After my first successful phase change project I planned my next project. This time I wanted a smaller unit, which is powerful enough to keep a high overclocked CPU cool enough. I chose R290 (propane) as refrigerant, because it’s very cheap and simply everyone can obtain it. Nevertheless it has a boiling point of -42°C, which is only a few degrees lower than the R404a boiling point.
The parts
Here’s a small list of components I’ve used:
- L'unite CAJ4452Y compressor (about. 120€)
- ECO condenser (30€)
- 3x filter drier (12€)
- 8mm copper tubing fort he high side (20€ /10m)
-10mm copper tubing fort he low side (20€ /10m)
- Flexible stainless steel line w/o steel braid (10€/m)
- Fan (10€)
- Electronical parts (c10€)
- Capillary tube 0,7mm (10€/5m)
- Copper blocks fort he evaporator (20€)
- Other stuff (30€)
You will notice that the price for this single stage unit is relatively low, but you need many tools to build such a unit, which increases the costs drastic. You can read more about the tools in the article “Tools and accessory”. Moreover you need a lot of “know how” to build a function able unit like in this article. As written above you should buy more than on filter drier, because when you open the circuit they must be changed (e.g. when shortening the cap tube)
After I got all needed parts I began with building the unit. First I bought a wooden base plate, where I placed the compressor and the condenser, then I bend the first copper tubing.
Afterwards I made the next piping. You should keep attention to the high side line, which is bended to a coil, to absorb vibrations coming from the compressor, and to unburden the brazing joints. On the other hand this coil prevents refrigerant going back to the compressor.
The liquid line should be build like in the picture below. The filter has to point down with the exit for the cap tube, this warrantees that the filter is only fed with liquid refrigerant. Only this way the filter works best. The next thing we should take care about is the suction line. There I used an “u-bend” which prevents flushing back liquid refrigerant. A liquid lock can damage your compressor!
The evaporator
The next step was building the evaporator. I decided for the "cap-design", where several copper caps are placed on a copper block. The refrigerant enters the evap in the middle of the first cap, then it travels through the next caps until it reaches the exit for the suction line. This evap is cheap and very easy to build, this is why I’ve chosen this design. When you braze the evap you should take care that you don’t clog the cap tube. This will happen when you heat it to much.
The next step
I ran the cap tube through the stainless steel line for subcooling (this will gain some performance). You can achieve the same effect by wrapping the cap tube round the suction line. Then I brazed the flexible line with the copper tube, I used silver brazing rods for this kind of job.
Afterwards I brazed all the other tubes, this was done quickly because I had routine in brazing.
Leak- Test
The next exercise was to leak test the circuit, fortunately I had only one leak, which was fixed quickly. Then I began with vacuuming, I used an old compressor, because I didn’t have a vacuum pump at this time.
The first run
After vacuuming I did the first test run, I charged the rig with R290 (propane). I charged it to 3bar static, then I fired it up the first time. While running I added refrigerant from time to time, until it reached -48,9° on the evap, but you should notice the room temperature was only about 10°.
The first test runs were quite successful, so I decided to transport the cooler from the garage to my room ;-) In comparison to her big brother (the first phase change rig I built) the new one is relatively small
Insulating
The next step was insulating the evap and the suction line. I used Armaflex tubes, Armaflex glue, and Armaflex tape. With the insulation I got lower temperatures than before, this shows that a good insulation is very important.
The first use
After I tuned the circuit properly I did a first test run on a CPU. But before I had to insulate the mainboard. I added a layer of Armaflex to the area of the socket, I also used some vaseline to fill the pin holes.
The CPU I used was a P4 3.0ghz with the new E0 Stepping.
Here are the specs of the system:
P4 3ghz E0 Stepping
Abit IC7 moddet
2x256MB Twinmos BH5 RAM
OCZ PSU
While building this phase change unit I was able to acquire a lot of knowledge, which will help me to build my planned cascade.
written by ice-man 16.2.05/ new upload by august123 15.11.09
DIY Phase Change by ice-man/ 2005
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