Abstract
The experiment of mass transfer in a turbulent flow, such as the dispersion of pollutant in a ventilated room mode, has implied the measurement of 3-D distribution of tracer concentration. However, a measurement with probes and sensors requires much of labor to obtain large amount of data for 3-D distribution; moreover probes can disturb the airflow. The work presented here describes the approach to mesure 3-D tracer concentration distribution through digital image processing by using aerosol particles as the tracer. The tracer particle images obtained in different depths illuminated with a laser light sheet are analyzed synthetically including the effect of ray extinction due to light scattering. The procedure to calculate concentration distribution is as follows; (1) Visualized images in different depths are digitized to gray levels with an image processor and spatially averaged for each small segment composed of several pixels. (2) The gray level data are corrected for spatial sensitivity distribution of the hardware and converted to luminous intensity using the calibration curves prepared. (3) The luminous intensity is corrected for the direction dependence of scattering intensity and the effect of light extinction is removed through numerical integration of turbidity following to the Lambert's law. The adequacy of the method was verified by calculating homogeneous concentration distribution. The result indicated that the method led to the relative error of several percent. The concentration distribution in a ventilated room model under three different conditions were measured as an application. The ventilated room in which the fresh air is supplied from an inlet on the ceiling and contaminated air is supplied from an inlet on the floor was modeled. The effects of the outlet height and a panel placed at the downstream of pollutant's inlet are studied through the comparison of concentration distributions.
