Simulation in the Field of Gas Filtration and Separation

The lecture will survey the history and present status of simulation of aerosol capture devices. The intent of these simulations is to explain the influence of various operating parameters on device performance, and, one hopes, to predict performance accurately when parameters differ from those previously used in testing. Thus simulation, in its broadest sense, includes the historic empirical and analytical descriptions of aerosol filtration and separation equipment, as well as the computational fluid dynamics (CFD) performance analyses possible today. Actually, many times lab testing itself is carried out with the intention to reproduce what is going to happen in service. However, laboratory tests cannot exactly duplicate complex field applications. In fact each application is unique but, as a contrast, the test methods used in established standards must be highly repeatable. In addition both particulate and gaseous contaminants technology test methods are not sophisticated enough to provide detailed information about in service behaviour.

If one goes beyond mere tables or graphs of test results (purely empirical simulation), one must assume some sort of mathematical model of the equipment, solve for analytical solutions to the mathematics, and run tests to determine the validity of the assumed model and measure derived parameters. The more completely the assumed model reflects the fundamental physics of the operation of the cleaning device, the more useful is the analysis in aiding both the design and application of the device. CFD and other numerical simulation techniques are powerful tools for analysis and prediction of processes in fluid flow, mass transfer and electrostatics too complicated for traditional mathematical analytical solutions.

The discussion will survey both particulate and gaseous contaminant capture devices, but is limited to practical equipment used in industrial processes and HVAC applications. It will present briefly a few empirical and analytical expressions which in the past provided incomplete, but sometimes useful, descriptions of particle and gaseous contaminant capture devices. The current status of numerical simulations will be presented in more detail for some gas-cleaning devices where progress has been made in understanding and simulating their behavior. Devices of all dimensional scales have been simulated. These range from cyclones and electrostatic precipitators with dimensions in meters to fibrous particulate filter media and activated carbon with important dimensions in the nanometer range.

Because the size range is so great, every fluid flow regime is present, from large-scale turbulence through viscous, streamline flow to Brownian movement driven by molecular fluctuations. Chemical, thermodynamic, and electrostatic effects are significant, and must be included in some simulations. Much careful experimentation and analysis is needed before computer software convenient and accurate for design and application of gas purification equipment can be delivered to professionals involved with gas cleaning technologies. That should, however, be our goal.

Keywords
Air Filter
Filtration Performance
Gas-Phase Filtration
Filter Test
CFD-Simulation