- hi Mike

makes lots of sense, thanks. i did an excel file after i posted

yesterday to see the variance in the ratio just like you mention. i

got different ratios than you (i used mm) but same ratios between

diameters (i.e. 1/2" was 4 times 2"). i tried putting them into Tonys

calculators but gave up quickly! Johan initialy had an undeformed

tube and still got high strength. i am planning on making one with

several columns. i found out 1/2" 316 s/s tube is cheaper than copper

for me so i will use that (just over 2euro per metre). i figure that

i can add many columns and if they are tall enough and identical i

should get an even output from each of them (and hence run at high

power). i am thinking of columns 4 or 5 metres high without

insulation for the top metre to cause some ambient reflux. i think if

they are outdoors then the long fall of 4 metres on the output side

may mean they need no cooling at all. i will make one and get it

right before replicating the other columns.

Peter

--- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:

> peter_vcb wrote:

> Subject: [Distillers] Re: Reflux Valve = Temperature Controller (?)

>

> MIKE N- could you please comment on Johans 1/2" copper tube still.

> 95% from a 3% wash with no packing, what is going on there! all i

can consider is that the tube is so narrow that the vapour is exposed

to a large surface area just like packing.

> =============================

> Hi Peter,

>

> I'll give it a go, but first thanks to Johan for the pic. Helps a

lot, so I've shoved it in here as well

> Rodmac is right ... with those indentations it's reminiscent of a

Vigreux condenser that has its internal surface area increased by

lots of indentations.

>

> As I see it, the main feature of Johan's procedure is that it is

deliberately kept very slow, so the vapor is moving up this column at

a very low speed indeed. As in a lyne arm, vapor will condense on

the walls and some of this liquid will be re-evaporated to give vapor

with a higher concentration of volatiles. Stripped liquid will

accumulate and trickle back down, and the richer vapor will condense

a little further up to repeat the process. As the vapor speed is

very low, we can think of the column in Tony's terms as having a very

small HETP, so we can envisage this liquid/vapor interchange being

repeated many, many times before the vapor reaches the top, resulting

in good separation.

>

> The low speed of the vapor is one important factor. The other is

the surface/volume ratio. Same reasoning that we use with

packing ... the greater the surface area of the liquid in a given

volume of vapor, then the more efficient the evaporation interchange

will be. Now the ratio between the internal surface area of a tube

and its volume (which will be the same thing as liquid surface

area/vapor volume) is very simple: it's 4/D, where D is the

diameter. Other things like length and Pi all cancel out. Johan is

using 1/2" diameter tubing, so the ratio is 8. Compare this with,

say, a 2" diameter tube where the ratio is just 2. He has also

increased this ratio slightly by getting busy with his trusty Thor's

Hammer, so the ratio could possibly be nearer 9 than 8. We can also

see that if he had used 1/4" diameter tubing them the ratio would be

up to 16.

>

> I reckon that it is this combination of slow vapor speed and fairly

high surface/volume ratio that makes Johan's method work so well. I

would also think that using several 1/4" diameter tubes would be even

better ... the surface/volume ratio would remain the same of course

(16), but the volume being processed would increase with every extra

tube used. However, if anyone cares to see is this works, I wouldn't

bother with the indentations. They are a good idea with 1/2" tubing,

but the slight increase in surface area you would get with 1/4"

diameter wouldn't be worth mangling a bunch of nice copper tubing

that could be used for other purposes at another time.

>

> Make any sense?

>

> Mike N - I agree that heatloss probably is a problem, but insulate it may not be so

hard since it is a coil.

Johan

Peter, what you are describing begins to sound a lot like a gas

chromatography column, which is often a very long coil of very fine

tubing.

The key problem I see with what you describe will be heat loss - the

smaller the column diameter, the faster the heat loss per unit

length, so there will be a maximum length you can run - as soon as

the column temperature falls below 78 deg C, you're hosed....

You're right that you would have more potential area for reflux, and

that it should proceed downward more slowly, but it will also only

coat a fraction of the tube diameter.

In short, worthy of an experiment!

Mike McCaw

--- In Distillers@yahoogroups.com, "peter_vcb"

<viciousblackout@y...> wrote:> Mike,

length

> yep i was working the same way using mm and using a standard

> of 1m.

or

> so do you think Johans coiled copper tube idea would work as well

> even better? if coiled the cooled vapour will flow down the tube

may

> whereas if it is vertical it may fall straight down and the tube

> experience less wetting of the available surface. conversely it

will

> only flow on the lower section of the tube so vertical may be

better.

> if a coiled one would work it would easier to use indoors you

could

> have 10metres coiled to a low height. it could coil up fully

i

> insulated and coil back down over itself with a fan blowing on it.

> still have this idea of a nice efficient radiator in my room

pumping

> out booze all day and keeping me warm :-)

to

>

> if it scaled up perfectly (i know it wont) a 2" column would need

> be 6m high to work the same as the 1/2" 1.5m column. the cross

to

> section area of a 2" column is 16 times that of a 1/2" column. so

> run at the same power i would need 16 columns at 1.5m which is 24m

of

> 1/2" tube (56euro to me) compared to 6m of 2" tube (105euro). so

has

> anybody heard of a very high column run with no scrubbers? cheaper

very

> than copper of s/s would be scaffolding poles. you could get 6m

> cheap and redistill the output to leave the nasties behind.

(?)

>

> Peter

>

>

> --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:

> > peter_vcb wrote:

> > Subject: [Distillers] Re: Reflux Valve = Temperature Controller

> >

i

> > hi Mike

> > makes lots of sense, thanks. i did an excel file after i posted

> yesterday to see the variance in the ratio just like you mention.

> > got different ratios than you (i used mm) .....

is

> > ============================

> > Hi Peter,

> > The way I figured it, the circumference of a cylinder diameter D

> (Pi)D, so the surface area is(Pi)DL

D2L ....

> > The volume of that cylinder is (Pi)D2L/4

> > so the ratio of surface area/volume came to 4(Pi)DL / (Pi)

> or 4/D

number

> > Snag is, the dimensions of this are "per length" so yes, the

> you get will indeed depend on what units you use, so it's better

to

> get rid of that length by comparing different tubes to get a

diameter

> dimensionless number.

> >

> > So if we compare tube A with diameter Da with tube B with

> Db we get TubeA/Tube B = Db/Da

is

> > Suppose Tube A is 1/4 inches diameter and tube B is 2 inches

> diameter, we get Db/Da = 2*4 = 8

> > In metric terms ... Tube A is 1/4 * 25.5 mm diameter and tube B

> 2 * 25.4 mm diameter, and the ratio is again 8.

than

> > In words, Tube A has 8 times as much surface area per volume

> tube B

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> >

> > Better?

> > Mike N

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