The paper deals with a comparison between numerical predictions, using the porous media concept and measurements of the two-dimensional model of power plant condenser. The real ribbon tube bundle of plant condenser „church window” is analyzed. The equations governing the conservation of mass, momentum, and air mass fraction are solved. The results of numerical simulation of velocity, pressure and air concentration fields are presented. The measurements included determination of difference between inlet and outlet water cooling temperature in tube. The results of simulation presents the conclusions relating usefulness of numeric calculations for diagnostics of working condenser.