Nano-MOUDI™ Cascade Impactor
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The principle of operation of the Nano-MOUDI is the same as that of the MOUDI™ impactor. It classifies particles according to aerodynamic size by inertial impaction in several multi-nozzle stages stacked in series.
The design configuration chosen for the nano-MOUDI adds three stages to the standard 10-stage MOUDI™.
The cut sizes of these stages follow the four cuts per decade of particle size progression of the standard MOUDI™. Therefore, the cut sizes are 32nm, 18nm and 10nm.
The absolute pressure after the last stage of the standard 10-stage MOUDI™ is about 0.60 atm.
By adding three stages, the absolute pressure at the stages will become low enough so that the volumetric flow will be larger than the flow that can be pulled through a micro orifice nozzle plate. Therefore, the flow rate through the nano-MOUDI stages is decreased to 10 lpm (the flow rate in the standard MOUDI™ is 30 lpm).
The design parameters for the nano-MOUDI stages are shown in Table I, along with the same parameters for the standard MOUDI™.
Note that the Reynolds Number is generally in the range of 500 to 3,000, the desired range for impactor operation1.
However, the Reynolds Number of the final stages are somewhat lower than this range. Also note that the value of the pressure at the last stage is about 0.12 atm.
Although this is a rather low pressure, it is substantially higher than that for a low pressure impactor which has pressures on the order of 0.03 atm for cut sizes of 0.05 µm.
Corresponding pressures for the MOUDI™ at that large of a cut size is 0.60 atm.
- air pollution
- pharmaceutical aerosol drug delivery
- diesel blow by and engine emission testing
- automotive airbag testing
- industrial hygiene studies
- Sharp cut-point characteristics
- 10-L/min sampling flow rate
- 3 impactor stages + after filter
- 32, 18 and 10nm minimum cut-point