Molecule Dynamics Simulation On Microscale Effect Of Heat Conduction Of Gas

With the rapidly development of micro electronics technology and micro electro mechanical systems technology, the electronic devices which were commonly used such as sensor was developed to microminiaturization. The Pirani vacuum sensor which was widely used in vacuum measurement system and equipment, it is depended on the amount of heat conduction of gas is different under different pressure, but it is unclear that heat conduction mechanism of gas in Pirani vacuum sensor. Molecular dynamics method has been commonly used in the field of particle by simulating the motion of particle to calculate the physical quantity in system. At present, molecular dynamics method has been widely used in researching thermal physical properties of matter in the micro or nanometer scale. Equilibrium molecular dynamics and non-equilibrium molecular dynamics have been mass used in simulating the thermal conductivity of the solid material and fluid to solve the related physical quantities. Molecular dynamics method is used to calculate physical quantity in system by simulating the movement of particles in system. This paper through molecular dynamics method to simulate the gas thermal conductivity in micro thermal gap, and analysis the related factors and relations of the microscale effect of gas heat conduction, and then it can be theory guidance in the design of Pirani vacuum sensor.This paper introduces the basic theory and simulation method of molecular dynamics, according to the structure characteristics of the Pirani vacuum sensor, the calculation model of the nitrogen and oxygen in the micro thermal gap were established. Non-equilibrium molecular dynamics method and Lennard-Jones potential were used to program the calculation program of the gas thermal conductivity by LAMMPS. And then the gas thermal conductivity was calculated under different size of micro thermal gap, different temperature and different pressure.According to the applied range of Pirani vacuum sensor and the ability of practical calculating. The temperature range of simulation is from300K to700K, the thermal gap size range is from17nm to102nm, the relationship between the gas thermal conductivity in micro thermal gap and the influencing factors is simulated. The results indicate that the gas thermal conductivity in the micro thermal gap is significantly less than the gas thermal conductivity under macros boundary condition, with the increase of temperature, the gas thermal conductivity increase, it has the same variation trend of the gas thermal conductivity changed with temperature under macros boundary condition. The micro thermal clearance is smaller, the smaller of gas thermal conductivity, and it presents a linear law. And the gas thermal conductivity decreases with the decreasing of the pressure.