New-Tech Europe Magazine | October 2018

omniCOOL: Introducing a unique approach to fan design

Jeff Smoot, VP of Application Engineering at CUI Inc.

The rise of IoT and Cloud data services has put data centers, housing powerful servers and storage devices at the forefront of the electronics industry. It is also a well-known fact that these data centers generate enormous amounts of heat, which has to be removed from critical equipment—a task that usually starts with a fan. The same holds true for other applications that we depend on. Products such as home computers, household appliances and industrial machinery will only function reliably if they are kept within a specified temperature range. In other words, fans play an incredibly important role in modern life. The sleeve bearing vs ball bearing trade-off At the core of every fan is the bearing. This critical component enables the fan rotor to turn and is key in determining a fan’s operational life, making it crucial for

designers and engineers to choose the right fan bearing to cool their application. Traditionally, this choice has been between a fan with a sleeve bearing and one with a ball bearing. Both have their strengths but picking one over the other will usually result in a trade-off somewhere along the line. This is why CUI has taken a new approach to bearing design that bridges the gap between ball and sleeve versions. However, before we look at how this new fan design works, we must first review the benefits and shortcomings of the more traditional sleeve and ball bearing types. Understanding sleeve bearings The shaft at the center of sleeve bearing fans spins inside a “sleeve-like” cylinder with a layer of oil lining the sleeve that enables the shaft to turn. The sleeve’s

role is to hold the rotor in the right position, making sure it is always the correct distance from the motor stator (Figure 1). Sleeve bearings are the more cost-effective of the two traditional designs and will hold-up better in applications that experience shock and vibration. However, its design does hold several drawbacks. To minimize rotor wobble, the sleeve needs to fit snugly around the shaft, but the greater this contact area is, the more friction you have to overcome and the longer it takes to start the fan. This means more energy is required, both to start the fan and to keep it spinning. Another issue with the sleeve design is the weight of the rotor is supported solely by the shaft in the sleeve. Consequently, as it rotates, it gradually wears down the inside of the bearing, distorting the shape of the bore. If your fan is always used in the same orientation, an oval- shaped sleeve cross-section will begin to

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