Molecular Dynamics Simulation Of Cu-H₂O Nanofluids Heat Motion

With the aggravation of energy problem,researches on heat transfer enhancement have received wide attentionss of investigators both domestic and abroad.Nanofluid is a new and efficient heat transfer medium which consists of nanoparticles and base fluids.In industry,nanofluids can replace the traditional heat transfer fluid to improve the heat transfer efficiency of the system.Based on the theoretical basis of molecular dynamics simulation,this dissertation adopted L-J potential function and dipole potential function to construct water molecule model.Meanwhile,the model of copper atoms was build with Morse potential function.Through the study of energy conversion and stress condition of particle in heating CU-H20 nanofluid,this paper obtained the microscopic mechanism of nanofluid heat movement.The main contents and conclusions are as follows:(1)The agglomeration of nanoparticles was influenced by nanoparticle diameter and simulated temperature.The larger nanoparticle diameter was,the slower the agglomeration of nanoparticles was.The higher the temperature was,the faster the agglomeration of nanoparticles was.(2)Through the research of arrangement of water molecules in nanofluid,it was found that there was an adsorption layer around the nanoparticles.In the same condition,the density of the nanoparticles was greater than the water molecular,and the structure was more compact.(3)Nanofluid heat movement was simulated.In the early stage of the nanofluid heating,the water molecule distribution in the nanofluid adsorption layer was compact.Although the outer layer of water molecule was unstable due to heating,the surface of nanoparticles had a strong attraction,it was difficult for water molecules to move far away.As the water molecule moved upwards into the cooling zone,the water molecule slowed down and hydrogen bonds were formed as a result of cooling,and the number increased so as to form new clusters.The simulation was continuous and the clusters were formed and separated continuously until the system reached a new steady state.During the simulation,the total energy of the system increased up to a steady value in 0.2 ps.(4)The calculated phase transition temperature of water was 342.4K in the simulated at latmosphere,which was similar to the actual value.When the temperature was 420K,potential energy of nanofluid changed sharply.(5)At latm,and 300K,the thermal conductivity of water was 0.47W/(m·K)by EMD,and the thermal conductivity of nanoparticle with its surrounding water was 400W/(m·K).The temperature difference between hot and cold source difference of water was 54.2K by NEMD.It reduced to 29.7K after added nanoparticles,which proved that nanoparticles can improve heat conduction efficiency.The micro movement of heated nanofluids was studied,it has important guiding significance for nanofluids experimental research and industrial application.