Tank volume calculations..what was the temp used?

[will_tekkie]

Standard atmosphere is a useful definition and allows to know the conditions that we can hope to find out there as a funtion of altitude...but maybe for manufacturers standard conditions are slightly different (applications are too)...i´ve seen some engineers using a standard conditions for their calculations, temp ranging from 273.15 K (0C, 32F) to 70F...being the pressure always 1 ata (14.7 psia).

 

[pescador775]

One more time. The term SCFM was discussed to reinforce a point about the temperature conditions for pumping and storing air. It was not meant to confuse anybody. However, several jumped on it which tends to make me believe that this whole area is not well understood by some. Both Standard Cubic Feet per Minute (flow) and CF (capacity) MUST be defined under the same (standard) conditions, in this case the standard under discussion is temperature. I have shown by factual presentation that the standard temp used to calibrate gas flowmeters is 70F. This confirms the standard temp specified for determining capacity of PST tanks as provided by "rab". (see above). There is no point of further discussion.

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

 

[WarmWaterDiver]

http://www.gascoonline.com/gaseng.html

 

[Sideband]

One more time. The term SCFM was discussed to reinforce a point about the temperature conditions for pumping and storing air. It was not meant to confuse anybody. However, several jumped on it which tends to make me believe that this whole area is not well understood by some. Both Standard Cubic Feet per Minute (flow) and CF (capacity) MUST be defined under the same (standard) conditions, in this case the standard under discussion is temperature.

I misunderstood what you were saying. I would agree with all of the above.

I have shown by factual presentation that the standard temp used to calibrate gas flowmeters is 70F. This confirms the standard temp specified for determining capacity of PST tanks as provided by "rab". (see above). There is no point of further discussion.

I can't agree that 70F is the end all be all defacto number yet though. You gave a gas example at 70F, WarmWaterDiver has posted a 'factual presentation' that uses 60F.
There may very well be "no point of further discussion" but there would be a point in further presentation of facts. If the answer was as cut and dried as a single universal temperature for all cases then it would be a constant. It appears to be more of a variable.

Joe

 

[pescador775]

Do you honestly think that the temp definitions for liquified natural gas storage, which is related solely to the billing practices of the suppliers, is relevant to this subject? Moreover, you are in a position to phone PST and ask about this but persist in your line of skepticism? Possibly, you are not anxious to troll the same line of questioning by them. Geez.

I misunderstood what you were saying. I would agree with all of the above.



I can't agree that 70F is the end all be all defacto number yet though. You gave a gas example at 70F, WarmWaterDiver has posted a 'factual presentation' that uses 60F.
There may very well be "no point of further discussion" but there would be a point in further presentation of facts. If the answer was as cut and dried as a single universal temperature for all cases then it would be a constant. It appears to be more of a variable.

Joe

 

[Sideband]

Do you honestly think that the temp definitions for liquified natural gas storage, which is related solely to the billing practices of the suppliers, is relevant to this subject? Moreover, you are in a position to phone PST and ask about this but persist in your line of skepticism? Possibly, you are not anxious to troll the same line of questioning by them. Geez.

I saw nothing there to indicate liquified gas storage. I did read several descriptions that said some amount of moisture was permissible using their systems. Maybe I'm wrong but that doesn't sound like liquified gas. It did sound like an answer different from yours though.

As to my skepticism, so far in this thread you have given 15C=59F, 68F and your latest 70F as the answer. I have become curious as to the correct answer and given the phone number would gladly call and ask. You are in the same position to call as I am.

How is my unwillingness to accept your current definitive answer of the moment a troll? Ending a post with, "No further discussion is necessary" does not make you right. Not blindly accepting your multiple guess answers does not make me a troll.

Joe

 

[will_tekkie]

http://www.gascoonline.com/gaseng.html

In this page clearly the gas meters are setting for stardard atmosphere conditions...60F (15.6C), 1ata...

 

[pescador775]

Now, let's see; Rab presented information from PST, a Scuba tank manufacturer. I presented data from Lake Metrology concerning flow meters used to measure compressed air, argon and nitrogen. These entities state that THEIR definition of standard temp is 70F. This is clearly done for the purpose of defining their products' performance at room temperature, something that their customers can relate to and confirm.

You refer to data from a maker of gas meters designed to measure and regulate natural gas, a petroleum product which liquifies under pressure and is quite different from compressed air, as different as GASoline is from water. They cite a standard temp (for their purposes as 60F). Their business is international in nature and is influenced by international standards. This particular standard, 60F, appears to be a compromise voted in committee. It lies between 32F and 70F, both common scientific and industrial standards in use for a century. The 60F definition appears to be for engineering use and to produce a standard for pricing purposes.

Hmmm, compressed air vs. natural gas. Now, who do you think you should believe? The people who regulate and store compressed air, the same stuff that is used in SCUBA, or those who pump natural gas?

In this page clearly the gas meters are setting for stardard atmosphere conditions...60F (15.6C), 1ata...

 

[will_tekkie]

friends...i´ve already made a request to the manufacturers ...i hope to receive a reply soon...they know exactly what values were considered... :06:

 

[pescador775]

Epilgue:
It doesn't hurt to stretch the brain once in a while, it likes it. It's been a long time since I studied basic physics under which this question falls. I had forgotten a lot of the little details, and responding to the seemingly simple question of 'what is standard temperature as it relates to measurement of tank capacity' stimulated some fact checking. One thing that I (we?) learned is that the scientific community likes round numbers and that these numbers may be different from those used in specific industries. You have to remember that the scientific definitions of standard temperature were decided on long before the era of personal computers. Therefore, calculations were done by hand. Hence, we can well surmise that they selected the values for standard temp as 0C and the value for room temp as 20C for convenience. (I still have no idea where the industry number of 15C comes form but I have an opinion on that which needs verification). Statements by others and my own literature search have settled on the number of 21C (room temp) as the standard temperature at which compressed air flow and compressed air capacity are measured. This makes sense because a higher or lower number would be difficult to verify and seen as slight of hand. However, technical manuals for military air compressors dating from the 1950's and 60's cite a standard temperature of 20C (68F) for purposes of measuring flow (cfm) from their machines. It is clear that they used this number because it is a 'scientific' standard and easy to insert in equations. There is no important difference here, I mean what is 1 (3F) degrees? Close enough for government work. Whether 20C or 21C I'm glad that they didn't select 0C. Now that would be cause for editorials galore on my part.

Nowadays, the makers of commercial air compressors for SCUBA care not a wit about international standards, industry standards, or any standards. It's all about one- upmanship. They measure and advertise the output of their compressors from results of hot fills and partial fills. They have corrupted the meaning of SCFM by redefining it as the air volume produced to conduct a partial fill divided by the time to complete that partial fill and then claiming that the resulting number is actually that needed to complete a full fill. Geez. Reading their 'fine print' it is apparent that there is deceit but who reads that stuff?