Comparative Fractional Efficiency Predictions by Selected Cyclone Simulation Models

The recently introduced ambient air quality standards for fine particulates expand the use of available control system simulation models, from the prediction of total particulate matter removal efficiencies, to the prediction of PM2.5 and PM10 (particulate matter with diameters less than 2.5 and 10?μm) ones. In order to assess the suitability of cyclone simulation models for this task, the fractional efficiency predictions of six prominent models (Lapple, Leith and Licht, Dietz, Mothes and Loffler, Iozia and Leith, and Mothes and Loffler with the turbulent dispersion coefficient of Salcedo and Coelho) are compared for a number of “standard” cyclone design configurations under a wide range of cyclone diameters and pressure drops. The results reveal a significant discrepancy among model predictions, suggesting that at least some of the models considered are unsuitable for predicting size-specific (e.g., PM2.5 and PM10) cyclone efficiencies. They also show that the sensitivity of fractional efficiencies to changes in the configuration ratios, diameter, and gas pressure drop varies widely, and in some cases even in opposite directions, among models. The above-noted results demonstrate the need for a systematic model validation against credible and sufficiently extensive experimental data sets.     

Sensitivity Analysis and Comparative Performance of Outfalls with Single Buoyant Plumes

This paper presents a new approach to analyze the performance of outfalls with single buoyant plumes in flowing ambient sea water, taking into account all three dilution mechanisms: the initial, the dispersion, and the effective dilution due to the decay of nonconservative substances. Simultaneous consideration of all dilution mechanisms, study of their functional relationships, sensitivity analysis of outfall behavior, and graphical presentation of the results, allows recognition of patterns of practical importance that remain otherwise obscure. The generated graphs afford an overview of the relative performance of outfalls with a single port and perpendicular line diffusers over a broad range of operating conditions, and portray the sensitivity of the single-port outfall behavior. The results show that, contrary to common belief, outfalls with a single port outperform those with perpendicular line diffusers over a broad range of operating conditions. They also show that higher rather than lower current speed is the critical factor in the design of single-port outfalls. These findings affect the construction cost of outfall systems and bear a significant impact on the sizing of new outfalls as well as on the performance evaluation of existing ones.