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Wednesday, April 11, 2012

CryoBUG Stable -150°C Operation

Well it took quite a few different tests and refrigerant variations, as well as some minor hardware changes to finally get what I consider to be a stable -150°C unit. To qualify for this prestigious stability award, it must have virtually no fluctuation in evaporator temperature (+/- 0.5°C), and meet the target temperature requirement (-150°C or colder). Today we did just that.

Evaporator Temperature -152 C, Total Unit Current Draw 2.36 Amps

Compressor running pressures were equally amazing at 26/180 psig, which is also the reason why the current draw was so moderate at 283 VA (226 Watts, PF=0.8).

CryoBUG 4-11-2012 --- 4.5 hour Test Run
Other then the strange oscillation in the CC SUCT temperature, the Evap was about as Flat-Lined as one could hope for. Reference V5 Piping Diagram for TC locations.

Cool down was also very fast and steady...
-100 C @33 minutes
-110 C @36 minutes
-120 C @41 minutes
-130 C @64 minutes
-135 C @70 minutes
-140 C @77 minutes
-145 C @85 minutes
-150 C @98 minutes
-152 C @just under 2 hours (flat line)

So what did I do to achieve this? Basically one thing, and that was to dramatically reduce the flow in the final cap tube (CT#2). The charge was the same N-butane, Ethane, R-14, Argon blend as my first V5 hydrocarbon test run, and in the same proportions.

The funny thing was it took me in quite a circle trying to zero in on what exactly caused my initial freeze-out problems. I tried using Propane instead of N-butane, which didn't freeze, but also didn't yield temperatures nearly as cold. This was probably due to the higher suction and discharge pressures. So I tried reducing cap tube flow, but still couldn't get down to where I wanted to be while still using Propane in the charge. Next I went back to N-butane, but used less of it. Still I wasn't able to achieve my target temperature. So I added more R-14, and got a tad bit of improvement. And then added more only to see the improvement go away, as the suction pressure once again started climbing too high.

So finally just for grins, I decided to try the original N-butane charge at the same proportions that I had originally started out with, while hoping that just by some weird stroke of luck the resized final cap tube would do the trick. Well it sure did!

The only other thing worth mentioning, is that the compressor discharge temperature was very comfortable, settling in at 51°C. This combined with the good running pressures, should insure a long and happy life for the compressor.

What's next?

I would like to try Isobutane (R-600a) in place of the N-butane (R-600). My gut feeling tells me that this should yield similar test results. And with the Isobutane's lower freezing point of -160°C, I would feel a lot more comfortable in the long term (N-butane freezes at -138°C). Now I just need to get my hands on some of this.

10 comments :

REFCFD said...

"Cryobug" discharge temperature is very low so I wonder what is the way
I then take up 90 to 100 Deg C haebomyeon
Your technology is very surprising

And you I wonder specification Cascade Condenser, Sub Cooler, Aux. condenser Tube in Tube Specification

Michael St. Pierre said...

The R600's high boiling point helps to remove heat while passing through the compressor, while it goes through it's final stages of evaporation, thus helping to maintain relatively low discharge temperatures.

The exact specifications for the HX's and cap tubes is proprietary.

REFCFD said...

Dr,St. Pierre


Thank you for your reply.
I am a graduated student in Korea Universty in South Korea.
I am doing a test that in order to get ultra temperatuer with mixed refrigerant,( in refrigerator unit)
(mixed refrigerant : R600A, Ethilene, CF4, Ar)
Yeah, We also use mixed the refrigerant together with R600A.Our point is that it is ok before used Ar . I mean it is 60~70 temperature before using Ar. But, After put it in, the temperature of compressor is over 100.
In your case, your discharge temperautre is about 50 temperature.
Wow!!

if possible, Let me know the way : to keep low discharge temperature

Michael St. Pierre said...

Hi REFCFD,

Yes using Argon will boost both your discharge pressure and temperature, there really is no way around this. However the use of a refrigerant in the blend with a fairly warm boiling point can counteract this to some degree. And even better if this warmer refrigerant blends well with the next one in the in the blend, thus lowering the overall vapor pressure to something in between the two. It is also important to have the cap tubes proportioned correctly, with the first cap tube being somewhere around 1-1/2 times the flow rate of the ones that follow.

REFCFD said...

Hi Pierre.

" with the first cap tube being somewhere around 1-1/2 times the flow rate of the ones that follow. " as you said ,do you mean that refrigerant state of Compressor Suction is flash ( Vapor Qualit <1 )?
I would like to appreciate at your cooperation and kinds reply.

Michael St. Pierre said...

REFCFD I'm not sure if I understand your question, but when I stated that the #1 cap tube would be normally sized for 1-1/2 times (150%) the flow of the other cap tubes in the system, this simply means that the first stage (Auxiliary Condenser-Cascade #1) requires a greater flow rate than the following stages and/or evaporator. Although in some systems the final cap tube feeding the evaporator may be of identical spec to the #1 cap tube, due to a poorer quality condensate, which means lack of constant liquid seal. However this is not the case for my CryoBUG.

REFCFD said...

Hi Pierre.

would like to appreciate at your cooperation and kinds reply.

I have seen your blog(web-page)for long time, As the content of your blog (web-page),
with the mixed refrigerant ( R134, R23, R14, AR : 130g / 50g / 40g / 8g ),
I have just calculated the discharge temperauture of compressor ( REFPRO 9.0)

In case :
Discharge Pressure : 15.0 kg/㎠.A
Suction Pressure : 2.0 kg/㎠.A
Suction Temperature : 10 ℃

Result)
By REFPROP9.0 , Discharge temperature is 92.37C

and We had also tested it with systems unit I made ,
and we also can comfirm almost same or little high temperature to (92.37c).

But in case of your contents, we can see around 50C temperature (Discharge temperature 50C)
Would you let me know the way to low the temperature?.


I had thought about the reason for long time, I think :

Michael St. Pierre said...

Some things I either have no explanation for, or due the proprietary nature of this project, I can not go into more detail about. If you attempt to duplicate what I have done on your own, I wish you much success in this venture, but at the same time, I have to say that what is being written about in my blog is not meant to serve as a tutorial on how to build anything I am discussing. And due to the explosive nature of some of the refrigerants I am using, can also be extremely dangerous to attempt by an inexperienced individual.

Michael St. Pierre said...

I have yet to see an autocascade simulation be dead on when translated to real hardware. On CryoBUG I went through various combinations of refrigerant, HX stages and sizing, as well as various cap tube ID's and lengths. In all cases I had no problem maintaining relatively cool discharge temperatures. Unfortunately I can not share what those HX or cap tube specs were, since for the time being this is my trade secret.

Autocascade design and charge tuning requires patience, intuition, and pattern recognition. All of which comes from experience.

Michael St. Pierre said...

"Your experience and I hope the theory is discussed further."

Yes I will hopefully be blogging this project all the way through to it's pre-production prototype. At which point I hope to have something of commercial value, that can perhaps be licensed to other manufacturers.

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