Today, elec­tronics cooling is largely based on axial compact fans, partic­u­larly because they are easy to inte­grate and offer high air flow rates due to their design. However, “normal” axial compact fans reach their limits when increas­ingly powerful elec­tronics need to be accom­mo­dated in the same space or have an even more compact construc­tion, because the aero­dy­namic resis­tances increase with increasing device compact­ness. To increase the cooling capacity, you could there­fore simply connect two axial compact fans in series – running in the same or in oppo­site direc­tions. In prin­ciple, this results in the required air perfor­mance. However, this solu­tion requires more instal­la­tion space and has disad­van­tages in terms of mechan­ical vibra­tions. In addi­tion, the fans can have an adverse effect on each other in terms of aero­dy­namics, which can result, for example, in increased noise.

Opti­mized fan pair cools high-perfor­mance
elec­tronics

For a power fan that delivers more power and is still as compact as possible, ebm-papst has there­fore adopted a new approach: with the AxiTwin 100, the motor and fan special­ists, in close coop­er­a­tion with a company from the telecom­mu­ni­ca­tions sector, have devel­oped a compact fan that has been designed as a contra-rotating system. With an edge dimen­sion of 10 cm and a depth of 9 cm, four of these fans fit into a 19″ rack, as is typi­cally used for cooling in blade servers.

Up to 536 m³/h air perfor­mance at up to 1,300 Pa pres­sure. (Graphic | ebm-papst)

This guar­an­tees reli­able heat dissi­pa­tion even when used with tightly packed elec­tronics, as each fan delivers up to 536 m³ of air per hour and a maximum static pres­sure increase of up to 1,300 Pa. In doing so, the new fan for elec­tronics cooling does not just combine two indi­vidual fans, but uses a newly devel­oped flow geom­etry for the two consec­u­tive blade rows which takes into account the aero­dy­namic oper­ating point, thus numer­i­cally opti­mizing both at the same time.

Second-stage fan impeller: turbu­lence and swirl are reduced. The blade’s extreme sickle shape also contributes to noise reduc­tion; the compar­a­tively small surface of the blades increases effi­ciency. (Graphic | ebm-papst)

The fan then consists of two rotors that are connected via an inno­v­a­tive flange. The first rotor, with its five blades, is largely respon­sible for the air flow, while the second three-blade rotor is primarily respon­sible for the pres­sure increase. Around two thirds of the pres­sure is gener­ated in the second stage. The second stage also reduces turbu­lence as a result of its sophis­ti­cated aero­dy­namics with its extremely sickle-shaped blades. It also contributes to noise reduc­tion because the compar­a­tively small surfaces of the blades increase its effi­ciency.

Noise Reduc­tion with flange

A major advan­tage of the contra-rotating fan prin­ciple is the reduc­tion of the speed compo­nent of the air flow in the circum­fer­en­tial direc­tion. In this design, the flange between the two stages is not just a support struc­ture or spacer, but a patented feat of engi­neering. It links both stages vibra­tionally in such a way that each stage atten­u­ates the vibra­tions of the other. The double-sided bearing tube, which connects the two stages together, and the inte­grated guide blades mean that the design is extremely compact.

The flange is more than a spacer. Thanks to its opti­mized geom­etry, it reduces the gener­a­tion of vortices and noise at the second stage. (Graphic | ebm-papst)

The geom­etry of the flange guide blades was also deter­mined using the simu­lated flow field between the two rotors at the intended device oper­ating point. This mini­mizes vortex gener­a­tion at the guide blades and inter­ac­tion of this vortex with the second row of blades, thus contributing to noise reduc­tion. The flange is made of aluminum, which ensures high rigidity and at the same time enables good heat dissi­pa­tion.

Powerful EC drives with new elec­tronics

The driving forces behind the fan impellers are energy-effi­cient Green­Tech EC drives with a motor power of up to 180 W. The three-phase motors are also very compact, work with a high level of effi­ciency both in normal partial-load oper­a­tion and at full load, and are designed for contin­uous oper­a­tion thanks to elec­tronic commu­ta­tion. The newly devel­oped 300-W elec­tronics also have a lot to offer. They have not been inte­grated into the motor, but have been installed in the corners of the housing for even better heat dissi­pa­tion and there­fore an even longer service life. This means that the surface of the flange can contribute to cooling them too.

The indi­vidual stages only require a small connec­tion board on the motor for the winding. Stan­dard­ized signal inputs such as PWM input, analog control input, as well as tach/alarm output signals, can be inte­grated indi­vid­u­ally as required. In the stan­dard version, the fan has a PWM input and an open collector tach output. Optional humidity protec­tion is also avail­able for demanding envi­ron­ments.

The flange links both stages vibra­tionally in such a way that each stage atten­u­ates the other. (Graphic | ebm-papst)

The two-stage design of the contra-rotating system also ensures the neces­sary redun­dancy for appli­ca­tions with crit­ical 24/7 avail­ability require­ments, such as computers at major banks. If a single rotor fails, there will not be any back­flow as the other rotor will continue to rotate. Each stage can be controlled sepa­rately, but always in coor­di­na­tion with one another. The speed ratio is defined, but it can be altered sepa­rately in indi­vidual cases, for example in order to opti­mize effi­ciency or reduce noise levels in certain ranges of the power level.

The AxiTwin 100 is an extremely powerful compact fan with small instal­la­tion dimen­sions for appli­ca­tions where a lot of computing power needs to be cooled in a small space. Its range of appli­ca­tions extends across all cutting-edge tech­nolo­gies, from rack cooling for blade servers and extremely diverse infor­ma­tion tech­nology solu­tions to super computers in the field of blockchain tech­nology. Appli­ca­tion-specific modi­fi­ca­tions are also possible, as the design can be adapted to other sizes.