TWO PHASE FLOW SIMULATION FOR NUCLEAT BOILING HEAT TRANSFER CAICULATION IN WATERJACKET OF DIESEL ENGINE

摘要

Basic understanding of the process of coolant heat transfer inside an engine is an indispensable prerequisite to devise an infallible cooling strategy. Coolant flow and its heat transfer affect the cooling efficiency, thermal load of heated components, and thermal efficiency of a diesel engine. An efficient approach to study cooling system for diesel engine is a 3D computational fluid dynamics (CFD) calculation for coolant jacket. Therefore, computer simulation can analyze and consequently optimize cooling system performance, including complex cooling jacket. In this paper a computational model for boiling heat transfer based on two-phase Mixture model flow is established. Furthermore, the phenomenon of nucleate boiling, its mathematical modeling, and its effect on heat transfer is discussed. Besides, the static, total and absolute pressure, velocity and stream lines of the flow field, heat flux, heat transfer coefficient and volume fraction of vapor distribution in the coolant jacket of a four-cylinder diesel engine is computed. Also, comparison between experimental equation (Pflaum/Mollenhauer) and two-phase Mixture model for boiling hat transfer coefficient is done and good agreement is seen. In conclusion, it is observed that at high operating temperatures, nucleate boiling occurs in regions around the exhaust port. Numerical simulation of boiling heat transfer process of cooling water jacket and temperature field in the cylinder head of the diesel engine is compared with the data measured on the engine test bench. The calculated results indicate that this method can reflect the impact of boiling heat transfer on water jacket rather accurate. Therefore, this method is benefit to improve the computational precision in the temperature field computation of a cylinder head.