An understanding of gas-liquid two-phase interactions, aerosol particle deposition, and heat transfer is needed. Computational Fluid Dynamics (CFD) is becoming a powerful tool to predict aerosol behavior for related design work. In this study, FLUENT 6 is used to analyze the performance of aerosol sampling and concentration devices including inlet components (impactors), cyclones, and virtual impactors. The ω − k model was used to predict particle behavior in Inline Cone Impactor (ICI) and Jet-in-Well impactor (JIW). Simulation provided excellent agreement with experimental test results for a compact ICI. In the JIW, compound impaction is shown to cause the device to have a smaller cutpoint Stokes number than the single impaction unit. The size ratio of the well-to-jet was analyzed to find its influence on the total and side collections. Simulation is used to analyze liquid film, flow structure, particle collection, pressure drop, and heating requirements for a bioaerosol sampling cyclone. A volume of fluid model is used to predict water film in an earlier cyclone. A shell-volume is developed to simulate thin liquid film in large device. For the upgraded version cyclone, simulation is verified to successfully predict cutpoint and pressure drop. A narrowing-jet is shown to describe the flow evolution inside the axial flow cyclone. Turbulent heat transfer coefficients and surface temperatures are analyzed and heaters are designed for this cyclone. A double-outlet cyclone was designed and its pressure drop decreased about 25%, compared with a single-outlet cyclone. A scaled-down 100 L/min cyclone was also designed and tested based on the 1250 L/min unit. CFD is used to design a Circumferential Slot Virtual Impactor (CSVI) which is used for concentration of bioaerosol particles. Simulations showed a 3-D unstable flow inside an earlier version CSVI, which could explain acoustic noise and particle loss observed in the experiment. A smaller CSVI unit was designed using simulation and its flow was shown to be stable. CFD was then used to analyze the wake flow downstream of the posts to reduce particle losses and eliminate flow instabilities caused by wakes. A successful solution, moving the posts outside was developed by the use of CFD.