274
LIU AND WHITBY
function
of the
ratio
Nt/(Nt).,
where (Nt). is a characteristic Nt
TTT
TTT TTF
I
TTT
{
TUTTTT
j
yO
I
Fig. 10—Characteristic Nt as
a function of particle size.
titiitl
T
108
TTT
(Nt).
10”
Liistitl
I
q
f
TUTTE
18
Litil
product depending upon particle size as shown in Fig. 10. In Fig. 10
the two experimental points shown are computed from the results of
these two tests, The agreement is seen to be satisfactory.
i
LLL til
0.01
po
0.1
PARTICLE DIAMETER, p
Similar particle charging data have been obtained at 0.1 atm with
various ar ‘lied electric-field intensities. The results are shown in
Figs. 11 to 16. Some data were also obtained at atmospheric pressure,
and these are presented in Figs. 17 and 18 for purposes of comparison.
It should be noted that the mobility curve in Fig. 18 for atmospheric
pressure shows a well-defined minimum at approximately 0.2 yu. This
minimum mobility has not been observed in all low-pressure charging
data obtained thus far. This is apparently due to the large variation in
the Cunningham correction to the Stokes’ law for particles of various
sizes at such low pressures,