Heat generated at the motor and bearings will conduct everywhere it can--into the frame of the hard drive, yes, but also into the platters, and from there into the air in the drive and then to the chassis. Sure, it's a less direct route, but it still transfers that way. The amount of air resistance in a drive is very small in any case--the platters are quite smooth.The part about heat transfer does not make sense to me. Without air of any type, there is no friction and thus no heat generated by the platters. The only heat would then be that coming from the motor, which is already attached to the steel case for heat dissipation from outside air. Helium seems to do well in heat transfer, but the steel case should be able to dissipate the motor's heat. I guess its a bonus to help the drive stay cool, but I doubt it's really needed unless the spindle is transferring heat from the motor to the platters. I'd be interested to know if that actually happens.
Even if you ignore the necessity of a gas in the drive (to let the heads fly over the platters), maintaining a vacuum for years under hundreds or thousands of thermal cycles is a challenge. Even if you engineer it so that the only penetrations are for electrical connections, it's still a matter of percentages--some (very tiny) amount is going to leak.
Air *is* a good insulator...when it's not moving. A vacuum, on the other hand, is an *excellent* insulator.plus isn't air an insulator?
Air is decent at transferring heat...when it's moving (as in an HVAC system).Nope, air is a decent conductor of thermal energy (HVAC guy here). It just depends on temperature differentials.