Autocascade Build for Gomeler

[XC] gomeler · 07-06-2006, 01:04 PM

I've spent the last few days poring over all the various designs and diagrams and I think I have finalized my design. Here is the design, will explain stuff below.

Starting from the Compressor it will go as follows
1)Small coil for vibration purposes
2)Air-Refrigerant Condenser
3)Phase Separator, most likely homemade, packed with copper wool
Low-side : Liquid line with sight glass, liquid-line filter/drier, and a test port
High-side : single test port leading into ".031 cap tube, I might put a filter drier here to keep the cap tube from clogging.
4)Heat exchanger, it'll either be a simple coil or maybe a plate HX if the budget permits it
5) High-side : Liquid-line filter/drier, a sight glass, another test port, and then a high pressure burst valve. Since I would like to avoid venting CO2 and r290 into the environment I will try to find a suitable cylinder to vent into. I suppose I just need enough volume to contain some overflow? Just an idea
Low-side : possibly spiral the suction line around the liquid high-side and then proceed to the accumulator
6) Some sort of metering device will be put before the evap, I'm not sure which valve to use, CPEV or TXV. I think I'd like to avoid cap tube as this will be the portion that really needs tuning.
7) High-side: suction line has another test port and then merges into the low-side.
8) Another test port followed by a liquid accumulator to keep from flooding the compressor, then a test port after the accumulator with the possibility of a sight glass.
Rinse, wash, repeat.

Now I don't know if this would be a valid design or not. I tried to incorporate enough test ports so that I would be able to monitor nearly every section of this machine. I forgot to include a test port between the compressor and the condenser to check for head pressures. Please give me some constructive criticism, if the design sucks, let me know. I don't want to screw this up as it will be a rather expensive design and I want it to work the first time, even if it can't handle a load.

edit: I included a test port after the compressor in the image.

Xeon th MG Pony · 07-06-2006, 01:10 PM

looks good, bit excessive on the Schroeder's though, and I've been toying mentally about utilizing a pressure tank to dump over load into to so I like your thinking.

[XC] gomeler · 07-06-2006, 01:19 PM

Heh well I have 10 of them to use, I might cut back 2 of them. I just want to know what everything is doing. Anyone see any potential problems with the design?

[XC] gomeler · 07-06-2006, 05:17 PM

Bump, 68 views and only 1 comment? Is it just that perfect?

~~Pete~~ · 07-06-2006, 05:34 PM

I'm not an expert but man thats look good on paper (well Paint). Looks like you have though lots baout safter with the Shraeder valves. Hope it works out

yngndrw · 07-06-2006, 05:38 PM

I like the idea of the burst tank, but please do have an aditional relief valve which vents into the air as normal ADITIONAL to your burst tank system but set at a slightly higher pressure, just in case all goes wrong.

[XC] gomeler · 07-06-2006, 05:43 PM

Good idea. Tomorrow or Saturday I'm going to go to United Refrigeration and talk to them about the parts I need in specific. What would be an acceptable burst pressure for the initial burst, 400 PSI? Still learning.

Nyx · 07-06-2006, 06:47 PM

Why not use an expansion tank and hook it up with a captube to have a smooth start up,without high pressure. And place a pressure relief valve at the high side. And i Wonder if there is a pressure relief valve that would allow u to braze a copper tube from the vent of the relief valve to the expansion tank that way you can avoid excessive high pressure refrigerant being release back into the system immediately. As it is diverted back to expansion tank where is it release slowly so there would be less pressure spikes. Only if such a relief valve exist.

[XC] gomeler · 07-07-2006, 12:07 AM

Are you saying use the expansion tank as a sort of buffer zone for the high-pressure refrigerant? While that would make things considerably more complicated, it would help curb immediate spikes in the high pressure line caused by uneven flows of the high pressure refrigerant. Not so sure if it would be easy/cheap/worthwhile to implement though.

Xeon th MG Pony · 07-07-2006, 12:12 AM

yes that is exactly what that type of system is, it smooths out the pressure curve of the high pressure refrigerants during start up and shut down, and during the off cycle it lowers the total internal pressure of the system.

[XC] gomeler · 07-07-2006, 12:15 AM

Interesting. Not sure if I have the $$ to afford two expansion tanks, plus all the sight glasses, filter/driers, and valves I'll be poring into this project. Perhaps I'll just create a buffer w/o a valve in between the HX and the TXV to store up excess liquid refrig and increase system volume. Still got more to plan on this one.

Xeon th MG Pony · 07-07-2006, 12:22 AM

they are nothing special, even a modified propane tank will work, you attach the blow out valve to the tank and there ye be

Nyx · 07-07-2006, 01:37 AM

"I'll just create a buffer w/o a valve in between the HX and the TXV to store up excess liquid refrig"
For this u are looking at a receiver.
Dont build it too big though, you just want a receiver big enough to provide a full liquid head for your TXV. You can look up for guides on this forum on how to build one And i find TXV a little cumbersome as the superheat settings on some are too big for our application and it will be kind of hard to troubleshoot.Else The TXV is not build for temps below -40C and u will have some problems finding why your HX is not getting to temps.But that also depends on your refrigerant. So there is a lot to consider. Since u are using R290 U would have to find a TXV which does not give u false reading. The expansion tank is to store gaseous high pressure refrigerant and not liquid. So dont get the wrong idea.

Xeon th MG Pony · 07-07-2006, 01:46 AM

A receiver should hold 120% of the systems expected full charge.

and TXVs are actually the best for chiller systems or multistage systems and you can easily adjust the superheat FYI your first stage will be rarely hiting -50, second stage perhaps.

Nyx · 07-07-2006, 01:50 AM

A txv on an autoc really is a challange. As normally ppl want the first stage to be as cold as possible to cool the second stage load. Thats why many Xs builders use captube to achieve it.

Xeon th MG Pony · 07-07-2006, 02:12 AM

true for Autos I was more thinking of multistage systems that use multiple compressors, but there are TXVs that are rated for ultra cold opperation.

Carlz0r · 07-07-2006, 10:00 AM

Your phase sep is upside down

Dark blue means liquid, light blue means gas from what I've seen in diagrams.

[XC] gomeler · 07-07-2006, 10:44 AM

liquid should fall to the bottom of the phase seperator, so i think I have it right. I thought using a TXV for the 2nd stage would help me tune it better, I am not worried if it takes 5-15 minutes for the HX to get down to -40 to -30 Celsius, I am more worried about being able to control the flow of the high pressure refrigerant. If TXV's operate how I think they do, when the bulb is under a certain temperature it will open the valve and let liquid refrigerant flood the evap till you pass your required temperature and then it'll cut back?

Carlz0r · 07-07-2006, 11:06 AM

Quote:

Originally Posted by gomeler

liquid should fall to the bottom of the phase seperator, so i think I have it right. I thought using a TXV for the 2nd stage would help me tune it better, I am not worried if it takes 5-15 minutes for the HX to get down to -40 to -30 Celsius, I am more worried about being able to control the flow of the high pressure refrigerant. If TXV's operate how I think they do, when the bulb is under a certain temperature it will open the valve and let liquid refrigerant flood the evap till you pass your required temperature and then it'll cut back?

Didn't look at it correctly, no, you have it right. I got confused with the black circle as the HX not showing the pipe layout. Disregard my previous comments

[XC] gomeler · 07-07-2006, 11:14 AM

Lol its ok =) I was doubting my self for a second when you said that, still learning.

Xeon th MG Pony · 07-07-2006, 01:15 PM

TXVs are a dynamic throttle, as heat goes up they allow more refrigerant to flow, as heat goes down they reduce flow. It will serve you best on the first stage to help ensure a stable temp for the exchanger.

[XC] gomeler · 07-07-2006, 02:11 PM

Just talked to the guys at the local United Refrigeration, he was saying TXV for first stage, CPEV valve for 2nd stage. How does that sound?

Xeon th MG Pony · 07-07-2006, 02:17 PM

idealy peachy

Nyx · 07-07-2006, 06:21 PM

Good luck with the Txv on the first.Just Make sure u have your first stage tune out of the range of the co2 triple point temperatures. Which i think with a txv it will quite challanging.As the temperature could well be withen that. Unless u have a different gas blend.

[XC] gomeler · 07-07-2006, 10:33 PM

I was just looking over the phase diagram of CO2 and I think I should be ok as long as I follow some guidelines. Here is some data

At 1 bar (~14.5psi), r290's BP is -42.1 *C
CO2's triple point lies at -56.6*C @ 5.11 atmospheres (~75psi)

Since propane isn't possible of cooling CO2 to its triple point, the only place I'll have to worry about solid CO2 forming will be in the evap where solid and gas will be capable of forming. If the evap is at 5psi then I am looking at an evap temperature of ~-85* celsius. I think the HX should be ok w/ a TXV, I am not a pro, but through the numbers I have pulled up I think it should be safe. I guess I will find out over the next week or two if this combination of valves is a good idea. I might have to settle for cap tube on the first stage due to the price of these valves, they are expensive :-\