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
