question

[agross]

If you have a fixed volume of refrigerant at a fixed temperature how do you find the percentage of liquid and the percentage of vapor? For example if I have a 1 ft³ of R-22 at 75°F (132.2psig), what volume is liquid and what volume is vapor? I know it's kind of an off the wall question, but it's something that's been bothering me, and I can't figure out how to calculate it. Vapor and liquid have different densities (right?) so that's my stumbling block. Thanks, Adam.

[HVAC/Stud]

Use a enthalpy chart for R-22


STUD

[icemeister]

Assuming first that this is a stable, static condition at equilibrium, given the parameters you stated there is no way to determine the amount of vapor or liquid that is present.

Consider a container of known volume that's been sitting quietly in an air conditioned space at 75 Deg F for a long time, you know that it contains R22 and you measure the pressure as 132 psig. Without also knowing the total weight, there is no way to calculate what you're looking for.

[hvacfella]

'If you have a fixed volume of refrigerant at a fixed temperature how do you find the percentage of liquid and the percentage of vapor? For example if I have a 1 ft³ of R-22 at 75°F (132.2psig), what volume is liquid and what volume is vapor?'

ME: Dang..i had this same dilemna
just last week. I was on my last job of the day, and i knew i was getting close to being out of R22 in my last 30 lb cylinder and was wondering how much was still in there in liquid form. So...as i opened the side doors to my 1998 Chevy Cargo Van with the 305 cid motor in it....i fixed my eyes on the R22 cylinder as i contemplated if i would have enough to recharge this customers a/c unit. So...with great apprehension and determination, i grasped the cylinder with my right hand on the top while i placed my left hand on the center of the cylinder. This allowed me a good grasp of the cylinder as i was hovering over it. Then, my brain signaled my hands as i coordinated a steady yet swift action which resulted in me picking up that cylinder and shaking it simular to shaking a blender of Margaritas. I did this for perhaps as long as 3 full seconds at which time i put the R22 back down and concluded that there was about 5 lbs of liquid monochlordifloromethane laying on the bottom of the cylinder.

Hope that helps in some way.

Dave

[Dowadudda]

Some of you, not all but some, think way too much.

[hvacbear]

Let me know when you find out.

[agross]

Ok, I was going through one of my textbooks (Modern Refrigeration and Air Conditioning, Althouse-Turnquist-Bracciano) and I found this chart on page 343. It lists Volume Vapor of R-22 at 75°F at .37 ft³/lb and Density Liquid at 74.8 lb/ft³. So if I understand this correctly (and I don't think I do), if I had 1 lb of R-22 there would be .37 ft³ liquid and since there are 7.481 gal to 1 ft³ that means there are 2.77 gal of liquid?

[Tom R]

Agross:

I was hoping that someone who could explain this better would jump in here with a procedure you could use. Since that hasn't happened I will try to outline a procedure that may be used to calculate liquid to vapor volume ratios.

From a practical standpoint, what you want to know may not be of much value to you as a Tech. However I don't presume to know what is important to you and what isn't. So I will give you a procedure and you can spend the time to work through a few different scenarios, then you can makeup your own mind if it is something you need to remember or if it is a total waste of time.

If you work the examples and can follow through the process it may clarify the saturation behavior of refrigerants and show the relationships of Temperature/Pressure, Vapor and Liquid densities and Volumes. So even though the actual ratio of liquid to vapor volumes may not be of significant interest to you in the future, just understanding the saturated state behavior of the refrigerant will be a big benefit to you.

If you know the actual volume capacity of the system (or container) and the weight of refrigerant charge you can use a table of saturation properties for that refrigerant and calculate how much of the refrigerant is vapor and how much is liquid (under static saturated conditions). There are several ways to do it (that I know of, there may be more?). The method I will type up is laborious and takes a lot of steps but just uses simple math and takes a number of logical steps through the phase changing process.

A couple of things to keep in mind as you follow through these examples are---

1. When liquid and vapor refrigerant are in contact with one another (in a confined space) they will behave as predicted by the saturation properties.

2. Under static condition a saturated refrigerant is controlled by the temperature of the container so the temperature will be the controlling variable and the pressure will be the controlled variable.

The following explanation is compiled from some of the notes I have collected over the years: It is impossible to cover even just the basics of this subject without ending up with a very lengthy discourse but in the interest of helping out a student I will do the best I can.

WARNING!! All information beyond this point is technogeek so if you are offended by technogeek do not proceed beyond this point.





The following saturation proprieties have been taken from a list of R22 proprieties
For the conditions you listed Temp @75°F

R22 Saturation Properties

Liquid Den. 74.67002 #/FT^3 Most Charts will list liquid properties as density. The reciprocal of density will give the volume of the liquid. .
(Volume = 1/ density) = (1/74.67002)= 0.013392256 FT^3/#

From the Saturations proprieties chart Vapor Volume (Sat)= 0.37513 FT^3/#

You can convert the values to whatever units you are most comfortable working with and you can round off values to whatever precision level you feel is close enough for your purpose.

Below is the Liquid volume of R22 @ 75°F expressed in Cubic ft per Pound, Cubic inch per pound, and Cubic inch per ounce

Liquid Volume (sat). = 0.013392256 FT^3/#
Liquid Volume (sat) = 23.14181783 In^3/#
Liquid Volume (sat). = 1.446363614 In^3/Oz.


Below is the Vapor Volume of R22 @ 75°F expressed in Cubic ft per Pound, Cubic inch per pound, and Cubic inch per ounce

Vapor Volume (sat) = 0.37513 FT^3/#
Vapor Volume (sat) = 648.22464 In^3/#
Vapor Volume (sat) = 40.51404 In^3/Oz.

Comment: I have a boatload of reference material on the proprieties of R22 and I don't think that any two sources are in complete agreement on the values; but they are all reasonably close to one another.

In these examples I will try to use (sat) to denote when the value is to come from the saturated properties table and (act) when you should be using the actual quantities that are present in the system. I addition I will use the OZ/In^3 units so that we don't end up with such small decimal values.







If you were to begin with an evacuated container or vessel that had 0.13368 FT^3 or 231 Cubic inches of displacement (1 gallon) and would carefully weigh in 16 Oz. (1 lb.) charge of R22 while the container was exposed to 75° ambient conditions the liquid would take up only 23.142 cubic inches of that container (if you could somehow keep it from vaporizing). The remaining void of the container would be (Vessel vol. - liquid volume (act). Or 231 - 23.142) = 207.858 Cubic Inches. In actual practice this void is filled with vapor as the liquid "boils off". Once sufficient vaporizing of the liquid had occurred the vapor expanding into the void would raise the pressure to the Saturated Pressure Temperature value of 75° and 132.2 psig and the P/T would stabilize here at the saturated properties equilibrium.

We use this Saturate Liquid Volume of the complete charge's total mass compared to Vessel's Volume (act) to find the mass that needs to vaporize to fill that void.


Void Volume = (Vessel Vol.-(Liquid Volume (sat)* oz). use the total charge weight here
(231-((1.446363614 * 16)) = 207.8581822 Cubic inch


When a given amount of liquid "boils" off, the vapor it creates will greatly expand (see the ratio of Vapor vol. compared with Liquid vol.)

However the liquid that boils off will decrease the amount of liquid in the system so the total effective volume "gain" Is found by subtracting the Liquid volume of a given weight from the Vapor volume of the same given weight. Vaporizing 1 oz of R22 at 75°F saturated conditions would create 40.51404 IN^3 of vapor but at the same time decrease the Liquid volume by 1.4463 IN^3. Since the first 1.4463 IN^3 of vapor is used to replace the void left behind when vaporizing the ounce of liquid only 39.0677 IN^3 of vapor is left to help fill up the containers initial void volume.

The table below will give the Volume Gain in Cu.ft/#, Cu.in/#, and Cu.in/Oz. For the 75°F saturated condition.
Vol. Gain =(Vapor Volume (sat) - Liquid Volume (sat)
Vol. Gain = 0.361737744 FT^3/# (0.37513 - 0.013392256)
Vol. Gain = 625.0828222 In^3/# (648.22464 - 23.14181783)
Vol. Gain = 39.06767639 In^3/Oz. (40.51404 - 1.446363614)

The next step would be to calculate how much of the original mass would need to be vaporized to fill the void.

Refrigerant mass in Vapor = Void Volume/Volume. Gain
( 207.8581822 / 39.06767639) = 5.32046442 Oz

Which of course would leave 10.67953558 OZ in Liquid mass

To find the area the actual vapor occupies = Vapor mass (act) * Vapor Volume (sat)
(5.32046442 * 40.51404) = 215.5535083 Cu in of the container is used for Vapor.


Vapor Volume (act) / total vessel volume = Vapor fill
215.5535083/ 231= .9331 or 93.31% of the containers area is filled with vapor

To find the area the actual liquid occupies = Liquid mass (act) * Liquid Volume (sat)
(10.67953558 * 1.446363614)= 15.44649168 Cu in of the container is used for Liquid.

15.44649168/231= .0669 or 6.69% of the container is Liquid filled.

All of the above examples assumed working under saturated static conditions where the saturated refrigerant is controlled by the temperature of the container so the temperature will be the controlling variable and the pressure will be the controlled variable.

Try changing some of the values like the amount of # of charge and see what effect it has, then change the volume of the container and watch the effect there. If you don't have enough container volume the charge will be all liquid with no vapor, or not in the saturated range, with the math the void volume will show up as a negative value (in the real world something would blow up when the temperature increased), if the charge mass doesn't have enough volume to fill the cylinder it becomes all vapor and once again not in the saturated range so you would end up with a Liquid Volume (act) that was negative (in the real world the charge would be all vapor so the pressure would be under the value listed for the given ambient temperature on the Chart). We have to have both liquid and vapor in the cylinder to have saturated conditions. . If you do spreadsheets set it up in a spreadsheet and by just changing the necessary data you can instantly see what effect your changes have made.

If your school still has some of the old calibrated charging cylinders like the "Dial-A-Charge" units you can actually perform the experiment from this example by plugging in the actual volume of your cylinder into these equations. The neat thing about using the charging cylinder is that you will be able to watch the liquid level change with different charge amounts and different temperatures.

Notice that under static conditions the pressure verses temperature readings only tell you that you are at a saturated condition (both liquid and vapor in the vessel) they do not tell you how much refrigerant is there or anything about the vapor to liquid ratio. A 30# cylinder of R22 with a few pounds of refrigerant left in it will give a pressure reading that corresponds with the saturated temperature from the chart just as it did when the cylinder was completely full. Even though we know that the nearly empty cylinder will be nearly full of vapor and contain very little liquid.




Another point to keep in mind: Under dynamic conditions (refrigerant in an operating vapor compression system) the pressures will be the controlling variable and the temperature will be the controlled variable in areas operating in the saturated region. Also under dynamic operating conditions some areas of the system may be operating with saturated refrigerant (both vapor and liquid in that area) while other areas containing liquid only may be sub-cooled (temp=less than Saturated value). At the same time there may be other areas where the refrigerant is 100% vapor so superheating(temp. = greater than Saturated value) may be present in that area.

Another thing to be aware of is that contamination such as non-condensable, a blend that has fractionated, or mixed refrigerants can also cause reading that are not consistent with the saturation properties.

[Diceman]

Open the can for a bit, soon you will see the frost line on it, that's how much liquid ya got left

[hvacfella]

What is the purpose of someone trying to mathematically or otherwise , figure out how much liquid vs. vapor is in a refrigerant drum ??? It reminds me of when i went thru trade school..the instructor had us calculate using a very long formula how many pounds per hour a compressor would pump under certain conditions --- totally useless in real life of an HVAC Tech. Same for 80% of what was learned (and now forgotton)-- from High School.

Your brain can only remember so much , so, why not fill it with useful info that can be useful to you making a living or....info that can be used regularly or...at least once in a while ?! When youre on a job and your freon tank runs out when your charging a unit... you can figure that its empty . Then, you go get another one from your truck. Make sense ???! Didnt mean to get snotty with you....just trying to be practical .

Dave

[frozensolid]

I don't see the point of knowing this. Unless you are looking for an exercise, of your mathmatics skills.

I have a container of r-22 that weighs ten pounds. The can weighs six pounds. How much refrigerant do I have.

[condenseddave]

Originally posted by Diceman
Open the can for a bit, soon you will see the frost line on it, that's how much liquid ya got left

This is the easiest method.

[condenseddave]

Originally posted by frozensolid
I don't see the point of knowing this. Unless you are looking for an exercise, of your mathmatics skills.

I have a container of r-22 that weighs ten pounds. The can weighs six pounds. How much refrigerant do I have.

Like TomR stated, it's really none of our concern whether or not it's important to him.

We needed a question like this. It had been waaaay too long.

BTW, you don't have enough.

AAMOF, you don't have any. The container is holding four pounds.

[hvacfella]

'I have a container of r-22 that weighs ten pounds. The can weighs six pounds. How much refrigerant do I have.
'

ME: Where did you get that 10 lb container from ?! Thats what i need to be carrying at the end of the day.

[agross]

Tom R, thanks for the great explanation. I worked through your examples, and now I understand. As for those of you it's just something I wanted to learn how to do. Not that I'll ever use it, but maybe sometime in the next 40+ years I will be working in this industry I might come into a situation that this will save my a**. In addition, don't any of you ever think about what goes into the engineering of a system? It seems like most on this forum can fix damn near any piece of equipment, but keep in mind that system we work on was engineered, that's why it works (most of the time). If we were out there designing these systems as we went; they would never work correctly or efficiently. Sorry for the rant. It aggravates me when people get the “I don't care how/why it works just as long as it works attitude.” Thanks again Tom R. Adam.

[Diceman]

As you get older you tend to get grumpier, it's human nature

[frozensolid]

Where did you get that 10 lb container from ?! Thats what i need to be carrying at the end of the day.

By then end of the day it was a six pounder. It's a new product from Little Richie in a yellow jacket. It is amazing the more you use it the lighter it gets. It is called the MTCAN.

[hvacfella]

Tom,

'In addition, don't any of you ever think about what goes into the engineering of a system? It seems like most on this forum can fix damn near any piece of equipment, but keep in mind that system we work on was engineered, that's why it works (most of the time). If we were out there designing these systems as we went; they would never work correctly or efficiently. Sorry for the rant. It aggravates me when people get the "I don't care how/why it works just as long as it works attitude."
'

ME: If you are going into design and engineering of hvac...you wont be required to know how much liquid vs. vapor is in the tank. But, if you want to go thru the excerise to broaden your knowledge...then i cant find fault in that per se. To answer your question...YES, i think about system design all the time that im working in this trade ; i have spent a tremendous amount of time and energy on it . It is important to know things like what is actually taking place during the refrigerant cycle with the physics as well as what went into the specific design of the components. Concentrating on THIS end of the design and engineering, will afford you practical knowledge that you can use and benefit from. Glad youve chosen hvac as your career --- its sure been a blessing to me and many others in here.

Dave, Owner since 1986
Started in trade in 1974.

[R12rules]

Originally posted by Diceman
Open the can for a bit, soon you will see the frost line on it, that's how much liquid ya got left

What's that name on the side of the bottle your drinking from?
maybe I should order me some......ROFLOL

[Diceman]

2 trains are 680 miles apart, one train is going west at 38 mph, another train goes east at 45 mph, when will they hit head on and explode into a ball of burning fuel and steel?