Bubbler - A Virtual Build

Perforated & bubble cap plated columns

Re: Bubbler - A Virtual Build

Postby chipboy » Tue May 05, 2020 7:51 pm

Go guys, tech drawing at school was my highest subject bit ended up doing engineering and ghe drawing subject was easy,

Love the cad work and watch with anticipation.
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Re: Bubbler - A Virtual Build

Postby Lesgold » Wed May 06, 2020 7:28 am

Thanks Chipboy. Well the build is almost complete. There is enough info here for a potential build. If I can get my laptop working properly again. I might draw up a cap plate as an option and a packed section. If it doesn’t want the play, I achieved what I set out to do.
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Re: Bubbler - A Virtual Build

Postby Lesgold » Wed May 13, 2020 8:43 pm

Got Sketchup up and working again. Exported a couple of bubble plate drawings and then it crashed. So I’ll pop them up and describe the dimensions. Plate is 106mm in diameter. Riser is 40mm x 40mm high. Bubble cap is 50mm x 50mm high with 32 x 1mm slots to a height of 5 to 7mm. Downcomber is 20mm with a length of 70mm. Downcomber cup is 25mm x 25mm. Cup is soldered to downcomer 10mm up from the bottom of the cup.
18EFC72B-4FF6-4461-BE48-4B1013478481.jpeg

7D9A902D-2026-428C-B7E8-3E2FA956975E.jpeg

Bath depth is 19mm.
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Re: Bubbler - A Virtual Build

Postby scythe » Thu May 14, 2020 3:47 pm

Just done some quick and dirty maths on that cap...
Is no good flow wise.

By my calculations you have a slot every 9.8mm.
General consensus is 1 slot every 5mm.
Your riser has a cross sectional area of 1134.1mm^2 (assumed ID of 38mm)
But your cap slots have an open area of 160-224mm^2
This will cause a restriction on the vapour flowing through the cap.

Upping the slots to 64x 1mm x 7mm gives open area of 448mm^2
Increasing the slot thickness to 2mm goes to 896mm^2

Now reducing the riser to DN40, which is actually 1.5" (38.1mm) pipe, with a wall thickness of 1.63mm has an ID of 34.84mm.
DN40 has a cross sectional area of 953.31mm^2 which is much closer to 896mm^2 so will flow better.


In theory anyway. :geek:
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Re: Bubbler - A Virtual Build

Postby Lesgold » Thu May 14, 2020 5:15 pm

Thanks scythe. OK, if I want the opening area of the slots close to the riser cross sectional area, I should be able to make some adjustments. The slots were spaced at approximately 5mm centres. Is it OK to have them really close? 64 x 2mm slots might be hard going as you would only end up with about .5mm space between each slot. Is there any advantages/ disadvantages to wide v narrow slots? Ie. how does it impact on bubble size, efficiency etc. Sorry to ask these questions, would like to put up something that is going to do a reasonable job.
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Re: Bubbler - A Virtual Build

Postby RC Al » Fri May 15, 2020 12:08 am

I cant say if making all the flow areas equal makes a cap work better, but on face value it seems a good approach. If you could work out the flow resistance/ pressure drop that would occur with the slot size and number vs bath depth vs the kw input, you could then find the perfect matching pipes, but at our level it comes back to the generalisations on slot size/spacing already mentioned to get in the ball park and feeding that seemingly restricted flow area with evenly spaced pipes or making it all the same with big slots. Havent seen anyone saying their big slot caps didn't work, but quantifying efficiency is next to impossible for us

Why dose this matter? Every restriction causes some back pressure to the boiler, the higher the boiler pressure, the higher the boiling point of the the contents, the bp's of ethanol and water are very different, but the effects of pressure are not proportional to each other and it works against us, making the bp's closer and thereby harder to separate. I have the idea that a lower boiler temp would help seperate fractions better too, but i havent seen anything to support that idea

Making the riser and cap envelope similar sizes seems intuitive, but in my opinion making the envelope a bit larger counteracts laminar flow effects from the donut shaped passage, you could even go as far as dropping the riser down to dn32 @ 700mm and not be too stressed as the main holdup is the slots (unless you go taller than 14mm, see next)

With the min recommend distance of 4-5mm between the slots, with a 2mm slot, into a 159 circumference cap = 26 slots @5mm high, 260mm plus 52 per mm of additional slot height.

The wider the slots, the larger the bubbles, reducing the amount of vapor/bath interaction, reducing the efficiency of the plate, making this style of large single cap more suited to making a flavoured product. Going taller slots is mitigated somewhat by more bath depth, but will still contribute to bubble size and reduce efficiency.

The cup on the downcommer needs to be at least the bath depth to create the hydraulic lock

Remember you can make any sized cap or pipe either with sheet or by taking a slot out of a larger pipe, A 56mm cap would suit the dn40 better and gain 3-4 slots

There is no need to make the riser/cap that tall unless you want to run a really deep bath. The riser can even be a bit shorter than the downcommer, the pressure/flow is sufficient to stop any reversal, the shorter the pathway, the less resistance, less pressure

The saw tooth pattern is a method to pass solids, frequently used with a clear space below the cap, haven't seen anyone worry about that on a home still in a while, more an industrial thing
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Re: Bubbler - A Virtual Build

Postby scythe » Fri May 15, 2020 6:18 pm

2mm wide slots spaced every 5mm should leave 3mm between each slot.

My calculations came up with a circumference of 314.15mm so that divided by 32 gave me 9.8mm.
2x Pi x R
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Re: Bubbler - A Virtual Build

Postby Lesgold » Fri May 15, 2020 6:54 pm

G’day scythe.
Between yourself and RC Al, you have made for some interesting discussion. Lots of learning taking place here. Plenty to think about. Will make the effort In future to be a bit more precise when discussing tube sizes. Will ask a few questions after feeding the face.. Just one point with your calc. DN50 copper has a diameter of 50.8mm and therefore has a radius of 25.4mm......... I’ll leave the rest to you.
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Re: Bubbler - A Virtual Build

Postby RC Al » Fri May 15, 2020 6:59 pm

The formula is C = πd. In this equation, "C" represents the circumference of the circle, and "d" represents its diameter. That is to say, you can find the circumference of a circle just by multiplying the diameter by pi. OR 2R x pi

2" 50.8 * 3.1415 = 159.58
4" 101.6 * 3.1415 = 319.17
Last edited by RC Al on Fri May 15, 2020 7:06 pm, edited 1 time in total.
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Re: Bubbler - A Virtual Build

Postby Lesgold » Fri May 15, 2020 8:27 pm

Spot on. Your earlier post had me thinking and looking back over some other member builds. If a riser made from DN32 is used, the area of just over 700mm turns out to be slightly larger than the open area of the perf plate design. Quite surprising actually when you do the sums. From what you are saying, it’s not really possible to match the combined slot area to the riser opening area if using a DN50 single cap. Looking back on many past builds, it appears that this may not have always been a major concern to the people making them. My initial cap design (32 x 1mm slots @ 5mm centres to a height of 5 or 7mm) only gives a slot area of 160 - 224mm. 26 x 2mm slots to the same heights gives areas of 260 to 364mm. It seams that every choice has positives but creates other issues. Which way would you go? Riser height could be dropped ( as you mentioned) and therefore the cap height could also be reduced. Any thoughts?
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Re: Bubbler - A Virtual Build

Postby RC Al » Fri May 15, 2020 10:52 pm

It really comes back to purpose and power availability, as you go up in caps, the smaller they get, the more slots are gained, more power is needed, takeoff speed goes up and a more refined product is produced

1-2 caps flavour
3-5 caps general purpose
6+ caps neutral maker

These are generalizations, how many plates you use and how you drive the unit can vary the output, run lots of reflux on the one cap and it will strip flavor, run a 6+ one with minimal reflux and you will get flavor carry through. This basicly points us to the 3-5 caps being the most versatile for the home experimenter who wants to do a variety of things with the one still

Another simple solution is to have different plates available, most seem to skip this option, a shame as it makes the units much more versatile, you can have your cake and eat it too

Most stills built with even vague nods at the flow areas will work just fine and if it uses a few hundred watts more or less than the next guy's or takes a bit longer is of little concern to many. I figure that every minute saved by efficiency is a minute longer doing more stilling or something else, added up over the lifetime of use, you can claw back many hours if not days
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Re: Bubbler - A Virtual Build

Postby Lesgold » Sat May 16, 2020 5:31 pm

Good stuff Al. The learning journey continues. Your input throughout this whole process has been invaluable. Thank you so much. The little snippets of wisdom and knowledge will be reference points for anyone heading down this path. I am already visualising a build with what I have learnt here. Hopefully there will be something in this thread for a few people, even though what has been presented has been quite simplistic from a technical perspective.
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Re: Bubbler - A Virtual Build

Postby scythe » Sun May 17, 2020 8:40 am

Lesgold,
Good pickup.
... :think: ... seems I was using the diameter in my calculations as the radius. :doh:
So my numbers were out consistently, but still wrong.
Ah well.

There was a good post by "meerkat" a number of years ago on the design of bubble caps.
Gave good ratios and calculations for open cap area and riser diameter.
But was coming from a commercial production side of things and did close out that, on still the size we are using, close enough is good enough for us.

But I'm with RC, if I can save a bit of power or time I'm for it.
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Re: Bubbler - A Virtual Build

Postby Lesgold » Sun May 17, 2020 2:49 pm

I think I read that post. Quite interesting and brain scrambling until you break it all down. And by the way, your input was very helpful in the sense that you made me stop and think, research a bit more and then try to improve what I had presented. Even though I haven’t started on a bubbler build (and I may not for a year or so) I have already designed a jig for cutting slots with the angle grinder. It’s quick, accurate and safer than many of the methods that I’ve read about. Might even post it up as it does a very good job on 2” caps.
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