double coil with cold finger & 3D printed formers

[jef]

I have been planning my first still, which may be a LM (Bokakob), I thought the following reflux coil build process might be of interest.

I'm not saying this is a better method than any other, these are the only condenser coils I've ever made, but I've not found this method mentioned on the forums. I have limited workshop space & tools, but have access to 3D a printer, I thought I would try making a few coil forming parts that would help me to build an unnecessarily dense and complicated double wound condenser with a cold finger.

If I can provide more detail or plans etc. then let me know. The designs I made are for 6mm OD copper, 0.6mm wall, though I made the channels 6.5mm, so the designs may work directly for 1/4" tube. The cold finger is 10mm OD. The designs are available at https://www.thingiverse.com/thing:6590441
I am pretty pleased with the result:

The coils are to fit within a 54mm OD tube with 1.2mm walls, therefore there was supposed to be a 2.9mm gap between walls & coils. In reality I had not accounted for flattening of the tube, nor for the need to slightly release the coils to get them off the formers, some gaps are smaller others are a bit bigger, but pretty close.

the tightest radius, at the bottom of the coils, is 9.65mm centreline. I made a little bending jig for that and found that stuffing some spare 1.75mm filament and ptfe tube helped to reduce flattening. Other than this I did not use any coil packing for the process.

the copper was annealed before bending, then a clamp put on below the bending jig
after bending the filament can be pulled out, then the outer tube.

I also made a little cutting jig to indicate where, after bending, the end of the tube should be cut. It turns out that this is also quite handy for gently unflattening tube, getting it slightly more circular again.

With that bit done I slotted the bottom bend into another former designed to hold the correct angle for the inner coil

then approached with my inner coil former that has a 21.8mm centreline diameter (note the 10mm tube at centre of the coil former)

the 10mm tube fits into the central hole in the square former to provide something to bend the first turn. Annealing a section at a time it is a matter of pull & turn, working in sections of 1/2 to 3/4 of a turn at a time. Note the grey steel pin - this is jammed into the end of the coil to help retain the position of the tube for the first couple of turns.


TBC...

[jef]

The outer coil uses the same initial bend of 9.65mm radius, but a different shaped former to run into the first turn of the coil

The outer coil is easier, 39.6mm centreline diameter, but I still needed to anneal for the first couple of turns.
I have a 1/2" Hex/Allen key and made the coil former a tight fit onto this.

The coils were supposed to be 15 turns each, 150mm in height, the bends at the bottom and an end cap plus the bends at the top add to the height. On one condenser the tubes rise about 45mm above the end cap and 200mm of condenser will be inside the main tube. The other condenser that I have wound was left with a longer riser at the top, as others on the forum have helped me to possibly change track and build a CCVM.

Another former allowed accurate drilling of the top cap for 2 x 6mm, a 10mm and a vent hole. Currently this cap is loose, I might solder it in. Before fitting the cap I slid on 9 PTFE washers that I'd made from 10mm rod. At 2mm thickness these should help to keep the coil off the outer walls.

I made some more formers (why not!) to bend the 6mm tubes at the top on this condenser, and added a 10mm elbow. In retrospect I possibly should have used 9mm OD for the cold finger - I have a bunch of John Guest type fittings, these are all imperial, the 5/16" fit an 8mm OD tube OK, but for the 3/8 fitting I had to get some 3/8" OD tube, swage one end to go into the 10mm elbow and the other fits the JG fitting.

I've made a couple of sets of coils in this way. Soldered one up for testing. Using a 12V, 18 Watt pump that is supposed to be rated for 5 metres head & a max 800 litres per hour I get a flow rate of about 950ml per 30 seconds through each coil. So that is something like 4l per minute in total. I may use a PWM controller of flow control tap when in use, or I have a smaller pump.

In testing various bits and methods I wasted about a metre of 6mm copper. To repeat the design you would require a minimum of 3 metres of 6mm, and 30cm of 10mm. 2.5 metres of copper are within the condenser, with about 10cm of each tube curving out of the top. I annealed the heck out some bits, but seem to have used less than 1/4 (<100g) MAPP gas.

[subbrew]

Looks nice. Much more efficient than me using a 3/4" PVC pipe for the inner mandrel and a 1.25" pipe for the outer. I wound some old coax cable between the coils to try and keep the gap consistent.

[Demy]

Nice work, yours is the technological version compared to mine (very crude)

[jef]

thanks both, subbrew - no efficiency here! I spent hours learning the Autodesk software to create the designs, then more hours printing and testing. It would have been cheaper in time to go buy some 3/4 & 1.25 pipe! but I like the process.

Demy - yeah that's the kind of work that I envy, not a skill I have yet.

one last pic - before soldering - that's another skill I need to improve on

[Yummyrum]

Dang thats a tidy job jef

Do you have a plan to balance the flow through both coils ?
I’d have thought the easy path would be though the middle one with less turns .How much it matters I don’t know . Probably can’t be any more funky than a dual wound coil having counter and contra flow happening between the two coils .

[jef]

thanks Yummyrum, I am trying to make as compact a reflux condenser as possible because I have a slightly low ceiling to work under and I want to keep as much height for packed column as possible.

I do have an inline tap that I could use, to balance flow on one of the outlets, but not sure I like the idea of restricting flow at the outlet end. When I was measuring the flow rate there wasn't much difference between the output from inner or outer coils, something of the order of 80ml a minute more coming out of the outer coil. In one test there was actually a little more flowing from the inner coil.

According to my plans the inner coil is 1084mm long, the outer 1810mm. So maybe (hopefully) the tighter bends & flattening of the inner coil naturally balances the extra 726mm in length of the outer coil ?

I will measure again once I've figured out the still for which the condenser is intended.

[pipes+hose]

For maximum efficiency i don't think you want equal flow through each coil, i think you want proportional flow. The bigger coil has bigger contact with vapors so needs bigger flow to remove bigger amounts of heat. But if you have tones of flow it may not matter.

I think it was asked but i can't find it: do you plan to introduce cold water 1) at the top of each coil or 2) in the cold finger and thus at the bottom of each coil? If it's (2) then you'll be able to measure the exit water temperature of each and easily play with the balance. If it's (1) then there is the possibility that one coil is fully saturated at 78 degrees c (and letting a little vapour escape) and the other is much lower but your exit water temperature could still be reasonable so you wouldn't notice.

I recall reading that people generally want to introduce cooling at the top so that it's warm at the bottom and doesn't cause overly cooled reflux at the top of the column to potentially throw off the temperature gradient.

[CaptMorgan]

Very well done, jef! My single wound coil isn't nearly as pretty but does a good job in my boka. Wishing I would have done a single or double cold finger. Make sure you have a way to control water flow to keep reflux coil water outlet temp pretty warm/hot 110-120F or 43-49C. Here is my coil.
Inlet (outside coil) has been bent to allow low restrictions from pump. I recirculate water from a tote with a 529 gph pond pump. 3.8l/1 gallon flow in around 5 minutes is about right for my rig. Let us know how yours performs.

[jef]

For maximum efficiency i don't think you want equal flow through each coil, i think you want proportional flow. The bigger coil has bigger contact with vapors so needs bigger flow to remove bigger amounts of heat. But if you have tones of flow it may not matter.

I think it was asked but i can't find it: do you plan to introduce cold water 1) at the top of each coil or 2) in the cold finger and thus at the bottom of each coil? If it's (2) then you'll be able to measure the exit water temperature of each and easily play with the balance. If it's (1) then there is the possibility that one coil is fully saturated at 78 degrees c (and letting a little vapour escape) and the other is much lower but your exit water temperature could still be reasonable so you wouldn't notice.

I recall reading that people generally want to introduce cooling at the top so that it's warm at the bottom and doesn't cause overly cooled reflux at the top of the column to potentially throw off the temperature gradient.

good point about not wanting equal flow, I'd not thought about that, what you say makes sense. The water will enter via the central cold finger, so coldest point at the bottom of the reflux condenser. Keeping an eye on output temperatures is also a good idea, I'm going to need more thermometers!

Have you any reference for the 'warmer at the bottom' idea? I would have thought that I would not be thinking about any temperature gradient from the bottom of the coil up. Vapour will cool and condense at the temperature it wants/needs to, so may as well knock it down as soon as possible, it'll not be any cooler or warmer wither way. Happy to be wrong though, I will look into that. Thanks

[jef]

Make sure you have a way to control water flow to keep reflux coil water outlet temp pretty warm/hot 110-120F or 43-49C. Here is my coil.
Inlet (outside coil) has been bent to allow low restrictions from pump. I recirculate water from a tote with a 529 gph pond pump. 3.8l/1 gallon flow in around 5 minutes is about right for my rig. Let us know how yours performs.

Thanks CaptMorgan, is maintaining that sort of temperature just a matter of efficiency? If the water was going down the drain I can see that it would be a waste if input it was only a few degrees below output. I have used recirculating water from a large bucket, lots of ice blocks and the occasional bucket refresh. On that basis I was thinking that it doesn't really matter at what temp the water comes out, but maybe I have the wrong end of the stick? The more questions I ask here the more I seem to discover that I am good at picking up sticks the wrong way around!

[Salt Must Flow]

Make sure you have a way to control water flow to keep reflux coil water outlet temp pretty warm/hot 110-120F or 43-49C. Here is my coil.
Inlet (outside coil) has been bent to allow low restrictions from pump. I recirculate water from a tote with a 529 gph pond pump. 3.8l/1 gallon flow in around 5 minutes is about right for my rig. Let us know how yours performs.

Thanks CaptMorgan, is maintaining that sort of temperature just a matter of efficiency? If the water was going down the drain I can see that it would be a waste if input it was only a few degrees below output. I have used recirculating water from a large bucket, lots of ice blocks and the occasional bucket refresh. On that basis I was thinking that it doesn't really matter at what temp the water comes out, but maybe I have the wrong end of the stick? The more questions I ask here the more I seem to discover that I am good at picking up sticks the wrong way around!

The main goal to not running water too fast is said to not super cool your reflux otherwise it 'could' destabilize the top of the column or something like that. I have a thermowell on the output of my reflux condenser. I tune the water to not exceed 140F. I've found that if the water's temp exceeds much past 160F, vapor soon starts escaping past the reflux condenser. The exact temperature you tune your water flow to is not critical. Cooler water is just less efficient than a warmer temp.

[Saltbush Bill]

, I'm going to need more thermometers!

You cant be serious ?.....if you cant run a packed reflux still using one thermometer , then you need to re-access what your doing
A packed column is one of the few stills where a thermometer is of use.....and it only needs one........that one thermometer will tell you when tails are hitting.

[Yummyrum]

Both the Salty ones are correct …… but …… my two cents .

SMF’s take is correct in that you can have too much coolant flow .

What does this mean or matter ????

So you probably understand that there is a temperature gradient that is happening up the column and right at the very top of the packing , the last bit of alcohol flashes off and hopefully , it is at 95% abv or higher .
For that to happen ,the packing at the top will be close to 78.3°C . Also, for that to happen , the reflux that falls on the top of the packing has to be close to 78.3°C to keep the equilibrium happening .

Sooo , if you have too much coolant flow , the RC could be cooling the Reflux way down ….. perhaps as low as 20-30°C . Now the top of the packing is way way way cooler than it needs to be .
The very cold reflux falls down through the packing and maybe takes half the column height before it reaches enough heat energy to revapourise it .( talking worst case scenario here)

So we are looking at a shit operating condition where not much vapour can make it up the column and the effective column height is significantly reduced .

In this situation , the cooling water exit temp will
be low .

As you reduce coolant flow to the RC , the temp of the Reflux gets higher .Happy days ….. the top of the packing is meeting falling reflux at a temp that will create flashing right at the top .

But …. Turn that coolant down a smidgeon more and we end up with vapour escaping out the top .

That is the Paradox . Measuring coolant exit temp is a good indicator of efficient RC cooling …… just enough to get the job done and not overcool the packing , but enough so that there is a safety margin that will not let any vapour escape out the top . There is a “typical “ exit cooling temp range that will get you in the ball park .


What has this to do with SaltBushBills “only one thermometer is needed “ theory ?

Well , I am in this camp .
But …. Always a but .
Like Saltbush , I have hands and fingers . The “actual” exit cooling temp feels like hot …. but not burn .
If the coolant temp ( touch the copper pipe exiting the RC) and its cool , turn the coolant down .
If the coolant pipe feels too hot ti touch , then there is also a good chance that the vapour is escaping out the top .
Oh , you will know that . Hold a finger over the top vent and you’ll feel it

Point is , if the coolant exit pipe is warm to hot , you have that coolant flow in the ballpark .

If it’s too hot to touch , you’ll feel and see and smell that vapour shooting out the top .

But even if the coolant outlet is cold , then worst is your ABV will not be as high as you might have hoped . .

Having said that , I always get a minimum of 95% at a good speed and my coolant exit water is often barely warm .

Don’t overthink it .

Oh and Saltbushes one thermometer is in the vapour path .Although it can be a help to newbys , you can still run the still without it.
Just before the thermometer starts to rise by 0.1° , you’ll taste the onset of tails . ….. iff’n you do tasting on the fly .

[quadra]

Great post Jef! and we all appreciate build posts and those jigs and links look interesting. If the rest of your build and distilling is as well thought out you will really enjoy the process of getting to know your still and how it runs!

[jef]

thanks for the encouragement, and advice, much appreciated, all seems to makes sense to me.

As I see it distilling & brewing are just cooking, which is a craft branch of chemistry. My approach with beer making has been to measure the heck out of everything I can and make copious notes. That way I can match process and results, when it works (or not) I can measure and repeat (or not) the process. For me that eventually leads to learning the feel of the process, which ultimately is more helpful and rewarding than the measurement.

Given a choice I prefer my meals prepared by a chef to a chemist, but I trust the likes of Kenji Lopez-Alt & Heston Blumenthal to help me unsderstand the principles behind the process, which is where this information is so helpful.
thanks!