SAMPLE STREAM DRYER

Using a dryer when analyzing atmospheric aerosols is  recommended by the World Meteorological Organization Global Atmosphere Watch as a routine part of air quality monitoring.  Aerosol physical and optical properties may change in humid environments – but, more seriously, there is the possibility of water condensation inside the instrument, which can lead to permanent damage. Many stations in hot, humid locations have air-conditioned interiors.  If the indoor air-conditioning temperature T_a is comparable to or lower than the dewpoint (condensation temperature) T_d of the outside ambient air, water will condense in the tubing and inside the instrument.  This will not only completely invalidate the data, but it can also cause permanent damage to the instrument.

The Sample Stream Dryer can be used for all aerosol particle measurements. It can be used for ambient air quality monitoring in humid locations, aerosol studies in laboratories, direct combustion emissions measurements, or any situation where water vapor must be removed from the sample stream.

There are several technologies available: membrane, diffusion, dilution, heating. Membrane dryers use water vapor-permeable materials to remove moisture from air flows. These membranes allow water vapor to pass through while blocking liquid water, driven by a partial pressure gradient. Nafion dryers, commonly used in practice, consist of single or bundled tubes and are effective for drying aerosol flows, especially within the particle size range of 0.05–1 µm.

Sample Stream Dryer uses membrane technology for several advantages over other methods:

• Consistent and precise humidity control – membrane dryers actively transport water vapor through selective permeable membranes.
• No thermal stress on sensitive aerosol particles, thus preventing unwanted chemical reactions.
• No moving parts, require minimal maintenance.

Yes! You can even connect a data logger to the Dryer to record the properties of the sample air stream.

Particle loss has been extensively studied and measured and is less than 4 %.  The Nafion membrane is selective for water vapor and does not affect any of the aerosol particles’ physical properties.

The Dryer performance depends on the actual T_a and ‘dewpoint’ (condensation, T_d) temperature of the inlet air.  For example: when the input dewpoint temperature is 22 °C, the Dryer will reduce the dewpoint by 14 °C at a sample flow rate of 5 LPM.  At lower flow rates, the reduction in dewpoint is greater.  The psychrometric performance data are shown as a function of inlet humidity in the Dryer user’s manual.

Yes!  You can connect the Dryer to an external datalogger or PC with an RS232 serial communication port.