Boka build

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Boka build

Postby hoody » Sat Jul 03, 2010 11:02 pm

Well, I've been slowly building up material's and doing ALOT of research on here and feel I'm about ready to start my build.
I managed to score about 2m of 2" copper tube (for free! :D ), 6m of 1/2" tube, a coil of 1/4" tube, Half a coil of 3/8 tube, a old copper hot water cylinder (figured it would be good to cut up and use for bit's and bob's), a old roughly made lieberg, some condensor mandrel's and a new gas torch!
I have pretty much made my mind up to make a boka. Was thinking of 1m colom (before a section containing plate's), 200mm condensor and useing a keg as a boiler.
Does this seem like a reasonable plan??

Also, what effect doe's the spacing between the plate's on a boka have? I noticed the template's say 1/4" (from memory) but have seen other build's ie; Pickluk's useing up to 3/4"??

Depending on left over material's I will make myself a new pot still head as well.

I have a few question's relating to sourcing material's in New Zealand;
1) Where can I source 100% copper or stainless pot scrubber's?
2)Where is a good place to find lead free solder?? Most place's I have been to seem to give me a funny look and say they have never stocked it)
3) What alternative's are there for the nice looking copper threaded fitting's I have seen on a lot of still's on HD?

Sorry for all the question's, just want to make sure I build it right first time!

Thank's

Hoody
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Re: Boka build

Postby rad14701 » Sun Jul 04, 2010 7:42 am

With regard to the plate spacing, here is my input on the subject... The gap between the plates is the potential constriction point in the column... Consider my two reducer small scale column that reduces from 1.25" to .75" and then opens back to 1.25"... The constriction point essentially increases vapor speed and resistance... With that in mind, the air gap between plates has the same effect... I'd consider a gap area of roughly 50% of the columns cross sectional area to be about the minimum as that would equate to about a doubling of vapor speed through the slant plate section... If the gap is too small you run the risk of back pressure below the plates which could increase the risk of packed column flooding...

Some numbers to prove my point... A 2" column has an area of 3.1416 square inches... A 1/4" gap between plates only provides 1/2 square inch of area for vapor to flow through and a roughly ~6x increase in vapor speed... Conversely, a 1" air gap provides 2 square inches of air gap for the vapor to flow through and a roughly ~1.6x increase in vapor speed... And a 1.5" gap will yield virtually no increase in vapor speed... A 3/4" gap equates to a 2x increase in vapor speed...

So, what's the big deal with the increase in vapor speed...??? Well, once the vapor speed increases it needs to be slowed back down so it doesn't rush past the reflux condenser without being efficiently condensed back into its liquid state... The greater the vapor speed increase the greater the potential for the need of a larger condenser and/or greater coolant flow...

So, to summarize, you can't really have too much air gap between plates, within reason, but you can definitely have too little... I think, and, again, just my opinion, that is is one reason why we see wide performance variations between Bokakob dual slant plate columns... When in doubt I'd say go with 3/4" minimum and 1.5" maximum air gap between plates for a 2" column...
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Re: Boka build

Postby hoody » Mon Jul 05, 2010 12:55 am

Nice explanation thank's Rad.
So it kind of end's up working like a "venturi"? My thought's (allthough a lot less technical! :oops: ) were that too small a gap would result in flooding.
Think I might aim for between 3/4 and 1".

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Re: Boka build

Postby Braz » Mon Jul 05, 2010 3:05 am

Rad's numbers seem sound. My 2" Bok has the plates spaced at 1 inch and it runs beautifully. I can get 96+% ABV all day long (and I did, yesterday).

Just FYI, I have 38" of packed column (pretty close to one meter) and my double-wound condenser coil is about 8" long so I think your plan will work just fine.

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Re: Boka build

Postby ELT » Fri Jan 31, 2014 12:20 pm

rad14701 wrote:With regard to the plate spacing, here is my input on the subject... The gap between the plates is the potential constriction point in the column... Consider my two reducer small scale column that reduces from 1.25" to .75" and then opens back to 1.25"... The constriction point essentially increases vapor speed and resistance... With that in mind, the air gap between plates has the same effect... I'd consider a gap area of roughly 50% of the columns cross sectional area to be about the minimum as that would equate to about a doubling of vapor speed through the slant plate section... If the gap is too small you run the risk of back pressure below the plates which could increase the risk of packed column flooding...

Some numbers to prove my point... A 2" column has an area of 3.1416 square inches... A 1/4" gap between plates only provides 1/2 square inch of area for vapor to flow through and a roughly ~6x increase in vapor speed... Conversely, a 1" air gap provides 2 square inches of air gap for the vapor to flow through and a roughly ~1.6x increase in vapor speed... And a 1.5" gap will yield virtually no increase in vapor speed... A 3/4" gap equates to a 2x increase in vapor speed...

So, what's the big deal with the increase in vapor speed...??? Well, once the vapor speed increases it needs to be slowed back down so it doesn't rush past the reflux condenser without being efficiently condensed back into its liquid state... The greater the vapor speed increase the greater the potential for the need of a larger condenser and/or greater coolant flow...

So, to summarize, you can't really have too much air gap between plates, within reason, but you can definitely have too little... I think, and, again, just my opinion, that is is one reason why we see wide performance variations between Bokakob dual slant plate columns... When in doubt I'd say go with 3/4" minimum and 1.5" maximum air gap between plates for a 2" column...


Ok - so for a 3" column would I stick with a 1.5" plate gap or open up to a 2" plate gap in your Expert opinion?
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Re: Boka build

Postby rad14701 » Fri Jan 31, 2014 12:36 pm

ELT wrote:Ok - so for a 3" column would I stick with a 1.5" plate gap or open up to a 2" plate gap in your Expert opinion?

For a 3" column a 1" - 1.5" gap between plates should be sufficient due to the larger volume of the column... A 3" column is so much larger than 2" that you probably couldn't push too much vapor for even 1" to handle... That's 3 square inches of air gap for an area of ~7 square inches for the column, or just over a 2:1 vapor speed increase at maximum flow efficiency that you probably won't run at a majority of the time... You definitely don't need 2"... I'd go with 1" as the 1.5" for a 2" column was more of a theoretical than for practical application...
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Re: Boka build

Postby Bob Loblaw » Fri Jan 31, 2014 4:27 pm

hoody wrote:3) What alternative's are there for the nice looking copper threaded fitting's I have seen on a lot of still's on HD?


Stainless sanitary fittings - ferrules + clamps. You can easily solder them to the copper tubing with a MAP torch and Harris Staybrite solder/flux (5% silver - check my "first" thread for a picture of the stuff). They are cheaper than copper and fit straight onto a sanke keg fitting. You can probably order from china via ebay. Or Stilldragon sells into NZ I think and their prices are good.
Easiest way to avoid being on a TTB list is to not purchase a boiler, full column, or condensor from a retailer. Build your own.
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Re: Boka build

Postby BIGBIRD123 » Sun Feb 02, 2014 11:52 am

I purchased these and they included two ferrules, ptfe gasket and clamp for $9.99. A great deal for the money...

http://www.ebay.com/itm/271389274860?va ... 1439.l2649
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2" Boka, 2" Pot..interchangeable with a 2" condenser head and a 3" Condenser head.Electric Kegs w/dual controllers complete and in training...
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