Double action (was) Re: temp misreradings
- Hi Harry.
Yes, I think I've to speak with somebody in my native language, also
because I found we say the same things but in different way.
Just for having a conversation, (and then I'll come back to my old
university to speak with some teacher) I've the impression that our
conversation is like the etern question if was born first the egg or
> that is < T1 because there are some heat losses.============= In my opinion here you confirm that the head column
> Yes and no. Yes because if the column is not perfectly insulated,
> you will get heat loss. No because there are heat transfers (not
> losses) to the descending liquid, which means that the vapour that
> arrives at the top is purer therefore it condenses at a lower temp
> than the parent liquid from where it came, which was not as pure.
> Heat TRANSFER is not loss, it remains in the system.
has a lower temperature than the bottom " ... the vapour that
arrives at the top is purer therefore it condenses at a lower temp
than the parent liquid from where it came...".
Of course heat transfer remain in the system, but I know that the
quantity of energy contained in a substance is correlated to the
quantity of that one: less the quantity, less the total energy, that
is the temperature (if the other parameters stay constant.
> > At temperature T2 you have only the fractions that can stay as
> > vapour, that means the lighter components: the heavier
> > are already condensated because T2 is less than the condensationDistillation
> > temperature of those ones.
> >>>>>>>>>>> In practice, no.
> They, (meaning components that are NOT ethanol) are not
> necessarily 'condensed', because there's a certain amount of
> ENTRAINMENT (meaning carried up with) of impurities (meaning
> anything NOT ethanol) in all fractions of a distillation. Pure
> separation is not possible via simple distillation. There is also
> the situation where some of these 'impurities' may be gases, not
> liquids or solids. You really need to understand this concept, or
> you will never understand the meaning of distillation.
> is a SEPARATION process.================ In practice, you are talking about "stripping":
O.K., I know what stripping is (I worked 6 years in a crude
refinery), but don't forget that I'm distilling "grappa", and so I
want to have some stripping of tails: not a lot, not a few, just the
quantity able to give flavours.============
> > Talking not in terms of temperature but energy (heat): you have
> > the bottom of column the 100% of energy: along the column youlose
> > some -let's imagine - 50% and so, to respect the balance onlythe
> > quantity of lighter components that can stay as vapour with that=============== Yes, is correct. But my sentence should be intended
> > quantity of energy are present on the top of column.
> >>>>>>>>>>> No. See my previous comment about entrainment. Think
> also that without a condenser on top to 'force' condensation and
> reflux, the column would need to be many metres long (or high) for
> this 'lighter' elements to gather and be noticeable.
as a "statistical" result. Of course some heavier components will be
included (the stripping), and those ones will not condense because
will not touch a colder substance (wall or colder surrounding
vapours). It's for this reason that a reflux device is used.
> > Let's imagine the phenomena: on the bottom of the column is a
> of===================== Yes, I was meaning "condensing", even if
> > elements that can stay as vapour because the temperature is = or
> > than the evaporating temperture of those components.
> >>>>>>>>>>>>> Ermm...I think you mean 'condensing' temp, not
> evaporating temp.
a "condensing" temperature is also a "evaporating" temperature.
Water boil at 100 °C and, under the same conditions, steam condense
at 100°C. =======================
> > Climbing along the column the walls are less hot than before,
> > some heavier elements will start to condense. This happen
> > the temperature in that point is lower than the condensingthis
> > temperature of those elements.
> >>>>>>>>>>>>>> So why is the temp lower at that point? Because
> happens if there is reflux/condensation/liquid DESCENDING. Thisof
> will be lower in temp. The DESCENDING liquid accepts a TRANSFER
> heat from the vapour and thus reboils. If there is NO DESCENDING================ Here it's possible to see the question about egg
> liquid, the vapour just goes on it's merry way up to the top, and
> carries its ENTRAINED impurities (anything NOT ethanol) along with
> it. Result is 'heavier' (less pure) product.
and hen: I wrote that the vapours condense because wall are cold,
you said that wall are cold because vapours condense ....
But, let's imagine to insulate so well the column that no heat
losses can happen: such in this way will happen what you described
above, I mean that result is heavier product.
So, if you insulate a column you will have an heavier product, the
opposite if you don't insulate the column. =================
> > The vapours, such in this way, become more "pure" because lostthe
> > heavier components, or not?===================== In my humble opinion a vapour condense when
> >>>>>>>>>>>>>>>>>> The vapour can't lose the heavier components
> unless there is DESCENDING liquid. See previous comment.
get in touch with a colder element, may be a colder liquid or a
colder wall. If you don't have a descending liquid but you have a
colder column wall, you will have a condensation. Yes, but you can
say that you have a colder wall because you have a liquid flowing
down .... ( egg or hen?)========================
>============== And let me say that that particular composition of
> > On the top of the column will stay (theoretically speaking) only
> > components that have their condensing temperature lower that
> > temperature existing on the top of the column in that moment.
> >>>>>>>>>>>>> I understand what you're trying to say, but the
> vapours will be at the temp of boiling/condensation point of that
> particular ratio of [ethanol : other-things] that make up that
ethanol and other components is reached because the heavier
components were already condensed: and, if so, the top temperature
result lower than the condensing temperature of heavier components
(otherwise also the heavier components will stay on the top, that
happen at the final time of distillation, when temperatures
> > If you insulate the column, the top temperature is higher than
> > before,
> >>>>>>>>>>>>> No it isn't. This is the thing about distilling
> people find so hard to come to terms with. Insulating the columnthe
> only contains the heat necessary for the separation process,
> preventing it being lost from the system and not doing anything.
> The temp at the top, bottom, or anywhere in between is purely a
> measurement of the boiling/condensation temp of the stuff inside
> column at that point.================= I agree with you.
Just to explain why I said that, I was assuming the (unexpressed,
unfortunately) condition of constance of heat supply. I mean,
considering the heat supply the same, both the conditions of
insulated or not insulated column.
But I'm also referring to what you wrote on the forum to me about my
column, now I'm a little bit confused. Let me attach here:
> Harry, thaks a lot for your drawing, is exactly what I have..........Pictures are better than words, yes? ;-)
> Only a thing: I have (at least, I think to have) also somethe
> condensing on the lower plates.
> In my opinion I have a temperature gradient along the column: so
> upper-boiling components that leave the boiler have a condensationa
> when they bump on a relatively cold plate. Such in this way I get
> partial purification of the vapours that climb along the column,................You are correct. But the reason is the surrounding
> isn't it?
air removes some of the heat from the column.
> Now I'm in doubt if I have to insulate my column or not: when it
> is "naked" the temperature difference between head and bottom
> is an average of about 9 °C for the 90% of the distillation time.........As I said before, you have a good potstill for grappa. DO
> When insulated this temperature difference is around 4 - 5 °C.
> What should be better and why?
NOT INSULATE the column, unless you want the grappa to be heavier in
tails. It is a good balance between heating and air cooling, and it
allows a little more reflux to make the grappa cleaner. It works
similar to the old Scotch potstills or the French brandy stills,
except you have a little more control with the water tube in the top.
If you insulate the column, the grappa distillate will be heavier
with impurities and taste much different. Try both ways and you
will see the difference. If you don't like it, you can always re-
So, I agreed with you and I did what you said: I had the idea that
insulating a column give an heavier product and a not insulated
column give a purer product.
Is something changed? ========================
> >>>>>>>>>>>>>>> If you haven't got the idea by now from what I'veshould
> explained, then there's not much more I can do. Perhaps you
> talk to some of the professional distillers in Italy to explain it================= Yes, may be the language. Anyway, now I'm a little
> better in your native language, Micio.
bit curious and so I'm activating to follow your advice.
Thanks a lot, Harry.====================
ciao a tutti
- The following Distillers poll is now closed. Here are the
POLL QUESTION: Potstillers
How do you decide when to make a cut in your spirit run ?
CHOICES AND RESULTS
- By Taste, 4 votes, 6.15%
- By Smell, 3 votes, 4.62%
- By Taste & Smell, 28 votes, 43.08%
- By Temprature, 15 votes, 23.08%
- By Alchohol Volume, 15 votes, 23.08%
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