Analysis Of Influence Factor And Numerical Simulation Of Subcooled Nucleate Boiling Heat Transfer In Gasoline Engine Water Jacket

At present, the development of engine is in the direction of the miniaturization, highpower, and high rotate speed. The heat load of the engine is higher and higher. Under thisdevelopment trend, the requirement to the cooling system is more stringent, not only a higherthermal efficiency, but also a smaller size. In such background, the ability of the convectiveheat transfer has not met the expected demand yet. Because of its highly efficient heattransfer capability, subcooled nucleate boiling heat transfer is in the research direction again.However, the influence factors of subcooled nucleate boiling heat transfer are not clear yet,which is needed to be worked on. When the mechanism is unknown, the subcooled boiling iseasy out of control and producing too many bubbles, which may block the narrow waterwayand cause heat transfer deterioration. This article will study the influence factors, then makesimulated calculation of the engine model, and verified the result with test data.In order to study the influence factors of boiling heat transfer within the engine waterjacket, this article has carried on the simple flow simulation calculation and analysis firstly.By contrast and analysis with classical experimental data, this article has verified thecalculation model of subcooled nucleate boiling model, and has analyzed and summarizedthe influence factors on this basis. Finally taking a four-cylinder turbocharged gasolineengine as the research object, this article has done two phase change thermal simulation,compared and analysed the calculated results with the experimental data.The application and validation to the numerical simulation of boiling heat transfermodel. With a simple rectangular passage as computing object, by using CFD softwareFLUENT, this article made a numerical analysis of the rectangular groove, and investigatedthe accuracy of the boiling model. Compared results with the experiment data, this articlefound the boiling model had a good match with heating curve data in low temperature, andwhich could be applied to the simulate of boiling heat transfer.To learn influencing factors and regularities of boiling heat exchange, the differences ofcalculation results are analyzed by changing the inlet flow speed, pressure, and physicalparameters. And the change rules and characteristics are summarized. To reduce thecalculation intensity and guarantee the calculation accuracy, the secondary factors are ignored in the subsequent simulation. In order to investigate influence factors of vibration,UDF function of FLUENT software is used to program vibration boundary. The effect ofvibration direction, vibration frequency and amplitude are all analyzed in boiling condition.Through the analysis of the vibration influence factors, a research direction is provided tonumerical calculation of boiling heat transfer with vibration in engine water jacket.An engine temperature bench test. In the engine block and cylinder head, measuringpoints is designed and arranged, and then the holes are sealed. Engine test are carried onexternal characteristic and load characteristics. By comparing the test data and the simulationresult, the working condition and the position, where may occur boiling, is summarized.During the mesh dividing of water jacket, the experiment data provides positions, wherelocal grid needs refinement. At the same time, the experiment data can evaluate and analysethe result of the simulation calculation.Use software ANSYS ICEM to mesh engine geometry model firstly. To guarantee thecalculation accuracy, according to the results of the temperature test, the grid refinement ismade at the key position of boiling heat transfer. Imported Grid to the FLUENT software,used coupling method to deal with solid-liquid interface, boundary conditions under enginerated speed are applied to the model, finally simulation calculation is made with two phasesflow boiling heat transfer. Calculation results show that the engine’s cooling system layout isreasonable, and the boiling model makes the numerical simulation results be close to realengine temperature field.