Numerical investigation of two-phase flow characteristics of subcooled boiling in IC engine cooling passages using a new 3D two-fluid model

Modern engine cooling systems use subcooled boiling as an effective heat transfer form. The significantly higher heat transfer rate achievable with boiling can keep the temperature in key thermal areas within an acceptable level. In this study, a three-dimensional two-fluid model coupled with RPI wall boiling model was adopted to simulate the local two-phase characteristics of boiling at different passages under low-pressure condition. Moreover, a modified bubble departure diameter correlation was developed and implemented in computational fluid dynamics code with user-defined function, and the correlation was verified by two sets of experimental data under different flow conditions. Results showed an improved agreement with the measured local void fractions. Finally, the verified model was applied to a practical cooling passage for a water-cooled diesel engine. The simulation results showed that present two-fluid model could get an accurate temperature field for cylinder head. The distribution of vapor phase in cooling passage was obtained, and it could be used as a reference to evaluate the reliability of local boiling. Moreover, due to the function of interphase forces, the majority of bubbles were quickly removed from near wall and the void fraction was below 0.149.