Stage Loading is a measure of the load on a
turbomachinery
Turbomachinery, in mechanical engineering, describes machines that transfer energy between a Rotor (electric), rotor and a fluid, including both turbines and gas compressor, compressors. While a turbine transfers energy from a fluid to a rotor, ...
stage, be it a part of a
compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Many compressors can be staged, that is, the gas is compressed several times in steps o ...
,
fan or
turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical ...
.
The parameter, which is non-dimensional, is defined as:
where:
Imperial Units
The imperial system of units, imperial system or imperial units (also known as British Imperial or Exchequer Standards of 1826) is the system of units first defined in the British Weights and Measures Act 1824 and continued to be developed thr ...
(SI Units)
acceleration of gravity ft/s/s (1.0)
mechanical equivalent of heat ft.lb/(s.hp) (1.0)
change in specific enthalpy over stage hp.s/lb (KW.s/Kg)
peripheral blade speed ft/s (m/s)
Average stage loading has a very similar definition, where the number of stages, n, within the compressor, fan or turbine is used to provide an average value:
In this case the change in
enthalpy
Enthalpy () is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant extern ...
is across the whole unit, not just a stage. Similarly, the blade speed used is a mean for the whole device.
The above equation shows that if blade speed cannot be increased for, say, mechanical or
aerodynamic
Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...
reasons, the number of stages has to be increased to get the
average stage loading back to an acceptable level, to obtain a satisfactory level of efficiency. The ideal average stage loading for a turbine is about 1.8.
Turbomachinery