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Sheath Flow Dryer


The Sheath Flow Dryer is a desiccant dryer designed to reduce the sheath air relative humidity (RH) in the TSI® Electrostatic Classifier 3082 or the Scanning Mobility Particle Sizer™ (SMPS™) 3938.

Product Details

Whether your application involves moderate to high relative humidity (RH) levels in the sampled aerosol or not, the addition of a sheath dryer can prove to be immensely valuable when utilizing an SMPS™ for continuous ambient air monitoring. In fact, in accordance with CEN/TS 17434:2019 for ambient air monitoring, the use of the Sheath Flow Dryer becomes essential to ensure measurement quality. It can also be a helpful addition for general laboratory work using the SMPS™ or Electrostatic Classifier 3082 where sheath air RH needs to be reduced. 

But why exactly is the Sheath Flow Dryer so beneficial?

When an SMPS™ or Electrostatic Classifier draws in high RH sample air, the water vapor diffuses from the aerosol flow to the sheath flow when the two flows come into contact within the Differential Mobility Analyzer (DMA). Assuming a consistent water vapor concentration in the sample flow, the sheath flow's water vapor concentration will gradually equalize with that of the sample flow over time.

Operating a DMA at high voltages, be it during scanning or as part of a monodisperse aerosol generation system, in the presence of a RH sheath flow can potentially lead to arcing, hygroscopic particle growth, and other undesirable effects. Arcing in particular is an issue as it causes a breakdown of the electric field within the DMA. Not only does arcing compromise data quality through the creation of artifacts (e.g., discontinuities in the particle size distribution), but it can also cause damage to the sheath flow laminarizing element within the DMA, or ablation of the highly polished inner surfaces. This damage necessitates troubleshooting and, in some cases, replacement of components.

To avoid these issues and ensure optimal performance, the Sheath Flow Dryer offers a simple solution. Incorporating this dryer into your setup helps maintain a low RH sheath flow, mitigating the risk of arcing and safeguarding your valuable data. It is easy to use and maintain, and offers flexible mounting location options.

Additionally, especially for continuous ambient monitoring applications such as those complying to CEN/TS 17434:2019, the Sheath Flow Dryer may only be one part of the complete solution. TSI offers the Sampling Systems for Atmospheric Particles 3750200 and 3750210 that include an additional low-loss aerosol sample dryer and other hardware to make sure the aerosol sample is representative and well-conditioned for RH, which will improve the effectiveness of the Sheath Flow Dryer over time as well.


  • In continuous ambient air monitoring compliant to CEN/TS 17434:2019
  • Any applications where the sampled aerosol has high RH or sheath air RH must be controlled/reduced

Features and Benefits

  • Maximum sheath flow rate of 5 lpm
  • Works with any Electrostatic Classifier 3082 or SMPS™ 3938 spectrometer systems
  • User-replaceable non-toxic silica desiccant
  • User-customizable mounting options