Flow Activation Energy Research Articles

Transient rotating nanofluid flow over a Riga plate with gyrotactic micro-organisms, binary chemical reaction and non-Fourier heat flux

Bioconvection for rotational flow is conceived to provide stability to improved thermal transportation for nanofluid flow over Riga plate design. Nanoparticles are considered due to their unusual characteristics like extraordinary thermal conductivity, which are significant in heat exchangers, advanced nanotechnology, electronics, and material sciences. Cattaneo–Christov theory and activation energy are incorporated. The unsteady three dimensional partially differentiate formulation is simplified in the form of two independent coordinates (ζ,η). For steady-state solution (ζ=1), Galerkin discretization in used to employ finite element simulation in MATLAB environment. The unsteady parameter rotating parameter, thermophoresis, and Brownian motion parameter escalated the nanofluid temperature field. Modified electromagnetic parameter MH accelerated the primary flow velocity and activation energy augmented the volume fraction of nanoparticles in the boundary layer region. The larger modified Hartmaan number MH reduces the coefficient of skin friction in primary direction but the magnitude of coefficient of skin friction in secondary direction is augmented. The local Nusselt number Rex1/2Nux is directly proportional to MH but it is inversely related to β. The higher values of Brownian motion and thermophoresis boosted the temperature. An excellent accord among the present and previously existing solutions is establishes the validity of the current findings.

The effect of TiO2 on the thermal stability and structure of high acidity slag for mineral wool production

In order to promote the application of Ti-bearing blast furnace slag in mineral wool manufacture, the viscosity, thermal stability and structure of melt were studied in this paper. And the concept of “Extreme Heat Release of Slag (EHRS)” was firstly proposed to quantify the thermal stability of melt. The results showed that slag viscosity decreased with the increase of TiO2 content in the range of 0wt% to 6wt% at acidity coefficient (Mk) of 1.0~1.6. TiO2 reduced the heat capacity of melt, but increased the EHRS. And when the Mk was 1.3, the EHRS was relatively large. The variation of activation energy of viscous flow had a good agreement with that of viscosity. In addition, TiO2 acted as network modifier in the melts, which decreased the average number of bridging oxygens from 2.93 to 2.71. Ti4+ mainly existed in the form of [TiO4] 4– monomers and O–Ti–O in chain or sheet units, resulting in the decrement of slag stability. At the Mk of 1.3, increasing TiO2 content to 6wt% would beneficial for the production of fibers with uniform diameter and length.

Rheological and NMR Studies of Cellulose Dissolution in the Ionic Liquid BmimAc.

Solutions of two types of cellulose in the ionic liquid 1-butyl-3-methyl-imidazolium acetate (BmimAc) have been analyzed using rheology and fast-field cycling nuclear magnetic resonance (NMR) spectroscopy, in order to analyze the macroscopic (bulk) and microscopic environments, respectively. The degree of polymerization (DP) was observed to have a significant effect on both the overlap (c*) and entanglement (ce) concentrations and the intrinsic viscosity ([η]). For microcrystalline cellulose (MCC)/BmimAc solutions, [η] = 116 mL g-1, which is comparable to that of MCC/1-ethyl-3-methyl-imidazolium acetate (EmimAc) solutions, while [η] = 350 mL g-1 for the commercial cellulose (higher DP). Self-diffusion coefficients (D) obtained via the model-independent approach were found to decrease with cellulose concentration and increase with temperature, which can in part be explained by the changes in viscosity; however, ion interactions on a local level are also important. Both Stokes-Einstein and Stokes-Einstein-Debye analyses were carried out to directly compare rheological and relaxometry analyses. It was found that polymer entanglements affect the microscopic environment to a much lesser extent than for the macroscopic environment. Finally, the temperature dependencies of η, D, and relaxation time (T1) could be well described by Arrhenius relationships, and thus, activation energies (Ea) for flow, diffusion, and relaxation were determined. We demonstrate that temperature and cellulose concentration have different effects on short- and long-range interactions.

Densification of glass powder studied by master sintering curve and master kinetic curve methods

AbstractThe master sintering curve method was applied to analyze the sintering and crystallization behavior of 15Na2O.10CaO.75SiO2 (SLS) and 17Na2O.33CaO.50SiO2 (NC2S3) glasses, in mol %. The densification of samples was successfully analyzed using the master sintering curve (MSC) method; it gives activation energy Q = 310–340 kJ.mol−1, which is in good agreement with the expected activation energy of the viscous flow. While the obtained activation energy enables predicting the sintering behavior of SLS glass, the actual results are different from the estimated data for NC2S3. The activation energy of crystallization of NC2S3, determined by constructing Master Kinetic Curves (MKC) was lower than the sintering activation energy: this impairs the prediction ability of MSC for NC2S3 glass.

Thermophysical Properties of Pipe Steel in the Liquid State

The temperature dependences of the kinematic viscosity and surface tension of liquid pipe steel with different modes of melt preparation were investigated. A transition zone was found on the temperature dependences of the thermophysical properties, which separates the regions with different activation energies of viscous flow and surface tension. At the heating stage in the transition zone, the thermal decomposition of clusters based on cementite Fe3C occurs. As a result of the decomposition, free carbon atoms appear which tend to give a uniform distribution in liquid iron with increasing temperature. At a low content of alloying elements and impurities, a high-temperature melt should have a large-scale cluster structure, which provides a more uniform distribution of chemical elements. The melt after vacuum degassing has a narrow transition zone near 1920 K, in contrast to the wide transition zone of the melt without vacuum degassing. The wider transition zone is shifted to high-temperature and this shift is associated with the thermal decomposition of carbides and oxides. Studies have shown that heating liquid pipe steel above the temperature of the liquid–liquid structural transition makes it possible to obtain a more homogeneous structure with a more uniform distribution of alloying and impurity elements in the melt. The sharp drop in surface tension at temperatures above 1920 K in the melt without vacuum degassing is associated with the diffusion of free S and O atoms, which are released after thermal decomposition of sulfides and oxides.

Life at low Reynolds Number Re-visited: The apparent activation energy of viscous flow in sea water

In a 1976 lecture entitled “Life at low Reynolds Number,” Edward Purcell examined constraints on mobility of small aquatic animals defining the energetic challenge as “to move far enough to beat diffusion.” We show that the essential requirement is the need to do sufficient work to overcome the activation energy of viscous flow. Raman spectroscopy shows that sea water is dominated (78–85%) by the hydrogen bonded forms, primarily as the large (H2O)5 tetrahedral pentamer form. Two hydrogen bonds must be broken to disrupt this structure. The strength of the hydrogen bond in water is ~8.4 kJ/mol and the experimentally determined activation energy of viscous flow (~16.7 kJ/mol) is approximately equal to that required to break two hydrogen bonds in water. For viscous flow to occur a molecular vacancy must form for a flowing molecule to move into; the smaller the vacancy needed the less energy required. The heat created by a small animal swimming breaks hydrogen bonds thus forming a layer of small non-hydrogen bonded H2O molecules around the animal. These “lubricate” the surface yielding far more efficient viscous flow. The activation energy of the viscous flow of water decreases with pressure most likely due to the weaker strength of the hydrogen bond under pressure – lab and field data support this observation. The dissipation of tidal energy as heat, often attributed to “intermolecular forces,” is directly related to the breaking of hydrogen bonds.

Rheological investigation and injection optimization of Fe–2Ni–2Cu feedstock for metal injection molding process

In this study, rheological behavior and optimized injection parameters for Fe–2Ni–2Cu feedstock in the metal injection molding process were investigated using the capillary and Taguchi methods. For this purpose, the critical solids loading obtained for the feedstock by analyzing various solids loading (56–64 vol%). In the next step, fundamental rheological characteristics of a homogenized feedstock, including flow behavior index (n), flow activation energy (E), and general moldability index (αstv), were studied. Optimization of the most important injection parameters, including injection speed, injection temperature, mold temperature, and holding pressure, was conducted applying the Taguchi method. According to the results of experiments, injection speed plays a significant role in increasing the density and flexural strength. Also, there are optimum points for injection temperature and mold temperature, while holding pressure does not significantly influence the density and flexural strength. Satisfying results have been shown in green density and flexural strength after the verification test. Rheological behavior analysis showed 60 vol% as critical solids loading, while the proper solids loading considered to be 58 vol% in order to make an easier flow during the injection for the feedstock. The flow behavior index of developed feedstock indicates the shear rate sensitivity was desirable since it shows less than one value. Also, flow activation energy, which shows the feedstock sensitivity to the temperature changes, came out to be 78.138 kJ/mol. Finally, The general moldability index was calculated to be 3.1302E-06 Pa−1 K−1 by using these parameters.

Design and synthesis of a novel spinnable polyborazine precursor with high ceramic yield via one‐pot copolymerization

AbstractSynthesis of spinnable precursors with high ceramic yield is a crucial issue in BN fibers manufacturing by polymer‐derived ceramics (PDCs) route. Spinnability and high ceramic yield are the basis of precursor processability, formability, and mechanical properties. Herein, based on DFT simulation, we designed and synthesized a novel polymer precursor poly[2‐propylamino‐4,6‐bis(methylamino) borazine‐co‐tri(methylamino) borazine] (PPMAB) via a facile one‐pot copolymerization strategy. The random copolymerization model of condensations was obtained through DFT calculation. The molecular chain structure, molecular weight, and molecular weight distribution were optimized by adjusting the synthesis conditions. The precursor PPMAB‐1:1 with a high ceramic yield of 62.43% and concentrated molecular weight distribution (PDI < 1.3) was obtained. Rheological performance research revealed the excellent and stable spinnability of PPMAB‐1:1 by the tunable viscosity and low flow activation energy (23.61 kJ/mol). As a demonstration of spinnability, continuous BN fiber with a fine diameter (>10 km, 7.60 ± 1.13 μm, and 1.6 GPa) was obtained after melt spinning. The present work effectively improved the ceramic yield and spinnability of polyborazine precursors. Simultaneously, it can be used extensively as a universal method to prepare multifunctional copolymers with precise structure control.

Estimation of the boiling point and prediction of the VLE in methyl benzoate + N-octane binary liquid systems via viscosity-temperature dependence at atmospheric pressure

Prediction and estimation of physicochemical properties of binary mixtures are of high importance for understanding the structure and molecular interactions. Excess and deviation properties exhibiting non-linear behaviour in methyl benzoate + n-Octane binary liquid mixtures at (303.15, 308.15, and 313.15) K for density and viscosity experimental values were presented in our earlier work. Here these experimental and calculated values were utilized to explore the applicability of the predictive Haj-Kacem equation and the recently proposed Messaâdi equation as well as their corresponding relative and derivative functions. Their correlation ability at different temperatures, with different parameters are also discussed in the case of limited experimental data. These relative functions are important to reduce the effect of temperature and, consequently, to unveil the effects of different natures of interactions. Despite the quasi-equality between the enthalpy for viscous flow activation ΔH*, and the viscosity Arrhenius energy of activation Ea, it limits excess partial molar energy of activation Ea1 and Ea2 for methyl benzoate and n-Octane, respectively, are investigated, along with their individual contributions independently. Molar activation energies at infinite dilution were deduced from different methods, activation parameters and partial molar Gibbs energy of activation for viscous flow against compositions were investigated. The results of these observations have been interpreted in terms of the structural effects of the solvents. In this context, a correlating equation is proposed in the present work and to estimate the normal boiling temperature of pure constituents and the nature of the isobaric vapour-liquid diagram in the binary liquid mixture. The obtained equations present a satisfactory result and are expected to be useful for future studies.

Enhanced thermally conductive and thermomechanical properties of polymethyl methacrylate (PMMA)/graphene nanoplatelets (GNPs) nanocomposites for radiator of electronic components

In this work, multi-layer hot pressing (MLHP) method was used to prepare the graphene nanoplatelets (GNPs) filled polymethyl methacrylate (PMMA) composites. Effect of GNP content on the viscoelastic behavior and thermomechanical properties of composites was studied via rheometer, scanning electron microscope (SEM), infrared thermal imaging (ITI) and dynamic mechanical thermal analysis (DMTA), etc. According to dynamical rheological testing, thermorheological complexity was clearly displayed at elevated GNP content, based upon flow activation energy (Ea) and time-temperature superposition (TTS) principle. The infrared thermal imaging (ITI) indicated that a filler conductive network was gradually formed with increasing filler content. The average heating rate of the samples increased from 0.74 to 0.92 °C/s. The Agari model was found to fairly interpret the variation of thermal conductivity as a function of GNP loading, which agreed well with SEM observation and indicative of the formation of a GNP network structure. Dynamic thermomechanical properties of the composites were heavily influenced by the temperature distributions within the samples. The addition of GNP increased the glass transition temperature of PMMA from 116.7 to 125.9 °C, which favored enhanced thermophysical properties of PMMA. The prepared composites in this work showed wonderful mechanical properties even at relatively high temperatures (e.g., having storage modulus of 1.3–1.9 GPa and yielding strength more than 58.0 MPa at 50 °C). The current work is practically significant for further expanding the application range of PMMA/GNP nanocomposites.

Hot Deformation Behaviour and Processing Map of Cast Alloy 825

Alloy 825 is a nickel-based alloy that is commonly used in applications where both high strength and corrosion resistance are required, such as tanks in the chemical, food and petrochemical industries and oil and gas pipelines. Components made from Alloy 825 are often manufactured using hot deformation. However, there is no systematic study to optimise the processing conditions reported in literature. In this study, a processing map for as-cast Alloy 825 is established to maximise the power dissipation efficiency of hot deformation in the temperature range of 950 to 1250 °C at an interval of 50 °C and strain rate range of 0.01, {text{s}}^{ - 1} to 10.0, {text{s}}^{ - 1} to a true strain of 0.7 using a Gleeble-3500 thermomechanical simulator. The processing conditions are also correlated to the Vickers hardness of the final material, which is also characterised using optical microscopy and scanning electron microscopy, including electron backscattered diffraction. The true stress-true strain curves exhibit peak stresses followed by softening due to occurrence of dynamic recrystallization. The activation energy for plastic flow in the temperature range tested is approximately 450,{text{ kJ mol}}^{ - 1}, and the value of the stress exponent in the (hyperbolic sine-based) constitutive equation, n = 5.0, suggests that the rate-limiting mechanism of deformation is dislocation climb. Increasing deformation temperature led to a lower Vickers hardness in the deformed material, due to increased dynamic recrystallization. Raising the strain rate led to an increase in Vickers hardness in the deformed material due to increased work hardening. The maximum power dissipation efficiency is over 35%, obtained for deformation in the temperature range 1100-1250 °C and a strain rate of 0.01, {text{s}}^{ - 1}-0.1, {text{s}}^{ - 1}. These are the optimum conditions for hot working.

Effect of Physical Fields on Highly Resinous Oil

This paper studies the effect of physical fields (i.e. ultrasonic and constant magnetic fields) on structural and energy properties (viscosity, limiting shear stress, pour point, activation energy of viscous flow) as well as kinetic (antioxidant) properties of highly resinous problematic oil. The results were obtained via viscometry, determining of pour point and voltammetric method of oxygen electroreduction. It was shown that the treatment of studied oil by acoustic and magnetic fields lead to decrease in viscosity and temperature parameters. Combined treatment displays an additional reduction of viscosity and pour point

Multiarm Star-Shaped Polydimethylsiloxanes with a Dendritic Branching Center.

New multiarm stars have been synthesized based on polylithium derivatives of high-generation carbosilane dendrimers. In the synthesis of multiarm stars based on the eighth-generation dendrimer, steric hindrances were observed even during the synthesis of a polylithium initiator. Subsequently, this led to chain transfer reactions between growing arms, as well as other side effects. As a result, dense nanogel formations with a higher tendency of ordering than in classical objects of this type were isolated from the reaction mixture. The study of the rheology of multiarm stars based on sixth-generation dendrimers made it possible to determine the activation energies of viscous flow in these objects, which makes it possible to consider them as objects with a macromolecular nature and a reptation flow mechanism.

Significance of Brownian motion and thermophoresis influence on dynamics of Reiner-Rivlin fluid over a disk with non-Fourier heat flux theory and gyrotactic microorganisms: A Numerical approach

Bioconvection for rotational flow is conceived to provide stability to improved thermal transportation for Reiner-Rivlin nano fluid over a disk with multi-slips. The nonFourier heat flux, binary chemical reaction, magnetic force, and activation energy are incorporated. A system of nonlinear differential equations in coupled form is acquired through the fundamental relations of Reiner-Rivlin fluids. The Runge-Kutta method of fourth-order is used to solved differential equations in MATLAB environment. The impact of various parameters are discussed and drawn physically with the help of graphs. The Reiner-Rivlin fluid parameter, magnetic parameter, thermophoresis, and Brownian motion parameter escalated the nanofluid temperature field. The electromagnetic parameter and Reiner-Rivlin fluid parameter decelerated the primary flow velocity and activation energy augmented the volume fraction of nanoparticles in the boundary layer region. An excellent accord among the present and previously existing solutions is establishes the validity of the current findings.

Effect of MnO and CaO substitution for BaO on the viscosity and structure of CaO-SiO2-MgO-Al2O3-BaO-MnO slag

The effect of MnO and CaO substitution for BaO on the viscosity and structure of CaO-SiO2-MgO-Al2O3-BaO-MnO slag was investigated using the rotating cylinder method and the structure was analyzed by employing FT-IR and XPS. The results showed that the viscosity at various temperatures decreased gradually when MnO content increased from 0wt% to 3wt%, and increased with BaO content rising from 0wt% to 5wt%, which was consistent with the corrected optical basicity (Λcorr). The activation energy for viscous flow (Eη) showed the similar trend. FT-IR and XPS spectra analysis indicated that both [SiO4]-tetrahedral and [AlO4]-tetrahedral were influenced by MnO and BaO content. The [SiO4]-tetrahedral and [AlO4]-tetrahedral network structures were depolymerized due to an increase in the relative fraction of free oxygen (O2−) and decrease of bridging oxygen (O0) with the increasing MnO content. As a larger amount of CaO was substituted by BaO, the trough depth of [SiO4]-tetrahedral and [AlO4]-tetrahedral bands became deeper, indicating the complexity of network structure and polymerization degree of slag increased, which led to an increase in viscosity.

Effect of Unburned Pulverized Coal on the Melting Characteristics and Fluidity of Blast Furnace Slag

A substantial amount of attention has been paid to viscosity due to its substantial effect on the fluid dynamics of molten blast furnace slag and slag metal reaction kinetics during the pyrometallurgy process. To clarify the influence mechanism of unburned pulverized coal (UPC) on blast furnace (BF) slag viscosity, the effects of different contents of UPC on the BF slag viscosity, free-running temperature and viscous flow activation energy were investigated. The slag viscosity was measured by the rotating cylinder method, and the microstructure of the cooled slag was observed by SEM. As a result, the main reason for a change in the slag viscosity, free-running temperature and viscous flow activation energy was that the UPC entering the slag formed a large number of white particles that predominantly comprised deposited carbon and a high melting point solid solution. In addition, the disintegration or polymerization of the SixOyz- structure was also a contributing factor. When the content of the UPC was 0.6%, the free-running temperature and viscous flow activation energy of slag were 1623 K and 120.969 kJ/mol, respectively, which are lower than those of the slag without UPC. However, the free-running temperature and viscous flow activation energy increased to 1668 K and 286.625 kJ/mol, respectively, when the content of UPC increased to 4%, which are higher than those of slag without UPC.

Hydroxyethylresorcinol- and hydroxyethylhydroquinone-containing poly(ethylene terephthalate) copolymers

Melt polycondensation incorporating meta-substituted hydroxyethylresorcinol (HER) or para-substituted hydroxyethylhydroquinone (HEH) regioisomers enabled the synthesis of poly(ethylene terephthalate) (PET)-based (co)polyesters with targeted comonomer mol %. Incorporation of either HER or HEH lowered the glass transition temperature (Tg) relative to PET, but the 5% weight loss temperature (Td,5%) remained unchanged. Similarly, the semi-crystalline morphology varied as a function of comonomer selection and mol % comonomer. Dynamic mechanical analysis confirmed decreasing β-relaxation intensities upon HER and HEH incorporation, while HER impacted β-relaxation intensity more substantially at similar mol %. HER incorporation also shifted the β-relaxation temperature (Tβ) to lower temperatures considerably more than HEH. Time-temperature-superposition (TTS) and Williams-Landel-Ferry (WLF) analysis of melt rheology probed various physical polymer properties including melt flow activation energy (Ea), fractional free volume at Tg (fg), and molecular weight of entanglement (Me). HER-based (co)polyesters exhibited lower Ea compared to HEH. Likewise, HER incorporation lowered fg while HEH incorporation increased fg. HER-based (co)polyesters possessed a higher Me compared to HEH-based (co)polyesters, although both copolymers resulted in higher Me compared to PET. Tensile testing revealed HER/HEH-based (co)polyesters ultimate mechanical performance compared to amorphous PET. Both HER and HEH incorporation increased Young's moduli and yield strengths, although comonomer incorporation above 25–30 mol % yielded minimal change. Establishing structure-property relationships provided insight into the role of regioisomeric variation at various comonomer levels on thermal, rheological, and mechanical performance for PET-based copolymers.

A polysaccharide from Lignosus rhinocerotis sclerotia: Self-healing properties and the effect of temperature on its rheological behavior

This work investigated the self-healing properties of Lignosus rhinocerotis polysaccharide (LRP) and the effect of temperature on its rheological behavior. Dynamic sweep tests (strain sweep, frequency sweep, and time sweep) showed that the LRP/water system possessed self-healing properties due to the entangled network formed by hyperbranched LRP molecular chains. The flow activation energy of LRP solution calculated by Arrhenius equation was shown to decrease with increasing LRP concentration, indicating that LRP solution at higher concentration was less sensitive to temperature. Temperature ramp test exhibited that LRP had a glass transition temperature (Tg) determined as 49.35 °C and the temperature effect was irreversible. Microrheological test revealed that the LRP aqueous solution can form a gel at room temperature with the concentration ≥ 20 mg/mL. This work provided a theoretical basis for the development of LRP-based self-healing materials and facilitated a deep understanding of the temperature effect on rheological behavior of LRP.

A net-shape forming process of Ti–6Al–4V sphere joints

ABSTRACT Near-net shape forming of the hollow sphere joints (60 mm in diameter) used in large space truss structure of spacecraft was realised by powder injection molding and diffusion bonding. For metal injection molding (MIM) process, two binder systems based on polyoxymethylene (POM) and paraffin wax (PW) are comparatively studied. The powder loading, power law index, viscous flow activation energy and integrated rheological factors of feedstock were systematically studied. Except powder loading, The feedstock based on POM system has a smaller strain and temperature sensitivity (n = 0.368, E = 17.95 kJ mol−1) and better rheological properties (α = 6.3). The lowest interstitials contents of as-sintered samples are 0.05 wt-% for C, 0.28 wt-% for O and 0.046 wt-% for N, which meet the Grade 5 PM (Ti–6Al–4V) specifications according to ASTM B988-13. The tensile strength and ductility reach 978 MPa and 6.3%, respectively, after 1300 °C sintering and capsule-free hot isostatic pressing (HIP).

Non‐isothermal gas‐assisted displacement of viscous Newtonian fluids at high capillary number in gas‐assisted injection molding

AbstractGas‐assisted injection molding is a polymer processing technology in which a penetrating gas bubble hollows out a plastic part as it cools and solidifies within a mold. In this study, non‐isothermal gas injection experiments at high capillary number illustrate the effects of delay time in gas injection, tube diameter, capillary number, and temperature‐sensitive fluid viscosity and flow activation energy on coating thickness. Experiments with polybutene H‐300 and Dow Corning silicon oil (DC‐200) in stainless steel tubing (1.27 and 0.635 cm) demonstrated fractional coverage increasing from 0.6 to a maximum in the range of 0.63–0.83 at short delay times, then decaying toward 0.6 at long delay times upon approaching the cooled isothermal state. Further analysis is drawn from simulations based on a simple theoretical model incorporating one‐dimensional heat transfer with convection at the outer surface of the mold, non‐isothermal behavior of the viscous fluid, and radial velocity profiles in the one‐phase fluid flow region. Quantitative agreement is found between experimental and simulated results. Two‐dimensional modeling and simulation methods extend the prior results to illustrate transient axial and radial heat transfer as well as flow behavior with respect to the penetrating gas bubble within the fluid flow region.