Aerodynamically induced power loss in hard disk drives

In this paper, the effects of rotational speed, form factor and enclosure conditions on power dissipation in hard disk drives are presented. The aerodynamically dissipated power losses by 3.5, 2.5 and 1 in. hard disks are experimentally measured using a vacuum chamber and compared to theoretical estimations. Experiments in open air without enclosure agree well with theoretical predictions; a 3.5-in. disk satisfies the turbulent model but 1 and 2.5-in. disks match the laminar one, which is inversely proportional to the half power of Reynolds number. Experiments using a single 3.5-in. disk in enclosure show that aerodynamic power loss is proportional to the second power of rotational speed and the fourth power of disk radius, which agrees with the laminar theory rather than turbulent one. It is also shown that the aerodynamic power loss is reduced as the axial gap and radial clearance of enclosure decrease.