Tank volume calculations..what was the temp used?

[will_tekkie]

Hi guys...i was wondering about the temperature considered by tank manufactures in theirs calculations related to the volume stored into the tanks...i don´t know if conditions such as standard atmosphere ( 15 celsius degrees, 101 KPa) were used here or other temp was considered instead...

thanks...

 

[rab]

PST's tanks are rates as 3442psi @ 70F (about 232bar @ 21C ?)

-Rob

 

[pescador775]

A 'bar' is a physical abstraction originally used only by scientists. It is not exactly one atm. So, 3442 psi = 237 bar. 70F = 21C.

PST's tanks are rates as 3442psi @ 70F (about 232bar @ 21C ?)

Unlike commercial manufacturers of Scuba air compressors which use deceptive practices and bogus definitions (SCFM), most other manufacturers, including those of SCUBA tanks and military air compressors, continue to adhere to the scientific definition of "STP" (standard temperature and pressure) and SCFM (called "standard air"). However, in some cases I've seen standard temperature defined as 68F. This slight difference is unimportant to the question. The response is correct and SCUBA tanks are rated at what most would call "room temperature".

 

[will_tekkie]

A 'bar' is a physical abstraction originally used only by scientists. It is not exactly one atm. So, 3442 psi = 237 bar. 70F = 21C.

Thanks guys...i have already considered 21-22 degrees but thinking about (solving a problem) a doubt came quickly because i had not info about it...20 degrees is closer to the possible ambient temp so it is a most accurate working condition in order to get a reference...

pescador info is right..1 atm=1.0133 bar...depends on how accuracy is needed, the most times the conversion 1:1 can be ok enough...like 70F=21.11C or 3442psi=237.32 bar

 

[DA Aquamaster]

Hmm...according to my Pratt and Whitney handbook, standard temperature and pressue is defined as 59 degrees Farenheit (15 deg Celcius) and 14.7 psi (or 29.92 inches of Hg).

In contrast, most scuba tank stats that I have seen are based on something close to room temperature at 68-70 degrees which is an industry standard of sorts but not the standard in terms of the scientific definition of standard temperature and pressure.

 

[pescador775]

I misspoke. I should have said 'industry' standard for STP. There are, or have been several scientific definitions of STP. Often, in chemistry, because reactions are most commonly observed at room temp (ambient) conditions it is specified as 68F. However, for gases, standard temp is sometimes set at 32F.
>>Measured volumes of gases are quite generally recalculated to 0 C temperature and 760 mm pressure, which have been arbitrarily chosen as standard conditions.<<
----Handbook of Chemistry and Physics

From an old edition. I would guess that 15C is commonly used today. In any case, all tech manuals for (military) compressors that I have read indicate a tank temp of 68F for purposes of defining system performance.

Hmm...according to my Pratt and Whitney handbook, standard temperature and pressue is defined as 59 degrees Farenheit (15 deg Celcius) and 14.7 psi (or 29.92 inches of Hg).

In contrast, most scuba tank stats that I have seen are based on something close to room temperature at 68-70 degrees which is an industry standard of sorts but not the standard in terms of the scientific definition of standard temperature and pressure.

 

[WarmWaterDiver]

SCFM is Standard Cubic Feet per Minute - a flow rate, not a capacity. Compressors can be rated in SCFM, but tank storage volume capacity would not be.

US Engineering units STP is typically 1 atmosphere at sea level (14.7 PSIA) and 60 degrees F. If you use natural gas in your home, these are the reference conditions for the SCF (Standard Cubic Feet) volume used on your bill. Somewhere, this all goes back to someone taking data and trying to determine the average temperature across the earth at any one point in time. For metric, depending on the material in question, I've seen 0 degrees C as a reference, 15 degrees C (almost = 60 degrees F), and 20 degrees C.

Crude oil is still bought and sold by the US Barrel of 42 gallons at 60 degrees F as a liquid example instead of a gas example.

 

[pescador775]

Well, that is a bit of quibbling because compressor manufacturers recommend that the user determine flow by measuring pump up time of a tank of known capacity at standard conditions.

Speaking of standard conditions, here is a typical industry definition from "Lake Monitor" flow meters, a maker of scientific instruments.

>>Standard Cubic Feet:
Lake's Monitors are calibrated to measure the flow of compressible media (gases) in SCFM - standard cubic feet per minute. A "standard" cubic foot is defined as a cubic foot of dry air at standard atmospheric conditions: 70ºF and 14.7 PSIA (0 PSIG) measured at sea level.<<

So, here we have it. Does anyone seriously think that mfgrs of compressed gas tanks would use a different standard of measurement than that employed to measure the systems used to compress the gas and fill those tanks in the first place? Not a chance. Therefore, the original statements stand, that standard temp is 70F and that is the norm used to define tank capacity.

SCFM is Standard Cubic Feet per Minute - a flow rate, not a capacity. Compressors can be rated in SCFM, but tank storage volume capacity would not be.

US Engineering units STP is typically 1 atmosphere at sea level (14.7 PSIA) and 60 degrees F. If you use natural gas in your home, these are the reference conditions for the SCF (Standard Cubic Feet) volume used on your bill. Somewhere, this all goes back to someone taking data and trying to determine the average temperature across the earth at any one point in time. For metric, depending on the material in question, I've seen 0 degrees C as a reference, 15 degrees C (almost = 60 degrees F), and 20 degrees C.

Crude oil is still bought and sold by the US Barrel of 42 gallons at 60 degrees F as a liquid example instead of a gas example.

 

[will_tekkie]

:06: Looking a bit into the manufacturers websites the conditions considered by they are not showed in their tables..(well i could not see them at least)...so we can just make especulations about it....a "standard atmosphere" is defined using a sea level temp of 15C. (presure 0.1013 Mpa)..and is widely known by everybody interested in aeronatics related issues for examples...but (always a BUT in life) ..for tanks..i´ve heard mostly a 20-22C range..i´m not sure...perhaps i´m wrong...maybe some of you got this info from the manufacturers (the best way to know exactly the value they used)...this is not a VERY important think but i was surprised that i had not never considered it before...

standard atmosphere vs. altitude (SI and US units): http://www.usatoday.com/weather/wstdatmo.htm

 

[Sideband]

Well, that is a bit of quibbling because compressor manufacturers recommend that the user determine flow by measuring pump up time of a tank of known capacity at standard conditions.

Speaking of standard conditions, here is a typical industry definition from "Lake Monitor" flow meters, a maker of scientific instruments.

>>Standard Cubic Feet:
Lake's Monitors are calibrated to measure the flow of compressible media (gases) in SCFM - standard cubic feet per minute. A "standard" cubic foot is defined as a cubic foot of dry air at standard atmospheric conditions: 70ºF and 14.7 PSIA (0 PSIG) measured at sea level.<<

So, here we have it. Does anyone seriously think that mfgrs of compressed gas tanks would use a different standard of measurement than that employed to measure the systems used to compress the gas and fill those tanks in the first place? Not a chance. Therefore, the original statements stand, that standard temp is 70F and that is the norm used to define tank capacity.

I don't have knowledge on this except what I have read here, but it doesn't make much sense to rate a tank capacity in cubic feet per minute. An 80CF tank holds ~80CF of air at the rated pressure if it is for a minute or an hour or 10 years.
Tire manufacturers don't measure rim size in PSI.

Joe