Morphing Air Conditioner into Autocascade System

[n00b 0f l337]

Excellent work! If only 1/2" benders weren't $100!

[Supertim0r]

wow, subscribed

too bad we don't have ultra low temperature class at school, only "big/commercial" refrigeration.

[jinu117]

Something like Noranda makes. Yes it has excellent heat exchange, but sometimes the small passageways can hold on to oil in the wrong place, and next thing you know, you're blocked by frozen oil. I think it was about 21 years ago we tried building an entire stack with this tubing. It worked great for a few hours, and then suddenly started loosing capacity. It would freeze up about 2/3 up from the bottom.

Of course this was before we ever heard of a coalescing oil filter such as what Temprite makes. And we also didn't know it until much later, that the new compressor we were using was a major oil pumper. Had to get the manufacturer to add a 3rd ring for oil control.

Yes I can see that but there are perpendicular as well as horizontal finned tube Perpendicular one I can see problem but horizontal one might not have that...

[n00b 0f l337]

No doubt, time to get r23 me thinkies
And watching with incredible rapt attention, do you think those capillary lengths are good though? Any reason to them or calculation? Seem sorta long after reading other lengths from Cryo-Tek.

[mytekcontrols]

...do you think those capillary lengths are good though? ...Seem sorta long after reading other lengths from Cryo-Tek

Actually they have slightly more flow then what I calculated from Cryo-Tek's example. Remember that the system that Cryo-Tek's captubes were specified for has a compressor with 3.6 times the displacement of mine.

If you are concerned about the length, also remember that I am using all the same ID captube. Cryo-Tek's example was using several different ID's, which is fine if you have many different ones to chose from. I tried to keep it simple by only using a single ID and ordered a 100 foot roll. Also keep in mind that captubes work best when the length is kept somewhere between 5 and 15 feet. Less then 5 feet starts to act more like an orifice, and can produce greatly different flow rates with only a few inches of change.

No doubt, time to get r23 me thinkies

Ethane works just as well, and can be used as direct substitute (might be cheaper).

[Freddie123]

The first 2 heat exchangers (aux and 1st cascade) have 2 inner tubes which are part of the discharge (or high pressure circuit).

That explains it. Cheers Michael, that HX is really nice looking too

[n00b 0f l337]

Nah ethanes more expensive it would seems.
Well no actually hmm, just checked matheson...
$100 will get me 3lbs of ethane. Is it just as good as r23? I'd imagine since its lighter it might not be able to hold a load as well. Also, what about ethylene? would r170/r1150 work decently theroetically?

[mytekcontrols]

That explains it. Cheers Michael, that HX is really nice looking too

Thanks Freddie I'm glad you brought it up. Often times I find it helps me do a better job at documenting a project, when people ask me to explain different aspects of it. Thanks also for your appreciation of the HX, because it was a bit of a struggle to build it that way. It sure would have been nice if the lever bender I was using, could have been separated into 2 parts after doing each bend. I'm almost wondering if I could make my own bender from something like a pulley.

$100 will get me 3lbs of ethane. Is it just as good as r23? I'd imagine since its lighter it might not be able to hold a load as well. Also, what about ethylene? would r170/r1150 work decently theroetically?

I do believe ethane (R-170) works just fine as a substitute for R-23, boiling points are virtually the same, and on the positive side it has better solubility with the oil. I made up a charge last week for a large Polycold unit I was working on, and increased the ratio of ethane as compared to the R-23 (15 psi R-23, 65 psi ethane) it worked quite fine, and even exceeded specification. I suspect I could have just gone with 80 psi of ethane, and eliminated the R-23 all together (have to try that some day).

As for ethylene (R-1150) being used in combination with the ethane, yes this would also be a viable mixture, although it wont get you quite as cold as using R-14 which boils 15C colder (R-1150 = -104C, R-14 = -120C).

Edit: Correction, R14 boils at -128C.

[n00b 0f l337]

Well what about r14 in combination.

[mytekcontrols]

Well what about r14 in combination.

No benefit in using R-1150 (ethylene) and R-14 together.

Edit (10/10/2009): I have recently discovered that R1150 and R14 can play well together. Of course this depends upon what other refrigerants are being used in combination with, and how many stages are in the AutoC. Under the right conditions, the R1150 and R14 combo will yield evaporator temperatures with a smaller gradient from the the inlet to the outlet.

However R-170 (ethane) and R-14 would be fantastic

[n00b 0f l337]

Just trying to see what might be decent with what I have
Hmmm r170 or r23....

[[XC] gomeler]

I'm going to see what Airgas will do with me tomorrow for R1150/R170, just opened an account with them and crossing my fingers that they'll be able to supply me with decent prices.

[n00b 0f l337]

Mathesons got good selection and great prices, but that hazmat fee is driving me nutters.
They have good prices on ethane, argon, butane hell just about everything.

[Unknown_road]

I tried r1150 in an autocascade but didn't have good results with it. r170 works much better. I think the leap between r290/r507 etc and r1150 is too big.

[n00b 0f l337]

I dont think its so much the leap as the lack of a gas like r11 or r123 that killed your setup thuogh Unknown.

[mytekcontrols]

How about a $4.00 3/8" od tubing bender? Only took a slight modification of an off-the-shelf 3" garage door pulley (used file to elongate holes in bracket). It works great for making a trombone style heat exchanger, clamp the pulley's shaft nut in a vice, and just walk the part you are bending around the pulley.

The v-shaped pulley helps to prevent the tubing from flattening out, and the bend radius = 1.5" which matches the one on my 1/2" bender. This ends up producing a better match for the 1/2" od heat exchangers, and allows it to sit perfectly on top of them (makes for a cleaner stack). So I'll be scrapping my original concept drawing for Cascade #2 and #3. I will provide details later.

Well here it is:

[mytekcontrols]

Here's a close-up of the completed pulley bender. The slot allows you to adjust the bracket for a tight fit on the tubing, this helps prevent the tube from kinking. The secret to using it, is to try and keep the part you are bending underneath the bracket, and maintain tension on both sides of the tubing (It can be a little tricky at first).

[mytekcontrols]

And here's what the first HXC produced with the pulley bender looked like (I miscalculated on the length, so ended up adding a swaged extension tube to make it right).

Edit: You'll notice that I reduced the number of turns by one from my original drawing. I needed the extra room, and felt that a little less length on the last 2 cascades was acceptable.

[PhilippF]

Reminds me of Tim Tayler on "Tool Time"

Great work! I look forward every morning to looking on this thread!

Regards,

Philipp

PS: I am planning on an autocascade in a very similar way like your drawing (I studied all the old threads by you and Cryo-Tek). Now that I have a starting point about capillary length (thanks to you), I think about the charge. How do you charge a unit like this? Do you mix the gasses up previously in an empty bottle and then charge from there or do you charge one refrigerant at a time up to a certain pressure? Or do you charge a unit while running up to certain points, eg. Ref#1 until HX#1 reaches -XX degrees, then Ref#2 until HX2 reaches -xx deg. and so on? I would appreciate the info very much.

[mytekcontrols]

Reminds me of Tim Tayler on "Tool Time"

I wonder if Binford ever made an autocascade? If they did, you know it would be powerful and get very very cold

Great work! I look forward every morning to looking on this thread!

I'm glad you are enjoying it

How do you charge a unit like this?

If you have an electronic scale, and your unit is not too heavy:

• Place the unit on the scale
• Zero the reading
• Charge in your 1st, 2nd, 3rd... liquid refrigerant (R123,R22,ect.) into discharge side only
• When all liquids have been charged, open all valves on manifold, allow pressure to balance, take pressure reading
• Add gases by pressure (allow 5 minutes for soak-in before going on to next gas, top off if needed, wait another 5 minutes, and repeat top off if needed --- repeat until pressure no longer drops)

If your unit is too heavy for a scale, then use a cylinder as a transfer tank. Same procedure as above, but when adding gases shake the cylinder to speed up soak-in.
Do the following when the entire charge has previously been put into the transfer cylinder:

• Connect hose from cylinder to unit
• Open valve, purge line with refrigerant
• Invert cylinder (for liquid), and open discharge valve only on manifold
• When flow slows down, open all valves on manifold and allow pressure to balance
• If compressor has suction valve, front seat it and close off discharge valve on manifold
• Run compressor and allow it to suck in remaining gases from cylinder

If you have a charging glass instead of an electronic scale, you can pre-charge the glass with the liquids, add them first, and then proceed with the gases, same as was done in the first example.

If your system has an expansion tank, you'll need direct access to it when adding your gases (a way to bypass the restrictive captube).

Of course this all assumes that you know what your total charge is going to be. When first developing the charge, you'll want to start out with about 2/3 of what you think you'll probably need. Later when the system is running, and based on temperatures seen at the exit of each heat exchanger, you can test adding small amounts of the different refrigerants. If the compressor discharge is running hot (0ver +125C), then very slowly add in additional liquids an ounce at a time through the suction port.

When adding gases, it is good to add these from a standard size cylinder with a known volumetric ratio as compared to the system volume.
For instance; before charging your refrigeration system, fill a small cylinder with nitrogen or argon to 100 psi. Put a gage on the cylinder, and a gage on the refrigeration system. Allow gas to flow from the cylinder into the refrigeration system until the system pressure has gone up 5 psi, and then stop the flow. Take note of how far the pressure has dropped in the cylinder (i.e.; dropped from 100 to 85, or 15 psi). Now you have a way to measure in a specific amount of gas (every 15 psi taken out of the cylinder will equal a 5 psi increase in the refrigeration system's static balance pressure). Of course this would be added into the suction side of a running unit.

Later as I get into the charging phase of my unit, I'll give you the refrigerants and amounts I will be starting out with (haven't gotten that far yet).

Have I forgotten anything? It's late, so my mind is getting a bit fuzzy, and this is a lot of stuff to cover.

[n00b 0f l337]

Picked up a 4" garage pulley and damn your right, just what I've been looking for!

[pythagoras]

Isnt the internal volume of those bullet strainers too low? Flow rates through a low volume tube like that would be too high to allow for phase seperation, wouldnt they?

Or are these bullet strainers larger than we are used to seeing?

Regards

John.

Edit: Meant refrigerant stream velocity, not flow rate.

[n00b 0f l337]

I think we've been overestimating the need for this kind of separation. If you have a liquid seal at the bottom, gas will leave gas passage

[pythagoras]

I think we've been overestimating the need for this kind of separation. If you have a liquid seal at the bottom, gas will leave gas passage

But liquid droplets can leave at gas outlet if the velocity isnt slowed or the droplets hit an impingement screen. And gas disolved in liquid will escape the liquid seal if not given enough time to come out of suspension

Regards

John.

[n00b 0f l337]

Which is true, but the way his seps are setup the mix comes in and heads to the bottom, a liquid seal is then created.