Droplets are encountered in nature and a wide range of science and engineering applications.[1]-[5] Natural droplets can be found in dew, fog,[6] rainbows,[7][8] clouds/cumuli,[9]-[11] rains, waterfall mists, and ocean sprays.[12] A dispersion of droplets in surrounding air can be produced by shower heads, garden hoses, hair sprays, paint sprays, and many other spray devices. A variety of important industrial processes involve discrete droplets, such as spray combustion,[ 1][13]-[15] spray drying,[2][16] spray cooling,[17] spray atomization,[ 4] spray deposition,[3] thermal spray,[18] spray cleaning/surface treatment, spray inhalation,[19] aerosol (mist) spray, crop spray, paint spray, etc. The related areas span automotive, aerospace, metallurgy, materials, chemicals, pharmaceuticals, paper, food processing, agriculture, meteorology, and power generation.