Teledyne 9110T instruction manual Teledyne Analytical Instruments 334

Model 9110T NOx Analyzer Principles of Operation

Figure 13-11: Semi-Permeable Membrane Drying Process

The process by which the water vapor molecules are collected and transported through Nafion® material is called per-evaporation and is driven by the humidity gradient between the inner and outer tubes as well as the flow rates and pressure difference between inner and outer tubing. Unlike micro-porous membrane permeation, which transfers water through a relatively slow diffusion process, per- evaporation is a simple kinetic reaction. Therefore, the drying process occurs quickly, typically within milliseconds.

Because this chemical reaction is based on hydrogen bonds between the water molecule and the Nafion® material most other chemical components of the gas to be dried are usually unaffected. Specifically, the gases of interest for the 9110T, NO and NO2, do not get absorbed and pass the dryer unaltered.

On the other hand, other small polar gases that are capable of hydrogen bonds such as ammonia (NH3) can be absorbed this way, too. This is an advantage since gases such as NH3 can cause interference for the measurement of NOx, NO and NO2 (see Table 13-1).

Figure 13-12: 9110T Perma Pure® Dryer

Teledyne Analytical Instruments 334