A fluid machine is a device which convert the energy stored by a fluid into mechanical energy or vice versa. The energy stored by a fluid mass appears in the form of potential, kinetic and intermolecular energy. The mechanical energy, on the other hand, is usually transmitted by rotating shaft. Machines using liquid (mainly water, for almost all practical purpose) are termed as hydraulic machines.
Fluid types of Turbines
- Steam Steam Turbine
- Gas or Air – Gas Turbine
- Water- Hydraulic Turbine
- Froen – Vapour Turbine
- Wind – Wind Mills
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 the flow of water are chosen
Radial Flow Machines
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 radius as shown in fig(b).
Axial Flow Machines
The water mainly flows through the runner in a direction parallel to the axis of rotation as shown in fig(c).
Mixed Flow Machines
The flow in the runner may not be merely in one direction. Water enters radially inward and emerges out axially, so that the flow is 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:
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 inner wheel is caused purely due to the tan gential force created by the impact of the jet, and hence an impulse turbine. The most common impulse turbine is Pelton turbine.
Tangential Flow Machine
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 fig(c).
Exchange of Energy
A machine wherein rotary motion is obtained by centrifugal forces which result from a change in the direction of high velocity fluid jet that issues from a nozzle.
A hydraulic turbine uses the potential and kinetic energy of water and convert it into usable mechanical energy. The fluid energy is available in the natural or artificial high level water reservoirs. When water from the reservoir is taken to the turbine, transfer of energy takes place in the blade passages of the unit. The mechanical energy made avail able at the turbine shaft is used to run an electric generator which is directly coupled to the turbine shaft.
Appropriate types of water turbines have been installed for most efficient utilization.
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