Sharma Prabhakar, Poulsen Tjalfe G
Department of Biotechnology, Chemistry, and Environmental Engineering, Section for Environmental Engineering, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark.
J Contam Hydrol. 2009 Jul 21;107(3-4):101-7. doi: 10.1016/j.jconhyd.2009.04.005. Epub 2009 Apr 18.
Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity.
使用氧气和氮气作为示踪气体，研究了气相在天然多孔介质（庭院废弃物堆肥）中的扩散与气体流速和堆肥体积含水量的关系。选择堆肥是因为它具有非常宽的含水量范围，并且代表了包括土壤和生物过滤介质在内的广泛多孔介质。在相对较低的孔隙气体流速下测量了氧气和氮气的柱突破曲线，这与例如土壤蒸汽抽提系统或沼气厂或堆肥设施中用于空气净化的生物过滤器中观察到的流速相对应。使用对流扩散方程的一维数值解从突破曲线拟合总气体机械扩散-分子扩散系数，并用于确定不同体积气体含量下的气体扩散率。结果表明，在所研究的所有含水量和孔隙气体流速下，气体机械扩散比分子扩散占主导地位，且机械扩散作用随着孔隙气体流速和堆肥含水量的增加而增强。结果还表明，在堆肥气体填充孔隙率较高时，气体扩散率相对恒定，但在气体填充孔隙率较低时，随着气体填充孔隙率的降低而增加。最后结果表明，气体扩散率的测量不确定度通常在孔隙气体流速较低时最高。
