Project Whop : Autocascade

[AliG]

you could always try checking craigslist to see if anyone nearby has a cylinder they don't need anymore. One time I even saw one on ebay with some free acetylene included, but it was pickup only (don't think you can ship it with refrigerants anyways)

[n00b 0f l337]

If someone on craigslist is selling r170 or r23 I'd be seriously surprised :P

[mytekcontrols]

Nol if you got the ethylene already, then go ahead and use it instead of R-14. If you want to get to lower temps, then just add a little Argon. If you also anticipate a big load, then go with a subcooler as well. Heck with 2hp you've got plenty of push to overcome any losses in implementing the subcooler.

[n00b 0f l337]

I have r1150 AND r14, a single pound of r14 to be exact (in gas form). I have r11 as well and r22, r134a, r290, r507a, r404a, r402a (a little), r407c, and a few other things I've collected. So basically what I dont have is a mid gas between the first set and r14. r1150 is sorta in the middle, mixed with r290 it could become a r170 like substitute, but I think the r290 might separate out in this style.

[mytekcontrols]

So basically what I dont have is a mid gas between the first set and r14. r1150 is sorta in the middle, mixed with r290 it could become a r170 like substitute, but I think the r290 might separate out in this style.

R290 (propane) mixed with R1150 (ethylene) probably wont get you where you need to be, and yes it probably would stay more as a separate component boiling off at -43C. However I am only guessing on this one, since I have never used either of these gases before.

If I owned the company I sub-contract to I'd get you the gases you needed, but the owners really like keeping it strictly in the Polycold service realm, especially since they get big bucks for selling the Polycold unit charges. They let me play around, because many times what I do comes back to benefit them in someway, shape, or form.

[AliG]

hey mytek, do you have an msn or some way I can contact you? I don't know why but I didn't find a pm feature for your account (no idea why because I tried other people's accounts and it worked) so I had to ask it in a thread

[n00b 0f l337]

He's turned off PM so he doesnt get bombarded me thinks

[AliG]

ahh

I just have some questions I have to ask him, that's all, though I suppose I'll have to accept it if he says he doesn't want to give out his contact info

[n00b 0f l337]

I'm sure if you ask out here he'd be happy to help, you've got a PM AliG.

[AliG]

mytek you've got email (sent you one from your site)

[mytekcontrols]

I got your email Ali

If you don't mind I would like to answer your question on this forum. But first I'll have to think of how best to do this.

[AliG]

Ok, I feel kinda noobish about it, but how do you guys know about what mixtures of refrigerants work and what not? I mean I understand that you would add a bit of r290 to r507 to move the oil, but I'm talking about when people do crazy mixtures of r410 etc to get low temps without the high static pressures?

[jinu117]

Huh? Getting crazy temp without high static pressure?
I SERIOUSLY doubt it if it was tuned to handle same amount of load to be honest. It's not like there probably aren't thousands of people researching refrigerant every day. And there are some basic rules on refrigerant mixing (or pre analysis of such) based on experimental data that has been gathered and based on composition of molecular structure. (My latest gain in knowledge from reading few cryogenic related books)
I mean, SS unit static pressure tuned optimally for 230-250w seems to stop around 55-70 psi range from what I've seen so far and 200w range as low as 45 psi.
Of course, auto-c is different story from SS unit.
Besides, what is HIGH/LOW static pressure? Everyone seems to have different opinion in this in some regards :P

[mytekcontrols]

I remember many years ago doing a blending test with 2 different refrigerants in a tank (unfortunately it has been so long ago that I forget which two were used). Anyway both refrigerants were charged into the tank as a liquid, and one was specified as having a lower boiling point then the other.

After both refrigerants had been charged into the tank, we saw a static pressure that seemed fairly close to what was expected for the lowest boiling point refrigerant (based on the tank temperature). Then we shook the tank. This is the amazing part... as we shook it, the static pressure actually dropped lower then what it was to begin with, and was now at a point somewhere between the two refrigerants as compared to a temperature/pressure chart.

We knew we had charged in sufficient liquid of both refrigerants to still have a saturated liquid present. And we also knew that by shaking the tank that the 2 refrigerants would be encouraged to blend with each other. But to see the pressure drop below the pressure/temperature properties of the lowest boiling component was quite a surprise to us. It was as if we had created an entirely unique refrigerant.

Perhaps we had!

Anyway I tell this story to highlight the unusual effects that can occur when blending refrigerants in an autocascade. This is why it can be so tricky to design the proper blend to fullfill the application. There are programs and tables that will describe the properties of two blended refrigerants. But when you get into 3 or more, I only know of one person that has ever created a program to accurately model such a thing, and he isn't sharing it (and unfortunately it's not me).

The best initial approach I can suggest (and could perhaps be considered a rule of thumb), is to try to pick refrigerants with a difference in boiling points of approximately 50C (+/- 10C). Of course an autocascade will work even if these conditions are not adhered to, but the idea is that this should give you the best initial results. The rest comes down to intuition based upon a lot of experimentation (or should we say a "gut" feeling). Some people also call it black magic.

[AliG]

So I take it I just need to practice experimenting with various refrigerants to get some practice. Any you recommend for me to try? I'm still in high school so I don't think my dad would allow me to mess with any too dangerous (though I can get a hold of them because my friend's dad works for a air conditioning company as a repair man

[n00b 0f l337]

r507a and r290

[AliG]

would regular propane work (like the home depot kind)? Also how much is a small amount of r507a, I've already stretched my budget as it is

[killermiller]

You can propane for a torch for about $3. Unless you have recovery equipment or your Dad's friend has a lot of time, I would just use propane.

[AliG]

that's what I was intending (though $3? where? it's like $10 where I live)

[killermiller]

If it is $3 in Alaska, it has to be $3 there.

[n00b 0f l337]

Hahahaha if anywhere needs propane its alaska :P

[AliG]

Probably I'll just have to go to a home depot, I generally just go to a place that's a few minutes away from my house but in return the prices tend to be higher since it's a small business instead of a franchise.

But what I'd like to know is how much does a reasonable amount of r507a to work with cost? If it's too high I'll just skip the idea and go with propane as it does give you pretty good temps anyways, but if it's reasonable, I can get my friend's dad to help me out

[killermiller]

I think the cost varies from market to market, depending on supply and demand. If you are the only person who wants it you will pay a high price. If the supplier has many customers who need it you will probably pay less. I wouldn't be so concerned about the price of aquiring it, I would be more concerned about recovering it if you needed to adjust tuning and such.

[AliG]

here's another one I've been wondering about, is there a general amount of psi for a given amount of load you want with all refrigerants, or does it vary per refrigerant? (ie in general for say 200w of load would you use x psi of refrigerant across the board or would it depend on the refrigerant?)

[Freddie123]

It varies by system, not even just by refrigerant.