Re: 760CD Keyboard Tilt

[Ted Frederick <tedf@cadence.com>]

Heat transfer seminar: Lesson #1:

Believe it or not, having the system lie flat on the desk, lap, table, etc.
is a far better thermal configuration than having a small air gap under the
system.

Why?

Well (unless there is a fan or "significant" free convection) conduction
through a solid material (even plastic or wood) is a better cooling method
than a small air gap under the system.  Remember, "still air" is the best
insulator on Earth (k=0.028 W/m*K).  By comparison, plastic (another good
insulator) has 
k=0.5 W/m*K (~200X more thermally conductive) That's where fiberglass
insulation gets its "R-value", not from the fiberglass but from the air
pockets the fiberglass forms.

The moral of the story is: I doubt that there is enough convection under the
system when the 755's legs are extended that provides the same amount of
heat transport than when the system lies flat on a table or desk.  Leave it
flat, the system will run cooler. (This is probably why they designed the
keyboard to tilt without lifting the system off the table)

(Old Theses die hard...)

Regards,

-Ted

At 02:22 PM 10/27/95 -0700, you wrote:
>> When the cover is lifted the keyboard detaches itself away from
>> the body of the computor at the screen end and is raised at an
>> angle supported by two spring metal clips clearly visible from
>> the outside. The base of the computor continues to lie flat on
>> the table.  When I saw this I wondered about the heat. In the
>> case of the 75x series, when the two "legs" are extended the
>> whole computor is slanted at an angle which provides a space for
>> heat dissipation. Here there is no such space since the base
>> remains horizontal.
>
>	On my 750C, it gets pretty hot under there, but...
>
>	I almost never use the little legs.  Not that I don't like
>them, but I just forget about them and don't go through the trouble
>of opening them up.
>