Thermal and EMC Simulation to Design Hard Drive

Pace Micro Technology used thermal and electromagnetic compatibility software to reduce temperature of a new set-top box by 5%, substantially increasing disk drive reliability and life. Alan Bate, senior design engineer for Pace Micro, used Flotherm software from Flomerics to simulate the thermal performance of the case. He used the simulation results to trade off the thermal performance of different heat sink geometries and materials and venting arrangements against their cost. Meanwhile, Bate used generic EMC design guidelines, developed by Araf Suhail, consultant EMC engineer for Pace, out of Flomerics Flo/EMC software to ensure that the mechanical design kept emissions below the level required to maintain electromagnetic compatibility.

Before beginning the use of simulation, Bate validated Flotherm results against physical testing and demonstrated its ability to predict internal enclosure temperatures within one half degree Centigrade. Because temperature is critical to the life of the hard drive, the fan is positioned to blast the hard drive directly while exhaust air is used to cool other electronic components. Bate developed a special cowling for this model designed to reduce hard drive temperature by augmenting the air flow around the hard drive and extracting heat from the sides of the drive.

In order to validate and optimize his design, he created a Flotherm model that allowed him to visualize airflow and temperature profiles inside the enclosure and predict the temperature of the hard drive body and air. In particular the cowling provides a thermal path from the sides of the drive to remove heat generated by the motor and air friction produced by the magnetic disk spinning at 7200 rpm. The heat is then transferred into the fan air stream using a specialized fin arrangement, which was developed using the thermal simulation software. The relative performance of aluminum plate versus mild steel as the cowling material was also carried out.

In evaluating the thermal impact of venting arrangements, Bate paid close attention to the guidelines developed by Suhail in order to assure that the resulting design also met EMC requirements. Suhail had previously evaluated generic metallic enclosures of the type used in nearly all of Pace Micro’s products using Flo/EMC to predict the electromagnetic interference (EMI) generated by the design and diagnose its causes. These simulations provided him with an understanding of how electromagnetic resonances are generated within the set-top box enclosures. He then developed design methods to reduce the magnitude of these resonances.