Technology Evaluations, Inc.
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Pneumatic Modulation Technology

Technical Issues

What is PMT

Pneumatic Modulation is a patented process that takes a continuous flow of air and creates multiple, rapidly pulsating flows. As one of the outlet flows reaches a maximum, the flow to other outlet/s are decreased to maintain a constant inlet pressure to minimizes any up-stream pulsation.

The pulsation frequency is typically kept less than 60Hz, which is below the lower limit of the human ear.

PMT Does Two Things:

  1. It lowers the 'internal friction' of powders on air-slides.
  2. It induces more random air flow through the powder on air-slides.

Why You Care:

  • 'Internal friction' in cement forms piles, blocks outlets & forms rat-holes. 
  • Less internal friction allows cement to flow faster from silos.
  • The better air flow distribution doubles particle to air contact, halving the air needed.
  • Less air needed means lower electrical costs.

PMT Power Needs:

The TEI Fluidizer modulates the energy already contained in the blower air,
and by itself draws less power than many light bulbs (much in the same way as a Conductor's baton uses little energy but controls the output of an entire orchestra).

How It Works:

PMT induces movement (micro-shear) of powders in contact with the air-slide, just a sufficient amount to over come its initial resistance to movement that develops during storage and compression.  This resistance is a characteristic of Bingham Fluids .

    PMT also improves air distribution.Even with new air-slide cloth, our research shows that the passage of air  will rapidly organize itself into micro-channels as it rises (see photo right).  This allows the air to rise with less resistance, but once the air enters a channel, its ability to fluidize is lost.  Worse still, micro-channels soon merge and merge again, ultimately leading to rat-hole formation, which can form in just a few minutes and within only a few feet.

In this movie (7MB) a rat-hole forms in 5 minutes with just 2 ft. of bed depth.  images/rathole.mov   It is significant to note that the test bin in this video is equipped with a full-floor air-slide arrangement and 25% of the bin's air-slides was active with an air flow that should have discharged 40% of the bin's volume.  Once the channeling starts no further mass discharge occurrs, and the rat-hole simply grows larger and become more efficient at venting that air flow.

Macro-channeling also occurs and is often referred to as pneumatic fracturing, and what is clear, is the impact of PMT on channeling.  Our tests show that once these fractures and channels form using continuous flow air, simply switching the flow to PMT collapses these internal structures in the vicinity of the air-slide and initiates mass flow of the powder.  

Our research and that of others also indicates that when bubbles rise in the presence of vibration, they tend to release from a distributer's surface in a smaller bubble.  This inhibits the bubbles from coalescing into larger bubbles.  Halving the bubble diameter will increase its effective surface area by a factor of four, and fluidizing effectiveness is proportional to bubble area not  just volume.

Both tests using the same volume of air and same equipment.
 Bubbles without PMT   bubbles with PMT
No PMT                             Using PMT

The advanced design of the TEI Fluidizer produces a unique PMT that virtually eliminates the reflected wave interaction:

  • Avoids the node and anti-node effects of reflected waves on the air-slide
  • Air-slides continuously discharge product right down to the air-slide's cloth
  • Maintains full discharge rates, even for the last 10% to 15% of inventory

The lower viscosity induced by PMT also cuts an air-slide’s working angle to about 4°, which can double the reach of enclosed aeration conveyors and lower their construction costs.

Micro Channelingair
Photo shows the rapid development of channel flow of air after passing through only a few inches of fine powder.

pneumatic fractures
Pneumatic Fracture & Bridging

Horizontal air fractures & rat-hole initation.

330 N. Jefferson St.  Batavia  IL  60510 USA
Ph: (630) 879-0297   Fx: (630) 389-0427