Bacteria sorting?

Dennis J. Young djyoung at UCSD.Edu
Wed Mar 13 18:32:32 EST 2002

Since the nozzle orifice is probably not exactly 70 microns, I used an
accurate volume measurement (100,000 drops repeated 10 times, 3.3% c.v) to
calculate back to the jet diameter (assuming spherical drops) and got a
*jet* diameter of 66.95 microns.

3.53j^3 = 4pi/3(d/2)^3 yields drops with diameter 1.8891 times the jet (as
Joe Trotter pointed out)

 From Pinkel and Stovel, the jet relaxes to as much as 0.866 times its
initial diameter. I got about 0.956

At 07:18 PM 3/11/2002 -0500, Howard Shapiro wrote:

>Alice Givan wrote-
>>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.
>I wouldn't have gone that route.
>>   Perhaps the best way to calculate
>>the volume of a drop is by  Dirk Van Bockstaele's method (calculating the
>>of the  "column" of liquid coming out of the nozzle in one second and then
>>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.
>Velocity for a stream-in-air nozzle, in m/sec, should be 3.7 * (sheath
>pressure(in psi))^(1/2).   This is from Pinkel and Stovel, also on p. 139
>of the 3rd Ed. of PFC.  Page 140 has the "column" volume calculation.
>>   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).
>I'm still here, obviously. And you can probably limit the calculation of
>stream volume to 1 minute; you'll divide by 60 to get the volume per
>second, and you'll get enough volume out in a minute (or two) to get an
>accurate enough calculation.
>And there's time (but not much) to clear this up in the 4th Edition.  Do
>you have a reference to Dirk van Bockstaele's calculation?


Dennis J. Young
Flow Cytometry Core Facility
University of California, San Diego
Internal Medicine Group, Bldg #4, Room 126
9500 Gilman Drive
La Jolla  CA  92093-0671

Mail:<<mailto:djyoung at>>
Telephone:(858) 822-0407        FAX: (858) 822-0403

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