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  1. #1

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    Nozzles near or far for double run emulsions?

    I'm not sure if this has been discussed -

    What advantages or disadvantages are there to having the nozzles hear or far when making a double run emulsions. I suspect it's best to have them apart, giving the halide time to disperse into the emulsion before the silver is introduced. If they are really close, then I can imagine you can get irregular mixing as the stream of silver ions mixed with the halide ions.

    And I'm sure it doesn't take much distance, especially if rather slow addition rates are used.

    But any thought, observations, or speculation?

  2. #2
    Ian Grant's Avatar
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    It will depend on whether the mixing chamber is being stirred, and how. Some emulsions require rapid mixing.

    Ian

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    Usually, the better the mixing the better the emulsion. This means close input jets and good mixing with rapid stirring. But you have to avoid air entrainment and cavitation.

    PE

  4. #4

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    But doesn't close input jets give you more variation in mixing?

    Given a set and more than sufficient amount of stirring, I can see having jets adjacent to each other would give you more variation in the size of precipitated silver halide. You have the randomness of two streams mixing into each other and into the surrounding liquid give you more variation than having one jet adding solution on one side of the kettle and having that stream most likely dispersed before it reaches the next nozzle. There's essentially only one thing being mixed (two of them independantly) into the kettle when they are on opposite sides.

  5. #5
    Ian Grant's Avatar
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    The secret is a small mixing chamber that the emulsion is pumped through, so the mixing is almost total in the chamber.

    Ian

  6. #6

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    Are you saying they are mixed upstream before introduction to the kettle? Is some gelatin included in one stream as well?

  7. #7
    Ian Grant's Avatar
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    No the main vessel (kettle) feeds the mixing chamber which in turn recirculates back into the main vessel.

    Ian

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    So - hypothetically - say I've got a heated stir plate which is stirring a 1 L beaker at 360 rpm (same as a CD rotates in a player) And a 750mL finished batch, with 300mL in the kettle to start,
    1. Id' want the two nozzles half way from the center and wall of the beaker, close together? Like nested L's.
    2. Would I want them sufficiently close to where the raw AgNo3 and salt solutions essentially came into contact before they dispersed into solution?
    3. Would I want two nozzles w/ multiple ports on each (like a water hose with holes in it) to disperse the solution wider into the mix?

    (assuming that the stated rpm is as high as I can go w/o bubbles or cavitation, and the shape of the nozzle is such that it doesn't cause cavitation or bubbles)

    Thanks, guys.

  9. #9
    Ian Grant's Avatar
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    Best get a wind-up gramophone playing 78's

    It really depends on what type of emulsion your making, some require that the AgNO3 and halides are mixed & combined in the emulsion rapidly, this is the key to T-grain type emulsions.

    Ian

  10. #10
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    If you can mix the solutions rapildy in a small area, then the inlets should be as close as possible and the mixing should be as rapid as possible. Actual values depend on scale and this is one of the problems with making some emulsions. Basically, a magnetic stirrer running at 300 rpm will do the trick with the inlets as close to the point of maximum stirring and the stirring will do the job. The vortex formed (minus as much cavitation as possible) will do the mixing.

    As the chamber size increases, then baffles will be needed to artificially induce a vortex or more than one, to disturb any dead spots and create turbulence without cavitation. Placement of the salt and silver are critical wrt rotation direction as well. Sometimes it is necessary to have more than one inlet jet.

    Kodak uses a unique method that is not described here or anywhere (AFAIK) in print or diagram. It basically calls on a model which varies rotation rate and baffles as a function of scaling. Just as a comment, rotation rate generally goes down with scale ranging from large values at low scales to very very small values at high scales due to the delivery rate of solution. This may be counter intuitive, but is correct.

    Now, for a side example in scaling. Lets say that I deliver 10 ml of 4 M AgNO3 in 1 minute for a given step in a 100 ml emulsion make. At 1 L this would be 100 ml / min, at 10 L this would be 1000 ml/min and at 100 L this would be 10,000 ml /M. Go to full production of 1000 L and you need 100,000 ml/min or 100 L in 1 minute added to 1000 L. It is rare to find pumps that can span such a range, and it is difficult to control fluid mixing over that range especially if you wish to avoid decorating the walls and yourself with emulsion.

    NOTE TO KIRK - How do you think my lab coat got to looking the way it did? I have been decorated liberally by "accidents". To the rest of you, I wear it in the DVD as a bad example of experiments gone awry.

    PE
    Last edited by Photo Engineer; 12-05-2008 at 05:50 PM. Click to view previous post history. Reason: spelling

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