Comparison of Capture Efficiencies Measured by Tracer Gas and Aerosol Tracer Techniques

Abstract The capture efficiency of an exhaust device was evaluated using a tracer gas (helium diluted in air), and an aerosol tracer of varying particle size distributions. Helium concentrations were measured by mass spectrometry, and those of the aerosol were evaluated using optical and photometric particle counters in order to follow the temporal evolution of the concentrations. This experimental study confirms the theoretical results obtained from mathematical simulations (CFD), and from the simple study of the particle relaxation time and sedimentation velocity of particles. It demonstrates that the transfer of an aerosol to a square local exhaust system of 20×20 cm2 is nearly identical to that of a gas when all the following conditions are fulfilled: •diameter of particles less than about 30 μm; •low initial particle emission velocity (of a few tens of cm/s); •direct capture and short transfer times between the source and the capture system (less than a few seconds). It is then possible to use the tracer gas technique to measure the capture efficiency of an aerosol if the above-mentioned conditions are fulfilled.