#### Grench

##### Forum Addict!

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- Oct 3, 2008

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IFF you're going to try something like that, may I recommend having it mounted high in the non-wired hinge side void (where Pandora has light pipes) and blowing -in- such that the SD card slots become the exit vent?

If the fan pushes -in- 1 mole of 21*C air and the air picks up enough energy to move to 100*C, a considerably larger volume of air will exit than enter.

1 mole of air weighs ~28.8 grams.

1 mole of air at 1 atmosphere and 21*C is ~24 liters (volume per mole in).

1 mole of air at SLC is ~24.5 liters.

1 mole of air at 1 atmosphere and 100*C is ~30.6 liters (volume per mole out).

Air Specific heat = 1.01J/gC

Changing air from 21*C to 100*C for 1g of air = (1*79)/1.01 = 78.2 Joules transferred per gram of air in.

Assuming the system needs to shed 3 Watts per hour, 3 Watt-hours ~ 10800 Joules.

10800/78.2 = 138.1 g of air per hour.

138.1 g ~ 4.79 moles ~ 115 liters per hour ~ 2 liters per minute in.

It wouldn't have to blow all that much air in to be effective. If you're going to consider this, be sure to have someone else run the numbers. What I did above is very back of the envelope and doesn't take into account any of the other methods for the heat to get out.

Boiling point of water won't melt the solder on the chips. I considered the above a 'worst case' scenario.

Yes, I am using * as a degree marker since the US QWERTY keyboard I'm on does not have the little degree circle symbol and I'm not interested in looking it up to type in by code a dozen times.

OK, it took me a bit to find it, but it looks like the max temp on the OMAP 5 is 85*C. Assuming good mixing and relatively slow air, the air exiting then could be around 75*C. Yes, that is still hot. No, I'm not overly concerned - and I wasn't concerned at 100*C. This is simply a math exercise.

Changing air from 21*C to 75*C for 1g of air = (1*64)/1.01 = 63.36 Joules transferred per gram of air in.

10800/63.36 = 170.44 g of air per hour.

170.44 g ~ 5.9 moles ~ 142 liters per hour ~ 2.37 liters per minute in.

For perspective, humans at rest inhale about 6-8 liters per minute, roughly 400-500ml per breath, 15 breaths per minute (then exhale a bit more as it warms and adds CO2).

All better?