Study On Properties Of Moist Air At High Temperature And Pressure By Using Molecular Dynamics Simulation

Because moist air at high temperature and pressure is currently being considered for use in the new thermodynamic circulation, molecular dynamics simulation (MDS) is adopted to investigate the properties of moist air which are used in moist air turbine and compressed air energy storage (CAES) system. Based on the theory of statistical thermodynamics, the way to calculate the properties parameter of moist air is presented. Results are given for temperature from 10℃to 600℃and humidity ratios from 0.01 to 0.445 mol/molh-air and pressure from 0.1MPa to 40MPa. Main contents of research are listed as fellows: 1. A suitable molecular dynamics simulation potential function model is chosen for calculating the properties of moist air by comparing the performance of Lennard-Jones model with TIP4P model when they are used in calculating the properties of water vapor. 2. The deflection between results of simulation pressure property in dry air and experimental data at state of low temperature and high density is analyzed. A reformative method to calculate pressure of moist air is presented. 3. Suppositional critical properties Pc,Vc,Tc of moist air are given for humidity ratios from 0.01 to 0.445 mol/molh-air by the help of Van der waals mixing-rule. 4. The PVT properties of moist air are calculated by chosen potential function model and modified virial pressure function, results agree well with experiment data. 5. The PVT properties of moist air in a more broad range of temperature and pressure are calculated by molecular dynamics simulation and modified virial pressure function. 756 groups data of PVT properties are obtained for temperature from 10℃to 600℃and humidity ratios from 0.03 to 0.445 mol/molh-air and pressure from 0.1MPa to 40MPa. 6. Virial coefficients and relating formulations which are associated with temperature are got from PVT properties obtained by molecular dynamics simulation. 7. By compared with standard Brownian motion, the fractional dimension number of path of practical liquid molecular motion is analyzed theoretically on the basis of fractal theory. The criterion of rational statistical size of fractional motion is given in the light of the theory of mean free path. The processes of argon molecular motion is simulated under the condition of constant temperature 84K and the fractional dimension number of path of liquid molecular motion is calculated according to different space and time size based on the molecular dynamics simulation. 8. The characteristic of fractional Brownian motion of argon molecular in saturated liquid phase and vapor phase is investigated under the condition of different temperature by molecular dynamics simulation. The phase pattern of velocity of molecular motion is compared in saturated state of liquid phase and vapor phase. Based on the theory of fraction and the reduction scale method that is presented in this paper, fractional dimension numbers of the path and Hurst exponent of molecular motion are obtained.