Cup on top downcommer

Perforated & bubble cap plated columns

Cup on top downcommer

Postby bluc » Thu Dec 14, 2017 6:20 pm

I have seen quit a few builds with a cup on top of the downcommer is this nesacary/ make a big difference?
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Re: Cup on top downcommer

Postby db1979 » Thu Dec 14, 2017 7:34 pm

I've never bothered but it should cut down on a small amount of dripping from the RC going straight down the downcomer instead of going to the top plate.

I recon it's probably not worth worrying about since in the random distribution of fluid in the top plate there is always going to be some recently condensed fluid going down the downcomer soon after entering the bath (simply because it landed in the bath next to the downcomer) as opposed to fluid that condensed and dripped into the bath away from the downcomer.

At the start of the run, heads being condensed and making straight down to the second top plate instead of the top plate by way of the downcomer will get vaporised by the higher temp in the second top plate and bubble up through the top plate into the RC again. So heads by-passing the top plate isn't really a problem. At the end of the run you actually want tails to be kept away from the top plate as long as possible so tails by-passing the top plate is a good thing.

Anyway, that's how I see it.
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Re: Cup on top downcommer

Postby bluc » Thu Dec 14, 2017 7:36 pm

Thanks db :handgestures-thumbupleft:
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Re: Cup on top downcommer

Postby db1979 » Thu Dec 14, 2017 7:45 pm

You're welcome mate. But if you feel the desire, go ahead and make something that you can remove and test it on the same wash, with and without, to see the effect. My money though is on "bugger all".
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equipment: Eve - 4" x 4 plate solid state bubbler (sieve plates), 330 mm packed section on a keg boiler with 2 x 2000 W elements.
Currently having a makeover: 2" x 4 plate solid state bubbler (1" bubble caps, no sight glasses...maybe not for much longer!) on a bain-marie boiler.

Re: Cup on top downcommer

Postby bluc » Thu Dec 14, 2017 8:02 pm

:handgestures-thumbupleft:
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4 plate 4" bubbler, 600mm packed section

Re: Cup on top downcommer

Postby scythe » Sat Dec 16, 2017 8:16 pm

Do you mean like a lid / cover over the down comer or like an open reducer/ flared opening?

The reducer/flared style is to stop bubbles "choking" the downcomer.
It bubbles up over the edge of the larger diameter, pops and then flows down.
Mainly used with smaller sized downcomers ie less than 3/4"
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Re: Cup on top downcommer

Postby bluc » Sat Dec 16, 2017 8:21 pm

Yea bigger diameter than downcommer "cup" on top of downcommer. I have 3/4 downcommer should be sweet yea? Will try put up my build thread tomorrow. My flux arrived and I got my sight glasses brazed but looks ruff really struggled to flow 5% silver solder and thats sitting on a bbq wok burner and hitting it with map at same time. Oxy set would be awesome.. :oops:
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50l keg boiler 4" still mount 4" sight glass 1" drain..
4 plate 4" bubbler, 600mm packed section

Re: Cup on top downcommer

Postby hillzabilly » Sat Dec 16, 2017 9:37 pm

This was my solution after watching a lot of refluxing liquid going down the downcomer,but it was mostly when I ran a packed section ,and you get a solid stream or two from the packed section wich always seemed ta be over the down comer,not like the even spread you get from a RC ,thin stainless 25mm wide bracket mounts to the downcomer cap then has a thin copper disk to deflect all reflux to the oposite side from the downcomer,works well fa me.cheers hillzabilly ;-)
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Re: Cup on top downcommer

Postby Professor Green » Sun Dec 17, 2017 8:59 am

That's a great solution hillzabilly.

Cheers,
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