Pressure drop in a split‐and‐recombine caterpillar micromixer in case of newtonian and non‐newtonian fluids

Abstract

Microreactors are very promising tools for the design of future chemical processes. For example, emulsions of very narrow size distribution are obtained at much lower energy consumption than the one spent with usual processes. Micromixers play thereby an eminent role. The goal of this study is to better understand the hydrodynamic properties of a split-and-recombine Caterpillar micromixer (CPMM) specially with regard to handling viscoelastic fluids, a topic hardly addressed so far in the context of micromixers in general, although industrial fluids like detergent, cosmetic, or food emulsions are non-Newtonian. Friction factor was measured in a CPMM for both Newtonian and non-Newtonian fluids. For Newtonian fluids, the friction factor in the laminar regime is f/2 = 24/Re. The laminar regime exists up to Reynolds numbers of 15. For shear-thinning fluids like Carbopol 940 or viscoelastic fluids like Poly Acryl Amide (PAAm) aqueous solutions, the friction factor scales identically within statistical errors up to a generalized Reynolds number of 10 and 0.01, respectively. Above that limit, there is an excess pressure drop for the viscoelastic PAAm solution. This excess pressure drop multiplies the friction factor by more than a decade over a decade of Reynolds numbers. The origin of this excess pressure drop is the high elongational flow present in the Caterpillar static mixer applied to a highly viscoelastic fluid. This result can be extended to almost all static mixers, because their flows are generally highly elongational

A Review of Passive Micromixers with a Comparative Analysis

“…Several micromixers involving 3D serpentine and/or SAR structures [42][43][44][45][46][47][48][49][59][60][61][62][63][64][65][66][67]80,81] (type 3 in Table 1) have been proposed. The 3D serpentine path induces a stirring flow at each bend and generates a secondary flow to enhance mixing [43,45].…”

Continuous Flow Methods of Fabricating Catalytically Active Metal Nanoparticles

“…(c) Schematic of the internal structure of a ramp-like caterpillar micromixer that drives split-and-recombine mixing. Reprinted with permission from ref . Copyright 2013 Wiley-VCH.…”

“…Parallel lamination of the fluids into very thin interdigitated streams results in shorter stream interdiffusion distances, thus requiring shorter reactor lengths for mixing (Figure b). , Alternatively, chaotic advection can be achieved through careful design of the reactor architecture by implementing obstacles in the channel path, altering the wall with ridges or grooves, or by altering the reactor channel geometry from a straight line into a zigzag or serpentine pattern, which perturbs the flow and generates a transversal component to the velocity . For example, a micromixer, called the caterpillar mixer, developed by the Institute of Microtechnology Mainz (IMM), used the principle of splitting and recombining in which the two fluids are split into multiple streams (∼300) in a channel containing ramp-like structures (Figure c) . This structure facilitates subsequent recombination of the two fluid streams in both the horizontal and vertical directions through folding, reorientating, and recombining, resulting in superior mixing compared to typical, straight laminar flow devices.…”

Numerical investigation of the performance of 3D‐helical passive micromixer with Newtonian fluid and non‐Newtonian fluid blood

“…Additionally, non‐Newtonian fluids with different power‐law indices were studied, and they found that at a fixed Reynolds number, mixing index increases with an increase of power‐law index value. Carrier et al 28 conducted experiments to examine the pressure drop in a caterpillar micromixer (CPMM) for Newtonian and several non‐Newtonian fluids. The results depicted that for Newtonian fluids, the friction factor scaling was related as f/2 = 24/Re.…”