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 >>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. > >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? > >-Howard > > > ---Dennis 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@ucsd.edu>> WWW:<<http://cancer.ucsd.edu/flow/>> Telephone:(858) 822-0407 FAX: (858) 822-0403
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