An Aerosol Wind Tunnel for Evaluation of Massive-Flow Air Samplers and Calibration of Snow White Sampler

Abstract

Massive-flow air samplers are being deployed around the world to collect aerosol samples for analysis of radioactivity as a result of nuclear tests and nuclear accidents. An aerosol wind tunnel capable of an 1100 m³ min⁻¹ flow rate was built at Lovelace Respiratory Research Institute (LRRI) to test the sampling efficiency of these samplers. This aerosol wind tunnel uses a stationary air blender to enhance mixing, and therefore it achieves the required uniform distribution of wind speed and aerosol concentration in the test section. The test section of the wind tunnel has a cross section that is 4.3 m × 3.7 m. The aerosol wind tunnel was tested for performance in terms of distribution of wind speed, turbulent intensity, SF₆ tracer gas concentration, and aerosol concentration. Test criteria consistent with U.S. Environmental Protection Agency (EPA) and American National Standards Institute (ANSI) standards were adopted as the guidelines for the aerosol wind tunnel. Additional criteria for aerosol wind tunnel were also recommended. Initial test of the aerosol wind tunnel showed that the wind tunnel could be operated in a wind speed range of 2 to 24 km h⁻¹. Within this range, the distribution of wind speed SF⁶ trace gas concentration and aerosol concentration in two-thirds of the central area of the test section showed coefficient of variances (COVs) of less than 10% for the range of wind speeds. This met the stringent guidelines for aerosol wind tunnel performance set by EPA and ANSI standards.

The LRRI wind tunnel was used to evaluate the collection efficiency of the sampling head of massive-volume air samplers, including the Snow White sampler. The sampler was tested in this aerosol wind tunnel for particles between 2 and 20 μm. The sampling flow rates were 500 and 700 m³ h⁻¹ for the tested wind speeds of 2.2 and 6.6 m S⁻¹, respectively. The results showed that sampling efficiency was influenced by both sampling flow rate and wind speed. The sampling efficiency decreased with an increase in particle size of between 2 and 20 μm. The sampling efficiency also decreased as the wind speed was increased from 2.2 to 6.6 m S⁻¹.