Perma Pure Indi-GASS - Manual (Page 6)

GASS Module User Manual
6 Bulletin #217
Ambient purge air enters the dryer at the sample outlet keeping that portion of the dryer cooled. This
counter current flow is required to produce a temperature gradient along the length of the dryer. To
effectively maintain the gradient, the temperature of the purge gas exhaust must be monitored and
controlled by an electronic temperature controller (customer provided).
As purge gas passes through the dryer, it is heated to desired sample inlet set point temperature. This
gradient allows for both rapid vapor removal and decreased final dew point. If purge gas temperature
begins to fall below the set point, module’s heaters will adjust to maintain the set point. The aluminum
housing will conduct energy from the heaters to the dryer’s shell tube. Purge gas traveling through the
dryer’s shell, acquires heat from the shell. This process allows final temperature of the purge gas to be
closely controlled and a consistent temperature gradient will be maintained.
It is important that the dryer removes water in vapor state only to avoid problems that arise when the
membrane comes in contact with liquid water. If liquid water is introduced into the dryer, efficiency will
decline and the dryer could fail to perform altogether. Tubing elongates approximately 10% over its dry
length when saturated with liquid water causing tubing to kink inside the dryer housing, reducing drying.
Nafion dryers will operate most efficiently when a portion of the dryer is heated to prevent sample from
condensing out liquid water.