Well, what about that tank of hot?

A tank heats when filled. Where does the heat come from? The air going in
is 70 degrees, the tank is at 70 degrees, how come the tank gets warm?
Could it be the motor used to drive the compressor gives off heat or the
compressor cylinders moving in the sleeves create friction heat that is
transferred to the tank, or such similar action?

Maybe the amount of heat produced by the tank being filled equals the amount
of cold when the cylinder is emptied - given relevant environmental factors
remain constant.

A tank heats when filled too fast. When it cools, the pressure
decreases. It's the aspect of Boyle's Law that too many shop monkeys
don't understand. The volume of gas in a hot filled tank is not as
great as the pressure reading suggests. The true volume is the volume
equivalent to the pressure at room temperature. Boyle's Law states that
pressure and volume are inversely related at constant temperature. If
you let the temperature rise (by filling too fast), you have screwed up
the relationship between pressure and volume, and you have to wait
until the tank cools before you can calculate the true volume.

There is no such thing as an "amount of cold." Cold is merely the
absence of heat.

Boyle's Law doesn't account for time. The reality of filling or
emptying tanks is that the faster you fill them, the hotter they get,
and the faster you empty them, the colder they get. I don't know if
they still do, but liquor stores used to sell CO-2 cartridges as
instant drink coolers. The metal cartridge can quickly get below
freezing upon a sudden release of pressure.

"Popeye" <Popeye@Finalprotectivefire.com> wrote in message
news:11rie53bcas2f4a@news.supernews.com...
>
> Jesus, you must be bored.

If you've studied diesel engines, that surely should cover the basics.
After all, it's why the damn things run.

On Mon, 2 Jan 2006 08:00:05 -0600, "ben bradlee" <up2u2figr@NoWay.zip>
wrote:

>A tank heats when filled. Where does the heat come from? The air going in
>is 70 degrees, the tank is at 70 degrees, how come the tank gets warm?
>Could it be the motor used to drive the compressor gives off heat or the
>compressor cylinders moving in the sleeves create friction heat that is
>transferred to the tank, or such similar action?
>
>Maybe the amount of heat produced by the tank being filled equals the amount
>of cold when the cylinder is emptied - given relevant environmental factors
>remain constant.
>

It comes from the work done compressing the gas in the cylinder.

The Temperature changes in response to compression due to addition of
more molecules of air to the closed, fixed-volume cylinder. Work is
produced. Temperature rises.

The temperature must change by following Ideal Gas Law:

P V = N k T

Where P = pressure, V = volume, N = number of gas molecules, k = is
Boltzman's constant and T is Kelvin.

The equation must balance. Pick any system of gasses at a specific
pressure, temperature and volume. Change any of those four conditions,
the others must change proportionately.

See also, http://scienceworld.wolfram.com/phys...ealGasLaw.html

"ben bradlee" <up2u2figr@NoWay.zip> wrote in message
news:Mr-dnZEfOKyzHyTeRVn-gQ@centurytel.net...
>
> "Popeye" <Popeye@Finalprotectivefire.com> wrote in message
> news:11rie53bcas2f4a@news.supernews.com...
>>
>> Jesus, you must be bored.
>
> If you've studied diesel engines, that surely should cover the basics.
> After all, it's why the damn things run.

You could just take a nitrox blending course, or read the Navy dive
manual, and get the same information about heat of compression.

"Geoff" <geoff@invalid.invalid> wrote in message
news:930jr1p22odt7mb22vkti03c7h0b8c722p@4ax.com...
> On Mon, 2 Jan 2006 08:00:05 -0600, "ben bradlee" <up2u2figr@NoWay.zip>
> wrote:
>
> >A tank heats when filled. Where does the heat come from? The air going
in
> >is 70 degrees, the tank is at 70 degrees, how come the tank gets warm?
> >Could it be the motor used to drive the compressor gives off heat or the
> >compressor cylinders moving in the sleeves create friction heat that is
> >transferred to the tank, or such similar action?
> >
> >Maybe the amount of heat produced by the tank being filled equals the
amount
> >of cold when the cylinder is emptied - given relevant environmental
factors
> >remain constant.
> >
>
> It comes from the work done compressing the gas in the cylinder.
> The Temperature changes in response to compression due to addition of
> more molecules of air to the closed, fixed-volume cylinder. Work is
> produced. Temperature rises.
>
> The temperature must change by following Ideal Gas Law:
>
> P V = N k T
>
> Where P = pressure, V = volume, N = number of gas molecules, k = is
> Boltzman's constant and T is Kelvin.

That sounds good, like most of the way there. But is the quantity of heat
the same from compression and decompression? According to the formula, the
temperature should vary directly and in proportion to the change in pressure
when holding V, N, and k constant.

ben bradlee wrote:

> "Popeye" <Popeye@Finalprotectivefire.com> wrote in message
> news:11rie53bcas2f4a@news.supernews.com...
>
>> Jesus, you must be bored.
>
>
> If you've studied diesel engines, that surely should cover the basics.
> After all, it's why the damn things run.

And there is nothing to replace bore. Except bigger bore

Matthias

On Mon, 2 Jan 2006 15:05:29 -0600, "ben bradlee" <up2u2figr@NoWay.zip>
wrote:

>
>"Geoff" <geoff@invalid.invalid> wrote in message
>news:930jr1p22odt7mb22vkti03c7h0b8c722p@4ax.com.. .
>> On Mon, 2 Jan 2006 08:00:05 -0600, "ben bradlee" <up2u2figr@NoWay.zip>
>> wrote:
>>
>> >A tank heats when filled. Where does the heat come from? The air going
>in
>> >is 70 degrees, the tank is at 70 degrees, how come the tank gets warm?
>> >Could it be the motor used to drive the compressor gives off heat or the
>> >compressor cylinders moving in the sleeves create friction heat that is
>> >transferred to the tank, or such similar action?
>> >
>> >Maybe the amount of heat produced by the tank being filled equals the
>amount
>> >of cold when the cylinder is emptied - given relevant environmental
>factors
>> >remain constant.
>> >
>>
>> It comes from the work done compressing the gas in the cylinder.
>> The Temperature changes in response to compression due to addition of
>> more molecules of air to the closed, fixed-volume cylinder. Work is
>> produced. Temperature rises.
>>
>> The temperature must change by following Ideal Gas Law:
>>
>> P V = N k T
>>
>> Where P = pressure, V = volume, N = number of gas molecules, k = is
>> Boltzman's constant and T is Kelvin.
>
>That sounds good, like most of the way there. But is the quantity of heat
>the same from compression and decompression? According to the formula, the
>temperature should vary directly and in proportion to the change in pressure
>when holding V, N, and k constant.
>

k is already a constant. When N is constant the equation becomes PV/T
= C (some constant). Then we have Boyle's law.

P1 V1 / T1 = P2 V2 / T2

Compress a gas in a dead headed piston and P and T will rise while V
gets smaller. Relax the piston and it springs back to its original
volume and P, T will fall. The amount of work done by the piston as it
relaxes can never be the same as the amount of work done to compress
it. Friction in the piston and heat lost to space account for the
losses. You can never get as much work out of a system as you put in.
This is a consequence of the first and second laws of thermodynamics.

Your scuba tank is a Carnot cycle device, not a Diesel.

See also adiabatic expansion, Carnot Cycle.

When filling SCUBA tanks it's always a good idea to keep them cool or
else fill slowly so that T does not increase rapidly.

1. Thermal stress promotes metal fatigue and we want to minimize that.

2. From Boyle's law, the pressure measured at the elevated temperature
will be high compared to the temperature after it cools, thus, a short
fill when T is not so high.

"George Cathcart" <aquadiver@comcast.net> wrote

>A tank heats when filled too fast. When it cools, the pressure
> decreases.

The same amount of heat is generated no matter how fast or slowly the tank
is filled.

> It's the aspect of Boyle's Law that too many shop monkeys
> don't understand.

Mine do. Sorry about yours.

> The volume of gas in a hot filled tank is not as great as the pressure
> reading suggests. The true volume is the volume
> equivalent to the pressure at room temperature.

The true volume, in terms of the amount of gas contained in the tank, can be
expressed only in terms of molecules or some measure of them. Neither cubic
feet nor liters does that.

> Boyle's Law states that pressure and volume are inversely related at
> constant temperature. If you let the temperature > rise (by filling too
> fast), you have screwed up the relationship between pressure and volume,
> and you have to wait
> until the tank cools before you can calculate the true volume.

Say what?

> There is no such thing as an "amount of cold." Cold is merely the
> absence of heat.

Well, at least you got one thing right.

> Boyle's Law doesn't account for time. The reality of filling or emptying
> tanks is that the faster you fill them, the
> hotter they get . . .

That's two more things right.

> and the faster you empty them, the colder they get.

That's one more right. You're doing better.

Lee

"Geoff" <geoff@invalid.invalid> wrote in message
news:3i8jr113hvp7nqfuf5113itdeatgkuhhvd@4ax.com...
> On Mon, 2 Jan 2006 15:05:29 -0600, "ben bradlee" <up2u2figr@NoWay.zip>
> wrote:
>
> >
> >"Geoff" <geoff@invalid.invalid> wrote in message
> >news:930jr1p22odt7mb22vkti03c7h0b8c722p@4ax.com.. .
> >> On Mon, 2 Jan 2006 08:00:05 -0600, "ben bradlee" <up2u2figr@NoWay.zip>
> >> wrote:
> >>
> >> >A tank heats when filled. Where does the heat come from? The air
going
> >in
> >> >is 70 degrees, the tank is at 70 degrees, how come the tank gets warm?
> >> >Could it be the motor used to drive the compressor gives off heat or
the
> >> >compressor cylinders moving in the sleeves create friction heat that
is
> >> >transferred to the tank, or such similar action?
> >> >
> >> >Maybe the amount of heat produced by the tank being filled equals the
> >amount
> >> >of cold when the cylinder is emptied - given relevant environmental
> >factors
> >> >remain constant.
> >> >
> >>
> >> It comes from the work done compressing the gas in the cylinder.
> >> The Temperature changes in response to compression due to addition of
> >> more molecules of air to the closed, fixed-volume cylinder. Work is
> >> produced. Temperature rises.
> >>
> >> The temperature must change by following Ideal Gas Law:
> >>
> >> P V = N k T
> >>
> >> Where P = pressure, V = volume, N = number of gas molecules, k = is
> >> Boltzman's constant and T is Kelvin.
> >
> >That sounds good, like most of the way there. But is the quantity of
heat
> >the same from compression and decompression? According to the formula,
the
> >temperature should vary directly and in proportion to the change in
pressure
> >when holding V, N, and k constant.
> >
>
> k is already a constant. When N is constant the equation becomes PV/T
> = C (some constant). Then we have Boyle's law.
>
> P1 V1 / T1 = P2 V2 / T2
>
> Compress a gas in a dead headed piston and P and T will rise while V
> gets smaller. Relax the piston and it springs back to its original
> volume and P, T will fall. The amount of work done by the piston as it
> relaxes can never be the same as the amount of work done to compress
> it. Friction in the piston and heat lost to space account for the
> losses. You can never get as much work out of a system as you put in.
> This is a consequence of the first and second laws of thermodynamics.

Well, we're right back to where we started. Compressing gas yields heat.
The question is not how much heat is lost in the process of compression but
rather is the heat given off by the gas equal to the heat the gas takes back
during decompression. Of course it takes work to accomplish the compression
and loss will result in that process, as you describe.