Cooling Water Cavity Boiling Heat Transfer Simulation And Cylinder Head Of State

The study of heat transfer in water jacket is a precondition for thermal fatigue investigation of cylinder head. Boiling heat transfer is one of the most important heat exchange modes in water jacket. Researching the influence of boiling heat transfer is a great help to the configuration design of water jacket. In this paper a single phase boiling flow model was developed. Take water jacket-cylinder head system of 226B engine as practical study application, the models of cooling jacket system and cylinder head is created. Using computational fluid dynamic(CFD), the velocity filed and heat transfer were calculated. Then an engine cycle simulation is analyzed firstly and the heat transfer coefficient of the intake-port, export and fire deck is confirmed accordingly, based on which the temperature field is obtained. Moreover, the finite element analysis for thermal-structure stress of cylinder head is calculated and the shape of which is modified. At last, the temperature measurement experiment system of water jacket in cylinder head is introduced.The main contents of this thesis include as follow:1. Based on the Chen model a single phase boiling flow model was developed, by making use of void fraction, the model regards boiling liquid as a single phase flow in which vapor and liquid are homogeneously mixed, so the whole flow field can be solved by the single phase flow equation. The mathematical description and the numerical implementation method of the model were also introduced.2. The flow field and heat transfer in water jacket were both analyzed by single phase boiling model and single phase convection flow model. The compare between the two results shows that boiling heat transfer had little effect on the velocity and pressure field, however, the influence of boiling on the heat transfer in water jacket should not be ignored.3. In order to discover the effect of both material and boiling heat transfer on the temperature field of cylinder head, the thermal boundary conditions of the cylinder head were confirmed by engine cycle simulation. It indicated that material which has better heat conduction could produce a more uniform temperature field and reduce the temperature gradient of fire deck, while boiling heat transfer can lower the whole temperature of the fire deck.4. When the material HT300 of cylinder head was replaced by HT280, according to the thermal-structure coupled stress results the shape of the cylinder head was modified. Also, the influence of boiling heat transfer on both thermal -structure coupled stress and thermal fatigue were analyzed, it shows that boiling heat transfer could reduced the thermal stress value, and the fire deck and other correlative parts could work in a lower temperature condition because of boiling heat transfer, which intensified their capability of preventing thermal fatigue.