Check my math

[omar]

Well it is obvious that you are someone that needs a road map and can not grasp the relevance of what was presented.

You did not recognise that you were making an error by calculating the volume without taking into account the atmospheric pressure for the gauge term. Hence the absolute and gauge pressures reference.

You did not grasp the fact that the compressibility factor is greater than 1 for air at 2640.

The compressibility factor indicates that the difference in calculated volume using a liner approximation (ideal gas equation/boyles law) for volume and real gas EOS is the most likely factor.

OMS is using the vdW EOS. Since they did not specify the reference for the constants it would be a guess which ones they used. (FYI, each reference has slightly different values for these constants, and some references even have different values for different editions.) Which is why I gave you the B-B EOS value. It was a BIG red flag that you missed.

Next, the temperature and altitude terms are right there in the equation. All you have to do is plug them in.

But it is very simple clown boy. When the pressure is reduced (by going to altitude) the apparent delivered volume will increase, the temperature will have the same relationship.

The best part of this is the the value for the OMS 108 is 17L not 19L. Another screwup by you. You really need to pay closer attention to what you are doing. Which was the whole point of the original post.

And just so you know, I use the altitude equation on a regular basis. That is why I could give the general equation and the derivation of it.

omar

 

[MikeS]

Omar,

Wow what a bunch of babble, now answer the question, “Do you dispute the fact that the volume as listed on the OMS webpage is rounded to the nearest liter?”

And if so do you stand by your statement “also oms lists the actual internal volume so you should use that?”

And yes I made a mistake on the 17 versus 19, guess I’m not perfect like you. But wait it seems you’ve edited your post, was that to make it more perfect?

I suspect you use the altitude equation on a regular basis to determine the pressure in the cavity between your ears as you go up a hill.

While trading insults is somewhat entertaining, if you have some insight on the subject, and can refrain from acting like such a Richard, I’d like to hear an explanation, because it’s may be possible to learn something even from someone as pompous and condescending as yourself.


Mike

 

[omar]

All of your “challenges” were addressed and you still don’t get it.

You can make an issue of the internal volume listed by OMS on their web site if you want. The fact remains that you made numerous errors in your math and you don’t have a grasp of the concepts either. If you did you wouldn’t be trying to deflect the attention away from your screw ups. You are the last one to be trying to play Bill Nye.

For the black hole that is in place of your grey matter:

The computed volume using the ideal gas equation (which is what you were screwing up) is only a linear approximation and is not what OMS has used for their calculations for delivered volume versus computed volume. They have used a real gas equation of state (EOS). The real gas EOS describes the difference in the rated volume and the actual volume delivered.

This is used in everyday practice by all the gas companies and also explains the difference in the volume of helium or oxygen or other gas in the same size cylinders. eg a “K” will deliver 213 ft^3 of He; the same “K” cylinder will deliver 249 ft^3 of O2, the same “K” cylinder will deliver 233 ft^3 of Air (these are Union Carbide values which can easily be found on the web. My gas supplier has slightly different ones).

Trying to back calculate the tank volume by using Boyles law will result in errors (even if you get the math right which is hard for some people). To minimize these errors it is standard practice to use the internal liquid volume listed by the manufacturer.

I am done with this, have fun and don’t trip over your feet.

omar

 

[MikeS]

Omar,

Okay, but before you go would you do me a favor, would you illustrate and example of calculating the liquid volume of a tank based on the free air delivery and pressure, and then calculating the free air delivery based on a pressure change. Insults and sarcasm aside I would really like to learn something here, and I suspect there are others on the board that would benefit as well. Please take it slow and easy.

The intent of my initial post was to share what I thought was a better understanding of the situation, if you can correct it or add anything so much the better. Sorry, for jerking your chain so much, perhaps I shouldn’t be allowed to watch football, drink beer, and make posts all at the same time.

Mike