  We study the growth of black holes (BHs) in galaxies using three-dimensional
smoothed particle hydrodynamic simulations with new implementations of the
momentum mechanical feedback, and restriction of accreted elements to those
that are gravitationally bound to the BH. We also include the feedback from the
X-ray radiation emitted by the BH, which heats the surrounding gas in the host
galaxies, and adds radial momentum to the fluid. We perform simulations of
isolated galaxies and merging galaxies and test various feedback models with
the new treatment of the Bondi radius criterion. We find that overall the BH
growth is similar to what has been obtained by earlier workers using the
Springel, Di Matteo, & Hernquist algorithms. However, the outflowing wind
velocities and mechanical energy emitted by winds are considerably higher (v_w
~ 1000-3000 km/s) compared to the standard thermal feedback model (v_w ~ 50-100
km/s). While the thermal feedback model emits only 0.1 % of BH released energy
in winds, the momentum feedback model emits more than 30 % of the total energy
released by the BH in winds. In the momentum feedback model, the degree of
fluctuation in both radiant and wind output is considerably larger than in the
standard treatments. We check that the new model of the BH mass accretion
agrees with analytic results for the standard Bondi problem.
