Coil Condenser Problem – Vapour Huffing / Not Knocking Down

[scythe]

I just noticed that you have 2 fairly major crimps in your condensor coil.
First under the cap and the other where the inner and outer coils transition.

If you sort that out it will probably improve greatly.

[Nays_Shine]

Good pick up on the crimping. Its not as bad as it looks in the photo (where the tube actually looks flattened!), but yeah, cant be helping. I will upload some better photos of the coil defects later. Is this bad because it reduces coolant flow (I am currently moving 1-5lpm through the coil) or for another reason?

I think there may be a few issues going here and that it is not going to be a one step fix.

Hillzabilly; I have been thinking about what you wrote re 1" reducer and think you are correct in assuming that this might increase the speed of vapour as it climbs through the condenser head. Even though it would slow down as it enters the 3" chamber, I think possibly it would keep most of its speed gained through the 1" section. Its hard to know for sure without modifying the collection cup; which is something I will look into if required.

As it might be an easy fix, I am also thinking about slotting a 19mm cold finger with an internal 12mm return, through the centre of my coil. I can make this easily using spare offcuts. Ill upload a diagram of this later also.

I will also try desoldering my end cap or drilling more holes into it. This is so that excess heat does not build up right? Or is it to spread/slow the vapour up-draft?

These solutions are all eluding towards a conclusion that my coil is not efficient at heat transfer. It would be good to hear from other people with a 3/8" coil double coil to see how much heat they are picking up and at what flow rates.

[Nays_Shine]

Edit: I would likely use a 9.5mm tube for an internal cold finger return.

Adding a cold finger wont solve my vapour speed issue, however it will eliminate the current 1" void in the middle of my coil (hopefully not exacerbating a possible vapour speed problem) to increase the contact surface area of the condenser, while reducing gap spacings.

If that doesn't work, I'll look into some 'still micro surgery' by widening the 2-1" reducer opening. I think this would be an improvement for my still, but I am tentative about doing it as the collection cup was by far, the hardest part of my build and I dont want to f@#k it up! :-)

[hillzabilly]

My opinion is that yes with your still huffing the efficiency of the condencer is comprimized severely,that's why I suggested you pack the area underneath the coil right down into your collection cup,to test wether the cup hood area could be the cause,this packing idear is used because it stops or reduces the cycleling pressure change that is to me huffing,and were there is a restriction or a quick change in direction and a change in area ,these seem for me to be the problem area's wich can cause a natural resonance like a musical instrument wich again to me is huffing .I took the Nixon Stone route because of un-restricted path to condencer ,but the Boka pic I posted is probably a better and more simple still to make and run,hopeing ya find a solution soon.cheers hillzabilly ;-)

[Nays_Shine]

Thanks Hilazabilly,

I havent tried the packing at the bottom of the coil yet, however I will give this a go on my next stripping run. I really appreciate yours and others input and help with this problem. Its encouraging to be able to get help on an issue after you run out of ideas yourself.

Nay

[Nays_Shine]

Thanks again Hillzabilly for your help. Although I haven't been able to prove it for sure yet, I think you might have nailed it with the vapour speed diagnosis (or find another house where I can use a a 1000 IFC - how does this help during the 35oC days of summer?). Which basically means I need to muck around with either more packing in the collection cup/ condenser head or, rebuild it. Not sure which way to go yet.

Here is how I could modify my current design:

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I did try packing scrubbers under the coil on my last run, however I was unable to ascertain if it made much difference as I tried a few different things at once - which is not a good approach to troubleshooting. I will be more methodical with my testing on the next run.

While acknowledging the above, I have also been thinking more about about this approach:

...increase my capacity to remove more heat by:
...
- Add a cold finger
- Replace 3/8 coil with a jacket condenser and 1/4 coil (I‘ll upload a sketch of this if required)
...

To do this I have come up with two modifications that I can do using parts I have lying around at home as per these sketches.

Add a cold finger

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jacket condenser and utilise a 1/4 coil I already have.

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[Nays_Shine]

In the end I just went ahead and built a cold finger to see how that would go. I had the copper and felt like firing up the gas torch!

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I have tested it but the results were inconclusive as with the cold finger sticking out, it makes it really had to get a mirror in close enough to see if any vapour is escaping! So I couldnt really tell how effective it was. I will have to add another vent hole or de-solder the end cap entirely.

(On that note, how do vent holes add to your performance? I cant help thinking that people who say this improves condensing are actually just fooled by the fact that it makes it harder to detect escaping vapour! :-D )

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I was hoping that by having the cold finger in there, my outputted coolant would be hotter than when the cold finger was out. Oddly (disappointingly?) it seemed to do the opposite which; would imply that it was in fact doing more harm than good! Sigh. Just by touching the coolant input and output tubes it did seem to be taking out noticeably more heat, so I might have just been using my thermometer incorrectly.

[Sam.]

Vent holes arnt for performance, they are there for if you run your still with your valves shut and cooling water off your still won't turn into a bomb ;-)

[Nays_Shine]

Is this the party line on vent holes? The only reason I ask is that ofter people say their still runs better with no end cap. Also, I have had advice on this thread to drill a wider vent hole. I can see that it could potentially help hot air (o2) escape which might reduce the temperature in the condenser head.

[Sam.]

Running with no cap means a big vent hole ;-)

You need some sort of vent if you are running a still where the outlet is shut by a valve, otherwise you are setting yourself up for a massive fail :angry-extinguishflame: :angry-screaming:

[Nays_Shine]

Wow, really? Who would have thought that if you seal a vessel filled with liquid and then heat it to boiling point that the expanding vapour and lliquid would cause a pressure build up and ultimately explode? This is important stuff. You really should let the rest of the distilling community know about this insightful knowledge of yours.

[Nays_Shine]

Sorry to sound sarcastic but it is frustrating when you ask for genuine constructive advice and someone hijacks the conversation with 101 remarks such as why it is important to open your still to the atmosphere. If you review my previous posts you will see that I do have a hole in my end cap for that purpose. Although I am a beginner, I have spent 18 months researching, building and operating my still. I realise that sometimes people overlook the obvious, but come on, give me a break!

What I am asking to this regard is; while a vent hole is a prerequisite for a boka design for safety reasons, does increasing the vent hole size (or removing the end cap entirely) improve condenser performance, by allowing excess heat (but not ethanol vapour) to exit the head?

[Zak Griffin]

There is no reason why that coil shouldn't work, hundreds of guys use a similar setup with great success. The only thing you've got different is the reducer/cover play thing going on, so maaaaybe that's got something to do with it?

[Nays_Shine]

I think hilzabilly and zak are right.

This is a vapour speed issue caused by my reducer design.

It could be acting like a venturi jet!

I played with placing scrubbers underneath the coil while packing the inside (at the bottom) of the coil and wrapping a little strip of packing around the outside of the coil (also at the bottom). This worked pretty well.

Sadly, I am not sure that my cold finger achieved anything!

Im going to modify my design this weekend by opening up the reducer.

[Nays_Shine]

I think my troubles are over thanks to widening the opening between the column and the collection cup/ condenser head; and by ditching my hood design in favour of a different design; as per Hilazbillys advice. So thanks for that. I never would have guessed that could have been the problem. I think this has slowed vapour speed, as the previous design was probably acting as a venturi (just a guess).

I still require some copper wrapped around the coil, however I no longer require very much. I now only use a single piece around wrapped around the bottom (using pete8686's configuration), where as previously I had to mummify the whole coil!

For the above configuration to work, I need to use my new cold finger. Without it (or without extensive wrapping of the coil), A LOT of vapour escapes. When I drop in the cold finger, I'm all good.

The one thing that made absolutely no difference to condenser performance was coolant temperature. Even blasting 14oC water from the mains tap failed to help prior to my initiating the above changes. I couldn't ever see noticeable changes in heat gain between input and output water as the reservoir heated up. Using my current setup, I am successfully cooling using a reticulated 150l reservoir while stripping with 4400w. The water is gaining about 13oC at 5l p/m (going in around 40-45oC, coming out around 55-60oC).

I keep coming back to this, but I think its important to reflect on what seemed to work, what didnt and what was unresolved:

“Am I achieving maximum heat transfer potential / extracting the expected heat energy out through the coil given my coolant flow rates and power input?” --- I never figured out what this should be or how to work it out. Without the cold finger, the coil is still not sufficient to knock back very much power. With the cold finger, I am now removing 2-3 heat as previously (approx 13oC at 5l p/m!)

If the answer to this key question is NO, then I probably need to address these issues to achieve the coils maximum heat transfer potential:
- Vapour passing over the coil too quickly (I have already tried to address this through packing and wrapping the coil with copper - not an ideal solution). --- I widened the vapour path to negate the venturi effect and still do require one wrap of copper mesh at the bottom of my coil
- Spacing between coils and the condenser head wall might be too widely spaced (or perhaps even to tight?), resulting in vapour not making contact with the coil --- putting in the cold finger has increased contact area and reduced the large cavity through the middle of the coil
- Issues with reduced thermal conductivity due to dirty or badly oxidized inner wall of condenser coil --- inconclusive/unresolved
- Issues with reduced thermal conductivity due to turbulence / air pockets as a result of kinks in the coil --- inconclusive/unresolved

If the answer to this key question is YES, then I probably need to reduce the amount of heat going into the condenser head by:
- Lowering vapour temperature (I am already more or less achieving azeotropic point so not sure how this is going to help my spirit runs)
- Reducing power (not a preferred option!) --- even dropping the power to 1000w made no difference; so this was not the issue
- Reduce the amount of heat energy passing up through the column walls into the walls of the condenser head (is this correct physics?) (possibly isolating the column, condenser head and the coil from one another) --- inconclusive/unresolved
- Enable excess heat (but not vapour) to escape through the top of the column by adding extra vent holes (as suggested)? --- If anything, my current air vent is smaller than what it was. Inconclusive/unresolved

Or, increase my capacity to remove more heat by:
- Is this where using colder coolant water would sit? Again, I am not sure how this would be the case as I would assume cooler input water just means cooler output water. Does water become less efficient at cooling as it warms up? If so, is there a threshold that you should sit below? Please explain if I am incorrect. --- Coolent temp made no noticeable difference
- Bigger coil --- duh!
- Add a cold finger --- this has definitely helped
- Replace 3/8 coil with a jacket condenser and 1/4 coil (I‘ll upload a sketch of this if required)
- Increased water flow ( I can already achieve 5l p/minute which hasn’t always proved to solve my problem)

[Zak Griffin]

Keep It Simple, Stupid :handgestures-thumbupleft:

Glad to hear you've got it sorted out now.