Search Results (78)

Inspired by the cutaneous wound healing mechanism observed in human scab formation, we engineered a series of multilayered silicone rubber composites through alternating polydimethylsiloxane (PDMS) and polydiborosiloxane (PDBS) laminates. The dynamic diboron–oxygen coordination bonds within PDBS enabled both autonomous self-healing through bond reconfiguration and enhanced impact resistance via energy dissipation. PDMS served dual functions as both a structural reinforcement matrix and a flow-restricting framework for PDBS, thereby improving the viscoelastic creep behavior and irreversible deformation tendencies characteristic of conventional non-Newtonian fluids. Notably, increasing the laminate count from 3 to 9 layers enhanced structural integration, yielding improvement in dimensional stability. All multilayer configurations demonstrated remarkable healing performance, achieving post-24 h self-healing efficiencies exceeding 95% across 3-layer, 5-layer, and 9-layer specimens. Rheological characterization revealed pronounced strain rate sensitivity under multiaxial loading conditions, with storage modulus showing proportional enhancement to applied strain rates in both transverse and longitudinal orientations. Full article

At present, most oilfields in China have entered the late, high-water-cut stage, commonly facing declining single-well productivity and increasingly pronounced reservoir heterogeneity. Prolonged waterflooding has further exacerbated permeability contrast, yielding complex, hard-to-produce residual-oil distributions. Accordingly, the development of efficient enhanced oil recovery (EOR) technologies has become a strategic priority and an urgent research focus in oil and gas field development. Weak gels, typical non-Newtonian fluids, exhibit both viscous and elastic responses, and their distinctive rheology shows broad application potential for crude oil extraction in porous media. Targeting medium–high-permeability reservoirs with high water cut, this study optimized and evaluated a weak gel system. Experimental results demonstrate that the optimized weak gel system achieves remarkable oil displacement performance. The one-dimensional dual-sandpack flooding tests yielded a total recovery of 72.26%, with the weak gel flooding stage contributing an incremental recovery of 14.52%. In the physical three-dimensional model experiments, the total recovery reached 46.12%, of which the weak gel flooding phase accounted for 16.36%. Through one-dimensional sandpack flow experiments and three-dimensional physical model simulations, the oil displacement mechanisms and synergistic effects of the optimized system in heterogeneous reservoirs were systematically elucidated from macro to micro scales. The optimized system demonstrates integrated synergistic performance during flooding, effectively combining mobility control, displacement, and oil-washing mechanisms. Macroscopically, it effectively strips residual oil in high-permeability zones via viscosity enhancement and viscoelastic effects, efficiently blocks high-permeability channels, diverts flow to medium-permeability regions, and enhances macroscopic sweep efficiency. Microscopically, it mobilizes residual oil via normal stress action and a filamentous transport mechanism, improving oil-washing efficiency and increasing ultimate oil recovery. This study demonstrates the technical feasibility and practical effectiveness of the optimized weak gel system for enhancing oil recovery in heterogeneous reservoirs, providing critical technical support for the efficient development of medium–high-permeability reservoirs with high water cut. Full article

The optimization of polymer extrusion processes is crucial for improving product quality and manufacturing efficiency in plastic industries. This study aims to investigate the viscoelastic flow behavior of high-density polyethylene (HDPE) through an extrusion die with an internal mandrel, focusing on the effects of die geometry and flow parameters. A two-dimensional (2D) numerical model is developed in COMSOL Multiphysics using the Oldroyd-B constitutive equation, solved using the Galerkin/least-square finite element method. The simulation results indicate that the Weissenberg number (Wi) and die geometry significantly influence the dimensionless drag coefficient (Cd) and viscoelastic stress distribution along the die wall. Furthermore, filleting sharp edges of the die wall surface effectively reduces stress oscillations, enhancing flow uniformity. These findings provide valuable insights for optimizing die design and improving polymer extrusion efficiency. Full article

Mechanical models are capable of simulating the deformation and stress distribution of oocytes under external forces, thereby providing insights into the underlying mechanisms of intracellular mechanical responses. Interactions with micromanipulation tools involve forces like compression and punction, which are effectively analyzed using principles of solid mechanics. Alternatively, fluid–structure interactions, such as shear stress at fluid junctions or pressure gradients within microchannels, are best described by a multiphase flow model. Developing the two models instead of a single comprehensive model is necessary due to the distinct nature of cell–tool interactions and cell–fluid interactions. In this study, we developed a finite element (FE) model of porcine oocytes that accounts for the viscoelastic properties of the zona pellucida (ZP) and cytoplasm for the case when the oocytes interacted with a micromanipulation tool. Atomic force microscopy (AFM) was employed to measure the Young’s modulus and creep behavior of these subcellular components that were incorporated into the FE model. When the oocyte was solely interacting with the fluids, we simulated oocyte deformation in microfluidic channels by modeling the oocyte-culture-medium system as a three-phase flow, considering the non-Newtonian behavior of the oocyte’s components. Our results show that the Young’s modulus of the ZP and cytoplasm were determined to be 7 kPa and 1.55 kPa, respectively, highlighting the differences in the mechanical properties between these subcomponents. Using the developed layered FE model, we accurately simulated oocyte deformation during their passage through a narrow-necked micropipette, with a deformation error of approximately 5.2% compared to experimental results. Using the three-phase flow model, we effectively simulated oocyte deformation in microfluidic channels under various pressures, validating the model’s efficacy through close agreement with experimental observations. This work significantly contributes to assessing oocyte quality and serves as a valuable tool for advancing cell mechanics studies. Full article

A hydrodynamic homogeneous model has been developed for the motion of mutually impenetrable viscoelastic non-Newtonian fluids taking into account surface tension forces. Based on this model, numerical simulations of cytokinesis hydrodynamics were performed. The cytoplasm is considered a non-Newtonian viscoelastic fluid. The model allows for the calculation of the formation and rupture of the intercellular bridge. Results from an analytical analysis shed light on the influence of the viscoelastic fluid’s relaxation time on cytokinesis dynamics. A comparison of numerical simulation results and experimental data showed satisfactory agreement. Full article

Cardiovascular diseases represent one of the leading causes of mortality worldwide, underscoring the need for accurate simulations of blood flow to improve diagnosis and treatment. This study examines blood flow dynamics in two different vascular structures—the aorta and the right coronary artery (RCA)—using Computational Fluid Dynamics (CFD). Utilizing COMSOL Multiphysics^®, various mathematical models were applied to simulate blood flow under physiological conditions, assuming a steady-flow regime. These models include both Newtonian and non-Newtonian approaches, such as the Carreau and Casson models, as well as viscoelastic frameworks like Oldroyd-B, Giesekus, and FENE-P. Key metrics—such as velocity fields, pressure distributions, and error analysis—were evaluated to determine which model most accurately describes hemodynamic behavior in large vessels like the aorta and in smaller and more complex vessels like the RCA. The results highlight the importance of shear-thinning and viscoelastic properties in small vessels like the RCA, which contrasts with the predominantly Newtonian behavior observed in the aorta. While computational challenges remain, this study contributes to a deeper understanding of blood rheology, enhancing the accuracy of cardiovascular simulations and offering valuable insights for diagnosing and managing vascular diseases. Full article

The viscoelasticity of fluids have a significant impact on the process of heat and mass transfer, which directly affects the efficiency and quality, especially for highly viscous functional polymer materials. In this work, the effect of elasticity on hydrodynamic behavior of pipe flow for highly viscous non-Newtonian fluids was studied using viscoelastic polyolefin elastomer (POE). Two constitutive rheological equations, the Cross model and Wagner model, were applied to describe the rheological behavior of typical POE melts, which have been embedded with computational fluid dynamics (CFD) simulation of the laminar pipe flow through the user-defined function (UDF) method. The influence of both viscosity and elasticity of a polymer melt on the flow mixing and heat transfer behavior has been systematically studied. The results show that the elastic effect makes a relative larger velocity gradient in the radial direction and the thicker boundary layer near pipe wall under the same feed flow rate. That leads to the higher pressure drop and more complex residence time distribution with the longer residence time near the wall but shorter residence time in the center. Under the same conditionals, the pipeline pressure drop of the viscoelastic fluid is several times or even tens of times greater than that of the viscous fluid. When the inlet velocity increases from 0.0001 m/s to 0.01 m/s, the difference in boundary layer thickness between the viscoelastic fluid and viscous fluid increases from 3% to 12%. Similarly, the radial temperature gradient of viscoelastic fluids is also relatively high. When the inlet velocity is 0.0001 m/s, the radial temperature difference of the viscoelastic fluid is about 40% higher than that of viscous fluid. Besides that, the influence of elasticity deteriorates the mixing effect of the SK type static mixer on the laminar pipe flow of highly viscous non-Newtonian fluids. Correspondingly, the accuracy of the simulation results was verified by comparing the pressure drop data from pipeline hydrodynamic experiments. Full article

Composite edible coatings based on arabic gum with mango peel hydrocolloids and mango seed extracts were prepared and used to evaluate grape conservation. Hydroethanolic solutions were used for the obtention of mango seed extracts, by microwave-assisted extraction, with total phenolic compounds (5.48 and 9.85 GAE/g of extract) and antioxidant activity (<13.03 µmol Trolox/g of extract). The extracts were selected for the development of edible coatings. The rheological properties of edible coating solutions present a non-Newtonian behavior-type shear thinning fluid; the addition of extracts improves their viscoelastic properties, favoring their application into grapes. The coated grapes maintained physicochemical parameters, such as weight, pH, acidity, soluble solids, and color during the 15 days of storage. The results of this research offer the possibility of using by-products from fruit industries, especially mango, to obtain functional ingredients and their application in food systems, taking advantage of their biological activity. Full article

Enhanced oil recovery (EOR) methods traditionally rely on polymer solutions to improve viscosity and elasticity; however, their effectiveness is limited under high-temperature, high-salinity, and high-shear conditions, leading to elevated operational costs. Anionic/cationic formulations have been studied in terms of interfacial tension reduction for EOR applications. This study presents a novel approach to EOR by enhancing the rheological properties of an anionic internal olefin sulfonate surfactant through interactions with cationic surfactants, eliminating the need for polymer molecules. This research demonstrates that cationic surfactants can induce micellization changes, resulting in substantial viscosity enhancement and viscoelasticity development. The effect is found to depend on the hydrocarbon chain length and concentration of the cationic surfactants, with longer chains yielding higher viscosity and more pronounced non-Newtonian behavior. Additionally, this study reveals that the addition of NaCl alters micellar organization, with the order of component additions playing a critical role in rheological performance. This kinetic-dependent micellization behavior, rarely explored in EOR applications, highlights the potential of counterion surfactants as viscosity enhancers in surfactant-based flooding processes. Oscillatory rheology confirms that cationic/anionic surfactant systems in this study exhibit stable viscoelastic behavior, making them potentially more suitable for harsh reservoir environments than polymer-based EOR fluids. These findings open new avenues for the development of cost-effective and tailored surfactant formulations, offering an alternative to polymer solutions under challenging reservoir conditions. Full article

This study investigates the three-dimensional, steady, laminar boundary-layer equations of a non-Newtonian fluid over a flat plate in the absence of body forces. The classical boundary-layer theory, introduced by Prandtl in 1904, suggests that fluid flows past a solid surface can be divided into two regions: a thin boundary layer near the surface, where steep velocity gradients and significant frictional effects dominate, and the outer region, where friction is negligible. Within the boundary layer, the velocity increases sharply from zero at the surface to the freestream value at the outer edge. The boundary-layer approximation significantly simplifies the Navier–Stokes equations within the boundary layer, while outside this layer, the flow is considered inviscid, resulting in even simpler equations. The viscoelastic properties of the fluid are modeled using the Rivlin–Ericksen tensors. Lie group analysis is applied to reduce the resulting third-order nonlinear system of partial differential equations to a system of ordinary differential equations. Finally, we determine the admissible forms of the freestream velocities in the x- and z-directions. Full article

Long-term polymer flooding exacerbates reservoir heterogeneity, intensifying intra- and inter-layer conflicts, which makes it difficult to recover the remaining oil. Therefore, further improvement in oil recovery after polymer flooding is essential. In this study, a weak gel system was successfully synthesized, and possesses a distinct network structure that becomes more compact as the concentration of partially hydrolyzed polyacrylamide increases. The network structure of the weak gel system provides excellent shear resistance, with its apparent viscosity significantly higher than that of partially hydrolyzed polyacrylamide solution. The weak gel system exhibits typical pseudo-plastic behavior, which is a non-Newtonian fluid as well as a viscoelastic fluid. Additionally, the weak gel system’s elasticities exceed its viscosities, and longer crosslinking time further enhances the viscoelasticity. The weak gel system achieves superior conformance control and enhanced oil recovery in highly heterogeneous reservoirs compared to partially hydrolyzed polyacrylamide solutions. The weak gel system is more suited to low-permeability reservoirs with strong heterogeneity, as its effectiveness in conformance control and oil recovery increases with greater reservoir heterogeneity. Enhanced oil recoveries of the weak gel system in low-permeability sandpacks increase from 22% to 48% with a rise in permeability ratios from 14.39 to 35.64 after polymer flooding. Full article

Despite the ubiquity and prevalence of rheological consistency across a wide range of industries, there is no clear consensus on its meaning or on one particular technique for quantifying it. Instead, there exist various definitions of “consistency” that are each specific to a given context, and each industry has its own procedure for measuring it. This paper organizes the many subjects and terminologies associated with consistency, providing a comprehensive guide of fundamental mechanics, fundamental properties, modeling techniques, and standardized tests that describe consistency. This includes outlining the rheological models that describe the behavior of viscoelastic and non-Newtonian materials as well as the identification of numerous parameters that can be individually evaluated to comprehensively understand and quantify consistency. Such an understanding of consistency and its underlying mechanical properties encourages the refinement of current consistency test methods and development of new ones. Full article

In this paper, the entire downhole fluid-sucker rod-pump system is replaced with a viscoelastic vibration model, namely a third-order differential equation with an inhomogeneous forcing term. Both Kelvin’s and Maxwell’s viscoelastic models can be implemented along with the dynamic behaviors of a mass point attached to the viscoelastic model. By employing the time-dependent polished rod force measured with a dynamometer as the input to the viscoelastic dynamic model, we have obtained the displacement responses, which match closely with the experimental measurements in actual operations, through an iterative process. The key discovery of this work is the feasibility of the so-called inverse optimization procedure, which can be utilized to identify the equivalent scaling factor and viscoelastic system parameters. The proposed Newton–Raphson iterative method, with some terms in the Jacobian matrix expressed with averaged rates of changes based on perturbations of up to two independent parameters, provides a feasible tool for optimization issues related to complex engineering problems with mere information of input and output data from either experiments or comprehensive simulations. The same inverse optimization procedure is also implemented to model the entire fluid delivery system of a very viscous non-Newtonian polymer modeled as a first-order ordinary differential equation (ODE) system similar to the transient entrance developing flow. The convergent parameter reproduces transient solutions that match very well with those from fully fledged computational fluid dynamics models with the required inlet volume flow rate and outlet pressure conditions. Full article

Some non-Newtonian fluids have time-dependent rheological properties like a shear stress that depends on the shear history or a stress overshoot that is a function of the resting time, when fluid movement is started. The rheological properties of such complex fluids may not stay constant while they are used in an industrial process, and it is therefore desirable to measure these properties frequently and with a simple and robust device like a pipe rheometer. This paper investigated how the time-dependent rheological properties of a thixotropic and viscoelastic shear-thinning fluid can be extracted from differential pressure measurements obtained at different flowrates along a circular pipe section. The method consists in modeling the flow of a thixotropic version of a Quemada fluid and solving the inverse problem in order to find the model parameters using the measurements made in steady-state conditions. Also, a Maxwell linear viscoelastic model was used to reproduce the stress overshoot observed when starting circulation after a resting period. The pipe rheometer was designed to have the proper features necessary to exhibit the thixotropic and viscoelastic effects that were needed to calibrate the rheological model parameters. The accuracy of rheological measurements depends on understanding the effects that can influence the observations and on a proper design that takes advantage of these side effects instead of attempting to eliminate them. Full article

The fused deposition modeling (FDM) process, an extrusion-based 3D printing technology, enables the manufacture of complex geometrical elements. This technology employs diverse materials, including thermoplastic polymers and composites as well as recycled resins to encourage sustainable growth. FDM is used in a variety of industrial fields, including automotive, biomedical, and textiles, as a rapid prototyping method to reduce costs and shorten production time, or to develop items with detailed designs and high precision. The main phases of this technology include the feeding of solid filament into a molten chamber, capillary flow of a non-Newtonian fluid through a nozzle, layer deposition on the support base, and layer-to-layer adhesion. The viscoelastic properties of processed materials are essential in each of the FDM steps: (i) predicting the printability of the melted material during FDM extrusion and ensuring a continuous flow across the nozzle; (ii) controlling the deposition process of the molten filament on the print bed and avoiding fast material leakage and loss of precision in the molded part; and (iii) ensuring layer adhesion in the subsequent consolidation phase. Regarding this framework, this work aimed to collect knowledge on FDM extrusion and on different types of rheological properties in order to forecast the performance of thermoplastics. Full article