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Thread: What is the air velocity required to convey fine particle dextrose.

  1. #1
    neufeneufeld Guest

    What is the air velocity required to convey fine particle dextrose.

    I am new to pneumatic conveying, and have built an excel macro that calculates the air velocity for every section of the pipe based on its compressibility and the pressure drop through the pipe. I have also used a Rizk calculation to estimate the conveying velocity required to convey the dextrose, but even when multiplying the saltation velocity by 1.5, my calculations seem to underestimate the velocity required to handle dextrose. If anyone has any experience in handling dextrose that would be greatly appreciated.

    Right now the rate is
    242 lbs/min
    5 Inch diameter pipe
    Horizontal length 80 ft
    Vertical length 40 ft
    Long radius material bends 3
    Short radius material bends 3
    Dextrose particle size 45-150 microns
    Air only length 180 ft
    13 air bends
    4 inch diameter pipe air only length

  2. #2
    Teus Tuinenburg

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    Dear neufeneufeld,

    You used the Rizk equation to calculate the saltation velocity of dextrose.

    Rizk equation:

    SLR = 1/(10^(1.44*d+1.96) * {Vs/sqrt(gD)}^(1.1*d+2.5)

    Here, a direct relationship is assumed between SLR and Vs.

    d = particle size in mm = 0.1 mm
    g = 9.81 m/sec2
    D = pipe diameter in m = 0.128 m
    Vs = calculated saltation velocity in m/sec

    If SLR=0 then Vs=0
    If SLR=0.5 then Vs=2
    If SLR=1 then Vs=7
    If SLR=5 then Vs=13
    If SLR=10 then Vs=17
    If SLR=20 then Vs=23
    If SLR=30 then Vs=26
    If SLR=40 then Vs=30
    If SLR=50 then Vs=32

    To use this formula for the calculation of the saltation velocity, you must know the pipe diameter, the particle diameter and the Solid Loading Ratio

    Obviously, you know the SLR (mass flow dextrose / mass flow air)
    Knowing the rate (242 lbs/min), you must also know the air mass flow.

    The average particle size of the dextrose is approx. 100 micron.
    The particle density is 1540 kg/m3
    Resulting in a suspension velocity of approx. 1.8 m/sec
    The air velocity at approx. atmospheric conditions is then estimated at approx. 8-10 m/sec.

    Back to the Rizk equation.
    It is hard to understand that, when the SLR changes from 50 to 20, the saltation velocity of the product drops from 32 m/sec to 23 m/sec.

    If you give the used compressor and the conveying pressure of your installation, a calculation can be executed.

    have a nice day
    Teus

  3. #3
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