R290 to CO2 ratio

[DFI pit bull]

Hi all,

I am currently in the process of building my first ever two stage cascade please feel free to see my build log here http://www.benchtec.co.uk/forums/thr...-first-cascade

I intend to eventually charge with ethylene but for the moment due to cost mostly I would like to have a go at an r290 + co2 combo. I have read some threads and have seen people use this combo but there is no mention of the ratio.

Also has anybody ever used co2 from an extinguisher? I already have one, I can only assume that the co2 is not as pure as r744 or at least not guaranteed purity.

One other thing, I would welcome any advice from you Xtreme experts regarding any other aspect of my build, as I already mentioned it's first cascade.



Thanks in advance.

[Ozzfest05]

I would like to start off by not entirely recomending Co2 in second stage due to dry ice formation.
Achievable temps are also not too great.
Ultimately ethylene is the best choice for second stage refrigerant. IMO.
If you can get your hands on r507 this would be ideal for first stage
And for that matter you could charge the second stage with 507 aswell until your ethylene arrives.

In the few cascades and ss I have built ive noticed even though r290 is vey easily tuned
It cant handle the load capacities r507 can.


Hope that helps, cascades are alot of man hours. Just be safe

[Ozzfest05]

Since its your first cascade i should plug a few things.
Read all stickies and build logs.
Second stage should have a high pressure cutoff. For safety.
Due to cold bugs on some cpus i recommend using hot gas bypass valve to the evap.
Bypass can save alot of time

[DFI pit bull]

I would like to start off by not entirely recomending Co2 in second stage due to dry ice formation.
Achievable temps are also not too great.
Ultimately ethylene is the best choice for second stage refrigerant. IMO.
If you can get your hands on r507 this would be ideal for first stage
And for that matter you could charge the second stage with 507 aswell until your ethylene arrives.

In the few cascades and ss I have built ive noticed even though r290 is vey easily tuned
It cant handle the load capacities r507 can.


Hope that helps, cascades are alot of man hours. Just be safe

Thanks for you help.
Ok, got you about the r290, I don't have access to r507, I only have r404a which is in the first stage, there isn't much difference between the two. I presume you mean use the r507 in combination with the co2?
I can also get hold of r410a if it's possible to use with co2. I was already aware of dry ice formation, I thought r290 flushes out the dry ice?

Since its your first cascade i should plug a few things.
Read all stickies and build logs.
Second stage should have a high pressure cutoff. For safety.
Due to cold bugs on some cpus i recommend using hot gas bypass valve to the evap.
Bypass can save alot of time

I have a lp/hp switch, i will install in the second stage, however i have not seen any hot gas bypass valve being sold in the UK, seems to be a very popular item in the US. I have read a few build logs and have seen not everybody uses them, why is that?

[Ozzfest05]

R404a is perfect for the first stage. And you are correct about r290 + co2 in the second stage.
I misunderstood thinking you meant first stage r290 second co2.
Your setup sounds good but ethylene in the second stage will make it the monster it wants to be.

A hot gas bypass is not manditory but believe you, me, its such a small step that makes the unit more attractive.
You can directly bypass a cold bootjust by a flick of the switch heat evap up 25c apprx.

[n00b 0f l337]

There is no ratio, same with charging you will find very quickly that its a matter of "How much till it works".
You will charge primarily CO2 and then have dry ice issues, and then the goal is to add just enough r290 to prevent these issues.

[DFI pit bull]

You can directly bypass a cold bootjust by a flick of the switch heat evap up 25c apprx.

Sorry I don't understand, can you please explain in another way.

There is no ratio, same with charging you will find very quickly that its a matter of "How much till it works".
You will charge primarily CO2 and then have dry ice issues, and then the goal is to add just enough r290 to prevent these issues.

Cool!!! thanks can't wait to try it.




Thanks guy's for your support.

[Ozzfest05]

Essentially all the hot gas bypass does, is dump the second stage gas prior to entering heat exchanger into the evap.
Since this gas is normally around 35c you can manage evap temp in a cold boot situation.

Its only handy for cpus which cold boot after a certain temp.

[Ozzfest05]

As for extra work all it requires ia the valve, some plumbing and a length of cap tube to the evap.

[n00b 0f l337]

Or a solenoid valve and PID if you want to regulate it automatically.

[piotres]

Co2 is quite hard to use in cascade.

R1150 is MUCH easier.

In mine very first cascade I've used co2+r290, temps without load were ~-80C, but with approx 200W of load I get -45C . Adding more of co2 cause dry-ice formation. but it's nice to beat -100c with co2 .

[DFI pit bull]

Thanks for sharing your experience. I will try co2&r290 for a little while for fun, will buy some r1150 in the near future

[DFI pit bull]

Co2 is quite hard to use in cascade. R1150 is MUCH easier.

You are very right, finally been playing around with co2 the last few days, keep getting blockages, presume dice buildup somewhere, best I can do is -70c before evap temp/pressure start rising, after a while I suddenly hear a whistling sound and a change in the tone from the cold compressor and the line set jumps, then the temp lowers again, then keeps repeating this.

[DFI pit bull]

Added a few images.

[Buckeye]

Nice job on this so far. That is one huge Evap also and you did a great job on brazing all that !

[Sk_rmouche]

I see that you have a LUVE condenser ( or affiliated ), could you give me the reference ? I'm searching for a nice condenser to replace the old one on my cascade

[DFI pit bull]

Nice job on this so far. That is one huge Evap also and you did a great job on brazing all that !

Thanks, yes the evap is pretty large, my intention was that it could handle a decent load, I made it on my lathe, was a lot of fun to make, very happy with the brazing job, my previous evap wasn't so great, but I guess you learn from your mistakes

I see that you have a LUVE condenser ( or affiliated ), could you give me the reference ? I'm searching for a nice condenser to replace the old one on my cascade

I don't know much about the condenser, I got it from work, it came from a retail outlet, the compressor was reused for something else, my boss said I could have it, I gave it a good clean and came out like brand new. There was a label with German writing but that has been covered by the desuperheater.

A small improvement.

[Calathea]

Are you running Co2 wiht those temps? Unloaded or what?

[DFI pit bull]

Are you running Co2 wiht those temps? Unloaded or what?

Yes co2, no load.

[Calathea]

Yes co2, no load.

Cool. Not many people do this, I hope you will get good results! Evap looks solid!

[DFI pit bull]

Still waiting on the ethylene, testing with co2 continues, dry ice blockages are a real pain. It's obvious the dice accumulates in the evap, then causes the block, I know this because the suction pressure goes very low (into deep vacuum) then the evap temp rises and rises, after a few moments there is a sudden loud whooshing noise and the suction line moves violently followed by a whistling sound in the compressor, after this happens the suction pressure suddenly rises and the evap temp lowers. No amount of propane flushes out the dice totally, its more of a problem under load conditions.

RIGHT!! been thinking, can only assume the evap is the problem. As you know I am using a stepper type evap which is great for all refrigerants, most evaps have a similar design to maximize heat transfer. So for the use of Co2 the evap must be less restrictive allowing the dice to pass out through the suction line with the least amount of restriction. Was also thinking the lineset could benefit with a larger diameter suction line.

I have an idea to make a new evap with an open plan design, I have faith co2 can be used effectively in pc overclocking cascades and is dead cheap. Have you guys tried experimenting with alternative evap designs?

[runmc]

great job!!! I hope you will be getting some 1150 soon.