An attempt is made to correlate droplets' Sauter mean diameter with the thermodynamic properties of a binary mixture at initial conditions, by means of the process efficiency interpretation and the ''available energy'' theorem. Two limiting cases are considered; an isothermal process and an adiabatic process. An idealized form of the isothermal model results in a simple correlation that clearly explains some of the relationships between the initial conditions of the binary solution and the spray quality. This is in the form of d(32) = 1 - y(beta,i)/y(beta,i) . 6 sigma/eta rho(alpha)R(beta)T(0)ln[P-sat(T-i)/P-0] The results of the adiabatic model seem to be more realistic and fit the experimental observations better. The process efficiency is found to be about 2 x 10(-4). It is possible that the process efficiency depends to a limited extent on the initial conditions.