  Massive stars lose a significant fraction of mass during their evolution.
However, the corresponding mass-loss rates are rather uncertain. To improve
this, we calculated global line-driven wind models for Galactic B supergiants.
Our models predict radial wind structure directly from basic stellar
parameters. The hydrodynamic structure of the flow is consistently determined
from the photosphere in nearly hydrostatic equilibrium to supersonically
expanding wind. The radiative force is derived from the solution of the
radiative transfer equation in the comoving frame. We provide a simple formula
that predicts theoretical mass-loss rates as a function of stellar luminosity
and effective temperature. The mass-loss rate of B supergiants slightly
decreases with temperature down to about 22.5 kK, where the region of
recombination of Fe IV to Fe III starts to appear. In this region, which is
about 5 kK wide, the mass-loss rate gradually increases by a factor of about 6.
The increase of the mass-loss rate is associated with a gradual decrease of
terminal velocities by a factor of about 2. We compared the predicted wind
parameters with observations. While the observed wind terminal velocities are
reasonably reproduced by the models, the situation with mass-loss rates is less
clear. The mass-loss rates derived from observations that are uncorrected for
clumping are by a factor of 3 to 9 higher than our predictions on cool and hot
sides of the studied sample, respectively. These observations can be reconciled
with theory assuming a temperature-dependent clumping factor. On the other
hand, the mass-loss rate estimates that are not sensitive to clumping agree
with our predictions much better. Our predictions are by a factor of about 10
lower than the values currently used in evolutionary models appealing for
reconsideration of the role of winds in the stellar evolution.
