>>>

Francis Turbine: Definition, Parts, Working, Velocity Diagram, Applications, Advantages & Disadvantages [PDF]

Download the PDF below!

In the last session, we had discussed briefly on the Kaplan Turbine and Hydraulic Turbine. Whereas in today's session, we will be discussing on Francis Turbine along with it Definition, Parts, Working, Applications, Advantages & Disadvantages.

Lets see the definition of it...

Definition of Francis Turbine:

Francis Turbine is a mixed flow reaction Turbine in which water enters radially at its outer periphery and leaves axially at its centre. The Francis Turbine is the most commonly used Water turbine and was developed by James B Francis.

Francis Turbine Diagram:

The Diagram of Francis Turbine is shown below.

francis turbine diagram
francis turbine

Parts of Francis Turbine:

The major Components or Parts of Francis Turbine are as follows.

  • Scroll Casing (spiral casing)
  • Speed ring (stay ring)
  • Guide vanes
  • Runner
  • Draft tube
  • Tailrace

The explanation for the parts of Francis Turbine are as follows.

Scroll Casing (Spiral Casing):

In Francis Turbine, Water from the Penstock enter a scroll casing (spiral casing) that surrounds the runner.

Speed ring (stay ring):

From the scroll casing, water passes through a speed ring or stay ring which consists of a series of fixed vanes called stay vanes.

The no. of stay vanes is usually taken as half the no. of guide vanes.

The function of the speed ring is to direct the water from casing to the guide vanes or wicket gates and further resist the load imposed upon it.

Guide Vanes:

From the speed ring, water passes through a series of guide vanes provided around the periphery (aerofoil shaped) of the runner.

guide vanes-francis turbine
By Stahlkocher, Cut-away view, with wicket gates (yellow) at minimum flow setting

Their function is to regulate the quantity supplied to the runner and direct the water on to the runner at an angle appropriate to the design.

Runner:

Francis Turbine blades are specially shaped that it has thin aerofoil cross-section, so when water flows over it, low pressure will be produced on one side and high pressure will be on another side. This will result in a lift force.

runner of Francis turbine
By Voith Siemens Hydro Power Generation, Three Gorges Dam Francis turbine runner

Draft tube:

A draft tube is a large pipe with an increasing cross-section area that connects the runner exit to the tailrace.

Tailrace:

The water after passing through the runner flows to the tailrace through a draft tube.

These are the components of Francis Turbine. Let's see the Working Principle of Francis Turbine in a detailed way.

Working Principle of Francis Turbine:

The Working Principle of Francis Turbine is as follows.

Water passes through various components of the Francis turbine to rotate the runner and generates electricity.

Firstly water enters into the penstock and surrounds the casing. The purpose of the casing is to provide an even distribution of water around the circumference of the runner, maintaining constant velocity for the water by gradually reducing the cross-sectional area of the casing.

figure of Francis turbine
By Stahlkocher, Francis turbine (exterior view) attached to a generator

From the scroll casing, water passes through a stay ring which consists of a series of fixed vanes called stay vanes. From the stay ring, water passes through a series of guide vanes provided around the periphery of the runner.

The vanes are so shaped that water enters the runner radially at the outer periphery and leaves it axially at the inner periphery.

The most important part of Francis Turbine is the runner. It is fitted with a collection of complex-shaped blades. In runner, water enters radially and leaves axially. One more peculiar thing about the blade is it is having a bucket type of shape towards the outlet so water will hit and produce impulse force before leaving the runner.

Both Impulse force and lift force will make the runner rotate. So Francis Turbine is not a pure reaction turbine but a portion of force comes from the Impulse action also. Therefore, it is a combination of Impulse and Reaction forces and thereby Francis turbine is also called a Mixed Flow turbine.

From the Runner, water enters into the Draft tube which converts a large portion of velocity energy into useful pressure energy that is rejected from the runner.

Finally, water moves out through the Tailrace after passing from the draft tube. In this way, by the usage of Francis Turbine, electricity is generated.

Representation:

Scroll casing> speed ring>Guide vanes>Runner>Draft tube>Tail-race.

Francis Turbine Velocity Diagram:

The Velocity Diagram of Francis Turbine is shown below.

This velocity diagram clearly shows that in ideal cases, the whirl component of outlet velocity is zero i.e at the outlet the flow is entirely axial.

Francis Turbine velocity diagram
By Anupamiit, Ideal velocity diagram, illustrating that in ideal cases the whirl component of outlet velocity is zero and the flow is completely axial

Blade Efficiency:

calculation of blade efficiency of francis turbine
This text is under https://creativecommons.org/licenses/by-sa/3.0/

Degree of Reaction:

Degree of reaction of francis turbine
Actual velocity diagram, illustrating that the whirl component of the outlet velocity is non-zero
Actual velocity triangle of Francis turbine (By Anupamiit, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=61660690)

Applications of Francis Turbine:

The applications of Francis Turbine are as follows.

  • It works over a wide range of head and flow rate
  • One of the most efficient hydro-turbines
  • Most widely used turbines to generate electricity

Advantages of Francis turbine:

The advantages of Francis Turbine are as follows.

  • Its control is easy even with variable heads
  • It has a small runner size
  • Very little change in efficiency with time

Disadvantages of Francis Turbine:

The disdvantages of Francis Turbine are as follows.

  • Inspection is relatively difficult
  • Problem of cavitation

FAQs on Francis Turbine:

What kind of turbine is Francis turbine?

The Francis turbine is a reaction turbine and it is a combination of Impulse and Reaction forces and thereby Francis turbine is also called a Mixed Flow turbine.

What is the hydraulic efficiency of the Francis turbine?

It is the ratio of work done on the wheel to the head of water (or energy) supplied to the turbine.

This is the detailed explanation of Francis Turbine. If you have any doubts, feel free to ask and we will reply you as soon as possible.

More Resources:

Kaplan Turbine
Pelton Wheel Turbine

References [External Links]:


Print Friendly, PDF & Email

About Mohammed SHAFI

Mohammed Shafi is the founder, managing editor, and primary author of Mechanical E-Notes. He is an Assistant Professor (Department of Mechanical Engineering) at the Sreenidhi Institute of Science and Technology. He has a 6 years of vast experience in design, research, and data analysis. Shafi has co-authored two journals 1. Dynamic and Fatigue Analysis on Tillage Equipment  2. Welding Procedure and Testing Analysis on Mixing and Nodulizing Drum.

Continue Reading

Draft tube: Definition, Function, Types, Applications, Advantages, Disadvantages, and Efficiency [Notes with PDF]

If you had observed our previous articles, you can notice that there is a component called Draft Tube which is attached to the end of the Kaplan Turbine and Francis Turbine. In this article, we elaborate on the Draft Tube along with its Definition, Function, Types, Applications, Advantages, Disadvantages, Efficiency, and Design calculation. Now, Let's […]

Difference Between Refrigerator, Heat Pump, and Heat Engine [PDF]

Hello Readers, in today's session, we will discuss on the Difference between a Refrigerator, Heat Pump, and Heat Engine in a detailed way with respective figures. Before going to the differences, let give you an overview of these three devices. What is a Heat Engine? A heat engine is a system that converts Thermal energy […]

Hydroelectric Power Plant: Definition, Layout, Parts, Working, Advantages, Disadvantages & Applications [PDF]

The generation of electricity by hydropower is one of the best methods of producing electric power. In this article, we are going to discuss Hydroelectric Power Plant along with its Definition, Working, Advantages, Disadvantages & Applications. Definition of Hydroelectric Power Plant: Hydroelectric Power Plant is an area where hydraulic energy is converted into electrical energy […]

Kaplan Turbine: Introduction, Definition, Components, Working, Application, Advantages & Disadvantages [PDF]

In the last session, we had discussed the Introduction to Hydraulic Turbines, Pelton Wheel Turbine, Centrifugal pump & Reciprocating pump in a detailed way. Therefore, in this article, we will discuss the Kaplan Turbine with its construction, working, advantages, disadvantages, and applications. So let's dive in. Introduction of the Kaplan Turbine: This Kaplan Turbine was developed in 1913 by […]

Hydraulic Turbine: Definition, Classification, Advantages, Disadvantages & Applications [PDF]

Hydraulic turbine or water turbine is a rotary machine that converts potential energy and kinetic energy of water into mechanical work. In this article, we are going to discuss the Hydraulic Turbine along with its Definition, Classification, Advantages, Disadvantages & Applications. Before going into the main topic, let's see the difference between Turbine and pump. Difference between Turbine […]

Centrifugal Pump: Definition, Components, Working, Priming, Advantages, Disadvantages and Applications [PDF]

Centrifugal Pumps are most commonly used in industrial as well as Domestic applications for the transfer of fluids from one place to another place.Today, in this session, we are going to discuss components, working principle, priming, Advantages, Disadvantages, and Applications of the Centrifugal pump in a detailed way. What is a Centrifugal Pump? Centrifugal pump […]

Pelton Wheel Turbine: Components, Working, Applications, Advantages & Disadvantages [PDF]

Pelton Wheel Turbine is the only impulse type of hydraulic turbine named after Lester A.Pelton, the American engineer. It is well suited for operating under high heads. What is a Pelton Turbine? The turbine capable of working under the high potential head of water is the Pelton Wheel Turbine which works on the head greater than […]

38 Basic Fluid Mechanics Questions and Answers [PDF]

This article on Fluid Mechanics questions and answers will be helpful to you when you are going for an interview in a core company. Considering that, I have collected all the Fundamentals of Fluid Mechanics & Hydraulic Machinery, which will be helpful to you in both aspects. One is for the case of Interviews, and […]