Flexible HX (heat exchanger)

[gclg2000]

Ok guys, this is the "goal" of this thread:

If you are to respond, please read all my thread so you understand what i mean.

"To develop an easy DIY HX line that is short, easily insulated, very effecient, flexable and easily manipulated."

Many of us have attempted and made some very nice HX's in our time (hat's off to Chilly, ICE, RUNMC and others...). I'm a huge fan of the new HX's that chilly has been using on some of his builds. Most currently the SLI rig he made for Det. (link here (http://xtremesystems.org/forums/showthread.php?t=53032&page=1&pp=25))

Below is a pic of how that HX works: (notice the inner surface area)

http://www.packless.com/desuper/supertube2.jpg

What i propose is similar design except using corregated steel tubing inside corregated steel tubing so its flexible. The extra surface area from the ridges in the tubing will cut down on the massive length we have to deal with and that leads to a long, large HX or a large box full of foam, which i personally think is huge.

Below is a pic of a Suction line i've been getting made up lately for phase change builds.

http://www.namike.com/albums/Crazy-Single-Stage/HPIM0139.thumb.jpg

As you can see, the stuff is pretty flexible, all steel w/ copper stubs on each end.

I propose making a larger hose say almost 5/8" I.D. or so out of corregated steel with 1/2" copper stubs running off each end that are about 2" in length. Then, inside that hose using a corregated steel hose with an I.D. of about 1/4" or so that stick out about 4" or so. Then use simple "T" couplings and 1/2" to 1/4" copper pipe reducers to step down the differences.

A picture of this below (a former HX i made a while back).

http://www.namike.com/albums/album02/Flexy_HX_Joint.jpg

Below is a pic i made in paintshop showing what i'm talking about.

http://www.namike.com/albums/album02/Flexy_HX.jpg

This huge benefit of this to me personally would be:

1) Very Effecient
2) Flexable
3) Easily Insulated
4) Can "snake" it around or arrange it anyway you like in your cascade

Some main questions i have are:

1) Will Steel be a good heat conductor?
2) Will 7-8 ft be long enough
3) What do you guys think?

[BB mods's]

I <3 that! it will cut down on size of the 2 stager's and make them easyer to move! :banana4:

[wr0x2]

Nice idea, but the steel flex hosing is expensive.

[saratoga]

Steel is also 10 to 20 times worse a conductor then copper (depending on alloy), so you'd need a lot more of it then Copper to make up for its poor thermal properties.

Seems like a well designed copper HX would be cheaper and more compact.

[cold_ice]

This is a good idea, but I'm waiting for responds from the experienced cascade builders. Are you shure that it is big enough for an interstage HX?

[pythagoras]

Sorry but this wont work anywhere near as effect as a standard hx :( . If you look at your diagram, the refrigerant will follow the shortest path. The inside tube will follow a straight path through the hx. The outside of that tube is braided and so the refrigerant in the outside tube will also follow a straight path, it wont spiral round in the corrugations.

The hx dosnt need to be flexible, although I understand that you feel standard hx surrounded by foam are rather bulky. You can still snake solid copper tube where ever you like and use standard insulating tubes, it would just be fixed where ever you decided to run it initially.

To sum up, that design will be less efficient than a copper in copper hx of the same length.

Regards

John.

[JSU]

the steel ruins the whole thing, besides the fact is probobly too short to have enough surface area in the first place.

[gclg2000]

Yeah, good comments guys. Anyone ever tried using the copper corregated tubing from like home depot for water heaters or anything.....Using the same principal just with copper....

The new HX chilly was using on the Det project was only around 7-8ft or so, but once again it was copper.

Pythagoras, i wasn't intending to use brade on the inside part for that exact reason, sorry i left that part out. The outer part would have it though.

[berkut]

i like the idea, but there is no way its going to be flexible. take a look yourself:

http://www.teampuss.com/berkut/testcascade/Istage/1.jpg

This is the HX i use in my cascade. Its a danfoss unit. Now see how thick the insulation is:

http://www.teampuss.com/berkut/co2cascade/Istageinsulated/3.jpg

Its 5cm thick in the thinnyest place. 4cm thick on the pipes. I still find it too thin and i will improove on it.

I can post all my HX designs and runmc has already made a exxelent hx for his autocascade based on my design. I find his HX currently the best anyone of us ever did.

SS is not a problem as its 0.1- 0.2mm thick. 1mm copper vs 0.1 SS. And has a large surface area

[pythagoras]

Agreed, the only insulation in the temperature range you guys are using is a vacuum :slobber: . Superconducting power lines use a vacuum shield.

Thinking about it, thats do able isnt it!!!!! A larger diameter pipe over the hx which is vacuumed down.

Sounds like a job for Berkut :D ;)

Regards

John.

Edit: Oh WOW this could be so cool, thanks mister thread starter, would never have gone down this thought process with out this thread. This idea is so simple and I cant for the life of me think of how it wouldnt work. You could even use steel or stainless steel tube for the outside envelope, which would have greater strength to hold the vacuum. The only way the heat could enter the HX would be where it joins the start and end point of the HX. Insulation there, and a bit over the HX would do the job.

[berkut]

Chilly already made one out of a thermos but i can try too


its not that far from a CO2 laser project i want to build

[pythagoras]

Sorry edited after your post ;) . This has a lot of potential, me thinks.

Regards

John.

[gclg2000]

Well about it being flexible....

How much insulation do you guys think a HX REALLY needs.

I agree with the surrounding the HX w/ a vaccum, that wouldn't be that hard to tack on a single shrader valve and see how it goes.

I'm talking about using the insulation like you use around a LN2 container or something. I don't really see the insulation on the LN2 container's for example getting really condensated. And i KNOW the temp in the HX (at least for a 2-stage) doesn't get near as cold as Nitrogen does.

But pythagoras, i think you have raised a good experiment here. My mini-gatorage cooler used in my chiller a while back never got any where close to condensating or even getting cold for that matter....and as we all know....air is the insulator in a thermos as mentioned above.

[gkiing]

I think im going to give the vacuum container as insulation a try.. Isint that how LN2 dewar's hold the ln2 without having it evaporate fast?

[saratoga]

I think im going to give the vacuum container as insulation a try.. Isint that how LN2 dewar's hold the ln2 without having it evaporate fast?

Dewar is vaccum with silver shielded sides to reduce radiation IIRC. The silver isn't going to make a huge difference, so don't worry about that. The bigger issue is how deep a vaccum can you get with your pump?

With luck you can get low enough for this to work.

[gclg2000]

Guys i think we have stumbled on the way to do this.

My main concern now is:

What about when the inside hose physically touches the wall of outer hose even though we have a vaccum inside it???? Are ya'll planning on using just straight pipe or something?

[gkiing]

I was referring to a vacuum container for hx's etc. I have access to a deep vacuum pump that can pull down to 10microns, over several hours of vacuuming. My main vacuum pump for phase change can only pull 29" which wont be eneough.

[i_like_penguins]

If you do a vacuum insulation, you will still have to insulate the ends of the HX where the outer jacket is joined to the inner HX. Also like gclg2000 pointed out, having the whole mess be flexable would screw it up even more because when you bent it, something would touch somewhere. Your best bet in this situation would be to wrap the HX with a layer of open cell foam before inserting in into the outer jacket. This would hold the inner HX away from the outer jacked when you bend it. The next problem becomes conductive heat loss through the open cell foam. However, this problem is minor compaired to brazing the outer jacket shut without melting the foam. If you could come up with a different substance to use to keep the two layers from touching, you might be on to something.

[kristos]

With risk of being flamed for my incompetent remarks :) :

My Uncle is an engineer for a big welding company and he uses some sort of little pebbles that isolate unbelieveably well. He can weld or braze something, throw it in those pebbles and the next day, the metal will still be hot/warm, the pebbles don't melt or burn or anything. if anyone is interested, I can ask him what exactly those pebbles are...

[i_like_penguins]

Interesting. My guess is some sort of ceramic or somethig. Never thought of that. Just had another thought. Fiberglass. You can get sheats of fiberglass at autoparts stores for automotive repair. This would be able to take the heat no problem and would also help to isolate.

[pythagoras]

It could be this stuff:

http://www.silbrico.com/hightmp.htm

Also you can purchase a flexible suction line that has a vacuum shield:

http://www.vbsflex.com/Vbsflex.pdf

And the evaporator is possibly the easiest item to vacuum insulate.

Regards

John.

[berkut]

I think a HX is the easyest part to vacuum insulate and i already have the right stuff to make such insulation.

[gclg2000]

I think a HX is the easyest part to vacuum insulate and i already have the right stuff to make such insulation.

Berkut, could you make a diagram of what your thinking of??

[bxa121]

daym, ive been thinking in the same lines as you guys but independantly!
i never thought of a flexable HX, but i did think about the better insulation for stuff.. like the tubing, etc, but yes the hx is more important in terms of insulation.
my idea was for a water chilller, where the evap chilled alcahol, which was insulated in a bif box/ resevoir tingy. that was insulated.
the tubes going from the resevoir to the cpu etc, would of course, condesate water, and so what i thought of was using two tubes, one gong inside another. the tubes would be sealed and the space vacuumed.
problem i though was if the sides touch, then conduction occours and so you gain heat. so i figured, use plastic beads like marbles or bearings or somit. ceramic beads are very cheap and easily avaliable. this way, the tubes wont touch. and the beads would provide a physical barrier to kinking as well as reduce the amount of heat that is gained through the two tubes!!

p.s kristois. find out about those pebbles dude! ;)

[kristos]

vermiculite (http://www.google.be/search?hl=nl&q=vermiculite&btnG=Google+zoeken&meta=) <-- this is what those pebbles are called :)

my uncle is going to mail me a brochure with more info



he said you can get it at builder suppliers (places where they sell all sorts off stuff for building houses...)