Materials and Particle Trapping

  1. Please excuse me if this isn't a physics question - I'm not sure where it belongs.

    Felt, such as this: http://www.ebay.com/itm/Felt-by-the...-36-INCHES-square-100-polyester-/261301533508

    And 3mil plastic sheeting, as this: http://www.homedepot.com/p/Husky-8-Ft-x-100-Ft-Clear-3-mil-Plastic-Sheeting-CF0308C/202184057

    --------

    How small of a particle size, will those block?
    For example: if I throw a .3 micron particle at the felt, will it go through?
    How about the plastic?

    Thanks!
     
  2. jcsd
  3. Baluncore

    Baluncore 2,699
    Science Advisor

    Assuming your medium is air and the 0.3 um particle is travelling slowly, it will not pass through the 0.003” plastic film, it will probably get caught up for some time in the felt. You could increase the chance of a particle being caught by the felt if you dampen the felt with oil or water. The felt is behaving like a HEPA filter.
    See; http://en.wikipedia.org/wiki/HEPA
     
    1 person likes this.
  4. Appreciated, friend.
     
  5. Baluncore

    Baluncore 2,699
    Science Advisor

    Note that felt is usually made from sheep's wool which has a diameter of about 20 um.
    To reliably trap 0.3 um particles requires a fibre size closer to 1 um.
    It is probable therefore that ordinary felt will only trap particles of 6 um and greater.
     
  6. Baluncore

    Baluncore 2,699
    Science Advisor

    Mass loaded vinyl will not pass air, let alone 0.3 um particles.

    What are you trying to accomplish here?
    How much area of filter do you need?

    You can buy rolls of HEPA filter material such as these.
    http://www.alibaba.com/showroom/hepa-filter-cloth.html
    You can search for your local supplier.
     
    1 person likes this.
  7. It's for making acoustic panels. The MLV is for diaphragm resonators, and the felt/plastic are for porous absorbers.
    I'm probably going to fill both with Mineral Wool, and I want to avoid fibrosis. ;)

    I asked about felt, as a possible alternative to plastic. But that won't work, as you pointed out.

    Thanks again!
     
  8. I'm back, again. :)

    My plastic sheeting (seems to be .31mil, not 2mil) is causing issues @ 2.5kHz, even with 1 layer of felt on top of it.


    So, my question: How well will satin work to block particles? It says "100% polyester."
    If that won't work well, is there a material that you would suggest?

    Thanks!
     
  9. Baluncore

    Baluncore 2,699
    Science Advisor

    I presume you are using the plastic film to stop glass dust escape.
    What problems does plastic film cause at 2.5 kHz.

    The thickness of plastic sheet will determine it's mass per unit area and resonance frequency.
    It will behave differently if it has a crumpled surface or if it is bonded to the felt.

    100% polyester satin is a woven polyester fibre, so it will probably not stop fine dust. You would need a bonded polymer film material such as is used to make car covers or disposable coveralls for contaminated sites. If it is waterproof it will probably stop fine dust.

    Sound absorption comes from a sandwich of different materials with multi-faceted surface orientation. For example, used egg cartons glued to a surface can make a big difference.
     
  10. AlephZero

    AlephZero 7,300
    Science Advisor
    Homework Helper

    That is one method, but "flat" acoustic panels (often used as internal dividing walls in office buildings) basically work like a transmission line with impedance changes along its length, to let the energy get "inside" the panel and stop it getting out again.

    The purpose of the filling material (rock wool etc) is to provide a huge surface area relative to the volume of the internal cavity, to absorb the kinetic energy (i.e. the sound) in the air into the viscous boundary layer in the air surrounding each individual fiber. Loudspeaker cabinets are filled with the same type of material for the same reason.
     
  11. The SPL is high, similar to not using a panel. I'm not sure about decay time, or anything else.

    It's okay, it goes away if I use *two* layers of felt. :)

    Thanks again, be well.
     
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