V
Vanguard
w_tom said:
kony was wondering where the substituted molecules were going (and said
they don't just disappear which is correct - but they are no longer
within the volume of air under discussion). Are you saying the
following statement is false?
"To see why humid air is less dense than dry air, we need to turn to one
of the laws of nature the Italian physicist Amadeo Avogadro discovered
in the early 1800s. In simple terms, he found that a fixed volume of
gas, say one cubic meter, at the same temperature and pressure, would
always have the same number of molecules no matter what gas is in the
container."
(Also see http://scienceworld.wolfram.com/biography/Avogadro.html.)
See http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/idegas.html#c4,
under "Molecular Constants". The Ideal Gas Law is "ideal" because it
neglects the energy levels in each shell and the number of shells for
different atoms and, as you say, elasticity changes at severely drastic
temperatures (which are not encountered, anyway). Where do you see the
Ideal Gas Law being violated when X number of nitrogen molecules are
removed and replaced with an equal X number of hydrogen atoms so the
same constant number of molecules is maintained within the same volume
(under the same pressure and temperature)?
Ideal Gas Law is: PV = NkT
where P is pressure and V is volume. These are constant in this
discussion because the focus was on how density might affect thermal
transfer rate, not how pressure or temperature affect density but rather
how changing the constituent atom types within a gas mix can alter its
density due to the different atomic masses but the total number of
molecules does not change. k = R/A where R is the universal gas
constant and A is Avagadro's Number (also a constant). So obviously N,
the number of molecules, cannot change unless you change pressure,
volume, or temperature.
With temperature and volume as constant, and if you remove N nitrogen
molecules and are trying to maintain the same total pressure (regarding
your argument about partial pressures), you would have to add the same
number of hydrogen molecules to maintain the same pressure as before.
So you swap some nitrogen molecules with hydrogen molecules to keep the
pressure the same but hydrogen has a lower atomic mass than nitrogen so
the total mass of that constant volume got decreased, and if mass goes
down in the same volume then density went down. So you start with:
PV = NkT
where V, k, and T are constant, so:
P ~ N
With 78% of the atmosphere being nitrogen, 21% oxygen, 0.93% argon, and
0.07% trace gases, you have:
P ~ 78% N (for nitrogen)
+ 21% N (oxygen)
+ 1% N (for argon and trace gases)
= 100% N
If you wanted to make 10% of the gas mixture be water molecules, you'll
end up with over 100% of the maximum molecules allowed within the fixed
volume at the constant pressure that you are trying to maintain (for
your partial pressures rule) and at the same temperature. So you'll
have to take out 10% of some other molecules out to put in the 10% of
water molecules:
P ~ 73% N (for nitrogen, reduced 5%)
+ 16% N (for oxygen, reduced 5%)
+ 1% N (for argon and trace gases)
+ 10% N (for the added water molecules)
= 100% N
Got any established physics formulae to backup your statements? So far
what the articles said and what I've said still comply with your Ideal
Gas Law.
There's a dimension missing in that spec. How could that relate to the
thermal transfer *rate* (to actually get *rid* of the heat)? A 1 C per
1 W spec would mean a 100W source would produce 100 C for a temperature
yet you know dunking the heatsink in liquid nitrogen won't have the
heatsink measuring 100 C. Also, the CPU would have an equivalent
rating: if you don't cool it then the die will reach some maximum
temperature (if it survives) under static operating conditions for the
number of watts consumed by the processor, but obviously that is not the
state under which you want to operate the processor because that
temperature level for that amount of power consumption is destructive.
Hold on while I go look at some heatsink specs ...
.... okay, found http://www.thermaltake.com/coolers/volcano/rs/a1889a.htm
which shows the graph that you are probably talking about which is the
*rise* in C over *ambient* temperature for the number of watts absorbed.
The Athlon XP 3200+ Barton produces 77 watts (so it is a bit outside the
graph). With linear interpolation (looks like 0.5 C per watt for this
fan-heatsink-compound combo), the 77W CPU would have its die temperature
supposedly run about 41 C ABOVE ambient (case) temperature. So with a
case (or system) temperature of 38 C (the 100 F that you mentioned
before), the CPU die's temperature would be around 79 C (still under the
critical 85 C die temperature maximum but getting damn close).
Understand that this is not a measurement for just one cooling
component. It is the effective cooling for the thermal compound they
must provide (to know its transfer characteristics), the heatsink, and
the specific fan they have matched with that heatsink (with no airflow
restrictions causing back pressure around the fan). Use a fan with a
higher CFM (with more noise), lap the mating CPU and heatsink surfaces,
and/or replace Artic Silver for whatever thermal compound they provide
and that graph changes. Since that rating is for a rise in temperature
ABOVE the ambient temperature, it already accounts for increased
temperatures. However, I'm pretty sure they also quote that rating
based on expected environmental conditions, like the computer isn't
submerged in liquid nitrogen.