Bacteria sorting?

Alice L. Givan Alice.L.Givan at
Fri Mar 8 11:43:47 EST 2002

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 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

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