Analytical Solution for Two-Region Diffusion with Two Well-Mixed End Chambers
Analytical Solution for Two-Region Diffusion with Two Well-Mixed End Chambers
复制标题
具有两个充分混合的端室的两区域扩散的解析解
DOI：
10.2136/sssaj1996.03615995006000060013x
复制
发表时间：
1996
影响因子：
2.9
通讯作者：
R. D. Glauz
中科院分区：
文献类型：
--
作者：
Y. H. El;D. Rolston;L. W. Petersen;R. D. Glauz
土壤中有效气体扩散系数（DP）的测定方法很多.一些常用的方法是单室和双室装置。此外，用于研究蒸气扩散、吸附和生物降解的实验室仪器可由土壤和蒸气室组成。用于这种装置的现有分析解决方案不能适应通过包含具有不同孔隙率和扩散系数的两个不同层的区域的扩散。这种双重孔隙率可以代表停滞的空气层，或在核心端部的结壳压实。我们发展了一个解析解的气体扩散在一个四区域室系统。该系统包括两个扩散区（具有两种不同的孔隙率），以及连接在两端的混合良好的端室。该解被用来模拟一维气体扩散装置中的两个扩散区与恒定浓度的边界条件。该解决方案也被用来量化误差估计D p翼单室装置时，空气室不混合，或当一个停滞的空气层存在于土壤表面上方。由于非混合的错误随着时间的推移而减少，并增加了水含量和空气室的大小时，进行分析，使用浓度在一个点接近土壤表面。分析了停滞空气层的影响，结果表明，误差随时间和空气室的大小而增加，随含水量的增加而减少。测试土壤结皮对扩散的影响所做的分析表明，尽管薄的土壤结皮，大的估计误差D p是可能的。
Many methods have been developed for determining the effective gaseous diffusion coefficient (D p ) in soils. Some commonly used methods are the one- and two-chamber apparatuses. In addition, laboratory apparatuses for the study of vapor diffusion, sorption, and biodegradation may consist of soil and vapor chambers. Existing analytical solutions for such apparatuses cannot accomodate diffusion through regions containing two distinct layers of differing porosity and diffusion coefficient. Such dual porosities can represent stagnant air layers, or crusting-compaction at core ends. We developed an analytical solution for gaseous diffusion in a four-region chamber system. The system consists of two diffusion regions (with two different porosities), and a well-mixed end chamber attached at either end. The solution was used to simulate one-dimensional gas diffusion in an apparatus consisting of two diffusion regions with constant-concentration boundary conditions. The solution was also used to quantify errors made in estimating D p wing the one-chamber apparatus when the air chamber is not mixed, or when a stagnant air layer exists above the soil surface. Errors due to non-mixing decreased with time and increased with water content and air-chamber size when analysis was done using concentrations at a point close to the soil surface. Analysis of the effects of a stagnant air layer showed that errors increased with time and air-chamber size and decreased with increasing water content. Analysis done to test the effects of soil crusting on diffusion showed that, despite the thinness of the soil crust, large estimation errors in D p are possible.