Numerical Simulation of the Formation Process of Zones with Increased Air Content in Tube Bundles during Condensation of Steam Containing Small Concentrations of Air

The formation process of a zone with an increased air content during the condensation of practically pure steam in a bundle of 397 smooth horizontal pipes has been numerically studied. The layout of the simulated tube bundle completely repeated the layout of the bundle of the experimental setup of D.H. McAllister, in which air was removed through two perforated tubes located in the center of the bundle. The processes of flow and condensation of practically pure vapor (mass fraction of air 1.22 x 10(-3)) at a pressure of 27.67 kPa and a velocity of a horizontally directed steam flow in front of the tube bundle of 12.3 m/s. Numerical modeling was carried out using the CFD model previously published by the authors. The local characteristics of the processes of heat and mass transfer in the tube bundle have been studied. Data were obtained on the quasi-stationary position of the boundary of the zone with an increased air content ("air pocket"), as well as the velocity field of the mixture and the mass fraction of air in the condenser. A significant nonstationarity of the processes in the "air pocket" zone was revealed, which leads to a noticeable change in time of the local values of the heat flux density on the pipe walls. This effect was previously discovered experimentally, which was reflected in a few publications and regulatory documents on the calculation of the heat-exchange surface of powerful condensers. Satisfactory agreement of the obtained results of calculations of local characteristics of heat and mass transfer with D.H. McAllister's experimental data and the identification of effects that were not detected when using models of a porous medium allow us to recommend the CFD model developed by the authors for optimizing the design of the designed condensing units.