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System Description
Flow System
Permeation Tube Oven
8-4
Model 146i Instruction Manual
P
NO
Condition 1:
R
NO
Condition 2:
RC
t
Condition 3:
R
F
where:
P
= the dynamic specification, determined empirically, to ensure
R
complete reaction of the available O3, ppm-min
[NO]
= the NO concentration in the reaction chamber, ppm
RC
t
= the residence time in the reaction chamber, min
R
[NO]
= the concentration of the NO gas cylinder, ppm
STD
F
= the NO flow rate, sccm
NO
F
= the O3 generator air flow rate, sccm
O
V
= the volume of the reaction chamber
RC
The flows through the Model 146i satisfy these requirements. The reaction
chamber volume is 150 cc. Flow through the ozonator is approximately 150
sccm using the back pressure regulator (set to approximately 3 psi) and the
capillary. All excess zero air flow bypasses the ozone generator. The dynamic
parameter conditions are met for any reasonable NO flow (12.5-100 sccm)
and [NO]STD (40-60 ppm).
The reaction chamber is only in the system during gas phase titration. This
is because the reaction chamber is only needed during gas phase titration,
the flush time (residence time) is approximately less than one minute, and
three flush times are necessary for a response of 95 percent.
Gas flow through the oven is low (approximately 150 sccm) to stabilize the
permeation tube oven temperature. The major portion of the flow bypasses
the oven and is directed to the mixing chamber with the stream from the
oven. This is achieved by using the same back pressure regulator described
above for gas phase titration with a capillary of identical size.
t
2.75
ppm
-
min
RC
R
F
NO
NO
STD
F
F
O
NO
V
RC
2min
F
O
NO
Thermo Fisher Scientific
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