The Model 135 MiniMOUDI is a low-flow rate, low-pressure drop cascade impactor intended for general-purpose aerosol sampling. This impactor is specifically suited for sampling applications where a low volume of air needs to be sampled with a low power consumption such as in personal sampling for occupational hygiene applications. However, this use does not preclude other types of applications such as atmospheric, industrial or other air sampling applications.
The Model 135 MiniMOUDI is currently available in four configurations (6, 8, 10 and 13 stages) depending on the particle sizing-range required.
The MiniMOUDI consists of an inlet cowl followed by 6, 8, 10 or 13 stages and a filter holder-base. Each stage combines a semicircular nozzle pattern and a semicircular impaction substrate for the stage above. Particles are collected on customized 37mm substrates with a semicircular hole for the nozzle half-circle.
The design of the MiniMOUDI stages relies on the use of multiple circular nozzles with cut-points equally-spaced in a logarithmic scale, following the same scheme used in the traditional 30 lpm MOUDI cascade impactor (Marple et al., 1991). The Model 135 MiniMOUDI™ has an inlet volumetric flow rate of 2.0 lpm in all four configurations.
The Model 135 MiniMOUDI has been designed with micro-orifice nozzles in the lower stages to achieve nanometer size cut-points with moderately low pressure drops. The 6 and 8-stage configurations can be operated with a personal, battery-operated sampling pump. The 10 and 13-stage configurations require a less-portable vacuum pump due to the larger pressure drop requirements.
The principle of operation of the Model 135 MiniMOUDI™ is inertial impaction using multiple circular nozzle stages in series. At each stage jets of particle-laden air impinge upon an impaction substrate. Particles larger than the cut-size of that stage cross the flow streamlines and are collected on the impaction substrate below the nozzles. Particles smaller than the cut-size can follow the flow streamlines and proceed on to the next stage where the nozzles are smaller, the air velocity through the nozzles is higher and the cut-size is smaller. This continues on through the cascade impactor until the smallest particles unable to impact on the last impaction substrate are collected by a final filter.
Specifically suited for personal sampling in occupational hygiene applications.