  The nonisothermal single-component theory of droplet nucleation
(Alekseechkin, 2014) is extended to binary case; the droplet volume V,
composition x, and temperature T are the variables of the theory. An approach
based on macroscopic kinetics (in contrast to the standard microscopic model of
nucleation operating with the probabilities of monomer attachment and
detachment) is developed for the droplet evolution and results in the derived
droplet motion equations in the space (V,x,T) - equations for V_dot, x_dot, and
T_dot. The work W(V,x,T) of the droplet formation is calculated; it is obtained
in the vicinity of the saddle point as a quadratic form with diagonal matrix.
Also the problem of generalizing the single-component Kelvin equation for the
equilibrium vapor pressure to binary case is solved; it is presented here as a
problem of integrability of a Pfaffian equation. The equation for is shown to
be the first law of thermodynamics for the droplet, which is a consequence of
Onsagers reciprocal relations and the linked-fluxes concept. As an example of
ideal solution for demonstrative numerical calculations, the o-xylene-m-xylene
system is employed. Both nonisothermal and enrichment effects are shown to
exist; the mean steady-state overheat of droplets and their mean steady-state
enrichment are calculated with the help of the 3D distribution function. The
qualitative peculiarities of the nucleation thermodynamics and kinetics in the
water-sulfuric acid system are considered in the model of regular solution. It
is shown that there is a small kinetic parameter in the theory due to the small
amount of the acid in the vapor and, as a consequence, the nucleation process
is isothermal.
