Fluid Machines

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 CLASSIFICATION OF FLUID MACHINES:

The turbines in general are classified in two ways:

  • According to the direction of flow of water through the runner
  • According to the action of water on the runner blades.

In order to classify machines according to the direction of flow of water through the runner, three mutually perpendicular directions for flow of water are chosen

RADIAL FLOW MACHINE:
The path of water particles is wholly or mainly in the plane of rotation. i.e., the water enters the runner at the outer periphery, flows inwards in the radial direction and leaves at a different radiusas shown in (b)

AXIAL FLOW MACHINES:
The water mainly flows through the runner in a direction parallel to the axis of rotation as Shown in fig(a).

MIXED FLOW MACHINES:
The flow in the runner may not be merely in one direction. turbines, water enters radially inwards and emerges out axially so that parallel to the axis of the shaft as shown in fig(d)

In mixed flow the discharge in According to the action of water on moving blades, the turbine way be placed in one of the two general categories: i Impulse ii Reaction. In a hydroelectric power scheme, water in a very large quantity is stored in a high level reservoir. In an impulse turbine, the water is brought to the turbine entrance through penstock pipes ending in one or more fixed nozzles. The entire pressure energy of water is converted into the kinetic energy of an unconfined jet. 

The jet of fluid then strikes the blades of the runner and loses practically all of its kinetic energy, i.e., the velocity of water at the exit of the runner is just sufficient to enable it to move out the runner. The static pressure of water at the entrance to the runner is equal to the static pressure at exit and the rotation of the wheel is caused purely due to the tangential force created by the impact of the jet, and hence an impulse turbine. The most common impulse turbine is called Pelton turbine.



The water strikes the blades or buckets of the runner in a direction tangential to the path of rotation. The tangential direction is perpendicular to both axial and radial directions as shown in figure 4.1(c).





Location: United States

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