The types of fans: Axial fans and radial fans
Depending on the design, fans are divided into two types: The axial fan and the centrifugal fan. Both have advantages and disadvantages and are better or worse suited for certain applications.
The axial fan:
Axial fans are used wherever high volumetric flows (air volumes) are required in conjunction with low pressures (resistances that must be overcome).
The structure of the axial fan ähneln to that of an airplane propeller. It sucks the air axially (over the engine axis) and blows it out axially
The features of the axial fan:
• Low space requirement due to compact design and straight air flow. Ideal for use in direct intake and direct exhaust, for example, wall or window fans.
• Simple design, thereby cost-efficient development and production.
• Due to the steep characteristic curve of the axial fan, the system pressure is to be calculated accurately for connected components of a ventilation system.
• High speeds increase the available pressure and air volume, but also contribute significantly to noise generation.
• A control can be done, for example, via throttle valves at unchanged speed (uneconomical). Alternatively, the blades of the impeller can be adjusted on some models. The flow rate then changes at almost constant speed. Another possibility is speed control in the case of speed-controllable motors.
The radial fan:
Radial fans are characterized by höhere pres- sungen (available drücke). They are therefore bes. tens für the use in Lüftungsanlagen with upstream or downstream filter, air heater u.ä. suitable.
Radial fans are comparable to a drum. They suck in the air üover the motor axle and blow it out again offset by 90°.
The properties of the centrifugal fan:
• Grö&erer space requirement due to air deflection by 90°.
• Usually a better efficiency than axial fans.
• Due to lower circumferential speeds result in less noise than the axial fan.
• Höhere available pressures (Drücke). This makes it ideal for use in ventilation systems with upstream or downstream units such as air filter boxes, heat exchangers, etc.
• The flatter characteristic curve compared to axial fans makes a centrifugal fan more tolerant of increases in pressure drop, e.g. due to gradually fouling filters.
• A control can be achieved by means of throttle valves, the installation of bypass sections, or by speed control (for speed-controllable motors).
• A distinction is made in centrifugal fans between impellers with forward-cranked and backward-cranked blades.
• In addition to the above-mentioned designs, there are some special forms. The tangential or crossflow impeller is
The tangential or crossflow impeller is used, for example, in tower fans. A design of the centrifugal fan. It sucks the air üacross the entire width of the impeller and blows out opposite. It is mainly used in column or tower fans, in smaller air-conditioning and ventilation units, and in window fans. The advantages of the cross-flow fan are its small footprint and low noise emission. However, this fan design is not suitable for overcoming higher drücks The motor is usually located in or at the end of the impeller.
• Another special form of the radial fan is the tube radial fan. It combines a higher available pressure with the advantage of axial airflow, which allows a straight airflow path. They are available as metal (CA-series) and plastic fans (CA-V0-series).
• Furthermore, axial fans with semi-radial impellers are strongly on the rise. Axial air flow at increased pressure characterizes this special form of axial fan. Such an impeller is used, for example, in the Lineo series.
A fan is by definition a unit for the conveyance of air. Which design is used is mainly determined by the type of application. Both axial and radial designs have their advantages and disadvantages.