Micro-mixing is an important research area for various applications in sensing and diagnostics. In this paper, we present a performance comparison of several different passive micromixer designs based on the idea of staggered herringbone mixers (SHM). The working principle in such designs includes the formation of centers of flow rotation thus leading to multiple laminations with decreasing sizes of the lamellae as the flow passes over staggered structures. We have realized different layout designs of staggered herringbones inside micro-channels and compared their mixing performance. An overall reduction in mixing time and length has been observed as the degree of asymmetry within these structures is increased. The layouts of these staggered structures are based on herringbone bilayers wherein these layers are positioned on the top and bottom walls of a micro-channel. Fluorescence microscopy and computational fluid dynamics (CFD) based modeling have been used to observe the extent of mixing and understand the reasons behind the enhanced mixing effects. We have further varied the degree of asymmetry of the herringbone bilayers and investigated mixing as a function of the asymmetry. We have developed a novel microfabrication strategy to realize these micro-devices using an inexpensive non-photolithographic technique which we call micro-replication by double inversion (MRDI). The paper basically attempts to develop an overall understanding of the mixing process by letting two fluids flow pass over a variety of asymmetric structures.Keywords Micromixer Á Micromixing Á Staggered herringbones Á Microfabrication Á Micro-replication by double inversion (MRDI) Á Bilayer Á Asymmetry

This paper presents the behavior of solute transport through mobile-immobile (MIM) soil column based on the laboratory study. The study considers that the advective-dispersive transport equation is used for mobile domain, and the solute exchange between two liquid domains is described as the firstorder process. A numerical model is developed for the MIM advective-dispersive transport equation including equilibrium sorption and the first-order degradation. Afterward, the numerical model is used to simulate experimental breakthrough curves (BTCs) for transport of chloride and fluoride through heterogeneous soil column using constant, linear, and exponential distance-dependent dispersion models. It is shown that the behavior of concentration profile produced with a constant dispersion model is similar to the distance-dependent dispersion model. It is found that the constant dispersion and the exponential distance-dependent dispersion models simulate experimental BTCs reasonably well as compared to the linear distance-dependent dispersion model. Hence, the exponential distancedependent dispersion model is a simple and practical approach to describe the solute transport through the MIM porous media.

No abstract