The Numerical Analysis Of Subcooled Boiling In Engine Water Jacket

The engine cooling system is to make the engine work in appropriate environment, theengine operating temperature will affect it work. Boiling heat transfer is an important heattransfer mode in engine cylinder head cooling water cavity, the rational use of boiling heattransfer can not only improve the engine cooling effect, make the temperature distributionuniform, effectively reduce the cylinder head thermal-mechanical stress but also can improvethe emission performance, reduce fuel consumption, and save the costs of engine, etc.Because of the engine cooling water jacket is complex, the coolant flow changeable and thetemperature distribution is not clear, it is difficult for traditional experimental methods toresolve. While CFD numerical analysis has special advantages in this field. This paper takesCFD simulation as the primary means to have a research around the boiling heat transfer inengine water jacket. In this paper, the main work contents the following sections:The concept of gas rate is introduced based on the Chen model and two-phase flowboiling mathematical model established. The mixture of flow boiling gas-liquid two-phaseflow is described with relative speed and solved using momentum equation. And then, writeuser-defined function (UDF) in C environment according to mathematical models andembed it to FLUENT extensible platform, which make up the defects of FLUENT softwareand two-phase flow heat transfer process of flow boiling can be achieved.1）The work environment of inline six-cylinder gasoline engine has a special similarity,this paper is innovative to intercept some single water jacket of the engine water jackets asresearch object, in order to reducing the burden of computer hardware and computing time。The results show that: the high temperature and low flow rate can enhance the boiling heat transfer. Then restore the engine water jacket model and have a comparison calculation.Further research proved that it is reliability of the single-cylinder model. Based on thecomplete model, there is a theoretically optimal flow rate can be find on the results of theheat flux-flow rate curve.2）Four kinds of ribs with similar characteristics proportion and different shapes ofrectangle, triangle, isosceles trapezoid and round are processed on the heating surface。Whether it can enhance the heat transfer effects by changing the structure of the heatingsurface through adding a rib is analysised. The results show that: the surface with rib caneffectively increase the heat flux, thus to enhance the heat transfer; the differences of heattransfer characteristics gradually increase with the increase of the fluid flow velocity andheating temperature; in these three shapes, triangles has the best effects, while round has theworse.3） Analysis of the shortcomings of the water jacket structure, three kinds ofoptimization program of water jacket structure are put forward for the purpose of enhancingthe flow and heat transfer, and then they are calculated respectively and get the conclusionafter the comparison: plan3is the most reasonable.