Total Pressure of refrigerant blend
Total Pressure of refrigerant blend
(OP)
How do you figure the total pressure of a cylinder with a mixture of two refrigerants? Will the total pressure be the pressure of the higher pressure refrigerant?
(I am not a military engineer....i am a mechanical engineer...i don't know how that got there.)
(I am not a military engineer....i am a mechanical engineer...i don't know how that got there.)





RE: Total Pressure of refrigerant blend
http://wine1.sb.fsu.edu/chm1045/notes/Gases/Mixtures/Gases06.htm
http://pumpjack.tamu.edu/~barrufet/PETE310/Labs/GasLaws/DaltonsLaw.html
It's been a while so I'm not sure if there is any significant error if used when not using an ideal gas, but it should get you close.
Hope this helps.
Regards Fred
RE: Total Pressure of refrigerant blend
Azeotropes (500 series)
Azeotropes are refrigerant blends which evaporate and condense exactly like a pure component at some temperature and pressure. They may not behave in this fashion at all temperatures and pressures but they will be close.
Example: R-502
Zeotropes (400 series)
Zeotropes are refrigerant blends which show some amount of temperature glide when evaporating or condensing. In other words they may not always have a precise Temperature/Pressure relationship like a pure refrigerant always has. Some may act like Azeotropes and glide may not be noticeable. Zeotropes with glide greater than 3 ºF will have one end of the evaporator warmer than the other which may affect system performance. If we put a pressure guage on a bottle of blended refrigerant we would read the pressure of the greatest P/T relationship at that ambient temp and it would be the one with the highest leakage rate
Roger
Roger
RE: Total Pressure of refrigerant blend
RE: Total Pressure of refrigerant blend
Regards,
Eng-Tips.com : Solving your problems before you get them.
RE: Total Pressure of refrigerant blend
Roger
RE: Total Pressure of refrigerant blend
Thank you for your responses!
RE: Total Pressure of refrigerant blend
R23 has a much higher vapor pressure than R22. But without knowing how much of each component you have, it will be very difficult determine the partial pressures by calculation. But if the existing pressure in the bottle high enough to keep all the R22 liquid then the pressure you are reading will be almost all due to the R23.
If you aren't in a pressure range to keep the R22 in a liquid state, you may be able to cool the bottle down to a point where all the R22 is sub-cooled, then the pressure you read will be almost entirely due to the R23.
Fred
RE: Total Pressure of refrigerant blend
We have a cylinder of recovered R22 and at 60F we have a pressure of 211 psi. We were using the R22 as part of the high side of cascade refrigeration system with R23 on the low side. We figured there must be a leak in the cascade condenser leaking R23 into the R22 side. To be positive we decided to have a sample taken of the recovered refrigerant and have it analyzed. I didn't know whether to take a liquid or vapor sample. I took a liquid sample (which now seems to be have been the wrong choice).
I was also trying to see if I could figure out the percentage of R23 in the cylinder using partial pressures and such. That led to my question about partial pressures.
Any thoughts?
RE: Total Pressure of refrigerant blend
Roger
RE: Total Pressure of refrigerant blend
Thanks for the details. I now understand what's the problem. Assuming you have eliminated the possibility of a non-condensable gas like N2 or air in the R22 side of the system, I agree with imok2 that you have a leak.
Also based on a matchbook calc you have about a 50/50 split in the vapor phase of your bottle. This is based on an extension of Dalton's law that states the mole fraction of the R22 will be the ratio between the pressure of the R22 (101.3) and the total pressure (226) (P_22/P_total)is approx 0.45
Certainly not rigorous, but likely to be close.
I hope this helps
Fred