Upgrade Time

Perforated & bubble cap plated columns

Upgrade Time

Postby Citystiller » Sun Jun 18, 2023 6:30 pm

Upgrading from my old pot still to something serious.
Long time lurker, been getting bits n pieces for a 4" bubbler for a while now.
Stuff.jpg

Access to a lathe and mill very handy.
My plan:
Still Plan.jpg

Machined down all s/s ferrules with a recessed groove for copper pipe to sit in snugly for easy soldering.
Ferrules.jpg

Reducers.jpg

Any suggestions where to position 3" view on the 4" pipe, I was thinking as low as possible & still have clearance to fit clamps? Ends up 20mm from bubble plate.
Tee2.jpg

Tee1.jpg

Now time to solder or braze (got lots 45% silver brazing rods), leaning towards soft solder or combination.
Also found this old soft silver solder, CIG 965 lying around, apparently lead free with small amount of silver for extra strength. Should be good for s/s to copper with same flux.
Solder1.jpg

Solder2.jpg

Still undecided with RC design, will be using my pool water for cooling. During summer pool heated to around 30 C.
1: 100mm with 7 x 3/4 tubes or
2: 120mm with 7 x 3/4 tubes or
3: 100mm with 9 × 3/4 tubes. ??
Any suggestions appreciated.
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Re: Upgrade Time

Postby RuddyCrazy » Sun Jun 18, 2023 6:59 pm

When i made my bubbler I put the bottom of the 3" site glass about 5mm above the plate drain so when the plates load the liquid wash's against the siteglass which makes it easier to see from a distance.
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Re: Upgrade Time

Postby RC Al » Sun Jun 18, 2023 10:38 pm

Ive lusted after the ability to machine the the ferrules as you have, keep going :handgestures-thumbupleft:

Agree with Ruddy, low SG's is good.

Jamm as many tubes into the RC as you feel comfortable gluing in (and a baffle...), Increase of diameter won't do anything for you, dealing with an over efficient cooler is easier than a poor performing one.

3/4 plates is heaps for scotch/bourbon/rum, the 100 riser isnt a massive help for puking, the small amount of volume will make stuff all difference (unless you add a sight glass to give you a second or two of warning) 3 plates and 880 packed will trump 5 plates with 500 packed any day of the week if your shooting for neutral

How are you planning to put the plates in?, with individual sections, soldered in gives least dramas - zero leaks

Speaking of plates, what's the plan there?

Which solder to use where? depends how many joins are in proximity to others, use the high temp stuff first and the soft solder last ie tubes in rc with silver then the ferrule with soft
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Re: Upgrade Time

Postby Citystiller » Mon Jun 19, 2023 9:46 pm

Thanks Ruddy and RC for info.

Will fit the sight glass as low as I can.

RC will be 100mm or 120mm in length not diameter, will be 4" dia.
Have read that if RC is too efficient will be difficult to control, ie longer waiting time between water flow adjustments.

Plate will be sandwiched between ferules, silicon gasket will seal.
Gonna flatten out 4" pipe to get a sheet, any suggestions for easy way to do this, anneal it I assume.
Plate.jpg


Bubble Cap plates are the plan. 4m of 1" and 5m of 3/4" new copper pipe been sitting is the shed for past 15 years, time to use it!
5 Caps on each plate made from 1' pipe end to be brazed on and finished off in lathe, 1mm slots 2mm apart x 5mm high. Will use 1mm blade on mill and dividing chuck to cut the slots.
Risers 3/4" pipe?? 1/4 holes drilled 15mm above plate., flared at base, end brazed on.
Not sure if 4mm gap is adequate between the riser 3/4" (19mm) and 1" (ID 22.96mm) cap for the vapour, some use 1/2", others have used 5/8 which gives 7mm gap.
Downcomers 3/4 pipe, 20mm above plate.
Bubble Cap.jpg
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Re: Upgrade Time

Postby Citystiller » Sun Aug 13, 2023 11:10 pm

Finally got back to doing a bit more.
Machined the PC plates and bubble cap plates. Almost done the Dephlag plates, pics of these to come later.
PC Plates.jpg

Bubble Plates.jpg

Plates.jpg

Going to squeeze in 6 x 1/2" pipes with a few diverter plates in between for good measure for the 2" PC, 500mm long should be enough.
Decided to go with 5/8" risers, 1" Caps and 3/4" downcomer after a lot more research/reading.

I'm a bit obsessive with the technical side of things, I like to make it once and hopefully will work efficiently.

Have read that the riser should be higher than the downcomer, yet have been unable to find any reason why?? Going for a 20mm high downcomer so assume riser will need to be a few mm higher, 22mm? at the lowest point of reversal area riser cutout or holes.
How I see it, the vapour goes up the riser, does a 180 at the reversal area, then down the area between riser and cap (annular area) then out of the cap slots creating bubbles. This whole area is occupied by vapour so what has the liquid bath depth (determined by downcomer height) got anything to do with the riser height?? The vapour is keeping the liquid out from entering via the bubble cap slots. Enlightenment required!

Looking at all the commercially available bubble caps (found some at local brewery shop) mounted to a 4" plate the risers vapour cutout are shorter than the downcomer by 5mm. ie the downcomer was 15mm high and the riser with cutout only left 10mm in height above the plate. Go figuire?

In the process of making these risers, all 30 of them. Flared the ends first then into a jig to get squashed into a nice flat flange, worked out well.
Bubble cap next on the list.
Riser1.jpg

Riser2.jpg

Riser3.jpg

Time for little night cap to calm my detail obsessive brain! :obscene-drinkingdrunk:
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Re: Upgrade Time

Postby Doubleuj » Tue Aug 15, 2023 12:01 pm

Damn this is looking good!!
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Re: Upgrade Time

Postby RC Al » Sat Aug 19, 2023 5:36 pm

Just re reading this, Have a read up on slot spacing

Theory says that 2mm is too close, they are spaced apart to let the bubbles form in small diameters, which increases the overall vapour to liquid ratio - better efficiency.

The close spacing will cause large inefficient bubbles as the vapour stream will rejoin the one next to it as it exits the slot.

Re risers - Indeed, the area inside the cap isn't frothed up liquid, its pressurized vapour that fills the whole area to just above the slots. There would be efficiency gains with a shorter distance to travel and if the caps are done right, a smaller volume to pressurize, both of little consequence to our little stills, but adds up quickly on big ones with lots of caps.
Last edited by RC Al on Sat Aug 19, 2023 5:40 pm, edited 1 time in total.
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Re: Upgrade Time

Postby Citystiller » Mon Aug 21, 2023 4:35 pm

Thanks for info RC Al
I have previously read that slot spacing should be 4mm - 5mm, with no explanation to why so thanks for explaining the reasoning.

4mm slot spacing leaves very little room left for the slots on DN25 1"/25.4mm tube (circumference 79.8mm).

Trying to get maximum spacing and still adequate slot area without flow restriction requires a bit of a compromise.
3mm to 3.5 mm slot spacing is about the maximum can go without flow restriction.

The best I could come up with using DN25 tube:
A: 18 x 1.5mm (5mm high) Slots with a spacing of close to 3mm
B: 16 x 1.5mm (5.5mm hight) Slots with a spacing of close to 3.5mm
C: 16 x 1.6mm (5.5mm high) Slots with a spacing of close to 3.4mm

Made a bit of a spread sheet that shows many combinations.
Bubble Cap Slots.xlsx

Last column shows the 4" plate area (minus dowmcommer area) to total slot open area (5 x Caps) as a percentage, have read (theory) that for bubble plates this should be 9 to 10%. Sieve plates are less, 7 to 8%. This 9 - 10% seems to match a cap slot area between 132 - 146 sqmm.
5/8 riser area (ID 13.86mm) of 150sqmm is slightly more than cap slot area. Slot area is the limiting function with this design.

The next size up is to use a DN25 coupling or cap with 25.4mm ID & approx 28mm OD. Or I could expand out the many meters of DN25 tube that I already have lying around.
Can get a few more slots than DN50 tube and still maintain 3 to 3.5mm spacing.
If I go to 4mm spacing, 16 slots of 1.5mm (5mm High) reduced slot area to 120 sqmm, perhaps this is still ok?

Commercial bubble caps (most common I have seen) are 28mm OD, they have 16 slots, guestimate around 2mm wide/ 4.5 mm high and spacing calculated around 3.5mm. These seem to flow well. The 2mm slot seems to be on the large side however they must be ok as many use them.
Cap2.PNG

Cap1.PNG


I will probably make the riser height a bit less than the downcomer height, doesn't seem to have much of an effect.
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