
A mathematical model for thermophoretic deposition [32], experimentally
verified, concluded that deposition efficiency (ratio of SiO
2
equivalent entering
tube to that contained in exhaust) may be expressed as e ¼ 0:8(1 T
e
=T
rxn
),
where T
rxn
is the gas reaction temperature and T
e
is the temperature downstream
of the torch at which the gas and the tube wall equilibrate. Typically, T
e
is about
400
C and T
rxn
about 2000
C, giving an efficiency value on the order of 60%.
Note that the efficiency is not a function of the maximum tube temperature.
Examination of the process of consolidation of the soot layer on the inner
surface of the silica tube revealed the ...