Ultrasonic agitation and mixing

Discussion in 'Physics' started by EatingSnakes, Oct 14, 2016.

  1. EatingSnakes

    Thread Starter New Member

    Oct 14, 2016
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    Hey guys

    I'm an amateur biodiesel enthusiast
    I want to increase the agitation between triglycerides and methanol to produce fatty acid methyl esters and want to use an ultrasonic transducer to do this.
    I have seen successful test batch reactions in ultrasonic cleaners and wanted some advice on optimising the process.
    Does the frequency/wattage need to be optimised to the size of the vessel in which the reactants are mixed?
    Does the frequency/wattage need to be optimised to the viscocity (or other properties) of the reactants?
    or is it as simple as increasing the frequency/wattage will increase agitation?

    Thanks in advance for all the help

    ES
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Mostly a function of wattage and viscosity. Lower viscosity materials are more easily mixed. Google "mixing energy".

    Also, if two phases are present, (oil and methanol, for example) the rate of the reaction will be dependent on the rate of mixing - specifically, the shear or turnover at the liquid-liquid interface to remove product from the interface and replace with raw materials.
     
  3. Paul van den Bergen

    New Member

    Dec 15, 2016
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    I think you have got the right idea - that improved mixing is required to improve reaction rate. The problem I can forsee is scale - you might not be able to move enough material at scale to make a difference. This is down to power. Power needs to scale with the volume of material being agitated.

    I'm going to preface this with, I don't know what I'm talking about... - but - IIUC, in terms of the circuit design, the resonance frequency of the circuit depends in part on the mechanical load/response from the material in the bath - increased viscosity will increase the load and change the resonance frequency (and current drawn - which is where trouble might arise).

    Personally I'd try a mixing pump first and if that doesn't work, perhaps you can bolt on a "closed bath" that the pump pumps through... YMMV...
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  5. Janis59

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    Aug 21, 2017
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    I am slightly sceptical about idea itself. Mine US strictor works with 2,2 kilowatts at range between 22 and 44 kHz and it is enough for small 50 gram glass to cause the cavitation. Yes, frequency must be adjusted in small range after each glass is replaced or other detail or other liquid is applied. Just seeing by naked eye how violently it `boils` (oh my worthy ears). Thus I suspect You ought to have a megawatt-scale strictor and full ass of coins to pay the electricity bill (sorry for vulgarism). Probably the cure MAY be (or not) the use of super-high frequency US, just like those in school demonstration unit where at 1,5 MHz US they cause the stable cavitation in water tank with just 8 Watts. But must be noted that there the cavitation area is very tiny, just few cm3 whilst You need a m3. Probably the cure is modern washing-machines piezo-strictors having far better efficiency than oldie-goodie magneto-striction beepers. A least them by few kilowatts are capable up-cavitate dozens of litres the water what is near the scale You want. Take a care about viscous damping of vawes, what is a main reason why as higher a frequency, as smaller circle one may see the cavitation. Therefore in the large barrel, I suspect, You need a rather low frequency, therefore giant power.
     
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