Theory of Roto-Dynamic machines?
Answer:
Rotodynamic type
There is free passage of fluid in rotodynamic machines between inlet and outlet. All machines have a rotating element called the runner, impeller or rotor, which rotates freely in the fluid. The transfer of energy between rotor and fluid is continuous and is a result of the rate of change of angular momentum.
Rotodynamic machines.
Rotodynamic Machines
Pumps, fans and compressors Turbines
Uncased Cased Impulse Reaction
Propellers Axial Windmills Axial flow (Kaplan)
Screws Mixed Flow Pelton Wheel Mixed flow (Francis)
Centrifugal Radial flow (Barkers Mill or early Francis)
Delivery is constant from these types of machines.
All machines have a rotor through which the fluid passes. In a turbine, this rotor is called the runner, and for a pump it is called an impeller. The fluid has a component of velocity, and therefore of momentum, in a direction tangential to the rotor, the rate of change of momentum corresponds to a tangential force on the rotor. In a turbine there is a reduction of the tangential momentum of the fluid in the direction of movement of the rotor, thus energy is transferred from the fluid to the rotor, and hence to the output shaft. The fluid leaves with reduced energy. In a pump, energy from the rotor is used to increase the tangential momentum of the fluid; subsequent deceleration of the fluid produces a rise in pressure.
The rotor consists of a number of vanes or blades, and there is a transfer of energy between fluid and this rotor.
2
Turbines: Impulse types have no change in static pressure across the runner.
Reaction types have a decrease in static pressure across the runner.
Impulse type converts fluid pressure into kinetic energy and transfers this energy to the runner. Reaction type, the change from pressure to kinetic energy, is slower and requires the runner to be enclosed and fully flooded.
Flow through rotodynamic machines
Axial flow: Perpendicular to impeller or parallel to axis of rotation.
Radial flow: Centrifugal machines – flow in the plane of impeller rotation.
Mixed flow: Partially axial and radial.
Axial flow and centrifugal impellers.
Also see handout on different pump and turbine designs.
There are considerable similarities between turbines and pumps, and a number of the formulae we shall derive are applicable to BOTH. Some machines can be run as a pump and a turbine, and are used in hydraulic pumped storage systems.
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