Total Pressure of refrigerant blend 1

[gem24]

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.)

 

[Fzob]

Dalton's partial pressure should get you close.

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

 

[imok2]

Blends are a mixture of 2 or more refrigerants. The mixture is formulated to provide refrigerant properties suitable for a specific temperature application. Blends come in 2 categories; Azeotropes and Zeotropes.

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

 

[gem24]

Thank you for your input. I actually have an accidental blend of R23 and R22. Since there is no specific 400 series or 500 series with this makeup, I was wondering the total pressure of the blend at ambient temp. So, Roger, I should assumbe the pressure gauge on this bottle would read the pressure of the R23 at ambient temperature, correct?

 

[quark]

If you say bottle, your pressure gauge will read the sum of partial pressures of R22 and R23. This may be true even for a refrigerant circuit if the condensing and evaporating pressures for the two refrigerants are quite different. The same method is used to check presence of air in the refrigeration circuit. Condensors are generally fitted with two pressure gauge ports, one at bottom and one at the top. The presence of air in the system indicates higher pressure in the pressure gauge installed on top of condenser.

Regards,


Eng-Tips.com : Solving your problems before you get them.

 

[imok2]

If I confused you I apologize! Quark is quite right as is Fzob at a constant ambient both refrigerants would be in a gas and liquid state and your pressure gauge will read the sum of partial pressures of R22 and R23.
Roger

 

[gem24]

Okay so I tried to validate this sum of partial pressures idea with a blend of R503 [R23/R13(40.1/59.9)] at a temperature of 60F and assumed 100 grams of R503. My numbers just didn't work out. Am I missing something? After taking a look at the ideal GAS law, does it not work for a saturated refrigerant when you have both liquid and gas? And will this then negate the idea of partial pressures of a saturated mixture?

Thank you for your responses!

 

[Fzob]

I'm not clear on what the reason is for finding the total pressure, but let me add this.

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

 

[gem24]

Thanks again for your help. I will explain my situation..

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?

 

[imok2]

Gem' I don't feel it's necessary to determine anything other then knowing if a leak exists. In my mind yes you do have a leak. A bottle of R-22 at 60*F will read 101.3*F if you have a mix of another gas it will read some other pressure. so if your sample was taken on the hi side and you get 211# you have to have some mixing going on
Roger

 

[Fzob]

gem24

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