Experimental and Theoretical Investigation of the Coalescence of Water Drops

Book excerpt: This report summarises results of the coalscence efficiency of colliding drops which were obtained from laboratory experiments and a theoretical model. Both theory and experiment suggest that the coalescence efficiency is a function of both drop radii and drop size ratio. Even though no clear dependence of coalescence efficiency on impact speed was observed experimentally, the theory does predict some dependence on velocity. Generally it is observed that the coalescence efficiency decreases with increase in the size of the large drop, R(L), and the drop size ratio, p. However, for small R(L) a decrease in the efficiency was also shown. Both theory and experiment demonstrate the strong dependence of coalescence on impact angle. From the experiments two empirical equations were obtained which relate the coalescence efficiencies and partial coalescence efficiencies with p and R(L). These could be used in numerical models of cloud and rain development. (Author).