tank phisics and measures? metric units please

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

Mario wrote:
> Hello,
>
> I would like to learn and understand more or less the measures and
> phisics of the tanks.

http://www.subaqua.co.uk/cgi-bin/cylinder-buoyancy.cgi

covers most of what you want to know...

- Keith

> 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 )

You can get a approx value if you know the material and capacity, but that
is just from averages of what certain tanks weigh - there's no formula to
it, depends on the manufacturer, but the values are easily available (they
are stamped on the tank itself).

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

Read the stamp - don't need to calculate it.

> How much more or less weight the tank valve?

They definately add to the weight, not sure how much but i'm sure someone
somewhere can tell you - try the manufacturers website (again different
manufacturer's valves will weigh slightly different).

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

See the link Keith gave...

> 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.

Temperature affects pressure, not density because its a sealed container
(effectively) - when you heat it up you aren't adding any extra molecules
into the cylinder, and so temperature won't affect weight, but will affect
pressure. Since, at a constant temperature, increased pressure means more
air molecules and so more weight, the physics formulae need to account for
the temperature difference (search for the "ideal gas equation" if you want
to know how it works)

David

That's a great site- very interesting stuff.

"Keith S." <false@ntlworld.com> wrote in message
news:2i0rkqFi1c5jU1@uni-berlin.de...
> Mario wrote:
> > Hello,
> >
> > I would like to learn and understand more or less the measures and
> > phisics of the tanks.
>
> http://www.subaqua.co.uk/cgi-bin/cylinder-buoyancy.cgi
>
> covers most of what you want to know...
>
> - Keith
>

Mario wrote:
> 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 )

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/phys...ealGasLaw.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.