ELECTROCLAMPING FORCES FOR CONTROLLING BULK PARTICULATE FLOW - CHARGERELAXATION EFFECTS

For circumventing mechanically attributable limitations, a novel elect rically based process is investigated for controlling the flow of soli d bioparticulates via application of a properly constituted electric f ield imposed directly upon the bulk-particulate bed. Electroclamping f low-control and metering experiments characterized the operational ran ge of applied-field magnitude (similar to 0.25-0.50 MV/m), frequency ( 0-25 Hz) and waveform (10-40% duty-cycle square wave), and over a rang e of dry-weight-basis moisture contents (3-13% MC) determined the effe cts upon flow control caused by the moisture-dependent particulate pro perties of electrical conductivity (6.7 x 10(-11)-3.0 x 10(-6) S/m) an d dielectric constant (5.8-32.4), i.e., the role of particulate charge relaxation. Mass flow rate is found to vary linearly (R(2) = 0.99) wi th % duty cycle of the control signal extinguishing the electroclampin g field and is invariant with moisture content over a 5-13% MC range. Flow rate of particulates dryer than 5% MC depends strongly upon moist ure content as the material's charge-relaxation time constant (similar to 200 ms) becomes comparable with the duration of the electroclampin g-field pulse. Since in practice most bulk-phase agricultural and biol ogical particulates have equilibrium moisture exceeding 5% MC, electro clamping is confirmed to be a viable method for mass-flow modulation a nd metering.