The Basic Research Of Multiphase Flow Numerical Simulation About Subcooled Boiling Heat Transfer In Cylinder Head Cooling Cavity

The demand of modern society for enhanced internal combustion engines is growing, which causes the increase of the heat load of engine. Cylinder head is one of the most complicated structures in internal combustion engine, and it is also one of the most serious parts involved heat load. The cooling water flow and heat transfer conditions in cylinder head directly influence the reliability and the service life of the engine. It has been demonstrated that there is subcooled boiling inside the cooling gallery of enhanced internal combustion engines. Due to the latent heat of vaporization, the boiling heat transfer effect is usually several times of the convective heat transfer effect or even dozens of times. Therefore, the heat transfer effect can be significantly improved by reasonable using the subcooled boiling heat transfer without changing the structure of cooling gallery. Applying the subcooled boiling numerical simulation research in the engine cylinder head cooling design, we can get the temperature distribution of cooling gallery, which benefits to the structural optimization design and shortens the design period of internal combustion engines.The traditional numerical simulations of subcooled boiling were mostly based on the Chen model, such as the single-phase model and the mixture multiphase model. Both models failed to agree well with the experimental data due to the ignorance of the velocity differences between the vapor phase and liquid phase. Therefore, the current paper employed the Eulerian multiphase model to explore the subcooled boiling process, which achieved better agreement with the actual state in comparison to the traditional single-phase model. Firstly, six sub boiling models of the Eulerian model were discussed in order to choose an appropriate model of the subcooled boiling process in a rectangle channel, based on the experiment conducted by Robinson. It was indicated that the multiphase model showed good agreement with the experimental data and the turbulent dispersion played a more important role in the numerical simulation of subcooled boiling. Secondly, the current paper further performed a numerical study of the fluid-structure interaction and obtained the cylinder head temperature and the distributions of temperature, velocity and pressure of the heat transfer medium inside the cooling gallery. The results confirmed the existence of subcooled boiling inside the cooling gallery as the temperature of bridge zone was higher than the boiling point at the saturation pressure. Lastly, it was found that the accuracy of the Eulerian model was much better than the mixture model by comparing the numerical results with experimental data inside the cooling gallery. In the cross section of a T channel, it was shown that the velocity of cooling medium was one of the determining factors during the convective heat transfer. However, the velocity of cooling medium turned out to be less important on the heat transfer during the subcooled boiling process. The application of subcooled boiling in the bridge zone improved the heat transfer coefficient by 50%, with the power loss less than 30%.