Liquid - liquid flows in microchannels

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In this work the flow patterns are investigated during the flow of an ionic liquid and deionized water mixture in a glass microchannel (0.2mm I.D) for two different inlet configurations (T- and Yjunction). The density, viscosity and surface tension of the ionic liquid [C4mim][NTf2] are 1420kg/m3 , 0.029Pa·s and 31.92mN/m respectively. The water phase has a density of 1000kg/m3, a viscosity of 0.001Pa·s and a surface tension of 73,69mN/m. In most of the patterns observed water was the continuous phase with the ionic liquid forming plugs or a mixture of plugs and drops within it. With the Y-junction and at high mixture velocities a separated pattern was observed with the two fluids flowing in parallel along the channel for the middle range of ionic liquid fractions, while water dispersed as drops was found at high ionic liquid fractions. Pressure drop was measured during regular plug flow which revealed that for the same ionic liquid superficial velocity the pressure drop was lower when it flowed in a mixture with water than when it was on its own in the channel. For a xonstant ionic liquid flow rate, pressure drop decreased as the ionic liquid fraction increased.The project is funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Energy Institute at UCL

Surfactant effects on the coalescence of a drop in a Hele-Shaw cell

In this work the coalescence of an aqueous drop with a flat aqueous-organic interface was investigated in a thin gap Hele-Shaw cell. Different concentrations of a nonionic surfactant (Span 80) dissolved in the organic phase were studied. We present experimental results on the velocity field inside a coalescing droplet in the presence of surfactants. The evolution of the neck between the drop and the interface was studied with high-speed imaging. It was found that the time evolution of the neck at the initial stages of coalescence follows a linear trend, which suggests that the local surfactant concentration at the neck region for this stage of coalescence can be considered quasiconstant in time. This neck expansion can be described by the linear law developed for pure systems when the surfactant concentration at the neck is assumed higher than in the bulk solution. In addition, velocity and vorticity fields were computed inside the coalescing droplet and the bulk homophase using a high-speed shadowgraphy technique. The significant wall effects in the Hele-Shaw cell in the transverse axis cause the two vertical velocity components towards the singularity rupture point, from the drop and from the bulk homophase, to be of the same order of magnitude. This movement together with the neck expansion creates two pairs of counteracting vortices in the drop and in the bulk phase. The neck velocity is the average of the advection velocities of the two counteracting vortex pairs on each side of the neck. The presence of the surfactant slows down the dynamics of the coalescence, affects the propagation direction of the pair of vortices in the bulk phase, and reduces their size faster compared to the system without surfactant

Mixing patterns in water plugs during water/ionic liquid segmented flow in microchannels

Circulation patterns and mixing characteristics within water plugs in liquid/liquid segmented flow were investigated by means of micro-Particle Image Velocimetry. Experiments were carried out in a glass microchannel with circular cross-section of 100 μm radius using [C4mim][NTf2] ionic liquid as the carrier fluid. A T-junction was used as inlet, while mixture velocities varied from 0.0028 m/s to 0.0674 m/s. Two main circulation vortices were found within the plugs while at intermediate mixture velocities two additional secondary vortices appeared at the plug front. The mixing rate was locally quantified by means of the non-dimensional circulation time, which was calculated across the plug length. Consistently with the circulation patterns, the non-dimensional circulation time was found to have a profile along the direction of the flow that mirrors the shape of the plug, with a minimum at the axial location of the vortex cores (where the circulation velocity is maximum at the channel centre) while it tended to infinity towards the liquid/liquid interfaces. For all the experiments the minimum value of the circulation time fell within the range of 1.00–1.75. For increasing mixture velocities (i.e. increasing Ca) and sufficiently long plugs (εIL=0.4) a general decrease (i.e. higher mixing rate) of the circulation time minimum was found, although the behaviour was rather complex. On the other hand, the circulation velocity linearly increased as the Ca number (mixture velocity) increased

Simplified mechanistic model for the separation of dispersed oil-water horizontal pipe flows

A mechanistic model that predicts the separation of oil-water dispersed horizontal pipe flows was investigated. Different droplet diameter averages were implemented in the model and the accuracy of the resulting predictions was assessed by comparing each case against experimental data. The experimental data used was obtained in a pilot scale two-phase flow facility using tap water and oil (828 kg m-3, 5.5 mPa s) as test fluids. The results show that the separation length is highly sensitive to the drop diameter, but further investigation is required to determine which drop diameter average produces more accurate predictions of the flow profile

Computational fluid dynamic studies of mixers for highly viscous shear thinning fluids and PIV validation

Agitation of highly viscous shear thinning fluids is normally conducted with complex impeller designs. Often, impellers almost as large as the tanks containing them and impeller blades equipped with holes are adopted in industry. In this work, we studied experimentally the main features of the flow generated by this type of impellers for a mixture of glycerol with a carbomeric gel by means of particle image velocimetry. The experiments were conducted at temperatures ranging from 40 to 60 °C and impeller speeds ranging from 40 to 140 rpm. In all cases, the flow regime was laminar or in the transition region. We also used computational fluid dynamics simulations to describe the behaviour of the mixer, validating the results experimentally with good agreement. We used the numerical results to obtain information on the performance of the mixer, determining the locations and size of vigorous agitation zones and the local effect of the holes present on the impeller blades. The power curves of the mixer were obtained, and the mixer efficiency in terms of power consumption was found to be similar to other impellers used to mix highly viscous non-Newtonian fluids

Side-effects of a number of insecticides on predatory mites in apple orchards

Background: Amblyseius andersoni is a common predatory mite occurring in fruit orchards located in Europe and North America. Its role in preventing spider mite outbreaks is widely recognized, in particular when selective pesticides are used. The compatibility between plant protection products and predatory mites is crucial to preserve their activity. There is a need to investigate the effects of pesticides on beneficials using multiple approaches. Objectives: Field and laboratory experiments were conducted to evaluate the effects of a number of insecticides on A. andersoni. Methods: The effects of neonicotinoids (i.e., acetamiprid, imidacloprid, thiacloprid, thia-methoxam) were compared with those of pyrethroids (i.e., tau-fluvalinate), well known for their negative impact on predatory mites. Insecticides were applied 1-3 times in an experimental fruit orchard located in Northern Italy. Laboratory trials focused on their effects on the survival and the fecundity of predatory mite females. Results: Field experiments showed a decline in predatory mite numbers in plots treated with neonicotinoids or tau-fluvalinate compared to the untreated control. However, predatory mites in neonicotinoid plots reached higher densities compared to those recorded in tau-fluvalinate plots. Spider mite (Panonychus ulmi) populations reached moderate to high densities in plots treated with tau-fluvalinate while their densities were negligible in the remaining plots. Amblyseius andersoni survival was moderately affected by some neonicotinoids in the laboratory while they significantly reduced predatory mite fecundity. In contrast tau-fluvalinate exerted severe effects on survival and fecundity of predatory mites. Finally, escaping rate increased after pesticide exposure suggesting possible alterations in predatory mite behavior. Conclusions: Neonicotinoid applications significantly affected predatory mite densities in field conditions and this phenomenon appeared to be influenced by their impact on female fecundity. Their effects on survival were less severe. Implications of these results for IPM tactics in fruit orchards are discusse

Optical measurements in evolving dispersed pipe flows

Optical laser-based techniques and an extensive data analysis methodology have been developed to acquire flow and separation characteristics of concentrated liquid–liquid dispersions. A helical static mixer was used at the inlet of an acrylic 4 m long horizontal pipe to actuate the dispersed flows at low mixture velocities. The organic (913 kg m−3, 0.0046 Pa s) and aqueous phases (1146 kg m−3, 0.0084 Pa s) were chosen to have matched refractive indices. Measurements were conducted at 15 and 135 equivalent pipe diameters downstream the inlet. Planar laser induced fluorescence (PLIF) measurements illustrated the flow structures and provided the local in-situ holdup profiles. It was found that along the pipe the drops segregate and in some cases coalesce either with other drops or with the corresponding continuous phase. A multi-level threshold algorithm was developed to measure the drop sizes from the PLIF images. The velocity profiles in the aqueous phase were measured with particle image velocimetry (PIV), while the settling velocities of the organic dispersed drops were acquired with particle tracking velocimetry (PTV). It was also possible to capture coalescence events of a drop with an interface over time and to acquire the instantaneous velocity and vorticity fields in the coalescing drop

Species-specific secondary metabolites from Primula veris subsp. veris obtained In Vitro adventitious root cultures: an alternative for sustainable production

Primula veris subsp. veris L. is a perennial herbaceous and medicinal plant species the roots and flowers of which are a source of valuable pharmaceutical raw materials. The plant tissues are used to produce expectorant and diuretic drugs due to their high content of triterpene saponins and phenolic glycosides. Underground roots of P. veris can be obtained only through a destructive process during the plant’s harvesting. In the present study, an in vitro adventitious root production protocol was developed as an alternative way of production, focused on four species-specific secondary metabolites. Root explants were cultured in Murashing & Skoog liquid medium supplemented with 5.4 µM α-naphthaleneacetic acid, 0.5 µM kinetin, L-proline 100 mg/L, and 30 g/L sucrose, in the dark and under agitation. The effect of temperature (10, 15 and 22 ◦C) on biomass production was investigated. The content of two flavonoid compounds (primeverin and primulaverin), and two main triterpene saponins (primulic acid I and II) were determined after 60 days of culture and compared with 1.5-year-old soil-grown plants. The accumulated content (mg/g DW) of bioactive compounds of in vitro adventitious roots cultured under 22 ◦C was significantly higher than the other two temperatures of the study, being 9.71 mg/g DW in primulaverin, 0.09 mg/g DW in primeverin, 6.09 mg/g DW in primulic acid I, and 0.51 mg/g DW in primulic acid II. Compared to the soil-grown roots (10.23 mg/g DW primulaverin, 0.28 mg/g DW primeverin, 17.01 mg/g DW primulic acid I, 0.09 mg/g DW primulic acid II), the in vitro grown roots at 22 ◦C exhibited a 5.67-fold higher content in primulic acid II. However, primulic acid I and primeverin content were approximately three-fold higher in soil-grown roots, while primulaverin content were at similar levels for both in vitro at 22 ◦C and soil-grown roots. From our results, tissue culture of P. veris subsp. veris could serve not only for propagation but also for production of species-specific secondary metabolites such as primulic acid II through adventitious root cultures. This would therefore limit the uncontrolled collection of this plant from its natural environment and provide natural products free from pesticides in a sustainable wa

New clinical and pathophysiological perspectives defining the trajectory of cirrhosis

Traditionally, the complications of cirrhosis, namely variceal bleeding, ascites and hepatic encephalopathy, were thought to result predominantly from circulatory dysfunction and altered organ perfusion arising as a result of portal hypertension. Over the past 20 years, large, international prospective studies have indicated the importance of systemic inflammation and organ immunopathology as additional determinants of organ dysfunction in cirrhosis, which not only manifests in the liver, brain, circulation and the kidneys, but also the immune system, gut, muscles, adrenal glands, reproductive organs, heart and lungs. This review provides an overview of the traditional and emerging concepts around the initiation and maintenance of organ dysfunction in cirrhosis and proposes a new paradigm based upon a better understanding of acute decompensation of cirrhosis. The interaction between the traditional concepts and the emerging perspectives remains a matter of great interest and the basis for future research

Experimental and numerical studies on the flow characteristics and separation properties of dispersed liquid-liquid flows

© 2019 Author(s). The local dynamics of spatially developing liquid-liquid dispersed flows at low superficial velocities, ranging from 0.2 to 0.8 m s-1, are investigated. The dispersions are generated with an in-line static mixer. Detailed measurements with laser-based diagnostic tools are conducted at two axial pipe locations downstream of the mixer, namely, at 15 and 135 equivalent pipe diameters. Different flow patterns are recorded, and their development along the streamwise direction is shown to depend on the initial size and concentration of the drops as well as the mixture velocity. The drop size is accurately predicted by an empirical formula. The variations in drop concentration over the pipe cross-section along the pipe result in local changes of the physical properties of the mixture and consequently in asymmetrical velocity profiles, with the maxima of the velocity located in the drop-free region. Computational fluid dynamics simulations based on a mixture approach predict the experimental results close to the experimental uncertainties for the majority of the cases. The simulation results reveal that gravity and lift forces, as well as shear-induced diffusion are the most important mechanisms affecting the drop migration. It is found that the drops behave as suspensions of rigid spheres for the conditions investigated, despite the deformation effects, which are found experimentally to be stronger at the densely packed region