SpudFiles

Hi .

Purpose of question .
Work out the atmospheric pressure available within a cylinder , pre compression .

So then can work out , a compression ratio .
Gain desired or expected psi of the compressed air part / after the compression.

Atmospheric pressure is stated at 14.7 psi per inch squares ( in2.)

Easy to work out volume of cylinder .
Cubic inches ( in3)

Where I get unstuck part .
Converting that in3 into in2 .

Or is there another way to go about this .


Hope that makes sense .

Thanks .

Boyle's Law. Not Susan Boyle.

For a given mass of confined gas at constant temperature, pressure multiplied by volume will be constant.

So for a starting state at pressure P₁ with chamber volume V₁, and a compressed state P₂ with final chamber volume V₂ :

P₁V₁ = P₂V₂

This gets combined with Charles' Law and - ummm - I forget - Gay-Lussac I think - to give the ideal gas law, which is pretty much what you need. This adds a new factor, temperature, and can be expressed variously as

PV = nRT

where n is the number of moles of gas, R is the universal gas constant, and T is the absolute temperature in °K (no freedom units here, it's science)

or

P₁V₁ / T₁ = P₂V₂ / T₂

Again, temperatures are absolute.

TL/DR version - ignoring temperature changes, if you halve the volume, you double the pressure. That will get you pretty close.

mrfoo wrote: ↑

Fri Dec 02, 2022 1:14 pm

Boyle's Law. Not Susan Boyle.

For a given mass of confined gas at constant temperature, pressure multiplied by volume will be constant.

So for a starting state at pressure P₁ with chamber volume V₁, and a compressed state P₂ with final chamber volume V₂ :

P₁V₁ = P₂V₂

This gets combined with Charles' Law and - ummm - I forget - Gay-Lussac I think - to give the ideal gas law, which is pretty much what you need. This adds a new factor, temperature, and can be expressed variously as

PV = nRT

where n is the number of moles of gas, R is the universal gas constant, and T is the absolute temperature in °K (no freedom units here, it's science)

or

P₁V₁ / T₁ = P₂V₂ / T₂

Again, temperatures are absolute.

TL/DR version - ignoring temperature changes, if you halve the volume, you double the pressure. That will get you pretty close.

Ta Mrfoo .

Ok.
Wow , learning curve ...lol.

I ran with this .
Or should I just used standard definitions?
( Are a few )

Particular where live in world.
311 meters above sea level =
14.1766 psi (97.74421624 kpa)
25 deg C ( 298.15 Kelvin)

Molar volume of gas ,
P.V= n.R.T

which can be rearranged :
V/n = (R.T) /P

where (in SI metric units):

P = the gas absolute pressure, in kPa
n = number of moles, in mol
V / n = the gas molar volume, in m³/mol
T = the gas absolute temperature, in K
R = the universal gas law constant of
8.3145

V/n= 8.3145 X 298.15 / 97.74421624
= 25.3617904835 m3/ mol.
Equiv to litres ?

Then ran with .
Break down to cm3 ( X 1000)

14.1766 psi / 25361.7904835 cm3 .
Psi Per cm3 = 0.00055897473
Not ( gauge pressure )

application too .

26.47 cm3 cylinder .
X 0.00055897473
=0.0147960611031 psi atmospheric pressure in above mentioned cc cylinder .

Boyles Law .
Initial parameters

Initial pressure (p₁)
psi 0.0147960611031

Initial volume (V₁
cm³ 26.47

Final parameters

Final pressure (p₂)
Psi 65.28
Final volume (V₂)
cm³ 0.006


Then Took a stab .
To compress 65.28 psi .
Is equivalent to 4.59 kgcm2 force .

Other than that .
Done my head in ....lol.