A novel method for measuring spatial uniformity of irregular boiling bubbles in a direct contact heat exchanger

As the binary image fails to reflect the density distribution of the bubble,
this paper proposes an improved new indicator for accurate measurement of
spatial uniformity based on gray image analysis: moment. Compared with
the inclination angle method in binary image, the test results show that the
two methods have significant positive correlation. The experimental results
also indicate that the evolution curve of bubble numbers is consistent with
its moment evolution curve, and the moment evolution fitting curve can
distinguish the high noise in the experiment. Compared with other methods,
mixing performance index (t) obtained by moment evolution fitting curveis correlated with heat transfer performance (Pearson correlation coefficient
a=-0.94). The variation in characteristic area of the bubble in the direction
of bubble growth can characterize the heat transfer performance. The index
of dispersion of the global moment and the local moment indicates that
the local moment can be used to precisely quantify the spatial uniformity
of boiling bubbles. This work could also be applied to study a variety of
problems involving spatial uniformity through visualization techniques.