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Re: [Phys-l] thermo question



On 03/03/2008 10:44 AM, I wrote:

9) One fun thing to think about is that the SVP of water is
a strong function of temperature. As a relevant example,
70% RH at 70 F corresponds to a dewpoint of 59.76 F as you
can verify at
http://einstein.atmos.colostate.edu/~mcnoldy/Humidity.html

Therefore it seems to me you could have essentially infinite
buffer capacity if you are in equilibrium with a puddle of
water at 59.76 F.

Let me clarify: You want the humidity to be in equilibrium with
the puddle, but of course you don't want the temperature of the
payload to be in equilibrium with the puddle. So you need a
heat exchanger:


________________ ______________
| | | |
| | | |
| | | |
| |___________________| |
| --> ___________________ --> |
| <-- ___________________ <-- |
| | | |
| | |wwwwwwwwwwww|
|______________| |wwwwwwwwwwww|

T1 counterflow T2
PP1 heat PP2
exchanger


The point is that the heat exchanger exchanger exchanges heat
but *not* humidity, so that partial pressures are equal
(PP1=PP2) even though the temperatures are not equal (T1>T2).

========================

BTW, another amusing use of a counterflow heat exchanger:
http://oikos.com/esb/49/gfx.html

An example of basic physics applied to real life.