Efficiency of a double helix vs dimroth condenser

[rubelstrudel]

I have been droolign over shiny copper and trying to make my own double helix copper pipe condenser to put in my still. But after contemplating the design for a while, I started wondering why none of the professional lab equipment used such a design. That again lead to having a good think about what we want to achieve with these contraptions.

What we really want from a counterflow condenser is that the warmest coolant should come in to contact with the warmest gas, then as the gas is cooled it comes into contact with colder and colder coolant. When the coolant is at its warmest, the whole point is to take that coolant with all the heat out of the system as fast as possible.

Dimroth condenser - straight output line with minimal contact with input.

dimroth_copper.jpg (3.77 KiB) Viewed 3210 times

A double helix works counter to this. When the hot coolant goes through a new spiral, maximising the contact between the hot and the cold coolant we will get heat transfer directly from the hot coolant to the cold coolant without drawing more heat out of the gas.

Double helix. Maximises contact between hot and cold end of coolant loop.

So I postulate that a "double helix condenser" looks nice, but is a really inferior design to the classic dimroth design. Even better would be to have the hot coolant exit the condenser at the hottest point, but let us now keep to the slot in design criteria.

[shadylane]

Your "double helix condenser" is also a dimroth

[Yummyrum]

I can see where your thinking is Rubel , I have often wondered about the counter flow condrum with the double helix . Regardless it works .
As efficiency goes , how do you compare ?
Perhaps get 10’ of pipe and wind both to see .
Now one will be longer than the other .

So I might tend to think that the longer single coil could handle a higher vapour speed as the dwell time would be longer compared to the shorter double helix .

But then is it all about efficency ?
Most of us prefer as shorter Reflux condenser if possible due to height restrictions .

Perhaps an over engineered double helix lets us get away with a shorter condenser .

Just my two bobs worth

[rubelstrudel]

Efficiency is energy/volume_of_coolant.

No disputing that a double helix works. But it will have some of the same problems a flow-direction cooler has. And I would not be surprised if a double spiral has an over all worse performance than the same length single spiral dimroth.

Even better would be to insulate the straight output pipe and block off the central volume of the single spiral dimroth. That would force the vapour into contact with the cooling spiral.

I have not found any laboratory grade double spiral condensers in my Web search. The only guys using it are home distillers. This leads me to believe a double spiral is counterproductive.

[Saltbush Bill]

I think you are over thinking things , these types of condensers are used mostly in reflux stills. They do and have worked just fine for many years now. To change what works is just change for the sake of change.

[rubelstrudel]

What I am postulating is that making a double spiral does not constitute an advantage over a single spiral, it is just more work and effort for at best the same result.

You'd think the boffins in the chemistry labs would use a double spiral design if it had an advantage, but they do not seem to.

[shadylane]

block off the central volume of the single spiral dimroth. That would force the vapour into contact with the cooling spiral.

It's counter intuitive, but I'd bet blocking off the center would make the dimroth less efficient

[rubelstrudel]

A typical laboratory dimroth condenser will have very little open room to maximise vapour/coolant contact.

https://www.google.com/search?q=dimroth ... F-8#imgrc=_" onclick="window.open(this.href);return false;" rel="nofollow

[Yummyrum]

Rubuls , don’t forget that all the labware glass condensers are going to be very inefficient compared to the copper ones we use . Perhaps that might be why you won’t find a glass one as a double helix .

[rubelstrudel]

Since glass is a bad heat conductor, it is even more important to use an efficient design.

[Yummyrum]

Since glass is a bad heat conductor, it is even more important to use an efficient design.

Well yeah , I'd say in the case of a glass one . AFIK all those Lab glass condensers are hand made by experienced glass blowers . If a double wound helix was a good option , we would see them ....but as you say , we don't .

Incidentally I am a Lab Tech in my day job and I have to say I peruse a lot of catalogs and I haven't seen them either .

[Setsumi]

no reason that a double has to be a helix. i have a 3 coiled condenser that have 3 seperate coils. feeding from a bulkhead and output into a single pipe.

[rubelstrudel]

no reason that a double has to be a helix. i have a 3 coiled condenser that have 3 seperate coils. feeding from a bulkhead and output into a single pipe.

So, a sort of Shotgun-spiral... Cool.

[Setsumi]

no reason that a double has to be a helix. i have a 3 coiled condenser that have 3 seperate coils. feeding from a bulkhead and output into a single pipe.

Not realy, bulkhead is prolly not the correct term. It is 3 6mm coils fed from a 13mm pipe and output to a 13mm pipe. The photo was before the last coil was tapped into thd 13mm pipes.

[Kareltje]

no reason that a double has to be a helix. i have a 3 coiled condenser that have 3 seperate coils. feeding from a bulkhead and output into a single pipe.

Not realy, bulkhead is prolly not the correct term. It is 3 6mm coils fed from a 13mm pipe and output to a 13mm pipe. The photo was before the last coil was tapped into thd 13mm pipes.

That is kind of an inverse shotgun: a series of parallel cooling pipes in one volume of vapour.
On top of that: in stead of a Liebig-kind shotgun this is a Dimroth-kind shotgun.
Nice touch, this coppersponge!

[shadylane]

Now that's a reflux condenser
Have you ever tested it with and without the copper mesh

[Setsumi]

Now that's a reflux condenser
Have you ever tested it with and without the copper mesh

thanks. The mesh is not necessary with the 3 coils. The condenser drives reflux on a 3" CCVM column but I have used it on my flute as well, a 4" 5 plates that have a 3" CCVM reflux chamber. on both without mesh I can make full reflux, if I run realy hard I do get drips into product line. But when al is said and done I have a single coil in 3/8" with an extra 3/8" pipe in a loop as cold finger, also fed from one pipe and it works just as well in both columns

[Pikey]

I use a dimroth as Product condenser instead of liebeg - mounted vertically with the input a little over half way down. It is completely open topped and I get zero leakage. It is not easy to clean though and I tink a double coil would be very difficult.

[rubelstrudel]

A multiple parallell spiral dimroth would be a good design for a high capacity condenser. But unless it is perfectly balanced and all spirals have the same flow and temperature gradient, it will be less "efficient" than a single, longer coil. Efficiency here defined as the amount of energy that can be removed per liter of cooling water. Multiple spirals would also risk creating vapour paths that mess up the orderly counterflow cooling operation.

[Bushman]

I have been contemplating a triple walled condenser. Some folks find shotgun style dephlagmater’s difficult to build so I have been thinking about newer designs similar to the one Myles built.

[Setsumi]

A multiple parallell spiral dimroth would be a good design for a high capacity condenser. But unless it is perfectly balanced and all spirals have the same flow and temperature gradient, it will be less "efficient" than a single, longer coil. Efficiency here defined as the amount of energy that can be removed per liter of cooling water. Multiple spirals would also risk creating vapour paths that mess up the orderly counterflow cooling operation.

the problem is you have to fill the void in your condenser chamber, or so it seems to me. in a 2" pipe a single 6mm coil works with a scruber but in 3" there is much more void. a 9.3mm single coil works well in 3".

in terms of balans for a multi coil, if you feed from a common larger pipe and output to a common pipe it will be balanced well enough. but I agree a single coil works.

[shadylane]

The problem is you have to fill the void in your condenser chamber, or so it seems to me.

That's what I thought, but it doesn't seem to be the case
Every time I've stuffed some copper mesh in the vapor side of the condenser, the knock down power has decreased

[Setsumi]

The problem is you have to fill the void in your condenser chamber, or so it seems to me.

That's what I thought, but it doesn't seem to be the case
Every time I've stuffed some copper mesh in the vapor side of the condenser, the knock down power has decreased

I am speaking of filling the open space with pipe, either more coils or larger diameter coils. I do not have easy acces to corugatetss pipe but I think part of the succes of condensers in cst is the lager daimeter that gives a bulkier coil.