The ideal gas law says that pV/T = constant!! So T absolute follows
pressure (p). Just make the proper calculations!
J.W.
On 17.06.2024 23:49, Jonathan Berry wrote:
I'm not sure what p=1 means, the initial pressure whatever it might be??
And then you say PSI is 1/3 not 5, well 1/3 of a PSI?? But what you
say contradicts the ideal gas law which applies to gas in the pressure
and temp range I am considering.
On Mon, 17 Jun 2024 at 21:15, Jürg Wyttenbach <ju...@datamart.ch> wrote:
As said, if you start at p=1 and increase T by 100C then psi is
1/3 not 5. For 200C its 2/3 etc...
J.W.
On 17.06.2024 11:01, Jonathan Berry wrote:
Yes but I am assuming the gas is hot enough to behave according
to the ideal gas law.
And it follows that to a presst decent temp close enough as I
understand.
For my purposes it only has to be close enough.
Now to be clear what I am talking about has NOTHiNG to do with
the TOTAL pressure, rather the pressure increase with a certain
amount of added energy (thermal).
So if you add enough energy to increase temp by 100 Kelvin from
say 300 or so Kelvin the pressure increase you get will be about
5 PSI, and if you put double the energy in, especially if the gas
is Helium say (Monatomic) you increase the temp by 200 K degrees
instead to a total of say 400K (roughly) then you get 10 PSI...
But the amount that 10 PSI must push a Piston to reach go back to
0 PSI (actually, it's sea level of 14+10 so 24PSI that has to
reduce to 10 btu whatever) is twice as far as if it were just 5
(technically 19) PSI.
So double the force over double the distance (kinda, pressure
drops every millimeter but I did check every millimeter of
movement and it does work out).
So I think I'm right still.
On Mon, 17 Jun 2024 at 20:50, Jürg Wyttenbach <ju...@datamart.ch>
wrote:
Jonahan
Classically pV/T = constant.. So to keep it simple if you
increase T by 100 (starting at 273K) then the pressure does
only increase about 1/3. 373/273 about 4/3.
Further gas internal energy is defined by the Gibbs equation
that includes the entropy. Pressure is not a linear function
of added energy only T absolute follows p.
The ideal gas law only matches real physics for a certain
band of T. Never for T below evaporation point that also is
defined as an equilibrium. So a gas must have enough internal
energy to overcome the Van der Waals attractive forces to
finally behave "ideal".
J.W.
On 17.06.2024 09:07, Jonathan Berry wrote:
Jürg, the problem with that is if that is so then the
thermal capacity of the gas would need to increase as
temp increases but with say Helium it's pretty flat.
Every time I look into the math for increasing temp it is
the same, if you heat it up twice as much it needs twice as
much energy not 4 times as much!
So if you aren't disputing the temp that is created with a
given energy input, then you are disputing the pressure, but
the pressure is predicted by the Ideal gas law.
So unless you are saying that either the ideal gas law or
thermal energy goes up at the square and not in a linear
manner (feels it might have been noticed) you can't be right.
On Sun, 16 Jun 2024 at 22:06, Jürg Wyttenbach
<ju...@datamart.ch> wrote:
The energy of a gas is the sum over all kinetic
energies. So you need 4x energy input to get 2x average
speed = pressure. (comes from momentum exchange!)
J.W.
On 16.06.2024 10:27, Jonathan Berry wrote:
Hooke's law states that if you compress a spring the
increase in pressure is linear, if you compress it 1 cm
you might have 1 lb of force, if you compress it 2cm
you get 2 lb of force.
As that is double the force over double the distance it
also involved 4 times more work to compress it and 4
times more work out.
Reference:
http://labman.phys.utk.edu/phys135core/modules/m6/Hooke's%20law.html
<http://labman.phys.utk.edu/phys135core/modules/m6/Hooke's%20law.html>
"If we double the displacement, we do 4 times as much work"
Ok, but this seems problematic when the thermal
capacity of a gas is not just changed by making it
hotter so if you put in 100 Joules and increase the
temp 100 Kelvin you get about 5 PSI of pressure
increase, but if you input 200 Joules you get about a
200 Kelvin increase and a 10 PSI increase and to
compensate for this greater pressure change the piston
moves about twice as far, so twice as far with twice
the pressure again is 4 times the energy.
At 10 times more input you get 100 times more out, at
100 times more in you get 10,000 time more energy out!
The energy increase is exponential with linear increase
of temp!
If this is not so please explain why not?
If the ideal gas law wrong about pressure increase
being linear with temp?
Does the thermal capacity of a gas change more with
temp than I'm finding out when I research it?
It sure does seem the gas will like the spring with
twice the pressure move about twice as much before the
piston isn't motivated, and as such it seems some laws
of physics are wrong.
Jonathan
--
Jürg Wyttenbach
Bifangstr. 22
8910 Affoltern am Albis
+41 44 760 14 18
+41 79 246 36 06
--
Jürg Wyttenbach
Bifangstr. 22
8910 Affoltern am Albis
+41 44 760 14 18
+41 79 246 36 06
--
Jürg Wyttenbach
Bifangstr. 22
8910 Affoltern am Albis
+41 44 760 14 18
+41 79 246 36 06
--
Jürg Wyttenbach
Bifangstr. 22
8910 Affoltern am Albis
+41 44 760 14 18
+41 79 246 36 06
