Tuesday, June 10, 2014

CryoSPRITE Testing Resumed with New Compressor

I received my new compressor from Rigid Auto Parts about 2 weeks ago, installed it into the CryoSPRITE prototype, and got some test data over the weekend with a fully insulated evaporator coil (simulated Cold Head).

Test Data (click on image to enlarge)

For this initial test, I left out the Argon, and went with a mixture of 4 hydrocarbon refrigerants. The cap tubes are presently optimized for a -80°C system, and as can be seen, under very little load this was exceeded.

Rigid ACXZ14DCH Compressor and Controller
The compressor model number ACXZ14DCH has a displacement of a mere 1.5cc per revolution, but unlike most conventional larger rotary compressors, can spin up to 6,500 RPM. This is nearly twice the speed of the conventional, thus giving it a mass flow much better than it's seemingly small size suggests.

The reason for this increase in speed, can be attributed to it's DC Inverter motor and drive electronics. Unlike a conventional constant speed AC motor, this one can be varied in speed by changing the frequency of the 3 phase output of the Inverter, taking it from 1,800 up to 6,500 RPM.

What's also cool about the Rigid compressor's controller, is that it's output looks more like a sine wave than a square wave as normally used. This makes for quieter low vibration performance. I also like the fact that you are supplied with a multi-turn pot for speed adjustment, and a pre-wired plug for the compressor. Basically this thing is ready to run out of the box. The only thing missing in my opinion is a mount for the compressor, but they do supply you with a silicone gasket-like material (to wrap around the body of the compressor underneath a user supplied clamp) and a set of rubber feet. I think the idea is to buy an off-the-shelf capacitor style clamp for mounting purposes. The controller also automatically controls the ramp-up speed, which prevents you from accidentally slamming the compressor at high speed upon start-up (which is what happened to me with the Aspen compressor I was previously testing).

CryoSPRITE running without insulation
Just for grins, I removed the fiberglass insulation surrounding the test evaporator coil near the end of my test, just to see how it would handle a bit more heat load.

As can be seen in the photo, it still maintained -80°C while frosting up. And it was able to do so without excessive running pressures or drawing too much amperage. And while I used a 240 watt 24VDC power supply to run this thing, it never exceeded what a 200 watt supply would comfortably handle.

Even after several hours running in this uninsulated state, it still stayed fairly close to an average temperature of -80°C, as shown in the test results shown below.

Non-Insulated Test Data (click on image to enlarge)

What's next? When I get some spare time from my 'real' job, I'll be trying some different refrigerant charge blends, as well as cap tube changes to see what I can get this little guy to do. Most likely we are looking at a -100°system in its final configuration. To ask more of it, would probably yield very little heat load capacity, making it fairly useless.


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