Se. Law et al., ELECTROCLAMPING FORCES FOR CONTROLLING BULK PARTICULATE FLOW - CHARGERELAXATION EFFECTS, Journal of electrostatics, 37(1-2), 1996, pp. 79-93
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.