High-efficiency particulate air filter test stand and aerosol generator for particle loading studies

Area of Science:

• Engineering
• Environmental Science
• Materials Science

Background:

• High-efficiency particulate air (HEPA) filters are critical for air purification in sensitive environments.
• Evaluating HEPA filter performance under diverse and challenging conditions is essential for ensuring their efficacy.
• Existing test methods may not adequately simulate real-world operational stresses on HEPA filters.

Purpose of the Study:

• To design and characterize a versatile test stand and high-output aerosol generator for evaluating nuclear-grade HEPA filters.
• To enable testing of HEPA filters under a wide range of controlled conditions, including variable flow rates, humidity, and temperature.
• To facilitate the assessment of HEPA filter performance at and beyond rated media velocities with challenging aerosol loads.

Main Methods:

• Developed a test stand with controllable volumetric flow rates (1.5-12 std m(3)/min), relative humidity (5-90%), and temperature (ambient to 150°C).
• Engineered a high-output aerosol generator utilizing spray drying and a heated evaporation chamber to produce aerosols (e.g., KCl, NaCl, sucrose, iron oxide).
• Regulated aerosol particle size distribution (120-160 nm count mean diameter) using solution concentration and a post-generation cyclone for challenging HEPA filters.

Main Results:

• The system consistently generates high mass concentrations (approx. 25 mg/m(3)) of dry aerosol streams at a nominal flow of 7 std m(3)/min.
• The test stand allows for simultaneous aerosol measurements upstream and downstream of the filter.
• Characterized aerosol streams include KCl, NaCl, sucrose, and iron (III) oxide, with controlled particle sizes near the most penetrating particle size for HEPA filters.

Conclusions:

• The developed test stand and aerosol generator provide a unique capability for comprehensive HEPA filter performance evaluation.
• This system supports critical studies including filter lifetime, efficiency, media velocity, high mass loading, and humidity effects.
• The ability to test filters under extreme conditions ensures their reliability in nuclear and other demanding applications.