内燃机用冷却介质纳米流体强化传热机理及场协同优化研究

Heat transfer in cooling water jacket has strong influences on the power, economy and dependability of internal combustion engine. The rapid increasing of engine specific power will inevitably generate higher combustion temperature, which results in more heat transferring to the combustion chamber components. The low heat transfer performance of conventional cooling medium has become the bottle-neck of developing highly strengthened internal combustion engines. In view of the excellent heat transfer performance of nanofluids, the present work attempts to apply nanofluids as the cooling medium of engine in order to enhance and control heat transferring. Because of the inadequate of strengthened mechanism of heat transfer by using nanofluids, the application process of nanofluids in internal combustion engine is restricted. By means of molecular dynamics method, the present subject intents to reveal the microcosmic mechanisms of strengthened heat transfer with nanofluids from two aspects: heat conduction and convective heat transfer. Furthermore, through visualized and quantitative experiments on flow of nanofluids combining with numerical simulation on two-phase flow of nanofluids, on the basis of field synergy theory the macroscopic essential reason for heat transfer enhancement through nanofluids will be revealed. In addition, a serial of new methods for the enhancement and control of heat transfer with nanofluids will be developed. Moreover, the basic research results are applied to the study on enhanced heat transfer in cooling water jacket by using nanofluids. The matching and optimization problems are investigated on the basis of field synergy theory, which lays a theoretical foundation for application of nanofluids in internal combustion engine to enhance heat transfer.

冷却水腔的传热，直接影响内燃机的动力性、经济性和可靠性。随着内燃机升功率的大幅提高，必然会产生更高的缸内温度，关键零部件的热负荷也随之增大，常规冷却介质的低传热性能已成为制约内燃机高强化发展的一个瓶颈。鉴于纳米流体良好的传热性能，试图将其作为冷却介质应用于内燃机强化传热及控制传热。但纳米流体强化传热机理的研究还不够完善，限制了其在内燃机中的应用进程。为此，本课题拟采用分子动力学方法模拟复杂分子基础液纳米流体的输运特性、流动与传热特性，在微观上揭示纳米流体导热和对流换热两方面的传热强化机制；并结合纳米流体流场可视化及定量化实验与纳米级颗粒两相流数值模拟研究，依据场协同理论从宏观上揭示纳米流体强化传热的物理本质，发展纳米流体传热强化与控制新方法。在此基础上，应用场协同理论开展纳米流体与内燃机冷却水腔实际传热过程的匹配与优化研究，为纳米流体在内燃机强化传热中的应用奠定理论基础。

冷却水腔的传热，直接影响内燃机的动力性、经济性和可靠性。随着内燃机升功率的大幅提高，必然会产生更高的缸内温度，关键零部件的热负荷也随之增大，常规冷却介质的低传热性能已成为制约内燃机高强化发展的一个瓶颈。新一代传热工质纳米流体具有良好的传热性能，将其作为冷却介质应用于内燃机强化传热及控制传热将能够满足高强化内燃机对传热量的需求。课题针对纳米流体应用于内燃机强化传热的机理问题开展基础研究，采用分子动力学方法模拟了复杂分子基础液纳米流体的输运特性、流动与传热特性，在微观上揭示纳米流体导热和对流换热两方面的传热强化机制；并结合纳米流体流场可视化及定量化实验与纳米级颗粒两相流数值模拟研究，依据场协同理论从宏观上揭示纳米流体强化传热的物理本质，以发展纳米流体传热强化与控制新方法，为纳米流体在内燃机强化传热中的应用奠定理论基础。