The present report documents the system and CFD code validation activity carried out at University of Pisa, dealing with the simulation of forced convective boiling flows. At first, a study of system codes capabilities in predicting boiling flow characteristics is presented; thanks to the expertise achieved by DIMNP researches in the use of these thermal-hydraulics tools, it was possible to perform steady state and transient analyses of a BWR fuel assembly with three different codes (namely RELAP5, CATHARE2 and KORSAR). Since simulation of boiling flows through CFD approaches is a rather new issue for our Department, a simpler case was chosen as study problem: forced convective boiling flow in a vertical heated pipe, with water at high pressure. Calculations were performed with ANSYS CFX-11.0 (“beta” version, embedding the RPI wall boiling model). Several sensitivity studies were conduced, in order to assess the influence of mesh size and model parameters on code performances. Numerical results, in terms of axial distribution of void fraction and liquid temperature, are compared against measured data from Bartolomei’s experiment and system code predictions obtained with RELAP5. This comparison showed that the axial void distribution and the void fraction at the channel exit can be accurately predicted by CFX (at least within the experimental uncertainty range).
Study of a Boiling Channel with System and CFD codes
D’Auria Francesco
Ultimo
Conceptualization
2007-01-01
Abstract
The present report documents the system and CFD code validation activity carried out at University of Pisa, dealing with the simulation of forced convective boiling flows. At first, a study of system codes capabilities in predicting boiling flow characteristics is presented; thanks to the expertise achieved by DIMNP researches in the use of these thermal-hydraulics tools, it was possible to perform steady state and transient analyses of a BWR fuel assembly with three different codes (namely RELAP5, CATHARE2 and KORSAR). Since simulation of boiling flows through CFD approaches is a rather new issue for our Department, a simpler case was chosen as study problem: forced convective boiling flow in a vertical heated pipe, with water at high pressure. Calculations were performed with ANSYS CFX-11.0 (“beta” version, embedding the RPI wall boiling model). Several sensitivity studies were conduced, in order to assess the influence of mesh size and model parameters on code performances. Numerical results, in terms of axial distribution of void fraction and liquid temperature, are compared against measured data from Bartolomei’s experiment and system code predictions obtained with RELAP5. This comparison showed that the axial void distribution and the void fraction at the channel exit can be accurately predicted by CFX (at least within the experimental uncertainty range).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
