DEFINITIONS AND TERMINOLOGIES
1. Fluid Machinery
Devices or machines that use, convey, or regulate fluids (liquids, gases, or vapors) in various
engineering systems. Examples include pumps, turbines, compressors, and fans.
2. Fluid
A substance that can flow and does not have a fixed shape, including liquids and gases. Fluids
conform to the boundaries of their container.
3. Types of Fluid Machines
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Hydraulic Machines: Operate with liquids (e.g., water turbines, hydraulic pumps).
Pneumatic Machines: Operate with gases or air (e.g., air compressors, blowers).
4. Pump
A device that transfers energy to a fluid, increasing its pressure or velocity to move it through a
system.
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Centrifugal Pump: Uses a rotating impeller to impart kinetic energy to the fluid.
Reciprocating Pump: Uses a piston or diaphragm for fluid displacement.
5. Turbine
A machine that extracts energy from a moving fluid (liquid or gas) and converts it into
mechanical energy.
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Impulse Turbine: Converts fluid energy into kinetic energy using a nozzle, such as in a
Pelton wheel.
Reaction Turbine: Partially relies on fluid pressure and kinetic energy, such as in a
Francis turbine.
6. Compressor
A device that increases the pressure of a gas by reducing its volume.
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Axial Compressor: Uses rotating blades to compress gas in stages along an axis.
Centrifugal Compressor: Uses a rotating impeller to transfer energy to the gas.
7. Fan
A machine that creates airflow by using rotating blades or impellers to increase pressure.
8. Cavitation
The formation and collapse of vapor bubbles in a liquid due to local pressure dropping below the
vapor pressure, potentially damaging fluid machinery.
9. Head
A measure of energy per unit weight of a fluid, expressed in terms of height (meters or feet).
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Static Head: The height difference due to pressure.
Dynamic Head: Related to the velocity of the fluid.
10. Efficiency
The ratio of useful work output to energy input.
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Hydraulic Efficiency: Related to fluid energy.
Mechanical Efficiency: Deals with mechanical components' performance.
Overall Efficiency: Combines hydraulic, mechanical, and volumetric efficiencies.
11. Flow Rate (Q)
The volume of fluid passing through a section per unit of time, typically expressed in cubic
meters per second (m³/s) or liters per second (L/s).
12. Velocity Triangle
A diagram showing the relationship between the absolute, relative, and blade velocities in fluid
machinery (commonly used in turbines and compressors).
13. Reynolds Number (Re)
A dimensionless number used to predict flow characteristics, whether laminar or turbulent, in
fluid systems.
14. Specific Speed (Ns)
A dimensionless parameter used to characterize pumps or turbines based on their speed, flow
rate, and head.
15. Net Positive Suction Head (NPSH)
The absolute pressure at the pump suction required to avoid cavitation.
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NPSH Available (NPSHa): Calculated from the system.
NPSH Required (NPSHr): Specified by the pump manufacturer.
16. Bernoulli’s Equation
A principle that relates pressure, velocity, and elevation in a moving fluid, assuming negligible
friction.
17. Power (P)
The work done or energy transferred per unit of time, usually expressed in watts (W) or kilowatts
(kW).
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Hydraulic Power: Energy associated with the fluid movement.
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Brake Power: Power delivered by the engine or motor to the pump/turbine shaft.
18. Flow Regimes
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Laminar Flow: Smooth, orderly fluid motion (Re < 2000).
Turbulent Flow: Chaotic fluid motion (Re > 4000).
19. Dynamic Pressure
The pressure due to the fluid's velocity, given by ½ ρv2 where ρ\rhoρ is density and v is velocity.
20. Viscosity
A fluid's resistance to flow, measured in units like Pascal-seconds (Pa·s).