ABSTRACT

The specific resistance can be measured by (a) parallel-plate electrodes, (b) cylindrical electrodes, or (c) needle-plate electrodes, as shown schematically in Figure 3.1. After particles are packed or deposited between the electrodes, the applied voltage V and electric current I through the powder bed are measured. Then the specific resistance r

1. Parallel-plate electrodes:

ρd 5

A d

V I (3.1)

2. Cylindrical electrodes:

ρd 5 

2l b a

V Iln ( )

(3.2)

3. Needle-plate electrodes:

ρd 5 DA

L V I (3.3)

where V 5 applied voltage (V) I 5 electric current (A) A 5 area of the main electrode (m2) d 5 gap between the electrodes (m) l 5 length of the cylindrical electrode (m) a 5 outside diameter of the inner cylindrical electrode (m) b 5 inside diameter of the outer cylindrical electrode (m) DV 5 electrical potential of the exploring needle (V) L 5 distance between the exploring needle and the plate electrode (m)

The specific resistance depends on the packing density of the powder bed. Therefore, measurements should be carried out after precise setting of the packing density. Needle-plate electrodes are suitable for measurement under the same conditions as in an industrial electrostatic precipitator.