Note: Readers of the Editor’s free email newsletter will have read this news the week it was announced. . It’s free!
Humans are not alone in taking the path of least resistance. Air in motion also prefers the easiest route. If a fan is optimally designed, structure-related air paths and the aerodynamic flow of air also fall into place.
The various aerodynamic effects, however, often superimpose each other.
A fan that is not designed to deal with this forces air to take "detours".
This results in reduced efficiency with drastically increased running noise.
Only a design that offers the air a "straight" route again can ensure efficient operation.
In the process, the straight route could well involve taking aerodynamic curves, whereby it is important that the breaking-up of currents and formation of vortices are reliably prevented.
Ventilation means that air is moved.
This necessitates an increase in pressure to force a particular amount of a gaseous medium per unit of time through the device to be air-conditioned.
Energy must be applied to the air to generate this rise in pressure.
There are basically two methods to achieve this: one involves centrifugal acceleration and the resulting increase in gas molecule velocity, the other works by "displacing" or "scooping" the air by means of suitably shaped fan blades.
The design, rotational speed, pressure, and the amount of air necessary determine the optimum fan principle.
Both forms of energy provision are used in practically all fan designs.
Radial and axial fans work best with one particular method while diagonal fans combine both of them.
The diagonal technology is by no means new for Papst.
This fan manufacturer from the Black Forest was already pointing out the advantages of this fan principle 10 years ago and has successfully implemented it, mainly in segments with demanding electronic cooling.
During initial diagonal development, the fan dimensions (at 200 and 172mm) were of central concern.
The fan specialist however, steadily continued development and can now present the first square serial production diagonal fan with an edge length of only 127mm.
The air sucked in by the fan always flows towards the intake from all directions of the surrounding space.
This is also true with greater feed performance.
In the process, the external housing adopts the function of an intake funnel; the inflow edges are thus rounded off.
Axial fans expel the air in the direction of the axis at the front of the fan.
This is carried out by the fan's profiled scoops that (in effect) push the air through the fan.
This changes drastically outside the optimum operating point, ie with increasing pressure: "substitution extraction" becomes increasingly superimposed by extraction through the centrifugal acceleration of gas molecules, as additional energy can only be supplied through an increase in the rotational speed.
The scoop geometry, and its substitution extraction, optimised for a particular rotational speed is thus overstretched.
Extraction by means of centrifugal acceleration of the gas molecules becomes increasingly important with rising backpressure.
As a result of this, the airflow of axial fans is increasingly replaced in the rear area of the fan wheel near the axis, and forced outwards.
Replacement vortices are formed instead in the area of the replaced flow near the fan axis.
These generate turbulences and thus noise.
In addition, this vortical zone is no longer available for any further supply of energy.
The efficiency of the fan drops and noise levels rise with increasing back pressure.
A purely axial fan can no longer be operated efficiently in the operating range of this vortical formation.
Papst has converted the above-mentioned disadvantage into an advantage by means of a suitable fan design.
With a fan geometry adapted to these flow conditions, both forms of energy supply (centrifugal acceleration and displacement) can be used simultaneously and largely free of loss.
This represents the birth of the principle of the diagonal fan.
The most important feature of a diagonal fan is its conical rotor hub.
Here too, the air is largely sucked in axially.
The hub, designed as a cone envelope, has a small cross-section in the inlet area.
The diameter increases towards the front.
The resultant greater peripheral velocity of the scoop tips at the outlet also means that there is a greater centrifugal acceleration of the air.
The flow path is thus adapted to the aerodynamic processes.
The pressure gradient that can be achieved is greater.
The formation of vortices is largely prevented by the cone shape of the fan wheel, and this fan is very quiet with a high pressure gradient.
The geometry of a fan hub cone adapted to the operating point and diameter is not the only aspect that is vital for optimum fan design the geometry of the scoop profile is also of particular importance.
The shape of the scoops must be evenly adapted across the radius of the changing, aerodynamic conditions.
The peripheral velocity of the scoops is low near the axis.
With increasing diameter, the peripheral velocity increases towards the outside.
With the lower peripheral velocity at the hub, the scoops must be more twisted in order to be able to accelerate the air sufficiently.
This twisting must become less towards the outside to prevent air replacements and the formation of vortices.
This is also the case in the aerospace industry: a slower glider has strongly twisted aerofoils, whereas a fast jet flies with relatively flat aerofoils.
Air moved by means of the scoop profile and centrifugal acceleration leaves the fan on a diagonal path transversely towards the exterior.
The main problem in the construction of such fans is the complex interaction between the aerodynamic processes of the two types of energy supply.
Papst has developed a wide-ranging calculation process that together with the company's many years' of experience in fan geometry has allowed this interaction to be optimised.
The diagonal principle for fans is not merely an end in itself, but meets practical demands.
Modern electronics operate with ever-smaller components and more highly integrated circuits.
Thus on the one hand the power density and dissipated energy rise, while on the other hand increasing numbers of components are employed within device sizes that are unchanged, hindering the flow of cooling air - a thankless development in two ways.
With more waste heat there is an inevitable rise in the pressure gradient as a result of "component obstacles", while the potential fan-specific ventilating power decreases.
Larger fans are often not applicable because of device sizes that remain unchanged or are even becoming smaller.
The diagonal fan offers a solution here.
The same size can transport more air with a higher pressure gradient.
Operating noise remains well below that of a conventional axial fan of the same power.
Moreover, the basic design of the cone-shaped fan wheel expanding towards the rear also permits the use of larger drive motors.
Thus, universal properties as provided for example by Papst's VarioPro motor with its integrated programmable control electronics, are also available in diagonal fans.
The integrated main control system, consisting of the microcontroller and EEPROM, allows the definition of minimum operating tolerances, prevents drift and provides maximum flexibility through digital control.
Aerodynamic efficiency of the defined fan dimensions remains unchanged.
As the flow of air only exits diagonally and is not deflected by 90 degrees, as is the case with radial fans, the arrangement of the components in the device is unproblematic.
In most cases only small modifications are necessary to convert from an axial to a diagonal fan.
• .
• Email this news to a colleague
• Contact details for ebm-papst Automotive and Drives (UK)
• Other news from ebm-papst Automotive and Drives (UK)
• 
Our RSS feed for news from ebm-papst Automotive and Drives (UK)
• Other news in Fans and Blowers
• Our RSS feed for Fans and Blowers news
• Electronicstalk Home Page
