Study On Thermal Conductivity Strengthening Mechanism Of Nanofluids Based On MPCD-MD Method

At present,most scholars usually apply MD method to research mechanism of the heat transfer enhancement by nanofluid.However,the MD method has great limitations in calculating the thermal conductivity of large systems due to the heavy calculation workload,and can only be used in small system.Therefore,the proposes of present work is to propose a numerical simulation method coupling MPCD and MD for the study of microscale heat transfer.In the first chapter,the studying background and sense of the subject and the developing situation of nanofluid heat transfer enhancement at home and abroad are introduced.Then,the differences between numerical simulation methods and experimental analysis methods.Finally,the numerical simulation methods and research difficulties are explained.In the second chapter,MD method,MPCD method and MPCD-MD method are introduced respectively.Then,how MPCD and MD are coupled and how to select the related parameters are described in detail.Finally,the outlines,the selection of statistical ensemble and boundary conditions are presented.In the third chapter,MPCD method is applied to simulate fluid flow.In this chapter,momentum exchange method which can calculate fluid thermal conductivity and viscosity is introduced firstly.Then,we judge some factor could affect results and show some rules.It is found that the angle of rotation and its probability in each collision step have the greatest influence on the simulation results.In addition,the pure argon system is simulated in this chapter also.By calculating the thermal conductivity and viscosity of the pure argon and we compare computed value with the theoretical value,it is verified that MPCD method and momentum exchange method can be used in the calculation of fluid thermal conductivity.This can provide a solid foundation for the calculation of nanofluid thermal conductivity.In the fourth chapter,MPCD and MD coupling method are used to analyze the influence of nano-particle aggregation microstructure on the thermal conductivity of nano-fluid.Firstly,the factors that may affect the aggregation microstructure of nanoparticles in nanofluids,such as potential function parameters,particle charge and shear flow were analyzed.Then,the coarse-grained solution of water molecules was selected as the base fluid of nanofluids,and using fractal dimension to characterizate the aggregation microstructure of nanoparticles.The results show that the fractal dimension is the smaller,the thermal conductivity is the bigger at same particle number and volume fraction.Because the lower the fractal dimension of nanoparticle aggregation,the more contact surface with coarse particles in the fluid,which increases the probability of collision between nanoparticles and coarse particles and subsequently increases the heat transfer of nanofluid.The fifth chapter is the summary and prospect.