Numerical Simulation of Steam Condensation in a Steam-Gas Mixture Flow in a Variable-Section Channel with a Bundle of Smooth Horizontal Tubes

Аннотация

In this paper, the results from calculations of heat and mass transfer in a variable-cross-section channel with a bundle of smooth horizontal tubes, on the surface of which steam from a moving steam-gas mixture (SGM) condenses, are presented. The decrease in the channel’s cross section and, accordingly, the number of tubes in the vertical rows along the SGM movement provides the mixture with approximately constant velocity as the steam condenses. The mathematical model used in this study is described in detail in our previous publications. The two-dimensional equations of single-phase hydrodynamics, energy, and diffusion are solved for the external SGM flow. The condensation process is modeled at the level of the boundary conditions on the tube surface, taking into account a moving laminar condensate film. The heat transfer through the tube wall from the film to the cooling water is described using a one-dimensional model of the wall. To account for the irrigation of the bundle’s lower tubes with condensate formed on the upper tubes (inundation effect), a simplified model is used. The data on the velocity fields and impurity concentration in the condenser and the heat transfer characteristics are presented. The calculation results of the heat transfer coefficients on the tubes of the first vertical row of the bundle and the heat transfer coefficients for individual sections of the simulated condenser containing several tube rows at a 0–8.5% volume fraction of air in the SGM at the inlet to the apparatus are compared with experimental data. A quite satisfactory agreement between the calculated and experimental data is obtained, which confirms the efficiency of the used model. The calculated data on the local velocity fields and the composition of the steam-air mixture indicate a significant heterogeneity of these characteristics. This complicates the development of relatively simple engineering methods for calculating the heat load of condensers at high air concentrations. The calculations were performed using in-house CFD-code ANES.