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41.
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Alexander Van-Brunt Patrick E. Farrell Charles W. Monroe 《American Institute of Chemical Engineers》2022,68(5):e17599
We present the Onsager–Stefan–Maxwell thermodiffusion equations, which account for the Soret and Dufour effects in multicomponent fluids. Unlike transport laws derived from kinetic theory, this framework preserves the structure of the isothermal Stefan–Maxwell equations, separating the thermodynamic forces that drive diffusion from the force that drives heat flow. The Onsager–Stefan–Maxwell transport-coefficient matrix is symmetric, and the second law of thermodynamics imbues it with simple spectral characteristics. This new approach allows for heat to be considered as a pseudo-species and proves equivalent to both the intuitive extension of Fick's law and the generalized Stefan–Maxwell equations popularized by Bird, Stewart, and Lightfoot. A general inversion process facilitates the unique formulation of flux-explicit transport equations relative to any choice of convective reference velocity. Stefan–Maxwell diffusivities and thermal diffusion factors are tabulated for gaseous mixtures containing helium, argon, neon, krypton, and xenon. The framework is deployed to perform numerical simulations of steady three-dimensional thermodiffusion in a ternary gas. 相似文献
43.
Model-based design of horizontal subsurface flow constructed treatment wetlands: a review 总被引:13,自引:0,他引:13
The increasing application of constructed wetlands for wastewater treatment coupled with increasingly strict water quality standards is an ever growing incentive for the development of better process design tools. This paper reviews design models for horizontal subsurface flow constructed treatment wetlands, ranging from simple rules of thumb and regression equations, to the well-known first-order k-C* models, Monod-type equations and more complex dynamic, compartmental models. Especially highlighted in this review are the model constraints and parameter uncertainty. A case study has been used to demonstrate the model output variability and to unravel whether or not more complex but also less manageable models offer a significant advantage to the designer. 相似文献
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多个工程实例表明:岩土体蠕变易引起锚固工程支护结构加固频繁、锚索重新张拉等工程病害,严重者导致锚固力失效,锚固工程失稳,如若处理不当,将直接危及施工人员的生命财产安全;本文以济南市某深基坑工程案例为依托,将岩土体由经典的广义Kelvin体代替,推导了其本构方程、蠕变方程、松弛方程,从理论上分析了锚索蠕变变形对预应力损失的贡献大小;并结合现场测试数据对比可知:该模型能够较好的反映蠕变变形引起的损失趋势,由数据软件拟合公式可知,理论计算结果与测试数据偏差不大,论证了上述分析的可靠性,为今后锚固工程的设计、施工提供了理论依据和技术支持。 相似文献
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一种双线性抗差状态估计方法 总被引:2,自引:2,他引:0
传统状态估计方法一般需要求解某个非线性非凸优化问题,并用基于梯度的方法予以求解,因而存在难以保证获得全局最优解、可能收敛困难等问题。文中基于国外学者提出的精确线性化量测方程构建了一种双线性抗差状态估计方法。该方法仅需求解一个线性加权最小绝对值估计问题(等价为线性规划问题)、一个非线性变换以及一个线性加权最小二乘估计问题(二次规划问题),从数学上可保证获得全局最优解,并不存在收敛性问题。最后,通过仿真算例验证了所提方法的有效性。 相似文献
48.
从实际改造工作出发,研究分析传动滚筒上物料运动轨迹的三种形式,进而根据实际情况确定滚筒的位置。这样,不仅提高了生产率,还有效地解决了实际工作过程中的各种附属问题,对皮带输送设备的安装和改进具有一定的指导作用。 相似文献
49.
Thomas Veltzke Lars Kiewidt Jorg Thöming 《American Institute of Chemical Engineers》2015,61(4):1404-1412
In many technical processes gas, multicomponent diffusion takes place in confinements that are rarely uniform in direction of their long axis (e.g., catalysts pores). Here, we show that in conical tubes multicomponent diffusion is hindered. This effect increases with ratio of inlet to outlet cone radius Λ, indifferent of the orientation of the tube. Based on the Maxwell–Stefan equations, predictive analytical solution for ideal multicomponent diffusion in slightly tapered ducts is developed. In two‐bulb diffusion experiments on a uniform tube, the results of Duncan and Toor (1962) were reproduced. Comparison of model and experiment shows that the solution presented here provides a reliable quantitative prediction of the temporal change of H2, N2, and CO2‐concentration for both tube geometries, uniform and slightly conical. In the demonstrated case (Λ = 3.16), mass diffusion is 68% delayed. Thus, for gaseous diffusion in “real,” typically tapered pores the transport limitation is more serious than considered so far. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1404–1412, 2015 相似文献
50.
Sarah E. Feicht George D. Degen Aditya S. Khair 《American Institute of Chemical Engineers》2015,61(4):1447-1454
The aim of this paper is to analyze moving front dynamics of ions and holes in a planar, mixed ionic‐electronic conducting polymer film. As cations invade the film, holes evacuate; thus, an ionic current is converted to an electronic signal. Recent experiments show that the location of the advancing ion front increases as the square‐root of time, a scaling typically associated with diffusive transport, which is surprising given the large driving voltages utilized. Ionic and electronic transport is modeled via the drift‐diffusion equations. A similarity transformation reduces the governing partial differential equations to ordinary differential equations that are solved numerically. The similarity transformation elucidates the origin of the square‐root‐of‐time front scaling. The similarity solution is then compared to the numerical solution of the full drift‐diffusion equations, finding excellent agreement. When compared with experimental data, our model captures the front location; however, qualitative differences between the ion profiles are observed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1447–1454, 2015 相似文献