Kondensation von Wasserdampf oder eines Wasserdampf / Stickstoff - Gemisches in einem horizontalen Rohr

In the thermal hydraulic test facility NOKO at the Research Center Juelich, several important components of passive safety systems, which are foreseen to be installed as a part of the safety concept of the innovative boiling water reactor SWR- 1000, have been investigated . In this work, the condensation of steam or steam/nitrogen-mixtures in a horizontal tube has been analytically and experimentally studied. A total of 35 tests has been carried out, where besides temperatures, pressures, pressure drops and flow rates, also the local distribution of the condensate film thickness was measured using moving needle probes. In a concomitant effort, a two-dimensional analysis model KANIWAR has been developed. The experiments with condensation of steam at different pressures (1, 3, 7 MPa) have shown that the film thickness varies significantly over the circumference inside the tube reaching values of more than 10 mm in the accumulated condensing layer in comparison to about 1 mm in the condensing thin film layer. The film thickness in the accumulated condensing layer decreases with increasing steam velocity at the inlet. Also the waviness at the surface of the accumulated condensing layer has been observed in some of the tests. In the experiments with condensation of a steam/nitrogen-mixture, the same dependency an the circumference was verifies in principle, too . However, they were smaller due to lower condensation rates . The temperature difference between the bulk of the mixture and the Interface was measured to be in the order of a few 10 K; they were lower at the bottom and top of the tube than an the sides. The analysis model KANIWAR describes the condensation of steam or steam/nitrogen mixtures in a long horizontal tube. It considers shear stresses, waviness, and the suction effect at the interface. KANIWAR allows the calculation of the local distribution, e.g., of the film thickness, the heat transfer coefficient, the temperature and the inert gas concentration in the bulk of the mixture as well as at the Interface. The analysis model also provides data, which could not be gathered in the experiments due to inappropriate measuring devices, thus, by means of parameter calculations, enables the study and improves the understanding of condensation processes. In particular, the dependency of film thickness an the circumference could be quantitatively verified. The condensation velocity in the circumference has been found to reach the same magnitude as that in axial direction . The condensation velocity in the circumference substantially depends an the axial steam velocity. At the presence of non-condensable gases, the temperature difference between the bulk of the mixture and the interface due to diffusion layer as well as the dependence an circumference could be quantitatively verified. The experiments have also been calculated using the ATHLET code. The comparison between the calculated heat flux using KANIWAR and ATHLET showed that at higher pressures, the heat flux values are in better agreement than at lower pressures; the maximum deviation is about 40%