Thursday, June 19, 2014

CryoSPRITE Sooo Close to -100°C

After doing some more charge tuning and a cap tube adjustment CryoSPRITE is now verging on the negative century mark.

This required pushing the RIGID compressor's speed higher than I would like to see it sustained at indefinitely. But with that said, current draw was not unreasonable, and compressor discharge temperature was still comfortable, well within the manufacturer's spec.

These test results were done with the evaporator coil wrapped in about 1-2" of loose fiberglass insulation, stuck inside a plastic bag to act as a vapor barrier. Nothing very sophisticated, and judging by a few frost spots I was seeing on the outside, far from perfect.

Test Data (Click on Image to Enlarge)

Based on these preliminary tests, I would think it safe to say that a -85°C bio-storage freezer could be built utilizing this technology, while still allowing a good margin of extra temperature capability.

It wouldn't be a very big bio-freezer, but it would certainly be the smallest ever built for this temperature range, and definitely the smallest AutoC version in existence. Of course if someone would like to challenge this assertion, I would be thrilled to hear from you, and see what you have created and/or discovered. Now I just need to get to work and create one myself based on the CryoSPRITE technology used in this first prototype.

CryoSPRITE "Un-Wrapped"

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.

Monday, June 9, 2014

Aspen 1.9cc Compressor Dissected

The Aspen compressors are miniature rolling piston rotary DC Inverter refrigeration compressors (see image below courtesy of Thermaltake for how the internal stuff works). This is also the same basic principle and implementation used in the RIGID Tiny compressor I purchased as a replacement for the Aspen that met an early grave at my hands.

I figured since I blew up my Aspen (p/n 19-24-1101), I may as well take it apart and see what makes it tick (click image to enlarge).
Top shell removed

Motor windings (stator) removed

Permanent magnet rotor removed

Inside view of rolling piston compressor

compressor top plate/discharge valve removed

Under side view of top plate

Eccentric crank removed

Rolling piston removed

Vane removed

Pretty cool design!

Stay tuned for exciting news about my tests with the RIGID compressor.