The spreading of a liquid drop on a plane solid

The theoretical spread factor analysis was experimentally verified for drops less than about 450 microns. For larger drops, the spread factor is larger than that theoretically predicted which implies a smaller contact angle for larger drops. Perhaps the receding contact angle is smaller than the advancing contact angle for large drops and may be the dominant cause of the discrepancy. The generation of large drops of uniform size by cyclic jet perturbation is very easy but drop spectrum distortion due to coalescence for small diameter jets (small drops) rules out the technique used in these experiments as a practical method for producing sprays with a narrow droplet size spectrum.