Flow regimes in the emptying of pipes filled with a Herschel–Bulkley fluid

The emptying of pipework from fluids of high viscosity is a significant multiphase flow problem in many food and personal care industries. Maximising product recovery whilst minimising cleaning time and effluent volume is important in minimising the environmental footprint of the plant. The cleaning of pipework fully filled by toothpaste by water under different process conditions has been studied and monitored by weighing pipes at intervals. Three flow regimes have been identified; a short core removal stage of product recovery, before water breaks through the filled pipe, and two in subsequent cleaning, film removal when there is a continuous wavy annular film on the wall, and patch removal in which the material is present as patches on the wall. The amount of product recovered in core removal is here not a function of flow conditions; however, conditions during core removal significantly affect the overall cleaning time. Overall cleaning time can be reduced by at least 25% by selecting the best removal conditions in the different stages. It is hypothesised that this is due to changes in the wall layer induced during core removal, with a very wavy wall layer leading to rapid subsequent removal. If this effect could be understood and scaled up it may be possible to improve commercial cleaning processes.     

Structural characterization of a biosurfactant produced by Bacillus subtilis at 45°C

Structural and biochemical characterization of a biosurfactant produced by Bacillus subtilis under thermophilic conditions was performed. Preliminary structural determination of CHCl₃/CH₃OH (65∶15) extracts by thin-layer chromatographic reagents showed it to be identical to surfactin. Also, the infrared, ¹H nuclear magnetic resonance, and mass spectroscopy analysis confirmed it to be identical to surfactin. Biochemically, the surfactant was a lipopeptide-containing lipid (17.05%) and protein (13.2%). The surfactant yielded a minimal aqueous surface-tension value of 28 dyne/cm and an interfacial tension value at 0.1% concentration of 0.2 dyne/cm against diesel oil. The critical micelle concentration of the surfactant was 35 mg/L. The biosurfactant exhibited an emulsification value (E ₂₄) of 90 against diesel oil and a sand-pack oil recovery of 62%. It has potential application in microbial-enhanced oil recovery in thermophilic, alkaline, acidic, and halophilic environments.     

Coupled CFD–DEM of particle-laden flows in a turning flow with a moving wall

The nature of the particle–solid interactions and particle–fluid interactions in rectangular duct bend geometry with/without a moving wall is studied, taking into account particle collision, colloidal, and hydrodynamic forces, and four way coupling between the fluid flow and particles. The focus is on systems where particles and fluid phase have similar length scales, fluid Reynolds number (Re_f) ∼ 1, and particle's Stokes number (St) ∼ 1. Particles move toward the walls of the channel near the bend, and have long residence times in these regions. Buoyancy force has negligible effect on particle motion, where adhesion and drag forces lead to particle motion and agglomeration patterns. The effect of a free surface on agglomeration sites in the turning flow is elucidated.     

Reaction of smectites with iron in aerobic conditions at 75 °C

The stability of six dioctahedral smectites with different crystal chemistry was studied in the presence of iron to simulate the possible reactions of clay minerals in contact with Fe canister in a nuclear waste repository. The batch experiments were performed at 75 °C for 35 days in air. The reaction products were examined by XRD, QXRD, FTIR, BWA analyses and UV–Vis spectroscopy. The reaction of bentonites with metal iron led to the consumption of iron and the formation of magnetite and 7-Å phyllosilicate. The original smectites were partially transformed from Al-rich to Fe-bearing. Appearance of the dioctahedral–trioctahedral domains in the octahedral sheets of smectites resulted in the partial destabilization and/or partial dissolution of the smectite structure indicated by the increase of the layer charge, splitting of the smectite particles and partial disruption of the smectite layers. Benefits of NIR spectroscopy were found in identification of FeMgOH and FeFeOH groups, which were not recognized in the MIR region of reacted iron–bentonite mixtures due to overlapping with other absorption bands. The comparison of the present study with the paper of Osacký et al. (2010) showed that smectites reacted differently with iron in air and nitrogen atmosphere. In the aerobic conditions more iron was consumed and less amount of magnetite was formed. The distinct experimental conditions (aerobic versus anaerobic) had the greatest effect on the layer charge and thickness of the smectite particles. Less pronounced changes of the layer charge and thickness of the smectite particles were observed for the iron–bentonite mixtures reacted in the aerobic conditions. It indicated that smectite destabilization was inhibited in the aerobic conditions.     

Structure and properties of pyrolytic carbons prepared in a fluidized bed between 1900° and 2400°C

Pyrolytic carbon deposits were produced in a fluidized bed between 1900° and 2400°C from a carrier gas containing between 1% and 15% methane. The carbons had either a ‘granular’, ‘laminar’ or ‘isotropic’ microstructure. Formation of “granular” carbon occurred at low methane partial pressures and low bed surface areas. Increasing the deposition temperature decreased the metallographic grain size and increased the density, X-ray apparent crystallite size, and preferred orientation of the granular deposits so that at the highest temperature, the deposits took on a laminar appearance. Increasing the deposition temperature increased the crystallite size and density of the isotropic and transition deposits. The elastic moduli and fracture stresses of the carbons deposited from 3% methane rose from 1.5 to 1.8 × 10⁶ psi and 18 to 32 × 10³ psi, respectively, as the deposition temperature was increased from 1900° to 2400°C. The isotropic and transition carbons had fracture stresses of ~30 × 10³ psi and elastic moduli that decreased from ~2.2 to ~1.6 × 10⁶ psi over the deposition temperature range of 1900° to 2400°C. The carbons had thermal conductivities perpendicular to the deposition plane in the range of 1 to 6 × 10⁻² cal/cm sec °C. The conductivities were highest for the isotropic carbons and lowest for the most highly oriented laminar carbons. The relations between deposition conditions, structure, and properties are discussed.     

Numerical Study of Solid-Liquid Two-Phase Flow in Stirred Tanks with Rushton Impeller (Ⅰ) Formulation and Simulation of Flow Field

Three-dimensional solid-liquid flow is mathematically formulated by means of the "two-fluid" approach and the two-phase k-ε-Ap turbulence model. The turbulent fluctuation correlations appearing in the Reynolds time averaged governing equations are fully incorporated. The solid-liquid flow field and solid concentration distribution in baffled stirred tanks with a standard Rushton impeller are numerically simulated using an improved "inner-outer" iterative procedure. The flow pattern is identified via the velocity vector plots and a recirculation loop with higher solid concentration is observed in the central vicinity beneath the impeller. Comparison of     

Methanation of carbon dioxide and fluidization quality in a fluid bed reactor—the influence of a decrease in gas volume

A large decrease of fluidization quality was observed when methanation of carbon dioxide was carried out in a fluid-bed reactor even if the catalyst particles had the optimal properties for good fluidization. The cause of this phenomenon was explored by measuring pressure fluctuations, bubble frequency and extent of CO₂ conversions. The results indicated that the decrease of the fluidity was caused by a reduction in volume of reactant gases due to the reaction. The voidage in the emulsion phase is considered to be an important factor affecting the fluidity. The fluidization quality and contacting efficiency could be improved by such devices as baffle internals or two-stage spargers.     

Strength and deformation of concrete with variable content of moisture at elevated temperature up to 90°C

It is known, that the change of mechanical properties of concrete due to elevated temperature is also influenced by the moisture content. This change was primarily studied for prestressed concrete reactor vessels (PCRV). Because a PCRV is a mass concrete structure, the results of this research cannot be transfered to slender members. To simulate drying conditions of the latter, specimens of differing initial moisture content were subject to elevated temperatures and defined climates. The results of tests reveal the differing influence of moisture on strength and modulus of elasticity. The compressive strength is partly increased, partly decreased as the moisture content grows. Tensile strength and modulus of elasticity are weakened by decreasing moisture. Also the thermal strain as function of type of aggregate and moisture content was studied. The changes are caused by the alteration of structure of cement stone and by microcracks due to incompatibility.     

Measurement and analysis of particle—particle interaction in a cocurrent flow of particles in a dilute gas—solid system

The experimental apparatus of Arastoopour et al.[3] was modified to measure pressure drop and solid velocities for cocurrent flow of particles in a pneumatic conveying line. The data were translated into particle—particle interaction expression using a force balance over the particles. The particle interaction is a combination of collision and drag force in a particles low relative velocity region. A correlation for particle—particle interaction with relative velocity between the particles of 0.3–4.6 m/s has been developed. The correlation describes our experimental data within the 10% deviation.     

LF-NMR to explore water migration and water–protein interaction of lamb meat being air-dried at 35°C

To decrease the drying time and energy consuming, water migration and water–protein interactions of lamb meat being air-dried at 35°C were investigated. Low-field nuclear magnetic resonance T_2b indicated the water–protein interactions changed during air-drying. Area of T₂₁ (intramyofibrillar water) decreased, meanwhile the area of T₂₂ (extra-myofibrillar water) increased when the moisture content decreased from 55 to 45%, indicating the water migrated from myofibril to extramyofibril. Drying rate (the rate of water migration from meat to air) could be predicted by the area of T₂ populations, and the correlation coefficient was 0.990. Change of water binding and hydration in myofibrils was evident by the increase in hydrophobicity and decrease in solubility of myofibrillar protein. Differential scanning calorimetry showed denaturation of myosin in dried meat which might result in water migration from myofibril to extramyofibril space. In conclusion, water–protein interactions changed, and then influenced the drying rate during drying.     

Creep of a Nextel™720/alumina ceramic composite containing an array of small holes at 1200°C in air and in steam

Tensile stress-strain and tensile creep behaviors of an oxide-oxide composite containing an array of small circular holes were evaluated at 1200°C. The composite consists of Nextel™720 alumina-mullite fibers in a porous alumina matrix. Test specimens contained an array of 17 holes with 0.5-mm diameter drilled using a CO₂ laser. The presence of holes caused reduction in tensile strength and modulus. Tensile creep tests were conducted at 1200°C in air and in steam at creep stresses ranging from 38 to 140 MPa. Primary, secondary, and tertiary creep regimes were noted in air and in steam. The presence of the laser-drilled holes accelerates the steady-state creep rates. Creep run-out, defined as 100 hours at creep stress, was attained for stress levels <60 MPa in air and for stresses <40 MPa in steam. The presence of the laser-drilled holes significantly degrades creep resistance of the composite. The retained tensile properties of all specimens that attained run-out were determined. Composite microstructure was examined; the damage and failure mechanisms were considered. The degradation of tensile properties and creep resistance are attributed to damage caused to composite microstructure by laser drilling.     

Multiscale investigation on fatigue properties and damage of a 3D braided SiC/SiC + PyC/SiC composites in the full stress range at 1300 °C

Monotonic tensile and fatigue tests of a SiC/SiC composites were conducted at 1300 °C in the full stress range. The macroscopic behaviors were studied based on the strain data. The mesoscopic morphology was observed by X-ray computed tomography, and the microanalysis was conducted using SEM, EDS and XRD. Besides, the interfacial debonding strength (IDS) were measured by nano-indenter. The results reveal that the fatigue behaviors can be divided into three zones. The inelastic strains accumulation and stiffness reduction can be observed in all three zones due to matrix cracking, interface damage, and failure of fibers. The fatigue life is long in the run-out zone because the maximum stress is lower than the proportional limit stress (PLS). In the stress-insensitive zone, the fracture depends on high-temperature and oxidation effects. The failure in the stress-sensitive zone is dominated by the fiber strength. The interface behaviors greatly affect the fatigue life above the PLS.     

Role of π-π interactions and chain flexibility in dispersion and dynamic-mechanical properties of nanocomposites with multiple wall carbon nanotubes

Two polymers of same functional group were used; one with greater chain flexibility, PA 6.6, and the other with two benzene rings in the main chain, PA 6I-6T (aPA), to evaluate how the structure influences on the nanoparticle dispersion homogeneity and on dynamic-mechanical properties. In the aPA nanocomposites, good dispersion and homogeneous distribution were observed for all CNT concentrations. However, PA 6.6 nanocomposites showed agglomerated regions in all formulations. The interfacial energy of the aPA/CNT was five times lower than that of PA6.6/CNT, resulting in greater compatibility in this nanocomposite. An increase of up to 26% was observed with 2.5% of CNT in aPA nanocomposites storage modulus. In the samples with PA 6.6, the increase was at most 5%. Even with greater flexibility of PA 6.6 macromolecules, the π-π interaction between the aPA aromatic rings and CNTs might be the decisive factor for dispersion improvement and positively influence on the dynamic-mechanical properties of these nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48195.     

Gas‐Dynamic Method of Combustion Control and Flame Stabilization in a Pseudoliquid Fuel Flow

A gasdynamic method for controlling combustion and flame stabilization in a pseudoliquid fuel flow is proposed. The method is based on injection of additional air jets with varied frequency into a chamber with abrupt expansion. It is shown that the characteristics of combustion of the pseudoliquid fuel can be controlled by varying the frequency of injection of periodic air jets.     

Ion-pair formation and walden product of some s-alkylisothiouronium salts in non-aqueous solvents at 25°C

Precise conductance measurements have been made on 11 s-alkylisothiouronium salts in dimethylformamide at 25±0.02°C. The experimental data have been analysed on the basis of Fuoss' equation [R. M. Fuoss, J. Phys. Chem. Ithaca79, 525 (1976), correction p. 1893, ibid.81, 1529 (1977). Proc. Natl Acad. Sci. USA77, 34 (1980)] using the NEW SCAN and R-PRESET programs. The parameters Λ₀, K_A and R have been calculated for each salt. Single anionic conductances (Br⁻, I⁻ and Pi⁻) in both DMF and DMSO were determined using the newly developed method [H. Sadek and A. M. Hafez, Electrochim. Acta21, 767 (1976)]. The validity of the suggested equation [H. Sadek and A. M. Hafez, Pak. J. Sci. Res.33, 24 (1981)] which relates the Walden product with the reciprocal molecular weight is proved for electrolytic solutions in dipolar aprotic solvents. Finally cationic conductances are recorded in both DMF and DMSO at 25°C and were found to decrease as cationic size increases.     

Experimental and numerical study of grain growth in alumina fibres heat treated at 1700°C

The studied material is an alumina fibre acting as a reinforcement in a NiAl/Al₂O₃ composite. The processing of this composite involves a 1700°C heat treatment. Grain growth phenomena taking place within the fibre during that step are investigated. Above 1600°C, the size of the grains reach the fibre diameter for a 1 h heat treatment. Further morphological evolution is discussed using thermodynamic calculations. Taking into account the presence of the liquid alloy, a deepened grain boundary groove is predicted and experimentally observed. The second part of this work deals with grain growth modelling during the heating and cooling steps. A cubic grain growth kinetics law is found and is used to predict final grain sizes as a function of heating and cooling rates.     

Ablation of graphite in oxygen and air at 1000–1400°C under flow conditions

The ablation of high-purity graphite in oxygen and air atmospheres was studied in the 1000–1400°C temperature range, gas pressures of 2–19 torr and flow rates of 7.6×10¹⁸ to 3.6×10²⁰ atoms/sec. Gas diffusion effects were eliminated by the use of small samples and fast flow-rates. Very fast ablation rates were observed. The kinetic data are best fitted to a model based on mobile adsorption as the rate limiting step with a heat of activation of 39,000 cal/mole.     

Mathematical Modeling of Gas–Liquid Flow Patterns in an Annular Space with a Rotating Inner Cylinder

Theoretical Foundations of Chemical Engineering - Gas–liquid flow patterns were mathematically modeled in the annular space between two coaxial cylinders, the inner cylinder of which rotates...