(404g) Application of CFD Simulation for the Development of a High Volume Personal Cyclone Sampler

Sampling for the purpose of determining dust exposure in the workplace is always conducted actively by means of samplers. A sampling device is specifically designed to enable the sampling of airborne dust which meets the sampling efficiency curve for one of the health-related dust fractions. For the respirable dust fraction, the most common are colloquially known as miniature cyclone samplers as they operate by employing cyclonic action to separate out particles. They should follow the convention for respirable dust sampling with a 50% cut at 4 microns.

Nowadays there is a variety of personal cyclone samplers for respirable dust fractions which operate at flow rates from 1 LPM up to 10 LPM. A series of limit values are already or will be reduced in the future and therefore there is a need for samplers operating at larger flow rates that can collect the required amount of particles for analysis at lower aerosol concentrations. Therefore the main objective of this work was to develop a cyclone sampler for respirable dust fraction at a flow rate of 20 LPM using CFD simulation.

For aerosol flow modelling the Euler-Lagrange method was applied where the continuous phase is treated in an Eulerian manner, whereas the dispersed phase is treated in a Lagrangian approach. For a proper calculation of the flow field, the Large Eddy Simulation (LES) technique was used. A dynamic Smagorinsky-Lilly model was applied to calculate subgrid-scale turbulence.

The developed model was validated on two cyclone samplers, a 9.5 mm in diameter sampling cyclone of the HD design and a 23 mm in diameter FSP 10 cyclone. For that, the simulated performance characteristics, such as a cut-size, the slope of the penetration curve, and the pressure drop, were compared with the experimental measurements. The simulation results agree well with the experimental data. The deviation in cut-size, the slope of the penetration curve, and the pressure drop between the experimental data and LES simulations of the HD cyclone do not exceed 7%, 18.4%, and 10.3% respectively. Regarding the FSP10 cyclone, the deviations in cyclone performance characteristics are even lower.

Two cyclone designs, the HD design, which was originally developed by Higgins and Dewell, and the GK design, developed by Kenny and Gussmann, were developed for a flow rate of 20 LPM. The velocities in the HD cyclone are higher because of the smaller cyclone diameter. As a result, the mean static pressure drop across the HD cyclone is 25% higher as well. Additionally, not the whole cyclone volume is used for particle separation in the HD cyclone. The vortex is not centralised. It ends on the cone wall and there is a dead zone below where the air velocities are close to zero and particles are separated there only due to gravity. In the GK design, the vortex is centralised, penetrates deep into the grit pot, and ends on its bottom wall. Both cyclones provide a cut-size of about 4 microns. However, the penetration curve of the GK cyclone follows the respirable convention better giving a smaller bias/deviation, especially for particles that are 4.5 microns in size and larger.