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Supramolecular Design of Cellulose Hydrogel Beads
Get PDFIn the present study, we report the supramolecular design of cellulose-sulfonate hydrogel beads by blending water soluble sodium cellulose ethyl sulfonate (CES) with the pretreated cellulose in sodium hydroxide-ureawater solvent system at −6 °C followed by coagulation in the 2M sulfuric acid system. The increasing of CES amount from 10% to 90% had a substantial effect on the viscosity and storage (G′) and loss (G″) moduli of the blended solutions. The CES concentration up to 50% in blends led to the formation of physically stable hydrogels after coagulation in acidic medium at pH-1 and showed the retention of nearly the same CES concentration at pH-6 after continuous water washings. The increased sulfonate content also enhanced the water holding capacity and internal porosity of the beads. Both ATR-FTIR and Raman spectrometry were used for the qualitative determination of sulfonate groups and SEM-EDX was used for the quantitative estimation in dried beads. In this research, we have established a correlation between the presence of anionic charge in the polysaccharide blend and stability of the prepared hydrogel beads. Hence our research provides a systematic methodology to design functional, highly porous cellulose hydrogels having the potential to be tested further in biomedical and healthcare applications
Computational Investigation of Droplets Behaviour inside Passive Microfluidic Oscillator
No full textRecently, modeling immiscible fluids such as oil and water have been a classical research topic. Droplet-based microfluidics presents a unique platform for mixing, reaction, separation, dispersion of drops and many other functions. In this paper, we suggest a numerical CFD study of microfluidic oscillator with two different lengths of feedback loop. In order to produce simultaneous droplets of gasoil on water, a typical geometry that includes double T-junction is connected to the fluidic oscillator. Droplets production is computed by volume-of-fluid method (VOF). Flow oscillations of droplets were triggered by the Coanda effect of jet flow. The aim of work is to get a high oscillation frequency in the output of this passive device, the influence of hydrodynamics and physics parameters on the droplets frequency in the output of our microsystem is also investigated, the computational results show that, the length of feedback loop, operating pressure and interfacial tension have a significant effect on the droplets dynamic inside microfluidic oscillator. Across the range of low Reynold number, the droplets generation and its dynamics have been accurately controlled by adjusting applying pressure ratio of two phases
Mixed Convection of a Nanofluid in a Vertical Anisotropic Porous Channel with Heated/Cooled Walls
Get PDFA numerical study is conducted to investigate the problem of mixed convection of a nanofluid in a vertical porous channel with one wall heated and the other cooled. The Darcy-Brinkman-Forchheimer model is used to describe the flow in the porous medium, considered as anisotropic in thermal conductivity, and the two-phase approach is adopted to simulate the motion of the nanofluid. The governing equations with the associated boundary conditions are solved by the finite volume method. The parametric study is focused on the variation of the Richardson number Ri, the heat fluxes ratio Rq, the Darcy number and the thermal conductivity ratio λ characterizing the anisotropy. The results revealed that the heat transfer rates for both channel walls increase with λ and decrease with Da. The mean Nusselt number for the heated wall increases with the rise of Ri and Rq, while that for the cooled wall evolves in opposite direction. In addition, it is found that the dynamical and thermal fields become extremely sensitive to the variations of the various parameters mentioned above when reverse flow appears. For this reason, maps showing the situations of occurrence of this phenomenon are performed
The Constitutive Relation of a Fabric Membrane Composite for a Stratospheric Airship Envelope Based on Invariant Theory
Get PDFThe study of stratospheric airships has become the focus in many countries in recent years, because of its potential applications in many fields. Lightweight and high strength envelopes are the keys to the design of stratospheric airships, as it directly determines the endurance flight performance and loading deformation characteristics of the airship. A typical envelope of any stratospheric airship is a coated-fabric material which is composed of a fiber layer and several functional membrane layers. According to composite structure, nonlinearity and viscoelasticity are the two main characteristics of such envelope. Based on the analysis on the interaction between the different components in the micro-mechanical model of the coated-fabric, several invariant values reflecting the characteristics of the envelope material are obtained according to invariant theory. Furthermore, the constitutive equation that describes the viscoelasticity of the envelope material is derived. The constitutive equation can represent both the individual roles of the warp and weft fibers, and their further coupled interactions. The theoretical computation results were verified by off-axial tension tests. The results can help gain a deeper understanding of the mechanical mechanism and provide a reference for structural design of envelope material
Prediction of Compressive Strength of Self-Compacting Concrete Using Intelligent Computational Modeling
Get PDFIn the present scenario, computational modeling has gained much importance for the prediction of the properties of concrete. This paper depicts that how computational intelligence can be applied for the prediction of compressive strength of Self Compacting Concrete (SCC). Three models, namely, Extreme Learning Machine (ELM), Adaptive Neuro Fuzzy Inference System (ANFIS) and Multi Adaptive Regression Spline (MARS) have been employed in the present study for the prediction of compressive strength of self compacting concrete. The contents of cement (c), sand (s), coarse aggregate (a), fly ash (f), water/powder (w/p) ratio and superplasticizer (sp) dosage have been taken as inputs and 28 days compressive strength (fck) as output for ELM, ANFIS and MARS models. A relatively large set of data including 80 normalized data available in the literature has been taken for the study. A comparison is made between the results obtained from all the above-mentioned models and the model which provides best fit is established. The experimental results demonstrate that proposed models are robust for determination of compressive strength of self-compacting concrete
The Stable Explicit Time Stepping Analysis with a New Enrichment Scheme by XFEM
Get PDFThis paper focuses on the study of the stability of explicit time integration algorithm for dynamic problem by the Extended Finite Element Method (XFEM). A new enrichment scheme of crack tip is proposed within the framework of XFEM. Then the governing equations are derived and evolved into the discretized form. For dynamic problem, the lumped mass and the explicit time algorithm are applied. With different grid densities and different forms of Newmark scheme, the Dynamic Stress Intensity Factor (DSIF) is computed by using interaction integral approach to reflect the dynamic response. The effectiveness of the proposed scheme is demonstrated through the numerical examples, and the critical time stepping in different situations are listed and analyzed to illustrate the factors that affect the numerical stability
Multiscale Nonlinear Thermo-Mechanical Coupling Analysis of Composite Structures with Quasi-Periodic Properties
Get PDFThis paper reports a multiscale analysis method to predict the thermo-mechanical coupling performance of composite structures with quasi-periodic properties. In these material structures, the configurations are periodic and the material coefficients are quasi-periodic, i.e., they depend not only on the microscale information but also on the macro location. Also, a mutual interaction between displacement and temperature fields is considered in the problem, which is our particular interest in this study. The multiscale asymptotic expansions of the temperature and displacement fields are constructed and associated error estimation in nearly pointwise sense is presented. Then, a finite element-difference algorithm based on the multiscale analysis method is brought forward in detail. Finally, some numerical examples are given. And the numerical results show that the multiscale method presented in this paper is effective and reliable to study the nonlinear thermo-mechanical coupling problem of composite structures with quasi-periodic properties
Mathematical Modelling and 3D FEM Analysis of the Influence of Initial Stresses on the ERR in a Band Crack’s Front in the Rectangular Orthotropic Thick Plate
Get PDFThis paper deals with the mathematical modelling and 3D FEM study of the energy release rate (ERR) in the band crack’s front contained in the orthotropic thick rectangular plate which is stretched or compressed initially before the loading of the crack's edge planes. The initial stretching or compressing of the plate causes uniformly distributed normal stress to appear acting in the direction which is parallel to the plane on which the band crack is located. After the appearance of the initial stress in the plate it is assumed that the crack's edge planes are loaded with additional uniformly distributed normal forces and the ERR caused with this additional loading is studied. The corresponding boundary value problem is formulated within the scope of the so-called 3D linearized theory of elasticity which allows the initial stress on the values of the ERR to be taken into consideration. Numerical results on the influence of the initial stress, anisotropy properties of the plate material, the crack’s length and its distance from the face planes of the plate on the values of the ERR, are presented and discussed. In particular, it is established that for the relatively greater length of the crack’s band, the initial stretching of the plate causes a decrease, but the initial compression causes an increase in the values of the ERR
Numerical Analysis on Unsteady Internal Flow in an Evaporating Droplet
Get PDFWe have investigated the unsteady internal flow occurring in an evaporating droplet interacting with a high-temperature atmospheric environment. The Navier-Stokes equations for both the liquid and the gas phases have been solved numerically in the framework of a Volume of Fluid (VOF) method relying on the so-called Continuum Surface Force (CSF) model. A specific kernel able to account for evaporation and related phase change has been incorporated directly in the VOF approach. The temperature distributions within the droplet has been found to be relatively uniform by virtue of the Marangoni flow. The transient evolution of the flow pattern and related heat exchange effects have been also investigated
Biomatrix from Stipa tenacissima L. and its Application in Fiberboard Using Date Palm Rachis as Filler
Get PDFThe present study investigated the preparation of biomatrices from Stipa tenacissima L. and its valorization for fiberboard application. Resins were produced by extracting lignin from the Stipa tenacissima L. black liquor by soda process and combining it with glyoxal as crosslinking agent to produce lignin-glyoxal-resin (LGR). The matrix was characterized by several methods, such as FTIR and ATG/ATD, and then mixed with date palm rachis as reinforcing fibers in different proportions of 30 and 50% (w/w with respect to the matrix) to produce biodegradable composite materials. Then, their thermal and mechanical properties were determined, using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results obtained show that date palm rachis particles were effective in enhancing the thermo-mechanical properties of the thermoset matrix