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Thursday, July 26, 2012

CryoBUG Accelerated Cool-Down (Turbo Charged)

Well it isn't actually Turbo Charged, but what I did is revert back to a higher flow in the final cap tube, and got a pretty phenomenal speedup in the cooling rate. Of course there was a small compromise, and that was a slight sacrifice in ultimate temperature, as well as a bit more work for the compressor (still quite comfortable for a R-410a compressor).

In my last test I was able to achieve a stable -156°C, but it took nearly 2-1/2 hours to get there (not exactly a speed demon). Anyway after going back over my notes on previous tests, I saw a rapid cool down in a test I blogged about on April 4th 2012. In this test I achieved nearly the same temperature, but in only 1-1/2 hours. The problem was that soon after it achieved this very cold evaporator temperature, it started to warm up. This was due to the R-600 (N-Butane) freezing in the final cap tube. At the time I only suspected this as a possible reason behind the warm up, and now I know this with absolute certainty.

So what was different? The final cap tube was much shorter, giving more flow to the evaporator. So yesterday I modified the cap tubes, making them both shorter, CT#1 only slightly, and CT#2 less than half the original length. I also added a bit more Argon to make up for what I knew would be a higher suction pressure, and thus a warmer evaporating environment (the extra Argon decreases the boiling point). And of course I was once again using R-600a (Iso-Butane) to avoid the freezing problem.

So here is a look at how the unit tested in this new configuration...
CryoBUG 7/25/2012 Test Chart
Note: If you forgot what the TC locations were, refer to this diagram: CryoBUG V5 Piping & TC Locations


Final compressor running pressures were 38/227 psig, and the Evap-In was -153°C, with an Evap-Out of -151.5°C. As can be seen, the cool down time was amazing! Hitting -100°C in about 19 minutes, and -150°C in barely over 50 minutes. This is nearly 3 times faster than the 7/24/2012 test run, and even faster than the April test using shorter cap tubes with R-600. Basically a "Guinness Book of World Records" moment for such a small AutoC.

All I can add at the moment, is that I am extremely happy with the progress I'm seeing in this prototype unit.

Saturday, July 21, 2012

CryoBUG Totally Stable at -156°C

Today I retested the CryoBUG unit with the following refrigerants in the charge.

R-600a (Iso-Butane)
R-170 (Ethane)
R-14 (Tetrafluoromethane)
Argon

Note: This would be the first time utilizing Iso-Butane instead of N-Butane.

The results were better then expected, allowing the unit to get down to -156°C, while still exhibiting stable temperatures and pressures.


TC Meter connected to Evaporator Feed


Test Data

In order to get a better feel for what the unit was doing at various points across the system, I have included a diagram that hopefully makes this a bit easier to see.


As can be seen, there is a very small temperature spread across the evaporator, being on the order of 4 degrees. The estimated evaporator load should be approximately 10 watts, which is primarily due to insulation losses.

The proposed oil control system shown may not be necessary, since I haven't seen any signs of oil freeze-out problems, which is most likely the result of utilizing two hydrocarbon based refrigerants in the charge, thus having better oil solubility than freons.

Switching to the Iso-Butane has also apparently cured my refrigerant freeze-out problem as I had expected.

During this test I took the opportunity to incorporate smaller cooling fans, going from two 100 CFM models down to a couple of smaller 41 CFM types. This allowed me to better gauge what will be needed for air flow when I build the more finalized version of this unit. As can be seen by the liquid line and discharge temperatures, the smaller fans still did the job (ambient air temperature in the room was about 22°C).


Technology Update

My experiments have shown that a very simple single-stage autocascade refrigeration system can reliably achieve temperatures in the cryogenic range. And furthermore that this can be accomplished with the use of open technology, no longer under the restrictions of patent protection or patent pending. Although obviously there are some trade secrets involved, such as HX and cap tube sizing, and of course the exact formula for the mixed refrigerant charge. Trade secrets that are currently held by Mytek Controls (aka; Michael St. Pierre). But none the less, this does not present any legal obstacle for anyone else wishing to exploit this technology on their own. And I encourage others to do so in the spirit of competition.

I say all this to discourage what I will call the practice of filing BS Patents. These would be patents that should have never been issued, which are nothing more then taking what would be common sense derivatives of previous inventions, and trying to monopolize on their use.

I would also like to acknowledge Andrija Fuderer for his great contribution and inspiration, as well as for providing the foundation that CryoBUG is based upon.

Posted by: Leonard Barden guardian.co.uk, 

"Andrija Fuderer, who died aged 80 last month, was an eminent chemical engineer and inventor with more than 50 patents to his name."

Link to Full Article: 
Andrija Fuderer, a gifted player and all-round talent, has died aged 80...

Friday, July 20, 2012

CryoBUG Iso-Butane charge experiments about to begin

I got my inexpensive R-600a (Iso-Butane) last week. Thanks to a friend who steered me in a direction I would have never thought of, I was finally able to get my hands on enough of this refrigerant to charge my CryoBUG well over 20 times. The source turned out to be an Ebay store called Med-Supply-Online who stocks a 5.5oz disposable cylinder of Iso-Butane used for fueling a Dental sterilizing burner. As you can imagine this has to be very pure, and according to the MSDS it is.

So who makes this stuff? A company called Wall Lenk does. And when checking online it varies from about $9.00 up to $12.00 per cylinder. Unfortunately most of the sources I found wont sell to individuals unless you are a dentist. But luckily this isn't a condition at Med-Supply-Online.

So here's a look at most of my stash...


After getting the cylinders as pictured, I discovered that I had no way to get the butane out of them. The fitting at the top is actually much more then a piercing type as used on R-134a cans. This one has a depression valve incorporated, that will shut-off if the burner head is removed. So I had to also order a burner head as well, and then modify it for use with a standard 1/4" refrigeration hose (I also got one more cylinder of butane fuel with the purchase of the burner head).


Then to make things easier to deal with, I transferred all 5 butane cylinders into a refrigerant recovery tank.

So I now have 27 ounces (765 grams) of pure Iso-Butane, and have already gone ahead and recharged CryoBUG for a test tomorrow.

The interesting thing I noticed when charging my unit, was that the R-170 (ethane) appears to have a much better affinity for the "Iso" versus the "N" type butane. Or in other words it soaks in more, yielding a lower vapor pressure. This could be very helpful.