Column Height Vs Diameter ratio

[diesel4ever]

The only things I see wrong with that equation is:

1. The person who wrote it needs to get laid or something and

2. Where in this equation does it prove that as column diameter increases so must column height?

If you have so much freaken time on your hands that you can actually calculate the CORRECT effective surface area of copper scrubbers or ceramic rings you should seriously consider a new hobby. I spent 10-15 seconds looking at this equation and can tell you it's severely flawed! Like I said before people tend to get too wrapped up on textbook theories that nothing ever gets accomplished. We are all here for one thing. Make great hooch with the least amount of effort.

Airhill I'm not disagreeing with that. You obviously have to change the heat output to make vapor speed a constant.

[kiwistiller]

1. The person who wrote it needs to get laid or something

No one is forcing you to participate in the discussion. If you don't like it, just don't join in No need to be obnoxious about it.

2. Where in this equation does it prove that as column diameter increases so must column height?

It doesn't. It shows that mass flow rate has an effect on HETP. Not sure if you've read the thread or are getting ideas confused, but the reason I think expressing design considerations in a ratio is wrong is because it implied just what you seem to think I believe - that a wider column needs to be taller. I don't think this. I think we should be talking design stuff in the simpler and less flawed unit of column height.
Cheers,
Kiwi

[airhill]

In practical terms the problems appear to be consistency of the packing media and the walls of the column. If we are talking columns under say 6" and assuming that the ratio of energy input is in proportion to the width of the column the wall effect is likely (guess) to be small in that a similar number of molecules will hit the walls. Packing could be a problem in that we use random packing and with its small cross section and relatively weak horizontal rigidity there could be a grip and gravity problem (? will it tend to sag in the middle leading to preferred flows of both vapour and condensate ie channeling).
Mr Nixon's book seems to indicate that on a 2" column the greatest thermal curve occurs in the lower half of the column (I assume this was when the column was in equilibrium and that he would have been running at ideal energy input for product take off) Although the top half appeared to be a 'reservoir' of hearts he seemed to think it was not quite that simple. I can only suspect that the top half was shifting in very small temperature increments.
What has that to do with design? To me it indicates that the bottom half does the coarse distilling and the top half does the fine seperation of the higher volatiles and that design considerations should concentrate more on that than ratios.

This is only a personal opinion and may bear no relation to reality

[diesel4ever]

Touche' Airhill. Touche'.

Finally some depth and bredth.

[Panache]

Hey Guys,

What a mass of wonderful information and discussion. I shall follow this with interest as it progresses.

However, as a complete newcomer to the hobby, does it help me decide on how much of my 42mm diameter column I need to pack?

It seems to me that with so many variables, each and all of which can change the calculated result, perhaps calculation is not the way forwards for me. A rough ratio system that allows me to decide on where to start is good - as is rad14701's rough guide of "Taking into consideration that the closer you get to 95% the more plates it takes to gain purity improvement we come up with the rough maximum of 4 - 5 HETP's worth of packed column... I use a figure of 2.5 column diameters equals 1 HETP as a rough approximation after running a range of column diameters, reflux ratios, and heat input..." At least these rough guidelines get those of us who are new to this moving in the right direction.

The theoretical discussion is very interesting, but we do need the practical approach as well.

Thanks again,

Panache

[kiwistiller]

1 metre to 1.5 metres would be a good height. This has nothing to do with your diameter in my books.

[Drosteo]

So.....
after reading this debate i am still confused.

I am planning on building a SS VM still with a 3" column. I was wishing to build with 3" rather than 2" as I am under the understanding that i will a faster output at the same purity? (please correct me if I am wrong)

In saying that am i going to achieve much of a difference in purity and or output with a 1m column vs a 1.5m vs 2m?

Apologies if this has already been answered but I was left a little confused and am relatively new to HD.

[olddog]

If you are building vm work out the height with a 24-1 ratio for the packed area + condenser and takeoff, it would end up around 8 foot high.

OD

[kiwistiller]

1-1.5, yes. 1.5-2... not so much. try plugging some parameters into the calculators on the parent site, and look at the results. The ratio doesn't really work for builds bigger than 2", which is one of the problems I have with it.

[rad14701]

Kiwistiller is right... The larger the column diameter, the lower within the range of ratios you can go... We have to remember that we are talking "home distillation" where house, garage, and shed ceilings are only so high and practicality starts coming into play... Anything over 4 - 5 feet of packed column starts becoming impractical, even for 3" or 4" copper...

[The Baker]

If you are building vm work out the height with a 24-1 ratio for the packed area + condenser and takeoff, it would end up around 8 foot high.

OD

That's what I will be building one day because I have 8 feet of 3 inch heavy copper tube and another piece longer than 1 foot that I can use for the condenser.
And I have the height available where I distill.

[rad14701]

I'm pretty sure you can get purity with less column height than 8 feet of 3 inch... The ratio of 24:1, or ratios in general, only work well with 2 inch copper... That is why there is a range rather than a single fixed ratio... The larger the diameter, the lower the ratio... Total packed column volume, and vapor volume and speed, come into play, amongst other criteria, and many different HETP calculations have attempted to prove this, so you can't use a specific ratio that works with every column diameter... With even the scientific experts not being able to agree on HETP calculations we are better off making height adjustments based on what works for our own set of particular circumstances... The ratios are simply a range to work within because we know that too short and too tall have diminishing results...