The MD-700 was developed at the request of our customers specifically for PM particle measurement and aerosol analysis. In order to minimize particle losses, a laminar sample flow should be maintained through the flow path of the dryer. For most analyzers, the required flow rate precludes the use of standard MD or PD Nafion® dryers. The MD-700 was developed to address these performance needs. Features and benefits of the dryer are listed below:
- Low particle losses due the special large diameter 17mm (0.700”) Nafion® tubing used in the design
- Eliminates the need for heating the sample gas stream, preserving the volitle particulate component in the sample
- Grounded Stainless Steel Tube and Shell Construction eliminates buildup of static electricity and provides long service life outdoors.
- Straight Configuration in 6,12, 24, and 48 inch versions minimize turbulent flow that can negatively affect measurements
- Dryer is continuously regenerating, eliminating the need to repeatedly replace desiccant
- Designed to be used with the vacuum reflux purge gas method where no dry or instrument air is available.
Principle of Operation
MD-700 Series gas dryers transfer moisture from one gas stream to a counter-flowing purge gas stream, much like a shell-and-tube heat exchanger transfers heat. Water molecules permeate through the Nafion® tube wall, evaporating into the purge gas stream. The water concentration differential between the two gas streams drives the reaction, quickly drying the air or gas. Purge gas should be dry (-40°C dew point) air or other gas. If no dry gas is available, a portion of the gas dried by the MD-700 Series dryer can act as the purge gas in a split-stream or reflux method. Visit the Purge Gas Configurationspage to learn more about the purge methods Perma Pure customers deploy in their equipment.