Morphing Air Conditioner into Autocascade System

[mytekcontrols]

Isnt the internal volume of those bullet strainers too low? Flow rates through a low volume tube like that would be too high to allow for phase seperation, wouldnt they?

Actually the volume is quite large as compared to the ID of a 3/16" od tube that feeds it, in fact my Bullet Strainer Phase Separators are probably 4-5 times the volume of what Polycold used on their P-100 and PGC-100 product lines for the upper phase separators. So what did they use? Believe it or not, a 5/16" copper tee, angled downward with the side port passing gas, and the bottom port passing the liquid. When you get into the upper separation points, the volume of refrigerant is considerably less than what you see in the first stage (hence the larger size of the 1st separator as depicted on the piping diagram, and the larger flow of the 1st captube).

Believe me, the bullet strainers will do just fine as phase separators

[mytekcontrols]

I know I have been showing great progress on this project this last week, but the holidays are over until Christmas, and now I've got to get back to my real job

So for the next couple of weeks there wont be much new stuff to show (sorry PhilippF). However there is a very real possibility that the new HXC stack will be completed by the end of this year

As it comes together I am getting more, and more excited. I think it will be very clean build, and something quite amazing if it meets my expectations.

[PhilippF]

...must...complete...unit...must...complete...unit ...

[[XC] gomeler]

lol PhillippF. Maybe that'll work

[Moc]

Hey Michael!


Look at my autocascade. My phasesep is quite huge with steelwool inside - but don't seperate as i want. I have two sightglasses, in each liquid-line.
It is charged with R290/R23. I get much R290 in the liquid-line from the r23-stage.

Any advice?

Thank you very much!

[quintus]

lol i already put in my subconstions that i have to reach -80c this year!

@ mytekcontrols: so the r22 and r123 they are mixing and create a ''new freon'' kind off .why not use just 1 r*** like lets say r134? is there any reason, could u explain a bit pls(i saw low presures and high temps for condensor so there is something )
would using a real extra stage just for r123 improove things?

second question: is it ok to use 0,7mm(0,028''?) cap lines?

thx

[jinu117]

I am no expert on auto-c (obviously) but there was some patent related to using the HFC only for autocascade. R-134a was definitely mentioned in there.
Thing would be imperical data will largely have to be rebuilt around new gas, and time and money spent getting to it while R-22 is still widely available.
Also, R-134a's efficiency isn't quite that good and will change balance of current design (cap tube, charge amount, etc) most likely (as well as PT... which if you noticed is shared among stages...)

PS) I also remembered something, some of the gases could fractionate (how much does it matter? not sure) and cause unwanted behavior too... don't think it will matter much in grand scheme of things but it surely would not be easiest thing to develop without good idea on what to look for.

[n00b 0f l337]

Beleive that mix is r123, r134a, r508a/b, r14.

[quintus]

Beleive that mix is r123, r134a, r508a/b, r14.

what the........ 123 and 134a? no r123 and r22?
are u using those types mytek?

thx,
q

[n00b 0f l337]

Thats for a more environmentally friendly mix I beleive.

[mytekcontrols]

Hi Moc thanks for joining the discussion

As for your autocascade: it's not the fault of your phase separator that is causing the problem, but the lack of a HXC before it (Aux Condenser). Coming in at room temperature is the limiting factor for good separation. If you put another plate HXC before it (exchanging with the suction return from the existing cascade plate HXC), you should see somewhere around -30C at the phase separator. Give it a try and let me know what happens.

mytekcontrols: so the r22 and r123 they are mixing and create a ''new freon'' kind off .why not use just 1 r*** like lets say r134?

If I could get R-114 (boiling point = 3.6C), then this would be what I'd substitute for the R-123/R-22 mix. However I don't believe there is a good alternative available, at least not in a freon. R-134A might work, although it does boil off at a colder temp, and probably wont work as well as either R-123 or R-114 in transferring heat at the air cooled condenser.

Edit: HFC R236fa is a good replacement for R114, although it will necessitate the use of POE oil in the system.

is it ok to use 0,7mm(0,028''?) cap lines?

Well it all depends on what displacement of compressor you intend to use, and what flow rates you need. Go back a few posts in this thread and you'll see a chart and a discussion on captube sizing.

[mytekcontrols]

what the........ 123 and 134a? no r123 and r22?
are u using those types mytek?

I'll be using R123, R22, Ethane,R14 as my first mix. And to improve the oil return, I'll be using POE since it is quite miscible with all my choices. The R123/R22 liquids will be a 50/50 ratio, and probably also the Ethane/R14 gases as well. This will be my starting point, and dependent on temperatures seen across the HXC's, additions will most likely be needed.

Speaking of temperatures across HXC's...
I said this before, but I'll say it again, when developing a new autocascade design it is very informative to thermocouple the In & Out of everything within the refrigeration circuit.

So I'll end up with the following TC assignments:

1. Compressor Discharge
2. Compressor Suction
3. Air Cooled Condensor-OUT (Liquid Line)
4. Auxiliary Condenser Suction-IN
5. Phase Separator#1
6. Cascade Condenser#1 Suction-IN
7. Phase Separator#2
8. Cascade Condenser#2 Suction-IN
9. Phase Separator#3
10. Cascade Condenser#3 Suction-IN
11. Cascade Condenser#3 Discharge-OUT (Final Strainer)
12. Evaporator-IN
13. Evaporator-OUT

This will give me a very clear picture of how efficient each stage is performing, and will help reveal the effects of refrigerant additions.

[PhilippF]

If I get it right: You dont charge every refrigerant in a row but start with 2 mixtures (R123/22 and R170/14) and change the ratio of these two mixtures in the tuning process?

EDIT: I wanted to charge the following way (please correct me if I tell nonsense):

Vacuuming and then breaking with R123 up to 1 barg (2 bara). Adding R22 up to 3 barg (4 bara) and then adding R23 up to 5 barg (6 bara). I imagine this will be a nice starting mix. Then turning the unit on and watching the first HX (where R22 mainly should evaporate) and perhaps add R22 until I have no significant temperature differential along the HX (I picture then being enough R22 to be there to cool the whole HX). Then repeating the same thing with the Evap (for R23). Do you think this will work?

Regards and thanks,

Philipp

[jinu117]

Going by pressure would be really hard to control to be quite honest with you unless you are sure of charging condition (R-123 would most likely not be issue as you will end up liquid charging most likely, R-22 would be as it will be from liquid -> gas, R-23 most likely not since it will be gas -> gas typically).
Go by weight... and pressure At least that's how I played on last mixed refrigerant build... (nearly a year and half ago or something...) Kind of failure back than as goal was to lower temp under load but I ended up gaining capacity -_-;
PS) Hey Mytek, how do you dispose of mixed gas? Link to place that are nationwide chain (or something like that) disposes of these mixed gas specifically? Only places I found were pretty damned remote and I am tired of having this mixed gas of recovery tank for.... damned long taking space.

[mytekcontrols]

If I get it right: You dont charge every refrigerant in a row but start with 2 mixtures (R123/22 and R170/14) and change the ratio of these two mixtures in the tuning process?

PhilippF look what time it is! Why am I still awake? I keep hearing a message in my head saying to complete unit... complete unit... I'm seeing spinning disks...

Seriously though, I talk about the ratio between the two mixtures, but I was just comparing what I call the liquids (R123/R22), and the gases (R170/14) as two separate groups, and applying a ratio of proportion. The liquids will be charged into the system by weight, and the gases by pressure. Each component is charged into the system (or transfer tank) one after the other, or in your words "in a row".

I wanted to charge the following way (please correct me if I tell nonsense):

Vacuuming and then breaking with R123 up to 1 barg (2 bara). Adding R22 up to 3 barg (4 bara) and then adding R23 up to 5 barg (6 bara). I imagine this will be a nice starting mix. Then turning the unit on and watching the first HX (where R22 mainly should evaporate) and perhaps add R22 until I have no significant temperature differential along the HX (I picture then being enough R22 to be there to cool the whole HX). Then repeating the same thing with the Evap (for R23). Do you think this will work?

As I said, the liquids are charged by weight. Then adding to the static pressure of the liquids in the system, you would add the R23 (in your case).

However if you do build a system with 3 cascades, you'll need something like R14 as well to get any appreciable cooling at the end (-110C to -120C system). If you don't want to use R14, then eliminate cascade#3 and phase separator#3. Of course this would be a -75C to 80C system.

Edit: Although having one less cascade wouldn't preclude the use of R14, it just wouldn't be quite as efficient.

When tuning the system by adding refrigerants the object is to minimize the temperature differential between the Suction-IN vs. the Discharge-OUT of each HXC, while still having a high differential from one end to the other. See example below:

[mytekcontrols]

Hey Mytek, how do you dispose of mixed gas? Link to place that are nationwide chain (or something like that) disposes of these mixed gas specifically? Only places I found were pretty damned remote and I am tired of having this mixed gas of recovery tank for.... damned long taking space.

A lot of times I can re-use it if it's not too bunged up, either as a top-off to a low charge, or sometimes by using a cold trap to separate out the liquids. Whatever can't be recycled internally, yes does unfortunately get disposed of by a refrigerant recovery place (I don't recall the name of the firm that my place of work uses). I am lucky, since I can dispose of my experiments along with their unusable stuff free-of-charge.

[n00b 0f l337]

Time to get a charging scale

[[XC] gomeler]

I am lucky, since I can dispose of my experiments along with their unusable stuff free-of-charge.

I'll stick with R290/R170/R1150. Yay hydrocarbons

[godmod]

mytek, you use r123, so if i intend to use hydrocarbons (290/170/1150), just like gomeler, would you recommend using R-600a or even R-600 as the refrigerant with the highest boiling point?

PS. I am following your thread eagerly, I like the high quality information you provide

Thanks for sharing all your knowledge!

[[XC] gomeler]

I'd say from my limited understanding, R-600 or R-600a would be ideal choices for the auxiliary cooler for the initial separation. Might have the term incorrect for the aux cooler, but it was a pre-stage HX meant to max out the condenser and to help increase efficiency. Feel free to correct me if I am incorrect, been a while since I've thought about this stuff.

[n00b 0f l337]

Yep I'd say r600 as its a higher boiling point.

[mytekcontrols]

I'd say from my limited understanding, R-600 or R-600a would be ideal choices for the auxiliary cooler for the initial separation.

would you recommend using R-600a or even R-600 as the refrigerant with the highest boiling point?

i intend to use hydrocarbons (290/170/1150), just like gomeler

Hydrocarbon Refrigerants that were mentioned:
R600 n-Butane -0.5C
R600a IsoButane -11.7C
R290 Propane -42C
R170 ethane -88.6C
R1150 ethylene -103.7C

I think between R600 and R600a, I'd go with the R600 (remember earlier I mentioned that R114 would be an excellent warmer boiling candidate to replace the R123/R22 combo).

In the CFC days, a polycold charge consisted of:
R114 +3.6C
R13 -81.5C
R14 -129.9C (hmm this looks colder then I remember -- maybe check other MSDS's)
Argon -185.7C (no it wasn't condensed, just absorbed)

I think a charge made from R600, R170, R1150 comes the closest to the first 3 CFC choices, and would be the simplest combination that would work for -100C operation. I would go with this first, and see what you get. Using only 3 components will make it a lot easier to tune. After you have gotten all that you can get from this combination, go ahead and try adding a small amount of R290 to see if it buys you anything.

Don't expect too much load capacity at -100C, since you will be operating close to 0 gage pressure, and not have a tremendous amount of mass flow. On the other hand you should see very good performance at around -90C to -95C.

Might have the term incorrect for the aux cooler, but it was a pre-stage HX meant to max out the condenser and to help increase efficiency. Feel free to correct me if I am incorrect, been a while since I've thought about this stuff.

I call the first HXC (before the 1st phase sep) an Auxiliary Condenser since it is essentially just an economizer, or what I believe some of you also call an SLHX. All the following HXC's are considered to be Cascade Condensers. Hey gomeler I read your article on autocascades... very nice

[godmod]

you said, that you recommenc a temperature difference of approximately 50°C between the refrigerants. Isn't the difference between R-600 and R-170 a bit high? According to a P/T-chart, ethane has a pressure of 27bar at 0°C
What about a mix of R-600/R-290/R-1150 or R-600/R-507a/R-1150? That would be closest to the "50°C-Rule"...
How much does Ethane in the US or in other countries than Austria cost? Here it is about 280€ for 3kg. A bit expensive

[n00b 0f l337]

In the r114,r13,r14 mix, would r12 in between not help a little? It seems the jump is rather high, even if r114 and r13 might make a mix in the r12 range. You seem to skip that stage as well, r600, r170, r1150. Would r290 not help that much? Or give better load capacity?

[bassie]

[offtopic]

Which program do you use to make your designs?