site search   

Filters and diffusers

Filtering is the removal of particulates from a fluid stream.  Open porosity design controls the fluid flow rate.  For the most part filters use the particle dimensions as the trapping mechanism.  Control of pore size and distribution will determine the minimum size particles that can be passed.  Molecular forces and surface energy could affect efficiency of filtration.  Dispersion of the collected particles is a wholly different issue that can affect filter design.

Diffusion is the distribution of one fluid into another, such as air into water.  Often the bubble size is critical to the process as it affects solution of one fluid into another [oxygen into water] or mass transport [flushing bubbles sweeping upwards].

Special designs allow a range or a gradient of pore properties to achieve unusual performance.  One technique, often called membranes, utilizes a thin layer of fine pore material on a coarser pore substrate.  In one design this allows high fluid transport but very fine filtration at low hydrostatic pressure, low pressure drop across the filter.  The coarse substrate provides structural ruggedness and high fluid flow. 
The thin membrane layer provides fine pores but little thickness to restrict flow.

Applications are varied.

• Filtering of corrosive, high temperature, or erosive fluids.
  • Molten metals
  • Ore particles entrained in acid streams
  • Particles in combustion streams
• Diffusion
  • Aeration of waste water or aquaculture systems
  • Oxygenation or ozonation of fluids for purification
  • Mixing with bubble streams
• Special situations
  • Dispersal of fluid such as ink or lubricant at a controlled rate from a solid reservoir that precludes excess accumulation or dispersal.
  • Ceramic molds where the diffusion of air into the mold surface ejects the formed part.