Supercritical water oxidation (SCWO) is a new technique for waste treatment. Some toxic organic materials can be oxidized rapidly into H2O, CO2, N2 and other nontoxic inorganic materials. The diffusion coefficients of gases are necessary for development of this technique. The experimental data about the diffusion coefficients of gases in supercritical water are difficult to obtain. Molecular dynamics simulation (MD) was employed to calculate the infinite dilute diffusion coefficients of oxygen and nitrogen in supercritical water ranging from 703.2K to 763.2K and from 30MPa to 45MPa. The results obtained show that the diffusion coefficients in supercritical water are one or two orders of magnitude higher than those at normal conditions. The diffusion constant increases with temperature, but decreases with pressure. The diffusion coefficients of oxygen are larger than those of nitrogen.%采用分子动力学(MD)方法计算T=703.2～763.2K，p=30～45MPa范围内，氧气和氮气在超临界水中的无限稀释扩散系数。计算结果表明，在超临界条件下的扩散系数较常温常压下要大1～2个数量级。扩散系数随温度的升高而增大，随压力的增高而降低，且氧的扩散系数稍大于氮的扩散系数。
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