## Re: De-tuning.

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• I replied, but the email seems to have got lost in the ether, so I will try again. ... No problems - I am only shooting from the hip though! ... Just one? ;-)
Message 1 of 19 , Mar 5, 2002
I replied, but the email seems to have got lost in the ether, so I
will try again.

> Thanx yet again for an excellent reply.

No problems - I am only shooting from the hip though!

> I just had *one* more question..

Just one? ;-)

> As column packing height has a direct correlation to
> the number of theoretical plates, what was the height

Normally, for vodka, my column is packed to 1.2 m with 18 large
scrubbers. For the 'de-tuned' run, it is 0.9m with 12 scrubbers.

I think not only is the packed height important, but also the packed
density. If it is assumed that all s/s scrubbers have similar thread
sizes, this can easily be calculated by weighing the scrubbers, and
calculating the volume of the packed height. Density=weight/volume.
If the assumption that all s/s scrubbers have similar thread sizes is
true, then the density is directly proportional to the surface area,
but a lot easier to calculate!

My scrubbers weigh 14.1g each (I just weighed them all and divided it
out), so 18 scrubbers weigh 0.2546kg and 12 scrubbers weigh 0.1697kg.

The volume of the 50mm column is easy = pi * r^2 * height
1.2m - volume=0.002356 m^3
0.9m - volume=0.001767 m^3

So the density=weight/volume:
1.2m with 18 scrubbers = 108.1 kg/m^3
0.9m with 12 scrubbers = 96.1 kg/m^3

So, in my case, the 1.2m packing height, whilst being higher packed,
is also more densely packed (=more surface area) - I guess because
the weight of the scrubbers compress the ones below? Whatever the
reason, the difference is over 10%, so there could definitely be an
effect.

I see a really neat experiment that could be done here, with the same
packed height column, and different densities (=surface area) of
scrubbers. There has to be an optimal packing density (=surface
area), which would probably be fairly easy to work out through
experimentation.

OK. Enough from me. I hope that answers your question in a long
handed way!

Matt (Bris)
• ... Hurray ! something a bit more precise than the breath through test Tony
Message 2 of 19 , Mar 6, 2002
> I see a really neat experiment that could be done here, with the same
> packed height column, and different densities (=surface area) of
> scrubbers. There has to be an optimal packing density (=surface
> area), which would probably be fairly easy to work out through
> experimentation.

Hurray ! something a bit more precise than the "breath through" test

Tony
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