Triple Coil Cold Finger Condenser

[moorem]

Well a I learned my less on about trying to build a Peltier cooled condenser. So I built one of these... What do you think?
I made it for a 3" Bokabob head.

Triple Coil Condenser

Triple coils
8 (20cms) inch long coils.
6 mm OD copper tube (4mm ID) -- 9 metres (29.5 feet) of copper
15 mm OD cold finger
Lead / cadmium free soldered joints
Pressure tested
Ultrasonic cleaning in Acetic acid

I had to make a special tube bender to achieve the 1 Radius bends (3 mm radius) but I'm set up now to make more if anyone wants one.

I used to teach metalwork at secondary school and it was nice getting to grips with a bit of real practical engineering again after many years away from a workshop.

Underside view

[toast860]

nice looking coil . very clean

[googe]

Well, your teaching skills certainly show through here mate!, that's got to be the most perfect coil I've seen!, awesome work!.

[DAD300]

beauty...

[Hound Dog]

That has to be the nicest looking coil I have seen posted to date! Great job!

[Halfbaked]

Moorem, I gotta say you got some skills. I think its the nicest cold finger i have ever seen and i have some nice ones. You have officially raised the bar. I would love to see some pics or vids of your process.

[Prairiepiss]

Nice looking condenser. But its not actually a cold finger.

How bout showing us how you bent the coils so nice?

[Halfbaked]

It has at least a 1/2 inch copper pipe running in the middle. What is diff on this and a cold finger?

[Prairiepiss]

A coldfinger is a condenser in itself. Not a return tube for hot water.

[Halfbaked]

What ever it is called I like it. Id love and you did a great job.

[Jkhippie]

Yeah, I'd like to see whatever jig, or arabian lamp you used to get a coil that good.

[moorem]

I stand corrected and educated.
It is indeed NOT a cold finger.

Thanks for the feedback and complements though.

I just checked on the design of a cold finger condenser and it has its own cold feed and return. At the moment the three coils return via the 15mm center tube. I could use the center tube as the cold feed so it is the coolest and because of the volume it would still be cold enough to feed the three coils. Not the right way around but one way of cheating to ensure that the "finger" is much cooler at the center of the condenser

Sorry folks about no demonstrations. It took me some time to make the rig for such tight 1 radius bends (6 mm tube - 3 mm radius bend) and the coils... its all in the background engineering assemblies and I don't really want to give away my designs just yet because I'm selling them elsewhere.

I can bend 6 mm copper pipe up to 180 degrees (U bend) around a 3 mm radius bend without the need for any salt, Cerrobend , sand or frozen water filling to stop the pipe collapsing.

So now I scrap that coil idea and get to work on a new design because if you set out to build the best then nothing less will do!

[Prairiepiss]

That thing will knock down anything you will be throwing at it. Don't know why you would need to scrap it.

And come-on. You come here to get free help to make a better product to sell. But you can't help us improve our methods. That's not cool. And most likely will get the attention of the management.

[Bushman]

So your design if I understand it has 3 waterlines in and exits through the center pipe? What is the total diameter, it looks like it's made for a 4" diameter column?

I understand your reluctance to not share your jig or process of building if your going through the patient process but this forum has been founded on sharing ideas. Having said that at some point are you planning on selling your jig designs with the instructions on use? You obviously have some great skills and hopefully since you are learning on this site you will share some of your skills or techniques that your not trying to make a living at with the rest of us as this forum is all about giving and taking and it needs to go both directions.

[Halfbaked]

scraping art like that should be punishable by 30 lashes unless you scrap it to my address. Show us what you did.

[pfshine]

Give the guy a break. Hw obviously intends to sell this design.

[moorem]

Yes... That's a fair comment. I'm not a selfish person so I do apologize.

There are two elements here..

1. The key to the build is a micro tube bender capable of 3mm radius bends.
2. The second is that I used to teach metalwork / engineering and I have a good home workshop.

Here is the design for my mini pipe bender.

To scale it just think of the bent tube as being 6mm diameter.

The lever is shown in two positions, upright and with a completed bend as a dotted outline.

Once the 90' bends are achieved at either end of the length of copper tube the rest is very simple... just wrap it around an appropriate piece of steel tubing. Nothing high tech really.
Diameter of tube x 3.14 x number of turns required (remember coil spacing) plus about 25cms (just for luck).

The two hex bolts press against a clamping piece that has a half round groove (3mm radius) cut along its length so that it does not distort the pipe.

As the lever is moved from upright it rolls the "shoe" around the former which I turned to give it a 3mm radius to suit the 6mm tube I wanted to bend.
The rollers are 12mm diameter at their largest with a 6mm wide 3mm deep half round profile machined in it giving you the final bend radius of 3mm and that, with the shoe, supports the walls of the tube.

Concentric 6mm coils. 15mm center. 1st bend shown.

There you go... all worked out.

[Prairiepiss]

Hell I thought you had some kind of jig for the actual coils. 90 deg bends aren't that hard. Most people have problems with the coil itself.

[aj2456]

hell i only saw the listing for that today-was wondering how long before it turned up here- turns out mighty fast

feedback wise it is the finest coil ive seen openly for sale (cheeky)- personally would have been interested in ones for 2" coil - then i saw the gas line condensor- and looks cheaper (but upgrade is a long way away - but i can dream)

only critisism is that the water lines dont seem all that easy to connect up- but that is truely minor

figure out a way to make as good a value/quality electric boiler and i reckon u could be a richer man

[moorem]

Hell I thought you had some kind of jig for the actual coils. 90 deg bends aren't that hard. Most people have problems with the coil itself.

Who needs a jig really when it is only 6mm tube. What really helps is knowing how to work metal. When to anneal it, knowing what you can get away with before things go "t**s up" just simple skills but ones that have been practiced many many times in the classroom in front of sniping kids just waiting for "teacher" to make a mistake... you sort of hone your skills really quickly because mistakes get remembered and kids can be so unforgiving.

90' bends are real easy... 90' bends as sharp as 1:r cause lots of people (and commercial firms) problems and makes them resort to lots of things like tube springs, salt, sand, frozen water and even lead (or other low melting point alloys).

If you only have a limited amount of copper tube then you can't afford to make mistakes or experiment... especially if it is going to become a showpiece. It is so easy to spend $10 or $20 on tube and end up with a mess.

I could teach someone how to make these, I could teach someone how to machine and assemble a jig but that still requires that they have the physical dexterity and the time.

Not everyone, given the drawings or even the tools, would have the confidence to put relatively expensive copper pipe to the test. You have to know you can do it before starting.

[moorem]

hell i only saw the listing for that today-was wondering how long before it turned up here- turns out mighty fast

feedback wise it is the finest coil ive seen openly for sale (cheeky)- personally would have been interested in ones for 2" coil - then i saw the gas line condensor- and looks cheaper (but upgrade is a long way away - but i can dream)

only critisism is that the water lines dont seem all that easy to connect up- but that is truely minor

figure out a way to make as good a value/quality electric boiler and i reckon u could be a richer man

Hi,
Thanks for the feedback. Yes I agree about the length of the tails, they could be a bit longer but as I made each coil to a fixed formula that was how the tail worked out.

I found that 6mm id plastic tube fits over quite easily and secure with a mini hose clip. Ending them the in a staggered fashion seemed to help me drill the top cap as each tube can be marked and drilled in turn to fit - which was a stroke of luck.

[moorem]

That thing will knock down anything you will be throwing at it. Don't know why you would need to scrap it.

And come-on. You come here to get free help to make a better product to sell. But you can't help us improve our methods. That's not cool. And most likely will get the attention of the management.

I agree and I'm sorry so I posted my mini bender for the tight bends and the details of the first and most difficult bend. This is the one that normally flattens for most people so a mini pipe bender is almost essential for a neat and repeatable pattern.

[Doogie]

My God, that is copper porn around here ...

If you can do it, sell them ... I wasted about 100' of tube trying to make something that looks like a copper abortion. If you can make sexy stuff like that, then sell it - shit, if the price was right I may even - figures I see this thread after I searched on ebay today and found a few coils ... that were dual, fit in my 2" pipe, but the 2 coils were right against each other, and there was no spacing between the levels, and had some serious flattening ...

Some of us just can't do it ... heck - call MileHi and offer them consignment ... lol

[Gandalf666]

Hi,

I must agree that is a spectacular well wound condenser. I tried to make a single coil for my 2 inch still, and ended up with misshapen copper tube abstract art. So I went back to basics and made a triple cold finger design. The cold fingers are at 120 degrees and the longest is 23 cms. The total length of copper tube is about 140 cms, its 8mm diameter tube.

triple cold finger

2013-10-24 10.22.14.JPG (43.09 KiB) Viewed 25198 times

Performance wise.Initial still testing (many months ago) with water gave the following. With 2.8kW power input to the boiler, the condenser was knocking back the full output and producing the equivalent of 2.2kW condensed water. (27mL/min/kW) . The 600Watt discrepancy must be the heat loss from the boiler, its not very well insulated. Unfortunately I did not note the cooling water flow rate. It would estimate between one and one and a half litres per minute.

So I guess what I am asking is just how much will this condenser knock back and is 3 coils an overkill for a domestic still?

[moorem]

Hi Gandalf666,
Thanks for the positive comment. I really don't know what the performance of the coil is. My heater can run just under 4kw and I've had it running at full power with just water boiling off and i seemed to cope easily enough. The water to the cooling coil was not even running full on... maybe a 1/3 to 1/2 of full flow (not sure of how many ltr/min that would be.

I also now have many litres of distilled water for the clothes iron / car etc... My still is based on a 35 litre hot water / tea urn.

It may be overkill for a home still but I made my first coil just because I wanted to see how much I could pack into a 3" ID column with the thought that I can always turn the cooling down but if there is not enough then I'd be stuffed! So overkill was the best I could think of... old English engineering tradition - "if in doubt - double it". One early pice of advice I was given was that a tripple coil would probaby handle anything I could throw at it... and it seems to do the job.

I used to teach jewelry design & manufacture, copper smithing, and other bits and pieces when I first started teaching so I guess the finer skills of working in metal have never really left me.

I wanted a design that had the minimum of joints, maximum flow possible while making the best use of the space available within the top of the Bokabob head. I thought about continuous concentric coils but one coil warms the next so its not as efficient. I tried stainless steel pipe but that first tight 90' bend is a real killer so it was back to copper with parallel coils and a common output pipe.

I've enjoyed making three of them so far, the original and two more for other people who wanted something similar. I don't find it difficult and enjoy the challenge of continuous improvement. My latest addition to my workshop is a 600 watt ultrasonic cleaner I made for another project but now use for cleaning my cooling coils... you should watch it clean copper when it is filled with 18 litres of 15% acetic acid at 80'C.

I've started on a new design, it uses a 12mm down-pipe so that I can space the coils a little better than a 15mm tube allows. The inner coil might be a bit of a challenge so I'll probably concede and make a jig for that coil instead of simple coiling it because I don't want the tube collapsing.

[moorem]

Well I ran my still for real this last weekend and it was very interesting.
25 litres of a sugar wash in a 35 litre stainless heater with a 3" column. The heater is capable of delivering 4000 watts. Once it was up to temperature and stabilized it was coasting at barely 800 watts.
I've decided that I don't need a still with a 3" column as I'm not likely to really need 35 litres or more so I've already started on a new still.

So starting with the cooling coil which will be for a 2" column.
Two concentric coils with a single return. Roughly 1/8" spacing between the pipe, inner and outer coils and around 1/8" clearance inside a 2" diameter pipe.

I like the comment from an earlier contributor... "copper porn"... because I'm quite proud of my copper-work.

1 3/4" diameter and 6 1/2" long.

Tricky bends returning to out pipe

Making a smaller, more compact coil design was actually more technically challenging. Getting those very tight bends without any flattening was an interesting task. Soldering was a bit tricky. I silver soldered the first one I made but that meant that the oxide was difficult to clean and besides, the copper coils were then so soft because they had become annealed that they distorted almost under their own weight. So Lead/Cadmium free potable solder is the way to go with these. Less oxide to clean and the copper pipe, which is already half hard, remains structurally more robust.

We live and learn.

[humbledore]

That bend going back to the return pipe is jaw-dropping. It defies belief that the pipe did not flatten. Fantastic work.

[Doogie]

Good Lord ... will you sell one of those already ... the only way I could even come close to making one of those is in photoshop ...

Most of the ones I have seen you can see flattening, and you can see the coils are all packed tight (inner to outter, side by each) ... those of us that cannot do have to deal with crap like this:

[moorem]

That bend going back to the return pipe is jaw-dropping. It defies belief that the pipe did not flatten. Fantastic work.

Thanks Humbledore,
That bend started life as a 1:r bend i.e. 6mm tube round at a 3mm radius... no salt or any other packing inside the tube at all. I think I've reached the limit with the bends I can achieve in my small workshop unless I start using 5 or 4 mm tubing which is always an option.

[moorem]

Good Lord ... will you sell one of those already ... the only way I could even come close to making one of those is in photoshop ...
Most of the ones I have seen you can see flattening, and you can see the coils are all packed tight (inner to outter, side by each) ... those of us that cannot do have to deal with creap like this:

Hi Doogie,
Yes I also saw that one listed. I would not have the cheek to put that up even as it was described. Apart from that it really would not be difficult to anneal, clean, straighten and start again , its all about having pride in your own work. I also spotted the one or two described as a double helix with the inner tubing quite badly flattened and touching the outer coil. The problem with that design is that one coil warms the next and the center area is a dead and a waste of space. Also, having the coils too close to each other does not provide the best path for vapor circulation around the cooling matrix.

Earlier I incorrectly used the term "cold finger", which was true, but the central return pipe serves to provide cooling where the plain continuous double helix design wastes this area.

I spent quite some time on a CAD package experimenting with the diameters and spacing of the coils, and with at least one, I had to machine my own former because nothing was easily available to suite my drawings. It was through the use of CAD that I came up with the 1:r bend arrangement and patterns.

Its so much harder to make the smaller twin coil than it was for the larger triple coil. Despite having one less coil it took more man hours to complete.