A quasi-three-dimensional algorithm is developed to simulate two-phase fluid flow and heat transfer in the shell-side of power plant condensers. The simulation method developed is based on the fundamental governing conservation equations of mass and momentum for both vapor-phase and liquid-phase, and air mass fraction conservation equation. The three-dimensional effects due to the cooling water temperature difference are taken into account by a series of two-dimensional calculations. The numerical predictions of an experimental steam condenser are compared with the experimental results. The predicted results are in good agreement with the experimental data. The predicted results also show an improvement over the results obtained using single-phase model.