Complex Rheology Research Articles

Interfacial Rearrangements of Block Copolymer Micelles Toward Gelled Liquid-Liquid Interfaces with Adjustable Viscoelasticity.

Though amphiphiles are ubiquitously used for altering interfaces, interfacial reorganization processes are in many cases obscure. For example, adsorption of micelles to liquid-liquid interfaces is often accompanied by rapid reorganizations toward monolayers. Then, the involved time scales are too short to be followed accurately. A block copolymer system, which comprises poly(ethylene oxide)110 -b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}170 (i.e., PEO110 -b-qPDPAEMA170 with quaternized poly(diisopropylaminoethyl methacrylate)) is presented. Its reorganization kinetics at the water/n-decane interface is slowed down by electrostatic interactions with ferricyanide ([Fe(CN)6 ]3- ). This deceleration allows an observation of the restructuring of the adsorbed micelles not only by tracing the interfacial pressure, but also by analyzing the interfacial rheology and structure with help of atomic force microscopy. The observed micellar flattening and subsequent merging toward a physically interconnected monolayer lead to a viscoelastic interface well detectable by interfacial shear rheology (ISR). Furthermore, the "gelled" interface is redox-active, enabling a return to purely viscous interfaces and hence a manipulation of the rheological properties by redox reactions. Additionally, interfacial Prussian blue formation stiffens the interface. Such manipulation and in-depth knowledge of the rheology of complex interfaces can be beneficial for the development of emulsion formulations in industry or medicine, where colloidal stability or adapted permeability is crucial.

Thermally developed electrokinetic bi-layer flows of Newtonian and non-Newtonian fluids in a microchannel

In the present study, thermofluidic characteristics of a combined pressure-driven and electrical field mediated thermally fully developed flow of an immiscible Newtonian and a viscoelastic fluid bi-layer in a microchannel have been analyzed. The simplified Phan-Thien–Tanner model with a linear kernel for the stress coefficient function has been utilized to describe the complex fluid rheology for the non-Newtonian fluid. Disparate zeta potentials have been assumed at the interfaces. Accordingly, distinct zeta potential values have been used at the channel walls and interfaces between the fluids to derive the closed-form analytical expressions for the pertinent velocity, stress, and shear viscosity distributions in the fluid layers. For thermally developed flows, the temperature and entropy distributions are obtained along the microchannel for constant wall heat flux boundary conditions. Major findings from our research show that amplification of the viscoelastic parameter designated by the Weissenberg number exhibits an enhancement in the non-dimensional axial velocity, flow rate, and stress magnitudes. Furthermore, the present study indicates that Joule heating and viscous dissipation significantly vary the dimensionless temperature profiles along the fluid bi-layer. The Nusselt number values are found to decrease with the augmentation of the viscoelasticity, Joule heating, and viscous dissipation parameters. The total entropy generation for the fluid layer systems increases with the increasing Joule heating parameter.

Potentials of 3D extrusion‐based printing in resolving food processing challenges: A perspective review

AbstractThree‐dimensional (3D) printing has promising application potentials in improving food product manufacturing, increasingly helping in simplifying the supply chain, as well as expanding the utilization of food materials. To further understand the current situation of 3D food printing in providing food engineering solutions with customized design, the authors checked recently conducted reviews and considered the extrusion‐based type to deserve additional literature synthesis. In this perspective review, therefore, we scoped the potentials of 3D extrusion‐based printing in resolving food processing challenges. The evolving trends of 3D food printing technologies, fundamentals of extrusion processes, food printer, and printing enhancement, (extrusion) food systems, algorithm development, and associated food rheological properties were discussed. The (extrusion) mechanism in 3D food printing involving some essentials for material flow and configuration, its uniqueness, suitability, and printability to food materials, (food material) types in the extrusion‐based (3D food printing), together with essential food properties and their dynamics were also discussed. Additionally, some bottlenecks/concerns still applicable to extrusion‐based 3D food printing were brainstormed. Developing enhanced calibrating techniques for 3D printing materials, and designing better methods of integrating data will help improve the algorithmic representations of printed foods. Rheological complexities associated with the extrusion‐based 3D food printing require both industry and researchers to work together so as to tackle the (rheological) shifts that make (food) materials unsuitable.Practical ApplicationsAs a processing technology with digital additive manufacturing methodology, 3D food printing over the decades has evolved greatly with the extrusion‐based type increasingly studied. This perspective review scoped the potentials of 3D extrusion‐based printing in resolving food processing challenges. In this work, we demonstrated how this extrusion‐based technique increasingly contributes to situate the 3D food printing as among innovative technologies with an upscale dimension. To fully embrace the extrusion‐based 3D printing, the food industry needs to primarily understand the potentials this technology would provide in enhancing food material properties/types.

A numerical investigation of granular shock waves over a circular cylinder using the discrete element method

Numerical simulation based on the discrete element method (DEM) is used to investigate the flow field generated when a cylindrical obstacle is placed in a supersonic granular stream. Robust validation of the simulation model is performed by comparing numerical results with experiments. Experiments are performed using a two-dimensional set-up generating rapid granular flow owing to gravity. DEM simulations demonstrate that a rapid gas-like stream of grains suddenly decelerates across the shock wave and finally collapses into a slow-moving heap at the cylinder. The volume fraction suddenly increases across the shock layer and remains constant thereafter. The flow physics of the shock wave and the granular heap is elucidated through fundamental fluid dynamic quantities such as the velocity, volume fraction, pressure and granular temperature. It is shown that the interaction of grains with a cylindrical obstacle results in the generation of pressure, which is responsible for sustaining static granular heaps on the cylinder. The total pressure is resolved into collisional and streaming components. A streaming pressure is generated owing to velocity fluctuations, and is found to be significant only in the shock wave region. The observations show that the rheological complexity offered by granular shock waves is a direct manifestation of the dissipative and frictional nature of granular collisions. The new insight into the granular heaps could be relevant to a variety of applications involving granular-fluid–solid interactions.

Technological and rheological bases for molding pasta in press houses with preliminary two-stage compaction, plasticization and warming of dough

One of efficient directions for pasta press designs modernization is installation of special conical-andcylindrical inserts in the pre-matrix space and matrix wells in front of the dies having, like Venturi tubes, narrowing zones (convergent), expansion (divergent) and a cylindrical path located between them. However, rheological aspects of such method of forming tool modernizing in relation to pasta presses have not been studied, recommendations for structural elements calculation and design have not been developed. All this is a significant obstacle for using the method in engineering and industrial practice. The research purpose is to develop rheological models the pasta dough flow in the conical-cylindrical channels of convergent-divergent inserts and to evaluate with their help the impact of structural dimensions and rheological properties on resistance to pasta dough flow. Pasta dough was considered as a rheological complex nonlinearly viscous plastic material. In technical calculations contribution of shear strength was neglected and a rheological analysis was performed using the Oswald-de-Ville power law equation. Analytical dependences obtained make it possible to calculate the pressure drops in the convergent-divergent insert and its elements. Numerical modeling was performed and calculated data were obtained regarding the impact of dimensions of structural elements of the insert and rheological parameters of pasta dough on its resistance to viscous flow. The results obtained can form the basis of engineering and technological calculations in design of convergent-divergent inserts for laboratory and industrial pasta presses.

Site-Specific PSHA: Combined Effects of Single-Station-Sigma, Host-to-Target Adjustments and Nonlinear Behavior. A case study at Euroseistest

This study takes advantage of the available information for an example, well-known, site in Greece (TST site at Euroseistest) to illustrate the epistemic variability in probabilistic seismic hazard assessment (PSHA) estimates. The purpose is not to perform an exhaustive site-specific PSHA at this particular site, but to investigate the sensitivity of the results to the approach used for including site effects, from basic ones to more demanding and realistic ones, in order to better appreciate the “benefits” versus the required costs and efforts of each approach. The TST site, located at the center of the Mygdonian basin in North-Eastern Greece is characterised by soft shallow soils over thick, medium stiffness deposits with a complex underground geometry, resting on very hard bedrock. Three different levels are considered for the incorporation of site response, from level 0 (generic or partially generic) to site-specific ones, with linear (level 1) or non-linear (level2) site response analysis. The basic methods rely on one or several site proxies (VS30, VSZ and f0), whereas the most complex ones couple site response assessment (instrumental or numerical, implying site-specific characterization or instrumentation) with various reference rock hazard adjustments (single-station sigma, host-to-target adjustments, depth correction). Results are compared in terms of Uniform Hazard Spectra for a 5000 years return period, a typical value for critical facilities. For each level, the epistemic uncertainties are described and their impacts on hazard estimates are quantified. The use of the VS30 proxy in ground-motion prediction equations (GMPEs) leads to a clear underestimation of the hazard for the linear case (i.e., short return periods), especially around the site fundamental period, because of resonance and basin effects. On the other hand, soil nonlinearity largely impacts the hazard estimates, and linear amplification approach leads to an overestimation of the hazard, with unrealistic high levels at very long return periods. Site- specific hazard estimates for thick, Euroseistest-like sites, with complex geometry and rheology, are thus shown to come up against several additional epistemic uncertainties implying a large approach-to-approach variability. This may lead to increased hazard estimates, counterbalancing the decrease due to the use of reduced, single-site aleatory uncertainty in reference rock hazard estimates. For the time being, it thus looks unrealistic to promise a systematic reduction in hazard estimates with site-specific studies, while it might also indicate that uncertainties in generic hazard estimates could presently be underestimated.

STUDY OF THE EFFECT DEGREE OF DEHYDRATİON OF OILS ON THE RHEOLOGİCAL PARAMETERS

As already mentioned, in the processes of extraction, storage and transportation of oils, they mix with each other or with water, which leads to changes in their rheological and physicochemical properties. The oils entering the refining and transportation stages are subject to strict requirements in terms of the amount of water, sulfur, chlorine salts and mechanical impurities in a number of indicators that determine their quality characteristics. Different types of oils have different qualities depending on the density and percentage of sulfur. It is these indicators that greatly affect the quality of oil and its selling price. High-viscosity oils with high density are usually not supplied to terminals and general purpose pipelines. To transport such oils, better quality, lighter oil or gas condensate is added to them. Oils with a high percentage of sulfur should also be refined or mixed with light oil or condensate. Mixing of different quality commercial oils can occur both in terminals and in transportation systems. The analysis shows that the quality of the mixture obtained is very different from the quality of the mixed oils. Given very little study of how the mixing of different types of liquefied oils affects their rheological, physicochemical properties and quality indicators, rotoviscosimetric rheological studies and physicochemical analyzes were performed in the laboratory for different mixtures of rheological complex oils and wetting rates. Mixing of different types of oil usually occurs when there are not enough tanks in the fields where acceptance operations take place. Sometimes different oils are injected into the same jaw in sequence and separately, without accounting. In such cases, the measurements made on the oil at the receiving points are different from the calculated price. Information on quality indicators of crude oils and their mixtures produced in mines (density, viscosity, freezing point, mechanical mixtures, chlorine salts, asphaltene, paraffin, amount of resins, etc.) It is also important for forecasting the operating modes of stations. In the existing normative documents and literature, as a rule, the definition of the main quality indicators of oils and their mixtures is based on established rules and dependencies. The study of the effect of mixing of different types of heterogeneous oils of Azerbaijan on their rheological and physical-chemical properties shows that the additive rule can lead to serious errors in the process of determining the predicted parameters, as many properties of complex oil mixtures are taken from calculations for ideal mixtures. Laboratory studies were conducted for individual oil samples, their different mixtures and degree of dehydration, oil and condensate, as well as mixtures of various types of light petroleum products, and the experimental results were analyzed. In the laboratory, the effect of the degree of dehydration of high-viscosity heavy oils taken from wells 43 (0%), 28 (15%), 37 (40%) and the storage tank of the "Jafarli" field of the "Muradkhanli" IPC on their rheological properties was studied. has been. All of the studied oils are high-viscosity, heavy oils and differ in the amount of water, mechanical impurities and chlorine salts they contain. Thus, the oil of well No. 43 was without water, and the oil of wells No. 28 and 37 had a water content of 15 and 40%, respectively. Most mechanical impurities (2.1%) were in well oil No 28, and most chlorine salts were in well oil No 37. Irrigation of the considered oil samples was artificially increased and their rheological parameters (γ ̇ and τ) were determined in the “Reotest-2” viscometer under different conditions at different irrigation levels. The increase in viscosity at small values of the velocity gradient at a certain degree of dehydration of wetting has led to a rapid decrease in the shear stress at large values. It was determined that the maximum value of the degree of dispersion of oils in water or the degree of saturation, indicating the saturation limit, was 70-80%, 40%, and 80% for mixed oil, respectively, for samples taken from wells 28, 37 and 43. Keywords: oil, mixed oil, mechanical mixture, degree of dehydration, rheological parameters.

On integral equations of cracks of a new type

For the first time, the paper develops a new type of crack modeling method that allows describing them in environments of complex rheologies. It is based on a new universal modeling method previously published by the authors, used in boundary value problems for systems of partial differential equations. The advantage of the method is the possibility of avoiding the need to solve complex boundary value problems for systems of partial differential equations by replacing them with separate differential equations, among which the Helmholtz equations are the simplest. Namely, with the help of combinations of solutions of boundary value problems for this equation, it is possible to describe the behavior of complex solutions of multicomponent boundary value problems. In this paper, for the first time, the method is applied to a mixed boundary value problem for cracks of a new type. Cracks of a new type, complementing the Griffiths cracks, were discovered during the study of fractures of lithospheric plates that converge at the ends during oncoming traffic along the Conrad boundary. In the course of the study, Kirchhoff plates were adopted as models of lithospheric plates. The method developed in the published article is aimed at the possibility of describing models of approaching objects similar to lithospheric plates in the form of deformable plates of more complex rheologies. In particular, it can be thermoelectroelastic plates or other rheology. In the process of solving problems using Kirchhoff models for lithospheric plates, there was a problem of calculating some functionals that needed to be determined. This method demonstrates an approach that eliminates this drawback. The derivation of integral equations of cracks of a new type, the method of their solution and the approach to application in more complex rheologies is given.

О КОНТАКТНЫХ ЗАДАЧАХ С ДЕФОРМИРУЕМЫМ ШТАМПОМ

This paper presents one of the methods for studying the behavior of deformable stamps on a deformable base. It is based on a new universal modeling method previously published by the authors, used in boundary value problems for systems of partial differential equations. Its advantage is the possibility of avoiding the need to solve complex boundary value problems for systems of differential equations by replacing them with separate differential equations, among which the Helmholtz equations are the simplest. With the help of combinations of solutions of boundary value problems for this equation, it is possible to describe the behavior of complex solutions of multicomponent boundary value problems, including for cracks of a new type formed by objects on a deformable base, and models of nano particles located on deformable multicomponent bases. However, without the ability to solve contact problems for deformable stamps, these models are not built. The mixed problem is reduced to the solution of the Wiener–Hopf integral equation. Two cases are considered: the case of a large-width strip stamp and the case of a semi-infinite stamp. A packed block element is accepted as a deformable stamp, as a solution of the Helmholtz equation in the specified area. Mechanically, it can be imitated as a membrane that is located on a multilayer medium occupying the contact area. A combination of such objects can be used to describe solutions to the contact problem for flat deformable objects of more complex rheology, as well as for three-dimensional ones. Along with the proof of constructing an exact solution to the contact problem under consideration, the appearance of unknown functionals is noted in the course of the study. In problems with an absolutely solid stamp, they do not occur. The paper finds a way to determine them and an analytical representation of them is obtained. It is suggested that their appearance will be typical for solving other contact problems with deformable stamps. The features of the method and the results obtained are discussed.

Analysis of the Dispersion of Viscoelastic Clusters in the Industrial Rotor-Stator Equipment

Materials with complex rheology and viscoelasticity may require special equipment for processing, such as for dispergation. Rheological and mechanical data of the material can help with finding the required equipment or designing equipment. For highly viscous and complex material, a rotor-stator mixer can be a good choice for dispergation. Due to the laminar or creeping mechanism of flow inside the equipment, the dispergation mechanism is assumed to be a combination of the shear stress and slicing of the material by the rotor and stator blades. For the validation of the theory, the mechanical properties of the viscose identified in a previous work were used for comparison with the data from the CFD simulation of the rotor-stator mixer. The comparison showed that the rotor-stator device can overcome the complex shear modulus and ultimate strength of the material and homogenize the solution through a combination of the shear stress and slicing. The theory was also confirmed on the process line proposed for homogenization of the specific material. The stability of viscosity during the process of homogenization was measured and used as the main parameter for quality assessment.

Vibration-Induced Heating of Energetic Materials: A Review

AbstractThe transport of energetic materials—whether by truck over rough terrain, or attached to the undercarriage of a high-performance jet aircraft—carries a certain level of inherent risk as the repeatedly applied stresses from vibration may lead to heating, mechanical degradation, and potentially even the triggering of an ignition event. Increasing knowledge of the underlying physics which control ignition is allowing us to better understand, and thus reduce, the risk of a catastrophic event occurring. The Apollo and Space Shuttle programmes provided motivation for research into the topic in the 1960s and 1970s, and some recent studies have focussed on the grain-scale physics of ignition. However, much of the useful insight has arisen from work with other primary applications in mind. Therefore, this review aims to bring together literature from several fields, with the intention of better understanding vibration-induced heating (VIH) phenomena in energetic materials. Sensitivity, VIH in viscoelastic polymers and inert composites, and a technique known as vibrothermography which uses VIH to detect cracks, are all considered where relevant read-across can be found. Often being viscoelastic materials and composites with complex rheology, energetic materials subjected to vibrational loading tend to warm up, with potential for even greater temperature rises due to anisotropy-driven localised heating mechanisms. Binders soften as temperature rises, and the chance of damage increases, which may lead to runaway heating and thermal failure (if mechanical failure does not occur first).

An experimental device for measuring radial flow velocity profiles of yield stress fluids

Measuring the radial flow velocity field of yield stress fluids (YSFs) between two parallel disks provides crucial data to understand the underlying flow phenomena. However, direct velocimetry of YSFs in the radial flow configuration remains a challenge, due to the complex fluid rheology and geometry constraints. In this paper, we present an experimental device for measuring YSF radial flow velocity profiles. Ultrasound Velocity Profiling (UVP) is used to non-intrusively measure the velocity profiles. The Tikhonov regularization method is implemented to obtain smooth velocity profiles, which are used to calculate the plug-flow region. Compared to our previous work on radial flow, the current contributions include: (i) additional structural frame members to maintain a constant aperture, (ii) wall slip reduction, and (iii) an improved velocity profile plug-detection algorithm. The results show that the experimental device and the measurement method are effective for further studying radial flow behavior of YSFs for industrial applications.

INFLUENCE OF THE WATER SATURATION DEGREE ON DEMULSIFICATION OF THE RHEOLOGIC COMPLEX OILS

Studies of recent years have determined that oil emulsions are also characterized by a degree of water saturation. Since as water saturation increases (water dispersion in oil), the viscosity of oil emulsions increases significantly. The article investigated the rheological properties of various artificially created emulsions based on rheological complex oils at different temperatures. It has been determined that with an increasing of water cut and water saturation, the viscosity of the system will increase. The article also investigated the effect of changing the water content of oil on its demulsification. It has been found that by purposeful enlargement of water saturation it is possible to significantly reduce the demulsifier consumption while maintaining the efficiency of the dehydrating process. Demulsifier Disolvan-4411 was used for demulsification process. Water-oil emulsions with an initial water cut 22%were dosed with various reagent additives and samples were taken for analyzing. Temperature kept identical during all studies. The effectiveness of water-oil emulsions before and after demulsification with the demulsifier was evaluated by the amount of water dropped from stable water-emulsion in graduated bottles (method Bottle Test). Analyzing the stability of oil emulsions depending on water drop, according consumption of demulsifier we found that 2 factors impact effectiveness of demulsification process: the content of aqueous phase and degree of its dispersion. The result of experimental studies show that with an increase in oil water saturation, consumption of demulsifier decreases. Only with increasing water saturation percentage 70% and higher, the water drop rate exceeds 99%, which meets oil treatment requirements Keywords: oil emulsions, water saturation, viscosity, demulsification, demulsifier, flow curves.

Designing Complex Fluids

Taking a small step away from Newtonian fluid behavior creates an explosion in the range of possibilities. Non-Newtonian fluid properties can achieve diverse flow objectives, but the complexity introduces challenges. We survey useful rheological complexity along with organizing principles and design methods as we consider the following questions: How can non-Newtonian properties be useful? What properties are needed? How can we get those properties?

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

Abstract. A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical tests have been performed to characterise the bulk mechanical, hydro-mechanical, and failure behaviour of Opalinus Clay, important questions remain about micromechanisms: how do microstructural evolution and deformation mechanisms control the complex rheology? What is the in situ microstructural shear evolution, and can it be mimicked in the laboratory? In this contribution, scanning electron microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated–undrained triaxial compression test at 4 MPa confining stress followed by argon broad ion beam (BIB) polishing. Axial load was applied (sub-)perpendicular to bedding until the sample failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the centimetre to micrometre scale showed that the samples exhibited shear failure and that deformation localised by forming a network of micrometre-wide fractures, which are oriented with angles of 50∘ with respect to horizontal. In BIB–SEM at the grain scale, macroscale fractures are shown to be incipient shear bands, which show dilatant intergranular and intragranular microfracturing, granular flow, bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed, indicating only localised permanent deformation. Thus, micromechanisms of deformation appear to be controlled by both brittle and ductile processes along preferred deformation bands. Anastomosing networks of fractures develop into the main deformation bands with widths up to tens of micrometres along which the sample fails. Microstructural observations and the stress–strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates, while bulk measurement shows compaction, with an inferred major effect on permeability by an increase in hydraulic conductivity within the deformation band. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows partial similarity and suggests that during long-term deformation additional solution–precipitation processes operate.

The effect of expanded graphite/clay nanoparticles on thermal, rheological, and fire‐retardant properties of poly(butylene succinate)

AbstractIn this study, the effect of clay nanoparticles on the flame retardancy, thermal stability, thermal degradation kinetics and rheological properties of poly(butylene succinate) (PBS)/expanded graphite (EG) composites were investigated. The composites were prepared by melt blending, followed by melt compression. The results indicated that the presence of clay, improved the dispersion of the EG, as confirmed by exhibited significant increases in the rheological properties (storage modulus (G′), loss modulus (G″) and complex viscosity (η)) when compared to the pristine PBS. The presence of Cloisite 15 A organoclay, however, decreased the overall thermal stability of the composite material, due to its catalytic effect. The degradation kinetics revealed that the presence of EG can impede the clay's catalytic effect on the degradation process of PBS. Based on the comparison between PBS and PBS/EG composites, the flame retardancy improved after the addition of clay due to formation of char, which acted as barrier layer against heat, oxygen, and flammable gases.

3D Printing High‐Resolution Conductive Elastomeric Structures with a Solid Particle‐Free Emulsion Ink

Fabricating complex structures on micro‐ and mesoscales is a critical aspect in the design of advanced sensors and soft electronics. However, soft lithographic methods offer an important approach to fabricating such structures, the progress in the field of additive manufacturing (e.g., 3D printing) offers methods of fabrication with much more material complexity. The rheological complexity of the printing material, however, often dictates the limitations of printing. In particular, the challenges involved in synthesizing printing materials that can enable shape retention at smaller scales (<100 μm), yet be conductive, limits many applications of 3D printing to soft microelectronics. Herein, a printing‐centered approach using a novel particle‐free conductive emulsion ink is presented. This approach separates the printing and polymerization of a conductive monomer (pyrrole) and renders a novel ink that is used to print filaments with heretofore impossible to realize 3D feature dimensions and build structures with high shape retention. The printability of the ink is evaluated, and post‐treatment properties assessed. Multidirectional strain sensors are printed using the emulsion ink to illustrate an exemplary application in soft electronics.

On the compressional rheology of fresh faeces: Evidence for improving community scale sanitation through localised dewatering

Non-sewered sanitation is currently dependant upon pit latrine emptying, the safety of which is compromised by the high costs of faecal sludge transport to centralised treatment facilities. Transport in turn is hindered by the complex rheology of pit latrine sludge. This study therefore characterised the compressional rheology of fresh faeces and modelled the implications for passive (gravity) or mechanical (forced) solid/liquid separation. This informs on the viability of decentralising dewatering for more efficient volume reduction and improving the economics of transportation. The gel point (ϕg) is the solids concentration where the material has a networked structure and signifies the point when mechanical intervention is required for further solid-liquid separation. For fresh faeces, ϕg ranged between 6.3 and 15.6% total solids (TS) concentration. This is significantly higher than the ϕg observed for wastewater sludge at centralised facilities, and it implies that passive gravity driven processes can suffice to improve localised dewatering. The kinetics of passive sedimentation of faecal material were modelled and illustrate thickening from 3 to 10% TS concentration in <0.5 h. This highlights that early intervention to thicken faeces while fresh can improve solid/liquid separation efficiency. Filtration of fresh faeces was characterised by lengthy cake filtration times and comparably short compression times, more similar to mineral slurries than to wastewater sludge. Consequently, fresh faeces presented improved dewatering characteristics, supporting higher final cake solids concentrations and improved dewatering kinetics. By complementing thickening with 300 kPa filtration, a 1.4 cm thick 25% TS product could be achieved in <24 h. Investigation of matrix properties highlighted that increased conductivity (e.g. exposure to urine) negatively influenced dewaterability, an effect which could be mitigated by introducing solid-liquid separation earlier. The thermodynamically favourable compressional rheology of fresh faeces has identified that focussing on localised dewatering could radically improve the economics of faecal sludge management, primarily through reducing transport costs.

Data-driven polynomial chaos expansions for characterization of complex fluid rheology: Case study of phosphate slurry

Mine transportation through hydraulic pipelines is increasingly used by various industries around the world. In Morocco, this has been implemented for the case of phosphate transportation. This allows to increase the production and reduce the transportation cost. Given the vital importance of phosphate in the global food security and regarding the huge amount of phosphate rock reserves in Morocco, it is detrimental to assess the reliability, to optimize and to increase its transportation in a safe manner. Usually hydraulic transportation of such fluids is fully quantified with a full characterization of its rheology related to its non-Newtonian behavior. The rheology allows to know the viscous and the elastic properties of a fluid exhibiting viscoelastic properties. In the case of water-phosphate slurry this behavior is not well-documented and classical constitutive laws for the rheology are of limited used, because of the high variability of different physico-chemical components of the slurry. The present work aims at quantifying the sensitivity of the water-phosphate slurry rheology to these components. In order to achieve this objective, a data-driven model based on polynomial chaos expansions (PCE) is developed and investigated. The choice of this class of models is motivated by the simplicity to conduct sensitivity analysis with the PCE and the limited amount of data available as the water-phosphate slurry pipeline is very new. In order to alleviate further the impact of the limitation given by the available data, we introduce the bagging technique which is an Ensemble based data-driven model using the PCE. Results presented in this study demonstrate that the bagging allows to reduce the validation error of the model by up to two orders of magnitude. Thus, it reduces considerably the variability on the estimation of hyperparameters in the model. Moreover, the sensitivity analysis shows that the variability on the elasticity coefficient is mainly due to the variability of the slurry density and the solid rate. Viscosity on the other side is not affected by the heterogeneity of the granulation distribution.

Pulsatile flow dynamics in symmetric and asymmetric bifurcating vessels

Bifurcating vessel is a characteristic feature of biological systems such as arteries in the cardiovascular system and pulmonary airways. In cardiovascular system, the bifurcations are often asymmetric, flow is pulsatile, and the fluid, blood, shows a complex rheology. In this work, we study computationally pulsatile flow in planar symmetric and asymmetric, three-dimensional bifurcating vessels. The fluid is considered to be Newtonian as well as non-Newtonian following Carreau's model, and the results are compared. While the flow divides in the two daughter tubes equally in symmetric bifurcations, the flow distribution is time-dependent during a cardiac cycle in asymmetric bifurcations. The flow pattern changes significantly during a cardiac cycle. The secondary flow caused by a turning streamline is analyzed in terms of secondary velocity, vorticity, and helicity. Significant variation is observed in the secondary flow in a cardiac cycle. The secondary flow is observed to be stronger at the start of the diastole despite reduced flow rate. The separated flow on the outer wall causes a significant reduction in time-averaged wall shear stress, a biomarker to assess the possibility of atherosclerotic plaque development. While no significant difference is observed in the results obtained for Newtonian and non-Newtonian fluids at high shear rates, for example, during systole, significant differences are observed when the shear rate is low, during diastole or in the separation region. The velocity profile for the non-Newtonian fluid is observed to be flatter than that for Newtonian fluid. Further oscillatory shearing index, relative residence time, the parameters used as biomarkers are presented.