Modeling of Water Vapor Generation at Longitudinal Washing of Tube Bundles

Abstract

The results of the study of the process of water vapor generation in the inter-tube space in the computer model of a direct-flow steam generator, performed with the help of the ANSYS CFX program, are presented. An attempt was also made to determine the strength of individual elements of the steam generator. As the boundary conditions, the values of the pressure difference between the inlet and outlet of the model were set. It is also taken into account that the body of the steam generator is thermally insulated. The k–ε turbulence model in the Realizable modification was used. Moisture droplets are modeled as a discrete phase in the form of spherical particles dispersed in a continuous phase (vapor flow) using DPM (Dispersed Fluid). The calculation of the discrete phase trajectory is carried out in the LaGrange formulation, which includes discrete phase inertia, hydrodynamic resistance and gravity for both stationary and non-stationary flows. The vapor was treated as a continuous medium and its parameters were determined by solving the Navier–Stokes equations, while the dispersed phase was solved by tracking a large number of droplets through the calculated flow field. The interaction of discrete phase droplets among themselves was not taken into account. The force of friction between layers of moving fluid was determined according to the Shiler–Nauman model. The Ranz-Marshall model was used to simulate heat exchange in the turbulent two-phase flow regime.

Modeling with ANSYS-CFX allows to visually determine the boundaries where exactly the phase transition occurs. The quantitative value of the heat transfer coefficient on the surface of the bundle of cylindrical tubes and the pressure loss in the evaporating area during boiling of water on the surfaces of the tube bundle was determined. The thermal power of the steam generator and the hydraulic resistance of its structures are determined. The obtained result was compared with the analytical calculation. Based on this, a conclusion was made about the satisfactory results of the simulation.