Unit – 3
Reaction Water Turbines
Q1) Classify reaction turbines.
Ans. Types of Reaction Turbine are
1. Radial Flow Turbines
Inward Flow Turbines
Outward Flow Turbines
2. Axial Flow Turbines
3. Mixed Flow Turbines
Q2) Explain construction & working of Francis turbine with neat sketch.
Ans.
Q3) Explain construction & working of Kaplan turbine with neat sketch.
Ans.
Q4) Draw and explain velocity diagrams for reaction turbines.
Ans.
The work done per second on the runner by water is given by equation
=Q[
Where
Velocity of whirl at inlet and outlet
= Tangential velocity of wheel of inlet and outlet
The work done per second per unit weight of water per second
=
=
=
Hydraulic efficiency =
=
Where
RP = Runner power
WP = Water power
If discharge is radial
= =
Q5) Define degree of reaction.
Ans.
=
If
=
Q6) Explain performance characteristics of reaction turbine.
Ans. Constant head curves
For a Pelton wheel
For reaction turbines
Operating characteristic curves for constant speed curves
Constant efficiency curves or Muschel curves or iso-efficiency curves
Q7) What is draft tube? State its functions.
Ans.
It permits negative head to be established at the outlet of the runner and thereby increase the net head on the turbine.
The turbine may be placed above the tail race without any loss of net head and hence turbine may be inspected properly.
It converts a large portion of kinetic energy ( at the outlet of turbine into useful pressure energy.
Q8) Explain various types of draft tubes with neat sketch.
Ans.
The following are the important types of draft tubes which are commonly used
1) Conical draft tube
2) Simple elbow tubes
3) Moody spreading tubes
4) Elbow draft tubes with circular inlet and rectangular outlet
Q9) What do you mean by cavitation? Write down causes & remedies for cavitation.
Ans.
The following precautions should be taken against cavitation
Q10) Explain governing of turbine with sketch.
Ans.
1) Servo motor also known as relay cylinder.
2) Relay valve known as control valve.
3) Actuator
4) Oil sump
5) Oil pump which is driven by belt connected to turbine main shaft.
6) A system of oil supply pipes connecting the oil sump with servo motor.
Q11) Explain similitude & dimensional analysis of turbines.
Ans.