Can you pls check my maths for my bubble caps and downcomers

[scottyd72]

So my bubble caps are 20mm dia copper end caps from bunnings; these are 15mm high on the inside.
I was planning on cutting all the vertical side wall slots in the bubble caps at 7mm high. so the riser on the inside is a 1/2inch pipe that will have the holes 10mm above the bubble plate (holes will be approx 1/8inch).

So would the top of the downcomer have to be at least 14-15mm? or would 10mm be high enough? (How much height do you need to have from the top of the bubble cap slots to the top of the downcomer?)

Now if I understand this right, the cap on the bottom of the downcomer has to be 5-10mm deeper than the height above the bubble plate of the downcomer or is it just 5-10mm higher than the slots on the bubble caps (ie 7mm + 10mm)?

IMG_3433.jpg

[scottyd72]

Ok so DB1979 has enlightened me on a few more rules of thumb.
So measurement D is not critical at all and doesn't need to be more than A.
So as long as C is more than A I'm ok? and by how much?

[rash]

Pretty sure mine are like this for my 3" column.
Per plate;
2 x 1" caps with 5mm high slots, 5mm apart. Caps are 30mm high.
Risers are 3/4" diam, 25mm high.
Downcomers are 3/4" diam, 20mm above plate but about 75mm total length with a 1" cup on the bottom (cap is about 15mm deep i think).

Works well so far. :handgestures-thumbupleft:
Ash.

[scottyd72]

Pretty sure mine are like this for my 3" column.
Per plate;
2 x 1" caps with 5mm high slots, 5mm apart. Caps are 30mm high.
Risers are 3/4" diam, 25mm high.
Downcomers are 3/4" diam, 20mm above plate but about 75mm total length with a 1" cup on the bottom (cap is about 15mm deep i think).

Works well so far. :handgestures-thumbupleft:
Ash.

Ah thanks for the measurements Ash :handgestures-thumbupleft:

[rash]

No worries :handgestures-thumbupleft:

[db1979]

Just make sure the hole you drill in your riser is not lower than the top of the downcomer. The caps in my 2" build were soldered to the plate so that the risers were not attached to them and a gap exists between them.

Why did you want 7mm slots in your caps? If you're going for only 10 - 15 mm bath depth I think you'll want bubbles forming lower than 7 mm off the plate. I think my 1" caps on my 2" bubbler had slots only about 2 or 3 mm deep. And they work fine.

Otherwise, hit go and build it :handgestures-thumbupleft:

[scottyd72]

Just make sure the hole you drill in your riser is not lower than the top of the downcomer. The caps in my 2" build were soldered to the plate so that the risers were not attached to them and a gap exists between them.

Ah ok thats handy to know. I planned to have the holes within a mm or two of the top of the cap which is 15mm high. I'll just notch out the holes so they are at the very top of the cap. Therefore the top of my downcomer cant be higher than 10-12mm.

Why did you want 7mm slots in your caps? If you're going for only 10 - 15 mm bath depth I think you'll want bubbles forming lower than 7 mm off the plate. I think my 1" caps on my 2" bubbler had slots only about 2 or 3 mm deep. And they work fine.

Otherwise, hit go and build it :handgestures-thumbupleft:

Thats another very handy detail I had not read about (referring to where the bubbles form). As my bubble caps are only 15mm high, I had guessed the height of the slots would be 7mm or roughly half way. So in light of your info here I will make the slots only 2-3mm high. I'll aim for a bath depth of 10-12mm.

[scythe]

Also why are your caps so small?
I would have thought a cap height of 25mm would be better, allowing your riser to be higher.

With cap design its mainly about open area, if you match it all up it will work better, it will still work if you don't, but it will be better if you do.
And by all of it i mean:
Cross sectional area of the ID of the riser,
Area of the holes you drill at the top of the riser,
Area between riser OD and cap ID,
And area of the slots you cut out.

Makes those the same and the vapour will flow freely, not smoothly.

[scottyd72]

Also why are your caps so small?
I would have thought a cap height of 25mm would be better, allowing your riser to be higher.

With cap design its mainly about open area, if you match it all up it will work better, it will still work if you don't, but it will be better if you do.
And by all of it i mean:
Cross sectional area of the ID of the riser,
Area of the holes you drill at the top of the riser,
Area between riser OD and cap ID,
And area of the slots you cut out.

Makes those the same and the vapour will flow freely, not smoothly.

I only picked that size cap because it was all I could find at the time and they are cheap. However with the modular design it will be easy to swap out different plates and try different sized caps etc. Thanks for you info too. I hadn't found that written anywhere as yet too.

[scythe]

It is written...
I found that info within this site.
Gimmie a sec.

Edit:
meerkat's post

[scottyd72]

It is written...
I found that info within this site.
Gimmie a sec.

Edit:
meerkat's post

Oh wow thanks for that.
I'll have to read that a few times and look at my design then.
Might increase the downcomer diameter though.

[ThePaterPiper]

would it not be slightly advantageous to make the area of the slots very slightly less than the area of the riser ID and holes at top to create a very slight pressure to stop liquid entering the bubble cap? Not that it would be that big an issue, but for maximum efficiency? :think:

[scottyd72]

would it not be slightly advantageous to make the area of the slots very slightly less than the area of the riser ID and holes at top to create a very slight pressure to stop liquid entering the bubble cap? Not that it would be that big an issue, but for maximum efficiency? :think:

Wow that sounds heavy! :handgestures-thumbupleft:
My brain is not really capable of working that out these days lol
I'd really like to though.

I'm using 1/2" copper water pipe for the risers which have a 10.88mm ID which = 93 square mm ;
20mm dia x 15mm high caps with 5mm high slots that will be cut out using a hack saw blade that will leave approx 1mm wide slots. So I would need 19 slots.

[scythe]

No don't restrict a bubble cap.
The entire column will be under the same pressure.
The bubble cap is a more difficult path than the downcomer and liquids are lazy.

I wouldnt use 3/4" caps.
Unless you have a few of them.
But the work involved in a 3/4" cap is the same as a 1" cap.

3/4" cap area
Pi × R^2 = area
3.1415 × 9.53^2 = 286.2mm^2

Cap - riser
286-93 = 193mm^2
So there is plenty of area in the reversal zone.


2×Pi×R = circumference
2×3.1415×9.53= 59.9
59.9÷19= 3.1mm between slots

So you will only have 1.75mm between cuts or less which is going to be a pain.
Go bigger caps and risers.

[scottyd72]

No don't restrict a bubble cap.
The entire column will be under the same pressure.
The bubble cap is a more difficult path than the downcomer and liquids are lazy.

I wouldnt use 3/4" caps.
Unless you have a few of them.
But the work involved in a 3/4" cap is the same as a 1" cap.

3/4" cap area
Pi × R^2 = area
3.1415 × 9.53^2 = 286.2mm^2

Cap - riser
286-93 = 193mm^2
So there is plenty of area in the reversal zone.


2×Pi×R = circumference
2×3.1415×9.53= 59.9
59.9÷19= 3.1mm between slots

So you will only have 1.75mm between cuts or less which is going to be a pain.
Go bigger caps and risers.

ah ok, just trying to get my head around all that math...
I would not have thought there would be much difference between 3/4" and 1", but my 3/4" doesn't have much height either. The circumference on these caps are 68.5mm. So if I had 19 slots they would be 2.6mm apart. But then that leaves room for extra slots.

Ah I just want to check that you know I plan on using 4 to 5 caps on each plate, not just one. If I go to 1 inch I wont have as much room on the plate too.

[Dig Brinker]

Think I recall a recent (last couple years) build where someone extended the height of their "off the shelf caps " to make them high enough. They need to be taller than your regular end caps :handgestures-thumbupleft:

[woodduck]

I haven't posted on this thread for a bit because I can't follow the math. I'm sure it does make sence but I'm a bit more practical than theory. My advice is, (please remember I'm no pro but I have some experience so take everyones advice and find what suits you) if you've already got the 3/4 caps and don't want to go buy more 1" caps (cause they can be a bit pricey) just use them. I would still stick to the 5mm high slots every 5mm around the circumstance. Since the caps are only 15mm high just run with 15mm bath depths, no big deal, the glass duck was 15 and I wish i hadn't changed them to 25. The bath can be higher than the top of the riser by a few mm so don't stress. Make the top of riser 12mm or something similar. Remember when it comes to small hobby setups, things aren't as critical as the big pro stuff, we can fudge the theory rules a little.

Just a different prospective.

[db1979]

:text-+1:
If I was in your position I would go ahead and use the caps you'd already bought simply cause it would be a waste of money not to.

Also, I don't think the design of the caps is as important as the design of the downcomers. If your downcomers are too narrow then your plate floods too easily, if there are fewer slots in the cap or smaller tubes in the riser then the vapour simply speeds up. Sure there may be an impact on abv or flavour but on your first still there's no need to stress about these things. If you find you want to have bigger caps or more slots later down the track then you can. Like woodduck said it's less important with us hobbyists.

[woodduck]

I should add that I in no way think the technical stuff isn't important on the contrary as it’s the maths and science that will progress this hobby into the future. I just didn't want scotty to feel he had to get every element precise for his still to work.

[db1979]

That's pretty much what I got from your post woodduck, when I made my first bubbler I made a fair few guesses at how the caps should be (especially spacing and length of slots) and it turned out fine. As I said earlier, go ahead and build it ScottyD :handgestures-thumbupleft: