tank phisics and measures? metric units please

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Mario - 31 May 2004 14:01 GMT

Hello,

I would like to learn and understand more or less the measures and
phisics of the tanks.

Please in metric units.

Is it possible approximatelly to calculate the weight of and empty
tank given its material steel or aluminium and its measures lenght and
diameter( of course generalizing if possible on the alloy grade used,
to know the specific weight or steel or aluminium )

What will be the calculation to get the empty tank weight ?

How much more or less weight the tank valve?

Given the capacity of the tank is it possible to calculate the weight
of the compressed air insde it ?

I will also depend on the depth ?

Please can you give me the formula to calculate the weight of the air
inside a tank depending on the depth and pressure inside the tank,
measured at the console pressure gauge. Or given the pressure , depth
is not necesary to be taken in consideration ?

I am not sure if air density depends on depth and temperature of the
water. Please take in consideration all the necessary parameters to
calculate the air weight inside a tank given the air pressure read at
the pressure gauge and tank capacity.

Thanks,

Mario

Reply to this Message

mike gray - 31 May 2004 16:17 GMT

> Hello,
>
[quoted text clipped - 7 lines]
> diameter( of course generalizing if possible on the alloy grade used,
> to know the specific weight or steel or aluminium )

Given the shape of a tank, it is not practical to calcuate the weight
with length/diameter/thickness measurements. Much easier to just drain
it and put it on a bathroom scale.

> What will be the calculation to get the empty tank weight ?
>
> How much more or less weight the tank valve?

Ditto. When completely drained, the valve is easily removed and
seperately weighed.

> Given the capacity of the tank is it possible to calculate the weight
> of the compressed air insde it ?

Yes. At 48 F at sea level, a cubic foot of air weighs almost exactly 1
1/4 ounces. (Sorry, do yer own conversions to metric.) A tank containing
100 CF therefore weighs an additional 100 X 1 1/4 or 125 ounces, 7.8
pounds or 3.5 kilo (not exact, but close enough for diver weighting
purposes).

Knowing the volume of the tank and the pressure, you can compute the CF
(or litres) using Boyle's Law (which is not precise, but close enough),
the ideal gas law, or more precise chemical measures. See:

http://scienceworld.wolfram.com/physics/IdealGasLaw.html

http://www.s-ohe.com/srk.html

http://www.chemicalogic.com/mwcalc/mwjava.htm

> I will also depend on the depth ?

No. The tank is a closed system; the volume, pressure, and weight of the
gas inside are unaffected by the external pressure on the tank. Remember
when we talk about an "80 cubic foot tank", that means that the
compressed air inside will occupy 80 cf at standard temperature and
pressure. It is a "normalized" measure.

> Please can you give me the formula to calculate the weight of the air
> inside a tank depending on the depth and pressure inside the tank,
> measured at the console pressure gauge. Or given the pressure , depth
> is not necesary to be taken in consideration ?

See above.

> I am not sure if air density depends on depth and temperature of the
> water. Please take in consideration all the necessary parameters to
> calculate the air weight inside a tank given the air pressure read at
> the pressure gauge and tank capacity.

Air density increases directly (almost) with pressure. and inversely
with temperature.

Again, inside a scuba tank, you have a closed system, unaffected by
external pressure. However, the diver on scuba is an open system, and
breathes gas at pressure and density dictated by depth (ambient pressure).

Suggest you first understand Boyle's law (simple) and Charles' Law
(simple) then read up on the ideal gas law (simple in concept,
complicated by the math and measures).

You then need to understand the difference between a closed, static gas
supply (a scuba tank) versus an open, dynamic gas user (a diver at
varying depth).

Hit the books, boy.

Reply to this Message

bullshark - 31 May 2004 17:14 GMT

>Hello,
>
[quoted text clipped - 7 lines]
>diameter( of course generalizing if possible on the alloy grade used,
>to know the specific weight or steel or aluminium )

Yes, but it won't be very accurate...around +/- 3 kg or worse.
There is no need to estimate. Every manufacturer tabulates dry weight
of every cylinder model, and most are available on the Web.

>What will be the calculation to get the empty tank weight ?

Total weight minus weight of gas.

>How much more or less weight the tank valve?

1 kg.

>Given the capacity of the tank is it possible to calculate the weight
>of the compressed air insde it ?

yes

>I will also depend on the depth ?

no.

>Please can you give me the formula to calculate the weight of the air
>inside a tank depending on the depth and pressure inside the tank,
>measured at the console pressure gauge. Or given the pressure , depth
>is not necesary to be taken in consideration ?

yes.

>I am not sure if air density depends on depth and temperature of the
>water. Please take in consideration all the necessary parameters to
>calculate the air weight inside a tank given the air pressure read at
>the pressure gauge and tank capacity.

W=moles*molecular weight.

bullshark

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