[EN 12792:2003, 166]:
there are five main types of a fan are defined according the fluid path within the impeller

• centrifugal fan

[EN 12792:2003, 166]:
fan in which the air enters the impeller with a substantially axial direction and leaves it in a direction substantially parallel to a radial plane. The impeller is defined as ‘backward curved’ or ‘inclined’, ‘radial’ or forward curved’ depending on whether the outward direction of the blade at the periphery is backward, radial or forward, relative to the direction of the rotation.

[AIVC, Air infiltration and ventilation glossary, 1992]:
a fan in which the air is turned from parallel to the axis of rotation on entry to a direction tangential to the are described by the tips of the rotating blades or vanes.

• axial flow fan

[EN 12792:2003, 166]:
fan in which the air enters and leaves the impeller axial to the fan.

[AIVC, Air infiltration and ventilation glossary, 1992]:
a fan in which the airflow, at all times, from entry to exit is predominately parallel to the axis of rotation.

• contra rotating fan

[EN 12792:2003, 166]:
axial flow fan which has two impellers arranged in series and rotating in opposite direction.

• reversible axial flow fan

[EN 12792:2003, 166]:
axial flow fan which is specially designed to rotate in either direction.

• propeller fan.

[EN 12792:2003, 166]:
fan having an impeller with a small number of broad blades of uniform material, thickness and designed to operate in an orifice.

• plate mounted axial flow fan

[EN 12792:2003, 166]:
axial fan mounted in an orifice or spigot.

• bifurcated fan

[EN 12792:2003, 166]:
fan where the direct drive motor is separated from the air stream.