97
Chapter 3
Fans
© Springer Science+Business Media Dordrecht 2015
E. Dick, Fundamentals of Turbomachines, Fluid Mechanics and Its Applications 109,
DOI 10.1007/978-94-017-9627-9_3
Abstract Fans are machines to move air or a similar gas. With regard to types,
there are axial, radial and mixed-flow fans. Principles for the analysis of axial turbomachines have been elaborated in the foregoing chapters, but for radial machines,
only a limited theory has been developed. The fan chapter is therefore also used to
complete the theory for power receiving radial machines. It is appropriate to do this
with the fan. Firstly, the fan is a simple turbomachine. Further, there are various
rotor shapes with radial fans (forward curved blades, radial end blades and backward curved blades), as opposed to radial pumps (only backward curved blades)
and radial compressors (radial end and backward curved blades). In this chapter,
we also discuss the performance evaluation of radial fans, rotor design choices with
radial fans and performance of axial and mixed-flow fans.
3.1 Fan Aplications and Fan Types
3.1.1 Fan Applications
A fan is a machine that moves air or a similar gas, producing a small pressure rise. A
general criterion is that the total pressure ratio should not exceed 1.25 ( p 02 /p 01 < 1.25).
The fluid density then only changes a little. The fluid may be considered, with a
good approximation, at constant density equal to the arithmetic average of the inlet
and outlet values (a justification for the application of the average density is given
in Chap. 4: compressible fluids). With total pressure ratios exceeding 2 ( p 02 /p 01 > 2),
the term compressor is used. It refers to a machine intended to increase the pressure of a compressible fluid. The term blower is typically used for intermediate
machines (1.25 < p 02 /p 01 < 2), but refers also to any device that blows air with rather
elevated velocity (snow blower, leaf blower, hot air blower). So, the term blower
may refer to a fan with a high work input or a compressor with a low work input,
mainly producing kinetic energy. There is no specific theory for blowers. Depending on the case, a blower is analysed as a fan (constant density) or as a compressor
(variable density).
Fans are primarily applied to exhaust polluted air from industrial spaces, office
buildings and homes. Fresh air supply, in some cases through an air conditioning
Chapter 3
Fans
© Springer Science+Business Media Dordrecht 2015
E. Dick, Fundamentals of Turbomachines, Fluid Mechanics and Its Applications 109,
DOI 10.1007/978-94-017-9627-9_3
Abstract Fans are machines to move air or a similar gas. With regard to types,
there are axial, radial and mixed-flow fans. Principles for the analysis of axial turbomachines have been elaborated in the foregoing chapters, but for radial machines,
only a limited theory has been developed. The fan chapter is therefore also used to
complete the theory for power receiving radial machines. It is appropriate to do this
with the fan. Firstly, the fan is a simple turbomachine. Further, there are various
rotor shapes with radial fans (forward curved blades, radial end blades and backward curved blades), as opposed to radial pumps (only backward curved blades)
and radial compressors (radial end and backward curved blades). In this chapter,
we also discuss the performance evaluation of radial fans, rotor design choices with
radial fans and performance of axial and mixed-flow fans.
3.1 Fan Aplications and Fan Types
3.1.1 Fan Applications
A fan is a machine that moves air or a similar gas, producing a small pressure rise. A
general criterion is that the total pressure ratio should not exceed 1.25 ( p 02 /p 01 < 1.25).
The fluid density then only changes a little. The fluid may be considered, with a
good approximation, at constant density equal to the arithmetic average of the inlet
and outlet values (a justification for the application of the average density is given
in Chap. 4: compressible fluids). With total pressure ratios exceeding 2 ( p 02 /p 01 > 2),
the term compressor is used. It refers to a machine intended to increase the pressure of a compressible fluid. The term blower is typically used for intermediate
machines (1.25 < p 02 /p 01 < 2), but refers also to any device that blows air with rather
elevated velocity (snow blower, leaf blower, hot air blower). So, the term blower
may refer to a fan with a high work input or a compressor with a low work input,
mainly producing kinetic energy. There is no specific theory for blowers. Depending on the case, a blower is analysed as a fan (constant density) or as a compressor
(variable density).
Fans are primarily applied to exhaust polluted air from industrial spaces, office
buildings and homes. Fresh air supply, in some cases through an air conditioning