Simulation of Halon Condensation Processes in Vertical Pipes by the VOF Method

The study of steam-condensation processes inside pipes of different orientation in space is an urgent task for many industrial applications, including the creation of heat-recovery plants based on the organic Rankine cycle. This paper presents the results of the validation of a mathematical model of a two-phase flow, which is based on the Volume of Fluid (VOF) on experimental data on the condensation of the downward flow of freon R-113 in a vertical round pipe. The data obtained by numerical simulation, both in terms of integral and local characteristics, are compared with experimental data for regimes with mass flux from 26 to 294 kg/(m(2) s), saturation pressures from 10(5) to 3 x 10(5) Pa, and heat flux up to 80 kW/m(2) for pipes with diameters of 9.0, 14.0, and 20.8 mm. The validation results showed the efficiency of the algorithm previously proposed by the authors for determining the relaxation coefficient in the Lee model for calculating condensation inside pipes. The best agreement between the calculations and the experimental data was found when using versions of Menter's SST turbulence model. Several simplified one-dimensional models of steam condensation inside pipes have been tested. Recommendations on the choice of the computational grid for the studied class of problems are presented. To describe the processes of halon condensation by the VOF method, the characteristic thickness of the liquid film should account for at least ten control volumes (computation mesh cells), and the longitudinal size of the cells should not exceed half the capillary constant. It is shown that it is possible to calculate the heat-transfer characteristics using a coarser grid (with a longitudinal step of up to two capillary constants); however, in this case, waves do not appear on the film surface, which significantly affects the hydraulic characteristics of the flow.