272
LIU AND WHITBY
0.14
x
TT TTT 77
T
TTT TTT
o TESTS 35, 36, AND 37: Nt=1.05 x 10%
a TESTS 38 AND 43: Nt=0.523 x 10
0.12 --
O TEST 42: Nr=0.27 x 10
x TEST 46: Nt =1.85 x 108
>
_ 0.10 t~
5
=
x
>
VU
hes
g
s
x
0.08 --
_
>
Y
x
~~
=
ao
O 0.06
=
4
Y
te
<
= 9.04
Fig. 8—Experimental
particle mobility for
p= 0.01 atm and E =
0.02 rT
0
oO
Po}
ttt |
0.03
|
240 volts/cm.
tot i yy
0.1
1.0
PARTICLE DIAMETER, yp
Np = adp
(7)
where a and b are constants. The exponent, b, for these tests ranges
from approximately 1.60 to 1.75. If the field-charging process is the
predominant mechanism of charging, then according to Eq. 1 the
particle charge, np, should be a function of the square of the particle
diameter (i.e., b = 2). If the diffusion-charging process is predominant,
then, according to Eq. 1, b should be more nearly ecual to 1.5 for par-
ticles charged under these conditions. The fact that the experimental
value of b is nearly equal to the average of 1.5 and 2.0 indicates that
both mechanisms are operating to some extent in the actual charging
process, and a satisfactory particle-charging theory probably should
take both mechanisms into account.
It is of interest to note that in Fig. 7 the horizontal intercepts of
the four experimental lines represent diameters of particles carrying
a unit charge. Since the minimum charge that any particle can carry is
a unit charge, the data thus appear to indicate that particles smailer
than those represented by the horizontal intercepts would be uncharged
under these conditions. From the standpoint of operating an electroStatic precipitator as an aerosol sampler, it is important to determine