  We propose a model of the accretion flow onto a black hole consisting of the
accretion disk with an accreting two-temperature corona. The model is based on
assumptions about the radiative and conductive energy exchange between the two
phases and the pressure equilibrium. The complete model is determined by the
mass, the accretion rate, and the viscosity parameter. We present the radial
dependencies of parameters of such a two-phase flow, with advection in the
corona and the disk/corona mass exchange due to evaporation/condensation
included, and we determine the transition radius from a two-phase disk/corona
accretion to a single-phase optically thin flow (ADAF) in the innermost part of
the disk as a function of accretion rate. We identify the NLS1 galaxies with
objects accreting at a rate close to the Eddington accretion rate. The strong
variability of these objects may be related to the limit cycle behaviour
expected in this luminosity range, as the disk, unstable due to the dominance
by the radiation pressure, oscillates between the two stable branches: the
advection-dominated optically thick branch and the evaporation branch.
