Fundamental research on the size and velocity measurements of coal powder by trajectory imaging

A trajectory imaging based method for measuring the velocity and diameter of coal particles was presented. By using an industrial charge-coupled device (CCD) camera and a low power semiconductor laser, the images of coal particles under relatively long exposure time were recorded and then processed to yield both the velocities and sizes. Fundamental research on this method with special attention to recording parameters, e.g., magnification factor and exposure time, was carried out. For most of the test cases, the results agree with those obtained by particle image velocimetry (PIV) and shadow imaging method. Measurements with good accuracy can be obtained when the imaging magnification factor and exposure time are set appropriately, making N be larger than 3.5, and R between 5-7, where N and R are the number of pixels occupied by the average width and the ratio of length to width of particle trajectory on the image, respectively. The work indicates the feasibility and potential application of the present measurement method for online measurement of coal powder in pipes in industrial power plants.