Vapors or gases that condense at a low temperature can be removed from the sampled airstream by passage through a vessel immersed in a refrigerating liquid. Table 5.10.1 lists liquids commonly used for this purpose. Usually forming a sampling train in which two or three coolant liquids progressively lower the air temperature in its passage through the system is recommended.
All freeze-out systems are hampered somewhat by the accumulation of ice from water vapor and can eventually become plugged with ice. Flow rates through a freeze-out train are also limited because a sufficient residence time in the system is necessary for the air to be cooled to the required degrees. For these reasons and because of the inconvenience of assembling freeze-out sampling trains, they
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