Bacteria sorting?

Gerhard Nebe-von-Caron Gerhard.Nebe-von-Caron at Unilever.com
Tue Mar 12 08:21:43 EST 2002


For the typical orifice shape the stream coming out of the orifice is slightly
smaller than the orifice (see lindmo in flow cytometry and sorting) but the
droplets get bigger as you introduce spaces in the column when you generate
droplets. The lower the vibration frequency the bigger the droplet will be as
you can see when you have a screen display of your droplets (more space between
the droplets). The volume you deliver through an orifice is at least dependent
on sheath pressure difference, sample pressure difference, surface tension,
viscosity, temperature and orifice geometry. The measurement is normally the
easiest and probably the most accurate way of volume determination per droplet.

Regards
Gerhard





-----Original Message-----
From:	Alice.L.Givan at Dartmouth.EDU [SMTP:Alice.L.Givan at Dartmouth.EDU]
Sent:	Friday, March 08, 2002 4:44 PM
To:	Cytometry Mailing List
Subject:	Re: Bacteria sorting?



In my comment on calculating the volume of a droplet,  I "guessed" that the
diameter of
the drop might be approximately the diameter of the nozzle orifice.  I knew
this was a
rough approximation --- as the stream can contract a bit as it leaves the
orifice and
then the droplet that forms can have a diameter greater than the diameter of
the stream.
Joe Trotter (whom I always trust) says that the droplet diameter is
approximately 1.89
times the nozzle diameter. In fact,  I just went and measured the drop and the
stream
on my monitor screen and I got about 1.6 (using a bad ruler and a roughed up
piece
of paper).  So my approximation that the drop diameter was equal to the nozzle
orifice
diameter was, obviously, grossly wrong either way.  Perhaps the best way to
calculate
the volume of a drop is by  Dirk Van Bockstaele's method (calculating the volume
of the	"column" of liquid coming out of the nozzle in one second and then
dividing
that volume into however many drops are being generated in one second).
However,  in
order to do this from first principles you need to know the diameter of the
stream and
also the velocity of the stream.....possible,  but awkward.  I suppose you
could also
do it simply by measuring the volume flowing from the stream in 10 minutes and
then
calculating the volume for one second (I might be missing something here --
Howard,
where are you (I know,	he is working on the fourth edition just when I need
him).

Alice
Alice L. Givan
Englert Cell Analysis Laboratory
of the Norris Cotton Cancer Center
Dartmouth Medical School
Lebanon, New Hampshire NH 03756
tel 603-650-7661
fax 603-650-6130
givan at dartmouth.edu

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