Problem with Baltic Blender, wrong calculation

[Agro]

I try to calculate:
Starting mixture EAN41.2, 191.5bar
Temp 14.5 celsius
Desired mix EAN40, 250bar
Solution Step-by-step:
Add O2 up to 199.3bar, get EAN43.4
Add Air up to 242.5bar, EAN40

I want 250bar, not 242.5bar. What's wrong?

I have other calculations which are even more wrong but let's first have an eye on this one.
Thank you very much for your help.

 

[rjack321]

Warm it up (to about 24C) and you'll have 250 bar. Problem solved.

 

[Agro]

Warm it up (to about 24C) and you'll have 250 bar. Problem solved.

It's a joke, but not a good one.

 

[inquis]

I don't use it, but I wonder if there's a setting being used for the dive temp, and it's set higher than 14.5 *C. After warming up to that temp you'd then have 250 bar.

 

[JohnN]

It actually presents an interesting dynamics problem, since as you add gas to the cylinder, it heats up. So since the tank temperature is not constant, what does "Add O2 up to 199.3bar, get EAN43.4". Is that after you cool the tank back down to 14.5 C?

 

[inquis]

Is that after you cool the tank back down to 14.5 C?

No. It's estimating the heating (and impact on pressure) as it goes.

 

[JohnN]

No. It's estimating the heating (and impact on pressure) as it goes.

Does it know the pressure/temperature of the gas being added?

 

[Sevenrider860]

It's a joke, but not a good one.

I don't think it is that far off from the truth.

Your Desired Mixture settings assume a "Standard Temperature" of 21 degrees unless you have changed it in the Settings menu. It states that in the instructions.

"Note that this pressure is always described at the configured standard temperature (defaults to 21 degrees); you do not enter a final temperature."

Adjust your Standard Temperature to 14.5 in the settings and you will get:

Add O2 up to 201 bar, get EAN43.9
Add Air up to 251 bar, EAN40

 

[Agro]

Sevenrider, that's it, thank you very much. I must change temperature in settings to 14.5 as well. Otherwise it assumes some best-guess temperature changings.

I blend this way:
- add oxygen to 202 bar, cylinder gets a little bit hotter
- let it cool down to 14.5 celsius
- measure, for ex 200bar
- add oxygen to 201, hardly any changing in temp.
- add air to 252 bar
- let it cool down
- measure, for ex 248 bar
- add air to 250 bar

This is the only way to have a constant temperature and therefore no mistake by temperature. Off course you need time to practice this kind of blending.

If having 21 degrees and 14.5 degrees the programm seems to assume you make a fast filling and starts best-guess calculation. No idea what parameters it takes:
- Filling speed?
- Temperatur of oxygen and air? Coming out of cylinder is much colder then out of a compressor or booster.
- Steel or alu tank? Different heat conduction.

Anyway if I have to make a fast filling perhaps program's best-guess-calculation is better then mine

 

[Agro]

Warm it up (to about 24C) and you'll have 250 bar. Problem solved.

Rjack, I thougt you were making a joke. It seems I was wrong, sorry for that.