake

– Brake power or Output power of the

shaft

T

– Torque applied to the shaft

N

– Speed of the shaft in rpm

F L – Load force from the weight of the plates d – Length of the lever arm

Pwater – Water power or Input power of the fluid γ

– Specific weight of the flowing fluid (water)

H Total – Total head experienced by the fluid P – Pressure of the fluid

g – Acceleration due to gravity z – Elevation of the fluid with respect to a datum

Efficiency – Efficiency of the Francis Turbine References B.Sandhya Rani & Ramesh, Dr.A. (2015). Performance of Francis Turbine and Hydro Electric Governing. Journal of Advancement in Engineering and Technology. Eisenberg, Philip. (1968). “Cavitation”. Hydronautics Incorporated. Faria, M. C., Paulino, O. G., Oliveira, F. H., Barbosa, B. H., and Martinez, C. B. (2010) “Influence of mechanical draft tube fish barrier on the

hydraulic thrust of small francis turbines”, Journal of Hydraulic Engineering, 136(11). p. 2 Gatte, M.T., Kadhim, R.A., Rasheed, F.L. (2010). “Using Water Energy for Electrical Energy Conservation by Building of Microhydroelectric Generators on the Water Pipelines that Depend on the Difference in Elevation.” Iraq J. Electrical and Electronic Engineering, Vol. 7, 185-186 Gatte, M.T., Kadhim, R.A., (2012). “Hydro Power.” Ministry of Science and Techonology, Babylon Department, Hilla, Iraq, 1-3 Potter, M., Wiggert, D., Ramadan, B., (2012). “Mechanics of Fluids”, 4th Edition, Cengage Learning, Stamford, USA, 602 – 605. Vlachopoulos, J., (2016). “Pumps and Turbines. Fundamentals of Fluid Mechanics”, 19/5.