(162a) A General Method for Accurate Size Determination From 2-D Images

Size distribution of the discrete phase objects such as particles, bubbles, and droplets can enhance the understanding of mixing, heat and mass transfer properties as well as complex phase interactions etc in multiphase flow systems. Numerous techniques including laser Doppler anemometry, tomography, intrusive probe measurement, and direct imaging have already been developed in order to determine the size distributions. Direct imaging is preferred over other techniques to give direct measurement of size and shape.

Discrete phase objects such as particles, bubbles, and droplets can be present at various distances from the imaging device when images are captured. Hence, the horizontal location of the object will need to be known in order to determine the actual size of an individual object. However, it is impossible to determine the horizontal location of the object from a two-dimensional image. A common magnification scale is normally used for all the objects in an image. For imaging devices such as borescope, there is substantial change in magnification scale with horizontal distance. The use of a single calibration scale would yield a deviation from the actual size. In this study, a statistical method is proposed to reconstruct the actual size distribution from the measured size distribution using a single calibration scale. The proposed method has been verified experimentally using particles of a known distribution. The stability of the proposed method is also analyzed theoretically against different viewable volumes, degree of change in magnification with horizontal locations, as well as different types of distributions.