DISCUSSION 183 
power of the particles. The detailed relationship 
will require much future work. 
Dr. Bernard Vonnegut—1 would like to ask 
about the pressure drop across the centrifuge. 
The thought occurs to me that because of these 
spirals, the air that is taken through the centri- 
fuge is experiencing a pressure change. 
Dr. Goetz—The average pressure in the chan- 
nels should not be different from the atmospheric 
because the flow restriction (the locus of the 
pressure drop) is at the exit of the channel. The air 
in the channel will, however, experience a shght 
compression because of the impeller action of the 
spinning helix prior to expansion in the jet when 
leaving the channel. Tests under stationary con- 
ditions indicated a maximal pressure difference 
of 5 em H.O, that is, 0.5% of one atmosphere. 
There should exist also a radial pressure gradient, 
analogous to a barometric variation of the pres- 
sure between the inner and the outer channel 
walls. Because of the small radial depth of the 
channels (0.63 em) this pressure difference should 
amount at 25,000 g to about 2% if the centrifugal 
force were constant across the channels. Since it 
is less at the inner than at the outer wall (about 
40% at inlet decreasing to 16°% at the outlet due 
to the conical rotor shape) this radial pressure 
difference should be even smaller. 
Dr. Vonnegut—How nearly adiabatic is the 
expansion? A change of pressure of this sort would 
amount to a very substantial change in the tem- 
perature, were it adiabatic. If this were so, the 
humidity might be considerably changed. 
Dr. Goetz—Because of the velocity distribution 
across a laminar flow a substantial fraction of the 
particle trajectories will pass a slow moving, al- 
most resting gas layer prior to deposition on the 
outer wall. This layer must be in thermal equi- 
librium with the rotor. Hence we believe that the 
minute radial compression would be closely iso- 
thermal rather than adiabatic with respect to the 
equilibrium conditions of the particles. 
