Glass Bubbler Bubble cap size

[navarau]

Well after quite some time away I have finally returned and are planning on building a Glass Bubbler.

I've spent many nights now looking at builds on here for both ideas and inspiration. I have come up with a plan based on Woodduck's Glass Duck but have a quiry about the down comer height in relation to the vapour tube length and was wondering if someone more knowledgeable than me can answer this question.

In the diagram attached you can see I have a down comer height of 15mm and the vapour tube is also 15mm. To me this means that the pool height is the same as that of the vapour tube top. Is this the correct way of doing this or should the vapour tube be higher than the top of the down comer? I would really appreciate your input on this.

Also, I will be documenting the build for you all to see and hopefully inspire others to give a glass bubbler a go.

Cheers

Dave

[db1979]

The riser (what you are calling your vapour tube) needs to be higher than the downcomer. Also, there is no need for the slots in the downcomer cup.

[Zak Griffin]

You also want a deeper vapour trap in your downcomer cup than the bath depth on the plate.

[woodduck]

Your risers can be lower than your bath depth, mine are. I have 20mm (may even be lower but can't quite remember) risers on 25mm bath. The vapour will keep the liquid out of you caps. It’s even been said that it may be beneficial to be slightly lower.

[woodduck]

Also I would try 1mm slots 5mm high and 5mm apart for your caps. As for the slots in the downcomer they're not necessary but I recon they look cool.

Good luck with the build :handgestures-thumbupleft:

[db1979]

Sounds like you should just give it a go :handgestures-thumbupleft:

[navarau]

Thanks for your input guys.

Me being me I have made a start on the bubble caps already and it was while I was doing them that I thought about the riser height. Seeing as I have already made quite a few caps I'm going to give them a try at the 1mm cut at 3mm spacing. I'm just curious what effect having less slots would be. With my 3mm spacing I have 20 slots but if I went to 5mm spacing I would only have 10 slots. I suppose I will let you know in a little while.

With the vapour trap on the down comer I'll change that to 15mm and give it a try. What's the worst that can happen....I get to build another still. ;-)

I'll start a build thread shortly and get some pictures up.


Cheers

Dave

[db1979]

So long as the slots allow a location for small bubbles to form you will avoid the situation where a single large bubble forms and makes its way through the bath with minimal contact with the bath. Smaller bubbles means more interaction between bath and vapour. The design for your slots looks fine.

[andybear]

While those slots on the vapour trap look cool they actually make the trap depth even more shallow. The trap depth has to be deeper than the tray/bath depth. :handgestures-thumbupleft:

[woodduck]

While those slots on the vapour trap look cool they actually make the trap depth even more shallow. The trap depth has to be deeper than the tray/bath depth. :handgestures-thumbupleft:

I'm not trying to argue, I'm just trying to understand the science. Why does the downcomer bath need to be deeper than the plate bath depth? Isn't the downcomer bath just there to stop vapour going back up the downcomer? How does the plate depth affect the downcomer?

[db1979]

While those slots on the vapour trap look cool they actually make the trap depth even more shallow. The trap depth has to be deeper than the tray/bath depth. :handgestures-thumbupleft:

I'm not trying to argue, I'm just trying to understand the science. Why does the downcomer bath need to be deeper than the plate bath depth? Isn't the downcomer bath just there to stop vapour going back up the downcomer? How does the plate depth affect the downcomer?

I don't think it matters, it's just the same as when syphoning. In syphoning, it's the difference in heights of the two levels of fluid that matter, so long as the fluid level coming down the downcomer tube is higher than the lowest point of the downcomer cup (as in the point where the fluid spills over and out of the cup) then there will be a positive pressure that the vapour coming up from the boiler or a lower plate will not be able to overcome.
In syphoning it does not matter how deep your two vessels are, it matters that the two fluid levels are different.
Downcomer tubes need to be a certain diameter for the amount of fluid that is flowing down the column from the RC. If the downcomer is too wide then the fluid will simply go down the sides of the downcomer and not form a bath until right at the bottom. Or if they are too narrow there will be a deep bath formed but the fluid takes too long to go down and the plate above floods.
I'm guessing that downcomer cups that are too deep might suffer some smeering as the replenishment of fluid in them takes a long time.
Just my 2 c.

[db1979]

I should clarify that I'm referring to the level of fluid inside the downcomer tube, not the bath depth of the plate. At some point inside the downcomer there will be a fluid level, it needs to be higher than the level of fluid exiting the downcomer cup. In many cases it might only be marginal, but that will be sufficient.

[Zak Griffin]

The way I see it, vapour takes the path of least resistance. If the depth in the downcomer cup is less than the depth on the plate, it'll just go up the DC.

Yeah? I obviously haven't tested it but it makes sense in my head

[woodduck]

Mmmm I see ya point but i recon there would be less resistance through the bubble caps. Either way it would be safer to make the downcomer cap deeper than the plate bath. But I will definitely check mine next time I'm near it and let you all know.

[db1979]

It looks to me like the FSD downcomer cups are more shallow than the plates are deep.

Screenshot_20170701-200544-01.jpeg

[andybear]

My theory is as Zac explained but the fsd set up seems to undermine this. I based this on the start up of the column. I'm guessing others start the same. And that is that as the plates load up vapour is traveling up the downcomer until it gets deep enough and then starts to exit from the bubble caps.i figured that if the depth didn't increase enough, vapour would take the path of least resistance as Zac said.

[woodduck]

Yeah thats right, to start with there is no vapour lock until the plate fills and runs down the downcomer. Mine will spew up the downcomer with the top plate loaded to 50mm deep with no vapour out the caps until I back off power and let the downcomer fill, but then I can turn it back up no problems.

[Magnus]

I spoke to Mac on the phone a while back when I was building my 3", he explained to me that the downcommers don't need to be so long or deep if you keep the gap between the downcommer tube and cap very small, only needs to be a couple of mm gap.

[navarau]

Wow..This seems a lot more complicated that I thought.

I figure that I just have to get in and do it. If it doesn't work I just have to try something else until it does.

As I mentioned earlier I have actually started on it so I will start a build thread shortly so you can see how it all goes.

Just a question though before I go too far, In the pic below the current design has a vapour trap depth (A) of 20mm and the distance from the bottom of the down comer to the base of the down comer cap (B) is 10mm.

The way I see it, if I was to decrease the gap referred to as "B" this won't increase the vapour trap depth referred to as "A" . The only way to increase the depth of the vapour trap is to remove the slots in the cap or make the cap longer. Given that I have made these caps already should I stick with the 20mm vapour trap depth and just decrease the gap between the down comer tube and down comer cap?

Thanks again for your help.

[Zak Griffin]

You only need a couple of mm between the bottom of the downcomer and the bottom of the cup :handgestures-thumbupleft: