Control Humidity of Your Aerosol Samples Without Particle Losses

The MD‐700 has been specifically developed for humidity control in particle measurement and aerosol analysis applications. In order to minimize particle losses, a laminar sample flow should be maintained through the flow path of the dryer. The MD‐700 addresses these performance needs while providing the moisture removal necessary to make accurate measurements across a wide range of flow rates. All moisture is removed in the vapor phase with a purge gas flow. Features and benefits of the dryer are listed below:

  • Low particle losses due the large diameter 17mm (0.700”) Nafion™ tubing used in the design
  • Eliminates the need for heating the sample gas stream, preserving the volatile particulate component
  • 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 minimizes turbulent flow that causes losses
  • 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™ tubing 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 Configurations page to learn more about the purge methods Perma Pure customers deploy in their equipment.
MD-700 Series Flow Diagram

Intelligent Product Numbering System
Perma Pure offers the MD-700 Series dryer with a variety of lengths and connection types. Choose the size based on your flow rate and dryness requirement and build your MD-700 dryer according to the selection guide and the part number table below:


1 – Series
MD (Monotube Dryer) Series MD
2 – Tubing Size
0.700″ Nafion™ Tubing 700
3 – Dryer Active Length
6″ (15 cm) 06
12″ (30 cm) 12
24″ (60 cm) 24
36″ (90 cm) 36
48″ (120 cm) 48
4 – Shell and Connector Material
Kynar and Stainless Steel F
Stainless Steel S
5 – Connection Ends
Sample Gas Connector Type
10mm OD Tube End 1
3/8″ OD Tube End 3
3/4″ OD Tube End 5

Recommended Sample Gas Flow Rates (Reflux /Split Sample Operation):
Dryers are selected based on target dryness or moisture level required and flow rate of the sample through the tubing normally
defined by the analyzer requirements. Below are performance curves for two common flow rates using the operating conditions
shown in the table to the right. Performance can be controlled by varying the vacuum and purge flow rate.
6″ (15 cm) – 0-1.5 lpm
12″ (30 cm)- 1.5-4 lpm
24″ (60 cm) – 3-8 lpm
36″ (90 cm) – 6-12 lpm
48″ (120 cm) – 8-16.6 lpm

MD-700 Dryer Series Performance Curves