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Multiple Choice: For each of the following sentences circle the most appropriate letter. A. pressure increases while velocity decreases. 1. In a reaction turbine, when steam flows through the fixed blades,



1. In a reaction turbine, when steam flows through the fixed blades,

A. pressure increases while velocity decreases

B. pressure decreases while velocity increases

C. pressure and velocity both decreases

D. pressure and velocity both increases

 

2. In a De-Laval impulse turbine, the nozzle is kept very close to the blades.

A. Yes  

B. No

 

3. In an impulse turbine

A. the steam is expanded in nozzles only and there is a pressure drop and heat drop

B. the steam is expanded both in fixed and moving blades continuously

C. the steam is expanded in moving blades only

D. the pressure and temperature of steam remains constant

 

4. In a reaction turbine

A. the steam is allowed to expand in the nozzle, where it gives a high velocity before it enters the moving blades

B. the expansion of steam takes place partly in the fixed blades and partly in the moving blades

C. the steam is expanded from a high pressure to a condenser pressure in one or more nozzles

D. the pressure and temperature of steam remains constant

 

5. A stage, in reaction turbine, is represented by

A. number of casing

B. number of entries of steam

C. number of exits of steam

D. each row of blades

 

 

6. In an impulse turbine, steam expands

A. wholly in blades

B. wholly in nozzle

C. partly in the nozzle and partly in blades

D. none of these

 

7. In a reaction turbine when the degree of reaction is zero, then there is

A. no heat drop in moving blades

B. no heat drop in fixed blades

C. maximum heat drop in moving blades

D. maximum heat drop in fixed blades

 

8. In a reaction turbine, when steam flows through the moving blades,

A. pressure increases while velocity decreases

B. pressure decreases while velocity increases

C. pressure and velocity both decreases

D. pressure and velocity both increases

 

9. In an impulse reaction turbine, the pressure drops gradually and continuously over

A. fixed blades

B. moving blades

C. both fixed and moving blades

D. none of these

 

10. In impulse turbines, when friction is neglected, the relative velocity of steam at outlet tip of the blade is ______ the relative velocity of steam at inlet tip of the blade.

A. equal to

B. less than

C. greater than

 

11. An impulse turbine as compared to a reaction turbine, for a given power has __________ row of blades.

A. equal

B. less

C. more

 

 

 

UNIT 3

COMPOUNDING IN STEAM TURBINE

The compounding is the way of reducing the wheel or rotor speed of the turbine to optimum value. It may be defined as the process of arranging the expansion of steam or the utilization of kinetic energy or both in several rings.

There are several methods of reducing the speed of rotor to lower value. All these methods utilize a multiple system of rotors in series keyed on a common shaft, and the steam pressure or jet velocity is absorbed in stages as the steam flowes over the blades.

Different methods of compounding are:

1. Velocity Compounding: The Rateau Design

2. Pressure Compounding: The Curtis Design

3. Pressure Velocity Compounding: The Rateau-Curtis Design.

 

Velocity Compounding:

There are number of moving blades separated by rings of fixed blades as shown in the figure. All the moving blades are keyed on a common shaft. When the steam passed through the nozzles where it is expanded to condenser pressure, its velocity becomes very high. This high velocity steam then passes through a series of moving and fixed blades.

When the steam passes over the moving blades, its velocity decreases. The function of the fixed blades is to re-direct the steam flow without altering its velocity to the following next row moving blades where a work is done on them and steam leaves the turbine with allow velocity as shown in diagram.


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