Occurrence of coexisting dendrite morphologies: immiscible fluid displacement in an anisotropic radial hele-shaw cell under a high flow rate regime

Viscous fingering morphologies during the displacement of a high viscosity fluid by a low viscosity immiscible fluid in a radial fourfold anisotropic Hele-Shaw cell are examined. By using the kerosene-glycerin system for which the µ/T ratio (µ being the relative viscosity and T the interfacial tension between the fluids) is about ten times higher than that for the commonly used air-glycerin system, we have been able to access the hitherto unexplored Nca 1 regime (capillary number Nca=Uµ/T, U being the advancing fingertip velocity). Within the anisotropy-dominated regime, and when flow rates are significantly high (capillary number well beyond Nca=1), a new phase is seen to evolve wherein the dendrites grow simultaneously along the channels and along the directions making an angle of 45° with the channels, both being kinetically driven. This new phase resembles the one observed in a miscible fluid system at all flow rates of the displacing fluid

Viscous fingering of miscible fluids in an anisotropic radial hele-shaw cell: coexistence of kinetic and surface-tension dendrite morphology types and an exploration of small-scale influences

The evolution of viscous fingering morphology is examined for the case of a system of miscible fluids in an anisotropic radial Hele-Shaw cell. It is shown that dendritic morphologies similar to the kinetic and surface-tension morphology types coexist for this case. The critical role of the means of introducing anisotropy in the Hele-Shaw cell is established, and an explanation of the pattern behavior is offered on the basis of shape discontinuities of the individual elements of the lattice used to induce anisotropy. The ramifications of such an explanation are experimentally verified by demonstrating a clear difference in the morphology evolution in two halves of a single Hele-Shaw cell, one half of which contains square lattice elements, and the other half of which contains circular lattice elements

Variation in viscous fingering pattern morphology due to surfactant-mediated interfacial recognition events

The study of the formation of finger-like patterns during displacement of a viscous fluid by a less viscous one is of technological importance. The morphology of the viscous-finger patterns generated is a function of many parameters such as the flow rate, difference in viscosities of the two fluids and the interfacial tension. We demonstrate herein that the morphology of patterns formed during viscous fingering in a Hele-Shaw cell during displacement of paraffin oil by aqueous solutions of the surfactant sodium dodecyl sulphate (SDS), is extremely sensitive to interfacial tension variation brought about by complexation of divalent cations with the surfactant SDS. The variation in morphology of the patterns formed has been quantified by measuring the fractal dimensions of structures formed in a radial Hele-Shaw cell as well as the average finger width in a linear Hele-Shaw cell. This technique shows promise for studying other interfacial phenomena in chemistry such as biorecognition as well as dynamic processes occurring at interfaces

Microdevices for extensional rheometry of low viscosity elastic liquids : a review

Extensional flows and the underlying stability/instability mechanisms are of extreme relevance to the efficient operation of inkjet printing, coating processes and drug delivery systems, as well as for the generation of micro droplets. The development of an extensional rheometer to characterize the extensional properties of low viscosity fluids has therefore stimulated great interest of researchers, particularly in the last decade. Microfluidics has proven to be an extraordinary working platform and different configurations of potential extensional microrheometers have been proposed. In this review, we present an overview of several successful designs, together with a critical assessment of their capabilities and limitations

Biosurfactants’ Production from Renewable Natural Resources: Example of Innovativeand Smart Technology in Circular Bioeconomy

A strong developed bio-based industrial sector will significantly reduce dependency on fossil resources, help the coun-tries meet climate change targets, and lead to greener and more environmental friendly growth. The key is to develop new technologies to sustainably transform renewable natural resources into bio-based products and biofuels. Biomass is a valuable resource and many parameters need to be taken in to account when assessing its use and the products made from its. The bioeconomy encompass the production of renewable biological resources and their conversion into food, feed and bio-based products (chemicals, materials and fuels) via innovative and efficient technologies provided by indus-trial biotechnology. The paper presents the smart and efficient way to use the agro-industrial, dairy and food processing wastes for biosurfactant’s production. Clarification processes are mandatory to use the raw substrates for microbial growth as well as biosurfactant production for commercial purposes. At the same time it is very essential to retain the nutritional values of those cheap substrates. Broad industrial perspectives can be achieved when quality as well as the quantity of the biosurfactant is considered in great depth. Since substrates resulting from food processing, dairy, animal fat industries are not explored in great details; and hence are potential areas which can be explored thoroughly

BIOSURFACTANTS’ PRODUCTION FROM RENEWABLE NATURAL RESOURCES: EXAMPLE OF INNOVATIVEAND SMART TECHNOLOGY IN CIRCULAR BIOECONOMY

A strong developed bio-based industrial sector will significantly reduce dependency on fossil resources, help the coun-tries meet climate change targets, and lead to greener and more environmental friendly growth. The key is to develop new technologies to sustainably transform renewable natural resources into bio-based products and biofuels. Biomass is a valuable resource and many parameters need to be taken in to account when assessing its use and the products made from its. The bioeconomy encompass the production of renewable biological resources and their conversion into food, feed and bio-based products (chemicals, materials and fuels) via innovative and efficient technologies provided by indus-trial biotechnology. The paper presents the smart and efficient way to use the agro-industrial, dairy and food processing wastes for biosurfactant’s production. Clarification processes are mandatory to use the raw substrates for microbial growth as well as biosurfactant production for commercial purposes. At the same time it is very essential to retain the nutritional values of those cheap substrates. Broad industrial perspectives can be achieved when quality as well as the quantity of the biosurfactant is considered in great depth. Since substrates resulting from food processing, dairy, animal fat industries are not explored in great details; and hence are potential areas which can be explored thoroughly

Numerical simulations of growth dynamics of breath figures on phase change materials: The effect of accelerated coalescence due to droplet motion

We present the growth dynamics of breath figures on phase change materials using numerical simulations. We propose a numerical model which accounts for both growth due to condensation and random motion of droplets on the substrate. We call this model as growth and random motion (GRM) model. Our analysis shows that for dynamics of droplet growth without droplet motion, simulation results are in good agreement with well-established theories of growth laws and self-similarity in surface coverage. We report the emergence of a growth law in the coalescence-dominated regime for the droplets growing simultaneously by condensation and droplet motion. The overall growth of breath figures (BF) exhibits four growth regions, namely, initial $\langle R \rangle \sim t^{\alpha_1 }$ , intermediate or crossover $\langle R \rangle \sim t^{\alpha_2 }$ , coalescence-dominated regime $\langle R \rangle \sim t^{\alpha_3 }$ , and no coalescence regime in late time $\langle R \rangle \sim t^{\alpha_4 }$ , where $\langle R \rangle$ and t are the average droplet radius and time, respectively. The power law exponents are $\alpha_1 \approx 1/2$ , $\alpha_2 \approx 1.0$ , $\alpha_3 \approx 3.0$ , and $\alpha_4 \approx 1/3$ . Moreover, the surface coverage reaches a maximum value $\varepsilon^2 \approx 0.35$ where the third growth regime $t^{\alpha_3 }$ starts. We also demonstrate that during the growth dynamics of BF, the random motion amplitude δ and its probability p(R) linked to the power exponent γ of droplet radius R have a specific limiting range within which its effect is more predominant