Perma Pure’s Rotating Monotube Dryer Offers Enhanced Installation Flexibility
Perma Pure MRD™-Series gas sample dryer series (Monotube Dryer) is a variation of the MD-Series dryer with a number of important enhancements. Just like the MD Series, the MRD Series uses a single Nafion™ selectively permeable membrane tube to continuously dry gas streams removing only water vapor. These dryers operate over a wide range of temperatures, pressures and flow rates, and dry to dew points as low as -60°C. Here are the benefits over the standard MD Series:
- Special rotating ends allow easy adjustment of the purge gas fitting placement without twisting the inner tube
- Standard materials of FEP tubing / Kynar end fittings
- Improved o-ring sealing system, separating the sample and purge gas
- A wider range of end connections available, including metric 6mm
- Available with 070 and 110 tubing sizes
Principle of Operation
MRD-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 migrate through the Nafion™ tube wall, transferring to the purge gas stream. The differential in the partial vapor pressure of water 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, the differential in the water vapor pressure can be created by pulling a vacuum on the purge side by using a portion of the gas dried by the MRD-Series dryer as the purge gas in a split-stream or reflux method. Visit the Purge Gas Configurations page to learn more about the purge methods Perma Pure customers deploy in their equipment.
MRD Series Flow Diagram
Recommended Sample Gas Flow Rates:
0.1-2 lpm: MDR-070 Series
1-4 lpm: MDR-110 Series
Selection Guide Notes – 2MDR-070 and MDR-110 offer approximately the same drying performance. Specify MD-110 when pressure drop is a concern, MD-070 to minimize dead volume. For higher flow rates, please see our PD-Series dryers.
MRD Dryer Series Performance Curves
NOTE: The pressure drop is per inch of dryer. For example, the pressure drop of 100 ml/min through an MD-050-24 is equal to 2.4 inches of water. These performance curves are based upon an inlet sample dew point of 20°C, a purge gas with a dew point of -40°C, and a purge flow rate which is 2-3 times the sample flow rate. For conditions higher than ambient temperature, it is assumed that the first half of the dryer will be used to bring the dew point down to ambient. For this reason, read the value of the next shorter dryer. For example, a stream with an initial dew point of 50°C, flowing at 2 slpm; an MD-070-48 should yield an outlet dew point of 6°C, the performance of the 24″ unit.