On-line particulate emission monitor

The design and development of a coaxial capacitance transducer for on-line measurement of particulates in air is described. The systemʹs performance is evaluated in response to changes in a number of operating parameters including relative humidity (8–78%), temperature (20–100 °C) and flow velocity (6.5–15 m/s). Important particulate characteristics investigated include electrical properties, density, mean size and shape. It is found that the effective dielectric constant, εeff, for all solids–gas dispersions tested is directly proportional to the solids concentration. However, in contrast to that for conducting powders, εeff for dispersions of insulating powders is found to be also dependent on the respective dielectric constant of the constituent solid particles, volumetric ratio as well as mean size. A ‘temperature capacitor coefficient’ is determined to account for the effect of temperature on the systemʹs signal. Typical system particulate volumetric concentration resolution in the range 0–0.004% v/v is ±2×10−4%.