Concentric 2 core condensers

[Myles]

I like to use a concentric 2 core shotgun condenser as it gives you more cooling surface in the same length.

Based on a liebig inside another liebig, they are a bit fiddly to build but it is do-able and they are nice and compact. I hope to build one for the pot still this weekend but here are some pics of the one that I currently use on my column.

newcond1.jpg (11.22 KiB) Viewed 2807 times

The basic version as shown above gives you 2 cold surfaces. Inside the 15mm core (A) and outside the 22mm coldwall (B). Mine uses a 28mm outer sleeve (C), with reducers and 35mm outer T's. The reason being that it is a bit difficult to solder the joint indicated at D, and the 35mm T gives you a bit more working space.

For my own I included an external coil to provide a 3rd cold surface by cooling the outer sleeve, but it will function fine with just the 2 cold surfaces.

For the pot still, as it already has a pre-condenser I might build it with a 35mm sleeve for aesthetic reasons. A coil could always be added later if required.

I will take step by step pics and put them in the pot still post when I build it. If you can build a liebig already, then with a bit of care you should be able to try one of these.

[YHB]

Myles, it looks good -------- but how do you know it works?

Liquids take the path of least resistance;

What is there to ensure that the vapour will flow through the relatively small central tube, which I would think will have much bigger friction losses, than simply take the easier route through the larger outer jacket?

Similarly the external coil will have much bigger friction losses than the internal core and I would expect the cooling liquid to take the central easier? route.

To get the maximum amount of cooling into my column I have two coils with individual feeds and returns so I can see the amount of coolant that is flowing through each coil. The difference of the flow through the two coils is very significant to get similar flows through each coil I have to substantially choke the free flowing one. I would have thought with the configuration that you show in the pictures similar forms of adjustment would be required.

I am in the process of adding a VM takeoff to my BOK and will be building a condenser in the near future. I had intended to use one of these

viewtopic.php?f=15&t=1021&p=8404#p7983

unless you can convince me otherwise.

Toodlepip

[Myles]

No problem, lets take a look.

15 mm tube, internal dia 13.6, CSA 145.3.
22 mm tube, CSA 380
28 mm tube, internal dia 26.2, CSA 615.7

So gap between 22 and 28 has a CSA of 235.7. 1.6 x bigger than the inside of the 15 mm tube. Now in such a short length of tube the pressure variations will be so small the vapour will travel down both. If not at exactly the same rate, it probably doesn't matter.

The internal liebig is functioning as a hollow cold finger. Compared to a solid 22mm cold finger, there is more cooled surface area exposed to vapour.

I too wondered about the coolant flow rates so I built this:

There is a 15 into 22 mm cold finger inside that 28 mm coiled jacket. The gate valve splits the coolant feed between the coil and the cold finger. I ended up balancing the flows just because I could, but even with the gate valve open there was still flow through the coil. Slower admittedly, but still flowing.
It is easy enough to put a T on a garden hose and monitor the flow through the 2 branches at different diameters.

Now moving on to your crimped core liebig. Yes these do work BUT you have to mount them vertically. I would favour multiple straight cores instead. Multiple smaller vapour cores (minimum 10 mm dia) give you more surface area than a single core with the same CSA as the total of the smaller cores. Whether you call it a shotgun or a multi core liebig depends on the length to dia ratio. Long and thin is a liebig, shorter and wider is a shotgun. The straight cores give you the option of not having it vertical.

I have this 3 core coiled liebig ready for the pot still.

3 of 10 mm vapour cores in the same jacket.

7 foot long and it occupies about a cubic foot of space

[Myles]

Sometimes an image helps.

These are to scale for a 15/28/35 and a 15/22/28

In both cases the gap between the cold core and the outer jacket is just over 2 mm, and the Cross Sectional Areas of the gap are about 1.5 x greater than the Cross Sectional Area of the inner 15 mm vapour path.

A 15 mm inside 22 mm, is a fairly standard liebi. Putting it inside another tube just makes the outer cold surface of the liebig available to condense vapour, in addition to the inner surface which was in use anyway.

The increased cold area means you can reduce the length for the same cooling capacity.

[YHB]

Lovely pieces, and thanks for the clarifications.

Due to other commitments I have a very tight budget for stilling related activities, I tend to work with the bits that I have got and look for a solution rather than finding a design and buying the materials for it.

I have just re-plumbed an old property and salvaged a fair amount of 22mm/15mm copper pipe and fittings. So the leiberg would be minimal cost. I also managed to re-cycle a copper water cylinder but more about that later.

One of the reasons that I like the crimped leiberg is the fact that it does work vertically. As well as lacking in disposable cash I am also lacking in space. I have just been looking at Lunabrille's fermenting box and was thinking that it was nearly the same size as my shed.

The vertical condenser will basically fit in the footprint of my boiler and will not take up any more room in the shed. The same could of course be said for your spiral multi-tube which looks much more fun.

[Almanac]

Isn't this just a little bit of overkill?

I run a 50l pot with a 600mm Liebig (15mm inside a 22mm water jacket) and it easily knocks down the vapour from the keg with a 3Kw element on full power during stripping runs. Even with minimal coolant flow the top T of the condenser doesn't even get warm and the coolant at the drain is hardly more than 30oC.

I only recently realised how much vapour my still produces at full power when I disconnected the Liebig from the lyne arm immediately after switching off the power to the element and was surprised at the steam pressure from the reduced end of the arm.

AM

[YHB]

.

Isn't this just a little bit of overkill?

--------------------------

Life would be very boring if we were all the same.

[Myles]

Overkill? Well my 100 litre keg has 6kW and many folks using propane could be using the equivalent of double that. For them a standard liebig might be too unwieldy.

Even on my reflux column which uses far less power, I have shortened the condenser to just 16". However, I wouldn't like to go much shorter than that as I like my product to come off cool as well as condensed. I think the 12" product shotguns might be going a bit far.

There are a lot of folks using 24" x 5 core shotguns as their product condensers with 4.5 kW elements, so I suppose it depends on what you want.

If you calculate that you are going to need a 5 foot liebig, you might find it more convenient to use a 2 to 3 foot multi core version instead.

I use this on my pot still for strip runs:

And this is the coil over 15 mm coldfinger, that is inside the 54 mm jacket:

However, I am willing to concede that possibly the worm for my strip boiler might be a bit OTT.

[Almanac]

Don't get me wrong, I'm not criticising just asking

I love shiny copper and have made some OTT pieces myself. )

I seem to remember having a similar discussion when I was building my own still and condenser. In trying to determine what size my condenser should be I proposed a size/design and put in on the forum for input by anyone with experience and the advice I received was that what I proposed in my design was capable of handling more vapour than my still could ever produce once it had an adequate supply of coolant!

My reflux condenser is a twin concentric coil measuring 10 inches and I know from running it that I really only needed half that size and it would still be too big for my column. But I suppose you can never really have too much condensing power and better too much than too little

AM

[Myles]

No problem. I am in the same boat as you wrt the reflux condenser. I still use the very first coil I ever made (that actually worked, I did scrap more than a few).

I didn't know at the time that it is difficult (but clearly possible) to wind 6 mm tube on a 15 mm mandrel for the inner coil. I did manage eventually.

It is a bit ugly with the T's instead of continuous bends - but it works, and I use it to this day. Too big? I am sure it is, but I have it horizontal so it does not matter.

On the product condenser side, folks are using more and more power. I started with 3 kW and although the current pot still has 2 x 3 kW elements I will probably only use full power on warm up.

The big worm was built for a gas powered boiler, and I estimate it could manage about 15 kW. As my burner is only about 8 kW so there is a bit of margin there.

I am quite shocked by some of the gas burners that folks propose to use. 18 to 25 kW seem to be available now. Just how they propose to cool the still I am not sure.

[Myles]

For those folks thinking about larger thermal capacity (or just shorter) product condensers, here are some things to think about.

Your standard 15 mm inside 22 mm liebig is a good benchmark. If your calculation indicates that the liebig you require is too long for comfort, you can always cut it in half and put both cores inside the same jacket. A conventional 2 core condenser.

You get a bit more cooling capacity (per inch of length) by utilising the outside of the 22 mm tube instead. The total cooled surface area works out to be the equivalent of 2.6 x 15 mm tubes.

For this reason the concentric version is a bit more compact than a conventional twin core version. However, trying to add in a further jacketed cold surface, means the build gets very complicated.

If you need that much cooling capacity, I suspect a better option might be to put 4 or 5 x 15 mm cores inside a 54 mm jacket.

You can off course use a larger diameter liebig with turbulators, or one of several other condenser designs.