Two types of compounding can be accomplished: a velocity compounding and b pressure compounding Either of the above methods or both in combination are used to reduce the high rotational speed of the single stage turbine. This is consistent with Eq. Types of compounding In an Impulse steam turbine compounding can be achieved in the following three ways: - 1. The nozzles are fitted to the casing and the blades are keyed to the turbine shaft. It is a three stage pressure compounded impulse turbine.
Energy input per stage is less, so there are more number of stages. This relation shows mathematically how is the time constant value is related to the values of design and operation parameters. This process has been illustrated in figure 3. The symbols in the figure have same meaning as above. Hence, there is a partial decrease in pressure of the incoming steam. The high velocity steam is directed on first set of moving blades and as steam flows over the blade it imparts some of its momentum to blades and loses some velocity.
In 1878, a Swedish engineer, Carl G. They are greater for the fixed blades and greater for the high-pressure than the low-pressure stages. Curtis to solve the problems of a single-stage impulse turbine for use with high pressure and temperature steam. The fluid stream suffers a loss of momentum while flowing past the blades that is absorbed by the rotating wheel entailing production of torque. The velocity diagram in figure 2, shows the various components of steam velocity and the blade velocity of the moving blades. .
Each stage comprises its ring of nozzle and blades. Velocity compounding of Impulse Turbine Fig-1:Schematic Diagram of Curtis Stage Impulse Turbine The velocity compounded Impulse turbine was first proposed by C G Curtis to solve the problem of single stage Impulse turbine for use of high pressure and temperature steam. In England , Charles A. Some part of high K. Discharge Mode, Example, Tutorial Sheet 8. Compounding of is the method in which energy from the steam is extracted in a number of stages rather than a single stage in a turbine.
A compounded steam turbine has multiple stages i. From Bernoulli's equation, we can write or, Dividing by , we obtain 19. Proceedings of the South African Sugar Technologists' Association. Necessity The steam produced in the has sufficiently high enthalpy when. Turbines can be condensing or non-condensing types depending on whether the back pressure is below or equal to the atmosphere pressure. The steam then enters the next ring of moving blades; this process is repeated until practically all the energy of the steam has been absorbed.
To overcome the wastage of steam compounding of steam turbine is used. Velocity Diagram Fig-2:Velocity Diagram of Curtis Stage Impulse Turbine As shown in the above diagram there are two rings of moving blades separated by a ring of fixed blades. Pressure compounding of Impulse Turbine Fig-3:Schematic Diagram of Pressure compounded Impulse Turbine The pressure compounded Impulse turbine is also called as Rateau turbine, after its inventor. In this type of turbine the pressure drops take place in a number of stages. In fixed static blade passage both pressure and velocity remain constant. Compounding of is the method in which energy from the steam is extracted in a number of stages rather than a single stage in a turbine.
The velocity diagram of the velocity-compound Impulse turbine is shown in Figure 23. This means that maximum power can be produced at much lower blade velocities. The process 2-3 shows expansion under super-saturation condition which is not in thermal equilibrium It is also called under cooling At any pressure between and i. It can be explained mathematically from the following formula i. Hence, the pressure thereafter remains constant. Only a part of the high kinetic energy is absorbed by these blades.
The high velocity jet steam is directed onto the first moving blades wherein nearly all of its velocity is absorbed. A schematic diagram of the Curtis stage impulse turbine, with two rings of moving blades one ring of fixed blades is shown in figure 1. The effect depicted by Eqn 25. The steam from the first ring of moving blades enters the second ring of nozzles where its pressure is further reduced and velocity increased again. Fluid machinery Lecture 23 Compounding in Impulse Turbine If high velocity of steam is allowed to flow through one row of moving blades, it produces a rotor speed of about 30000 rpm which is too high for practical use. Then it is fed into the next set of moving blades, and this process is repeated until the condenser pressure is reached. The Velocity - Compounding of the Impulse Turbine The velocity-compounded impulse turbine was first proposed by C.
Optimum Velocity It is the velocity of the blades at which maximum power output can be achieved. The pressure partially decreases and the velocity rises correspondingly. It is clear that the nozzle must converge in the subsonic portion and diverge in the supersonic portion. The minimum cross-section of such ducts is known as throat. Pressure-Velocity compounded Impulse Turbine Fig-5:Schematic Diagram of Pressure-Velocity compounded Impulse Turbine It is a combination of the above two types of compounding. A duct which decreases the velocity of a fluid and causes a corresponding increase in pressure is a diffuser. A supersonic diffuser must be a converging channel.