Gas and aerosol sampling from high temperature, transient pressure environments

Abstract

The equations used to calculate the mass or volume of a gas sampled from a high temperature, transient pressure environment are developed. The equations and criteria developed are useful for designing systems that sample aerosols from nuclear reactors during a loss of coolant test. The equations describe an aerosol sampling system that functions in a high temperature, steadily decreasing pressure environment. The aerosol sampling system includes a dilution gas to reduce the temperature and particle concentration of the incoming sample and a critical orifice at the outlet of the sampling train to provide a constant gas velocity through an inertial aerosol sizing device (e.g., cascade or virtual impactor). Calculated gas sample volumes were compared to measured volumes using laboratory scale test apparatus. The calculated and measured volumes agreed to within 0.3 liters for initial pressures as high as 4 × 10 5 Pa, transient times on the order of 1 to 10 minutes and for total sample volumes less than 13.1 liters. Finally, the equations are able to accurately predict the undesirable back flow regime where the gas from the sampling train flows back into the reactor plenum. The regime must be avoided to insure that the sampling train will collect the desired aerosol.