Size Spectra of Particles at CFD Outlet |
Particles in the air coming out of the CFD pass through the optical particle counter and produce electrical pulses. These pulses go to a MultiChannel Analyzer (MCA) which measures the amplitude of each pulse and sorts it into one of 256 channels. Over a period of 10 seconds, the pulses are accumulated into a frequency distribution, or spectrum. The channel number corresponds to particle size ~2 to 16um.
This plot shows five minutes of MCA spectra. Each small plot is a spectrum
showing 10 seconds of data. In the corner of each small plot is the clock
time (hhmmss) and total number of counts.
The time period shown is 22:18 to 22:23 UTC (first plot) and 22:23 to 22:28 UTC (second plot). The humidity in the CFD was about +5% SSw (supersaturation with respect to water). The CFD was adjusted to give a brief period of very high supersaturations (up to +21%). The MCA spectra show a strong response of particle formation during this period. Counts greater than 500 correspond to SSw > 12%.