Study of Thermal Properties of Thin Fluid Layers by Molecular Dynamics Simulations

• Main Authors: Chi-Chung Chang, 張至中
• Other Authors: Wen-Jenn Sheu
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/03553119281493396533

碩士 === 國立清華大學 === 動力機械工程學系 === 93 === In order to study the differences of the fluid properties between nanoscales and macroscales, the method of molecular dynamics is adopted to investigate the physical phenomena of a thin fluid layer with the thickness of nanometers. Both water molecules and argon atoms are chosen as the working fluids for the problem of interest. However, with the presence of temperature gradient, the rotational motion of the water molecules frequently results in numerical errors. To keep the accuracy of results, we employ the argon atoms instead of water molecules for non-isothermal systems. The TIP4P model is applied for isothermal systems. The radial distribution function is used to verify the equilibrium states, and then the Green-Kubo integration method is utilized to calculate the transport properties of water such as the viscosity, thermal conductivity and diffusion coefficient respectively. A systematic investigation is made to obtain the values of macroscopic properties accurately. The present numerical results are in agreement with experimental data. For non-isothermal thin-layer fluid system, the argon and the platinum atoms are arranged to simulate the system in which the platinum atoms are placed on the top and the bottom layers and the argon atoms are filled inside the clearance between the platinum layers. The thickness of the system is also of nanometers. To investigate the effect of positive and negative pressures, the saturated region in the presence of gas and liquid phases simultaneously is considered. It is found that the argon atoms near the platinum walls are crystallized due to a great attractive force between the argon and platinum atoms. To examine the validity of the Fourier’s law for thin fluid layers, the thicknesses of 40 and 80 under positive pressure and those of 40 , 60 , 80 , and 100 under negative pressure are investigated. The simulation results show that the Fourier’s law is valid except for the case of 40 under positive pressure. Keywords: TIP4P model, Fourier’s law, molecular dynamics simulation, thin fluid layer