The Accurate Reloading Forums
Physics Question for you Rocket Scientists/Reloaders
08 January 2014, 07:24
jeffeossoPhysics Question for you Rocket Scientists/Reloaders
quote:
Originally posted by mike_elmer:
Great discussion.
Question, If there were a chamber strong enough to contain all the released gasses of x amount of y powder, with none escaping, what would that pressure/volume be?
strong enough isn't the only sample ... large enough would work and or low enough starting pressure ...
funny thing.. a 55 gallon drum will COLLAPSE and made be jump, at about -20psig (-5 absolute).. catastrophically
quote:
Originally posted by mike_elmer:
Great discussion.
Question, If there were a chamber strong enough to contain all the released gasses of x amount of y powder, with none escaping, what would that pressure/volume be?
Assuming a gas yield of 1000 l/kg, if you burn 1 kg of powder confined in a volume of 1 l, you would reach a pressure of 1000 bar after the gas has cooled to room temperature.
If you assume the gases reach 1000 deg. C after combustion, you would get a pressure of app. 4660 bar before temperature is dissipated (I have no idea if the assumption of 1000 degrees is realistic).
09 January 2014, 08:18
bartsche
Dog-gone!!! I forgot my note book!

roger
Old age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone..
09 January 2014, 09:24
SR4759Jeffeosso
You need to look at the ideal gas law
PV=nRT
What do you see?
n= the number of moles of gas - not changing for this discussion
R= the ideal gas constant - constant right
V= Volume - not changing for this discussion
That only leaves P = pressure
and T= Temperature and they are on opposite sides of the expression.
quote:
Originally posted by jeffeosso:
quote:
Originally posted by Allan DeGroot:
To a physicist "Temperature" and "pressure" are essentially the same thing, an expression of energy.
not really, no.. as that would include every other expression of energy, and while inter dependent, they arent, except in the extreme, dependent variables...
in a CLOSED system, adding more energy (then its not really closed) can change temp and pressure.. as volume would be inelastic .. unless we are talking about cooking off 2g of h335 in a 55gallon drum at 0 psi absolute..
09 January 2014, 09:49
SR4759ALF
The ideal gas law does apply to the relation ship of pressure and temperature.
When
Temperature = Zero degrees Kelvin mathematically pressure HAS to be zero when the other factors are constant.
quote:
Originally posted by ALF:
Ideal gas law does not apply to the internal ballistics event. Rate of reaction and magnitude of pressure to Great.
Need to apply thermodynamic principles. It introduces the theory or concept of covolume to the gas equation.
The temperature scale is not celsius or fahrenheit but Kelvin scale.
This is important because the Kelvin scale infers a measure of the internal energy or specific heat of the combustible substances and their products.
So Alan de Groots assertion not entirely wrong.
Ideal gas law has to be substituted with the gas law of Noble and Abel ( 1860) These are the two dudes who gave us the time pressure curve, the Copper crusher and the basis of the thermodynamic foundation of internal combustion.
It is all about energy ! the whole event from start to Finnish is about energy. And then off course there are some here who still claim it's the bullet that does the killing
09 January 2014, 11:57
SR4759Perhaps you missed the basis of the issue.
A person claimed that Pressure and temperature are not directly related in the context of physics.
It is easily demonstrated via the ideal gas law the Pressure and temperature are directly related. If either one of them is zero in the ideal gas law the other has to be zero.
Try to drag the ideal gas law into another context is not part of the previous argument.
quote:
Originally posted by ALF:
Im done with arguing on the net:
Go check it for yourself.
The gas equation for a ideal gas shows a huge error in computing pressure when compared to the Noble- Abel equation !
This is fundamental to the numeric modelling of the internal combustion process in guns.
09 January 2014, 22:58
Alberta CanuckAnd now we can all remember why a simple question asked of 10 physicists in a single room can lead to 47 longer and longer answers, name calling, and amongst the more avid, maybe a couple of fist fights.

My country gal's just a moonshiner's daughter, but I love her still.
11 January 2014, 06:06
jeffeossoquote:
Originally posted by SR4759:
Jeffeosso
You need to look at the ideal gas law
PV=nRT
What do you see?
n= the number of moles of gas - not changing for this discussion
R= the ideal gas constant - constant right
V= Volume - not changing for this discussion
That only leaves P = pressure
and T= Temperature and they are on opposite sides of the expression.
quote:
Originally posted by SR4759:
When
Temperature = Zero degrees Kelvin mathematically pressure HAS to be zero when the other factors are constant.
i have to save this .. its been a rough week and i needed a laugh.. sorry its at your expense sr ...
run the math the other way, sir .. and then try to defend that 0.0000 pressure "becomes" 0 kelvin ...
then figure out what the law applies too ...
that will be fun.. and its ONE word
but, alternatively, if you can figure out how to get to 0k on a planet, in a universe with the first subatomic particle of mass or photon of light, you have to name me in the patent ...
11 January 2014, 07:45
JBrownquote:
Originally posted by SST:
Interesting thread. How fitting that the following adage was shared with me today:
"If you can't explain it well enough for your grandmother to understand, you probably don't understand it yourself."
Hence, I will not try.
Sam
OTOH: "If you can't dazzle them with brilliance, baffle them with bullshit."

Jason
"You're not hard-core, unless you live hard-core."
_______________________
Hunting in Africa is an adventure. The number of variables involved preclude the possibility of a perfect hunt. Some problems will arise. How you decide to handle them will determine how much you enjoy your hunt.
Just tell yourself, "it's all part of the adventure." Remember, if Robert Ruark had gotten upset every time problems with Harry
Selby's flat bed truck delayed the safari, Horn of the Hunter would have read like an indictment of Selby. But Ruark rolled with the punches, poured some gin, and enjoyed the adventure.
-Jason Brown
11 January 2014, 08:49
jeffeossoquote:
Originally posted by JBrown:
OTOH: "If you can't dazzle them with brilliance, baffle them with bullshit."
+1
Also, please be aware that the ideal gas law deals with a hypothetical gas. It delivers excellent approximations of the behavior of most real gases as long as you stay away from extreme conditions, i. e. very high pressures, very high temperatures, very low temperatures. It is not a universal law for real gases.
11 January 2014, 18:07
mike_elmerquote:
Originally posted by ALF:
I thought the context of this discussion has to do with Leopardtrack,s opening question relating to the combustion of a propellant in a chamber ????
If we were discussing a simple gas gun such as a air gun then yes I fully agree but we are not.
We are discussing closed bomb experiments and guns and powder ??? Noble and Abel used a 150 cc capacity closed bomb with a 20 tonne per inch pressure capability
For reference purposes, am I correct that, a 30-06 case is about 4.43 cc?