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• Superhydrophobic coatings were fabricated with edible waxes via one step spray process. • The resulted surface can repel not only water but also various non-Newtonian viscous food liquids. • The superhydrophobic surface exhibited excellent resistance to repeated bends and several abrasion damages. • The coating can be applied to all kinds of food packaging inner surface. Superhydrophobic coatings were fabricated with edible candelilla wax and rice bran wax via one step spraying a wax-in-ethanol hot solution on polypropylene (PP) substrates for food containers. Beautiful "flower-like" surface microstructures were formed only by self-roughening of the coating without adding any nanomaterials or any lithography step, making the coatings display great superhydrophobicity for a variety of non-Newtonian viscous liquids with contact angles higher than 150° and sliding angles close to 0°. The as-coated PP can keep excellent superhydrophobic properties after impact from hot aqueous solution (about 70 °C) or 1200 repeated bends, exhibiting good heat resistance and superior flexibility. Importantly, the excellent durability could make it super-repel non-Newtonian fluids after various types of damage (including finger touching and multiple abrasion cycles with sandpaper). This approach can be applied to the inner surface of all kinds of food packaging to reduce liquid food residue. [ABSTRACT FROM AUTHOR]

Highlights • Micromixing efficiency in RPB with non-Newtonian fluid was studied experimentally. • A 2D CFD model coupled with shear-thinning rheological property was developed. • Effects of operating conditions were discussed by experiment and CFD results. • RPB micromixing time with non-Newtonian fluid ranged from 4.1 × 10−4 to 1.9 × 10−3 s. Abstract Micromixing performance of reactors has great influence on fast reactions such as polymerization, pharmaceutical and crystallization applications. In this work, based on Villermaux–Dushman iodide–iodate reaction system, an experimental investigation of micromixing with non-Newtonian fluid (CMC solution) in a rotation packed bed (RPB) was carried out. And a two-dimensional RPB Computational Fluid Dynamics (CFD) model coupled with shear-thinning rheological property was developed. Both experimental and numerical results indicated that increasing rotational speed could dramatically improve the micromixing performance due to the shear-thinning behavior in the RPB. Especially, the CMC concentration was an important factor that should be carefully considered, which showed quite different impacts on micromixing efficiency with liquid flow rate. In addition, based on incorporation model and experimental results, the micromixing time of the RPB with non-Newtonian fluid was determined as 4.1 × 10−4 s–1.9 × 10−3 s. This fundamental research had guiding significance for practical operations of RPBs when processing non-Newtonian fluids. [ABSTRACT FROM AUTHOR]

• Multi-physics model and multi-objective optimization algorithm are established. • The effect of outlet angles of MCR on optimal configurations is revealed. • Darcy friction term is modified using a polynomial function. • Strict volume constraints and pseudo-design domain concept are introduced. • The optimal configurations of NMCR and nNMCR are obtained. This study proposes an improved multi-objective density-based topology optimization (TO) model for Newtonian and non-Newtonian fluid micro-channel reactor(NMCR, nNMCR) to substantially improve the overall performance of MCR. Flow, catalytic reaction, and heat transfer in MCR under constant pressure driving is described by built a multi-physics model of continuous-flow exothermic reaction. TO adopts the material density as the design variable to control the changes in fluid and solid domains. The artificial Darcy friction improved by polynomial function is used to add the impermeability of intermediate density, and the Helmholtz partial differential filter and hyperbolic tangent projection are applied to eliminate the checkerboard phenomenon and structural ill-conditioning. The improved multi-objective algorithm based on the weighted-sum method and pseudo-design domain concept are proposed to avoid the local topological structure simplification and unreasonable. In examples, the effects of reactor geometries and outlet angles θ on optimal configurations and performance parameters of NMCR and nNMCR are investigated. Additionally, optimal solution set under multi-objective functions with different weight factors ω 1 is solved, and Pareto frontier is established accordingly to reveal the trade-off relationship between the single-objectives. MCR responds to the proportion increase of flow single-objective in multi-objective function by homogenizing the local catalyst blocks distribution and increasing the flow channel length, thereby affecting the flow, diffusion and mixing. The local catalyst distributions of NMCR and nNMCR are significantly different due to different fluid properties. From the perspective of engineering, this study provides an efficient and applicable optimization method for designing MCR with higher comprehensive performance. [ABSTRACT FROM AUTHOR]

Complex rheology of non-Newtonian fluids often leads to non-homogenous mixing due to the spatial viscosity gradients. The non-intrusive electrical resistance tomography (ERT) technique was employed to study the mixing of non-Newtonian fluids in a chaotic SMX static mixer. For the first time, the effect of the rheology of the yield-pseudoplastic fluids on the quality of distributive mixing was explored in this study. The non-Newtonian fluid used in this study was the xanthan gum solution, which is a yield-pseudoplastic fluid obeying the Herschel-Bulkley model and its rheological parameters change as the solution mass concentration increases. The tomography images were utilized to investigate the efficacy of the distributive mixing of two different types of the secondary streams (Newtonian and non-Newtonian) in the primary stream of xanthan gum solutions (0.5 wt%, 1.0 wt%, and 1.5 wt%). Experiments were conducted for three different primary flow rates ranging from 3.5 L/min to 12.5 L/min while keeping the center-line injection of secondary stream fixed at 100 mL/min for all experiments. Our results revealed that the Newtonian secondary stream favored effective axial mixing over the non-Newtonian secondary stream. However, interestingly, for both types of the secondary streams, a more effective radial mixing was observed as the xanthan gum mass concentration increased at low Reynolds numbers. [ABSTRACT FROM AUTHOR]

Many chemical and biochemical processes operated in airlift reactors are limited by the gas-liquid mass transfer of the reactants. Therefore, it is essential to have good understanding of the mass transfer characteristics and gas distribution in airlift reactors to be able to design effective reactors and to optimize aeration conditions. To accomplish this goal, experimental studies on the mass transfer characteristics, i.e. gas holdup, bubble size, interfacial area, volumetric mass transfer coefficient and liquid-side mass transfer coefficient were performed in an annulus-rising airlift reactor with Newtonian and non-Newtonian fluids. A 3D electrical impedance tomography (EIT) technique was used to measure local gas holdup and visualize gas distribution. The influences of aeration rate and liquid viscosity on local gas holdup and interfacial area were investigated at three axial positions along the riser. The EIT results show that the uniformity of gas distribution reduces with increasing liquid viscosity. Bubble size was observed to have a bimodal distribution in highly viscous liquids at high gas superficial velocities due to the intensified coalescence and breakup of bubbles. The maximum value of the local interfacial area is found at the fully developed flow zone in the riser. The liquid-side mass transfer coefficient was found to depend on liquid viscosity and bubble size for non-Newtonian liquids. Empirical correlations based on the experimental data obtained in this work predict well the local gas holdup and volumetric mass transfer coefficient. [ABSTRACT FROM AUTHOR]

In the present work, non-Newtonian properties of activated sludge are investigated using a bench test device specially developed for the purpose of this work. This set-up consists in a bioreactor equipped with a helical ribbon impeller (HRI configuration), and a recirculation loop of the sludge (pipe flow (PF) configuration). The HRI configuration is equipped with a motor and a torque-meter allowing in situ determination of sludge rheogram under stirred reactor conditions. On the PF configuration, differential pressure and flow transducers are implemented, allowing in situ determination of sludge rheogram under piping conditions. Both configurations are then compared. The yield stress, flow and consistency indexes of sludge suspensions (Herschel–Bulkley rheological law coefficients, τ y , K and n ) are determined over a large range of total suspended solid (TSS) concentrations, (12–38 g L −1 ) in the laminar flow regime. The analysis of experimental data shows that measurements performed with the PF configuration have to be corrected in order to take into account a wall slip phenomenon. A correction model is proposed that shows that slip mechanism is mostly due to wall static depletion at low solid concentrations (12–17 g L −1 ), then turns to shear induced migration effect at higher solid concentrations (26–38 g L −1 ). [ABSTRACT FROM AUTHOR]

• The novel designs of micromixer were obtained based on topology optimization method. • The mixing quality maximization problem of topology optimization was formulated. • The mixing mechanism for non-Newtonian fluid at low Reynolds number was investigated. Improving the mixing performance is a crucial and widely concerned topic in microfluidic devices for low Reynolds numbers (Re). In this paper, the mixing unit as the design domain in a typical T-shape micromixer considering non-Newtonian fluid effects is investigated using topology optimization. The objective of topology optimization is to maximize the mixing quality under the prescribed pressure drop of the micromixer. Based on the optimized structures obtained by topology optimization, high-fidelity calculations are performed to eliminate the influence of the greyscale problem. For the Newtonian fluid, the optimized structure has better mixing performance than the reference structure with the same pressure drop. For the non-Newtonian fluid, cross-comparison is conducted to obtain the optimized structure. The results show that the mixing qualities of the 25-period mixing unit are 93.90% (Newtonian fluid, Re = 8) and 93.84% (non-Newtonian fluid, Re = 0.24), respectively. [ABSTRACT FROM AUTHOR]

Abstract: A numerical investigation is performed into the mixing characteristics of electrokinetically-driven non-Newtonian fluids in microchannels containing patterned blocks. In performing the simulations, the rheological behavior of the fluid is described using a power-law model. Two different types of patterned blocks are considered, namely rectangular and wavy. The effects of the geometry parameters of the patterned blocks and the flow behavior index in the power-law model on the mixing efficiency within the microchannel are systematically explored. The results show that the rectangular patterned blocks yield a better mixing performance than the wavy patterned blocks. However, for both types of block, the mixing efficiency can be improved by increasing the width and length of the blocks and extending the total length of the block region. In addition, the results show that the flow behavior index in the power-low model has a significant effect on the mixing performance. Specifically, the volumetric flow rate increases with a decreasing flow behavior index, and therefore results in a poorer mixing performance. It is shown that a heterogeneous patterning of the zeta potential on the upper surfaces of the rectangular and wavy blocks prompts the formation of local flow recirculations, and therefore improves the mixing efficiency. In addition, it is shown that the mixing performance improves with an increasing magnitude of the heterogeneous surface zeta potential. Overall, the results show that the mixing efficiency of non-Newtonian fluids with a low flow behavior index can be improved by utilizing blocks with an appropriate geometry, applying a heterogeneous distribution of the surface zeta potential, and increasing the magnitude of the zeta potential. [Copyright &y& Elsevier]

Abstract: Gas holdup, bubble behavior, interfacial area and gas–liquid mass transfer in a 5m internal-loop airlift reactor with non-Newtonian fluid were studied in the superficial gas velocity (U g) range of 2–12cm/s. Air and aqueous CMC solutions of 0–0.45wt% were used as the gas and liquid phases, respectively. It was found that increased U g or CMC concentration led to a wider bubble size distribution and an increase in the bubble Sauter diameter. The volumetric mass transfer coefficient increased with an increase in U g and a decrease in CMC concentration. In the air–water system, k l a/α g was found to be independent of U g and was 0.21/s, and a constant liquid-side mass transfer coefficient (k l) was found in the heterogeneous regime. However, in the air–CMC solution system, the influences of the superficial gas velocity and liquid viscosity were much more complicated: k l a/α g was not constant and was affected by the superficial gas velocity and CMC concentrations; the interfacial area increased with an increase in U g and a decrease in CMC concentration; k l increased more significantly with increasing U g, and no obvious trend was found for the influence of CMC concentration on k l. [Copyright &y& Elsevier]

Abstract: The coalescing mechanism of in-line two-unequal bubbles rising in a bubble column with a non-Newtonian fluid has been experimentally studied. The non-Newtonian fluid is the 1.5wt% polyacryamide in demineralized water and the bubble gas is air. Both qualitative flow visualization and quantitative full-field measurements using particle image analyzer have been conducted for two examples of two-unequal bubble coalescences. The instantaneous flow structure and the shear stress contour varying in different time lags are presented. As two-unequal bubbles are getting closer, the drained liquid is circulated to the back of the trailing bubble. Due to the drainage flow and the mutual interactions, the flow structure and the shear stress contour show a dramatic change from a two independent bubbles to a single bubble. Due to encounter these dynamic flow structures, the shape of the trailing bubble also has serial changes. However, the case of large trailing bubble with large momentum can affect the deformation of the small leading bubble earlier. Due to the dragging force caused by the negative pressure and the shear-thinning effect and the pushing force caused by the viscoelastic effect, the acceleration of the trailing bubble to the leading bubble is evident. It was found that the coalescence of two-unequal bubbles has higher acceleration than the coalescence of two-equal bubbles. [Copyright &y& Elsevier]

A model of liquid-to-particle mass transfer in packed beds with single phase non-Newtonian creeping flow is derived using a coherent approach which associates the Le´veˆque solution with a capillary-type representation of the porous structure. The model is compared to experimental data obtained with spherical and anisotropic parallelepipedal particles, respectively, as well as to literature results. The model allows to predict mass transfer in fixed beds of spheres and anisotropic parallelepipedal particles with a mean relative error of 11%. It is also shown that a better prediction of mass transfer is obtained for parallelepipedal particles if the surface area really offered to fluid flow is considered. Dimensionless numbers based on the pore dimension are shown to be more suitable than those based on a particle diameter. [Copyright &y& Elsevier]

• The multi-objective optimization method is developed for thermal-fluid problems. • Pareto-optimal solutions based on the multi-objective function are provided. • A novel model for heat transfer enhancement and pressure drop reduction. • The influence of non-Newtonian fluid on the microchannel heat transfer system is considered. This paper presents a multi-objective topology optimization method for convective heat transfer problems based on Navier-Stokes and heat transport equations. In this research, the pressure drop (or energy dissipation) function and the recoverable thermal power function are combined and optimized as a multi-objective function. A Pareto algorithm is constructed, based on a weighted-sum method using different weight coefficients. The Pareto solutions composed of a set of optimal solutions are obtained to reveal the trade-off relationship between the objective functions. The effects of non-Newtonian fluid on the flow-channel arrangement and heat transfer performance are numerically studied. In the numerical method, the interpolation term in the density-based topology optimization method is modified, while the filtering method is used to solve the problems of grayscale and the flow channel discontinuity. The results show that the differences between the optimal structures for non-Newtonian fluid and Newtonian fluid are more obvious at Re = 0.01 in the dual-terminal devices. Under the same situation, blood (non-Newtonian fluid) has greater energy dissipation and better heat transfer performance than water (Newtonian fluid). [ABSTRACT FROM AUTHOR]

• The No-moving-part microvalves are modified based on topology optimization. • The influence of non-Newtonian fluids on the microfluidic system is considered. • The reversed area makes Tesla microvalve have a highlighted advantage in comprehensive performance. • Tesla microvalve is an outstanding microdevice with diode performance of the sample. This paper proposed a topology optimization method for modifying the No-moving-part (NMP) microvalves to enhancing performance and reducing drive power. No-moving-part microvalves are check microvalves without movable devices, which allow fluid to pass freely in one direction while hindering flow in the reverse direction. They only depend on the inertial force of flow rather than the mechanical mechanism. Taking into account that the fluid being transferred in the microsystem is often a biological or chemical medium, the non-Newtonian fluid (such as blood) is selected necessarily for optimization. At the same time, several previous studies have widely used diodicity to indicate the performance of NMP microvalves. However, higher diodicity does not reflect the degree of forwarding energy dissipation, leading to a significant pumping power to drive flow. Therefore, the pressure drop of forwarding flow and the performance of the NMP microvalve are handled independently by a bi-objective formulation, during the design of the NMP microvalve. In the numerical implementation, Helmholtz-type Partial Differential Equation (PDE) based filter and smoothed Heaviside projection filter are utilized to produce discrete solutions, thus solving ill-posedness. This paper presents a density-based bi-objective topology optimization (TO) method of Tesla microvalves, in which the modified artificial Darcy friction force term is added to the Navier-Stokes equations. Finally, several numerical examples of the bi-objective functions are studied and the validity of the topology optimization method presented in this paper is demonstrated. [ABSTRACT FROM AUTHOR]

• New power & Reynolds numbers for gas dispersion in non-Newtonian fluids were proposed. • Gas-liquid mixture properties were incorporated into the new correlations for the first time. • A critical speed ratio in upward pumping co-rotating mode was identified. • Above the critical speed ratio, the anchor acted as a barrier against the flow. • The critical speed ratio was a function of the anchor speed and fluid rheology. Coaxial mixers are efficient in mixing of highly viscous fluids. The main objective of this study was to assess the power consumption for the gas dispersion in carboxymethyl cellulose solution, a power-law non-Newtonian fluid, with a coaxial mixer consisting of an anchor impeller and two central impellers as a function of the speed ratio (central impeller speed/anchor speed), fluid rheology, pumping direction of the central impeller, and the rotation mode (co-rotating vs. counter-rotating). This goal was achieved using both experimental and numerical approaches. A computational fluid dynamic model (CFD) was developed and validated using the experimental data. Electrical resistance tomography (ERT) was employed to measure the gas holdup. New equivalent impeller speed and diameter were defined and two novel correlations for the Power number and Reynolds number were proposed and successfully validated at different operating conditions. Additionally, new dimensionless correlations for the ratio of the gassed to un-gassed power consumption and the aerated power number as a function of the flow number, Froude number, and Reynolds number were developed and successfully tested for different coaxial mixing configurations. [ABSTRACT FROM AUTHOR]