The rise of a buoyant sphere in a gas-fluidized bed

The rise velocity, V, of a single sphere, released in the bottom of a bed of sand fluidized by air, was measured: the sphere had a diameter of 9.0 or 13.2 mm; its density ranged from 900 to . These experiments with a single sphere used: (i) a bubbling bed, diameter 141 mm, with 1.05<U/U_mf<2.00, (ii) a slugging bed, diameter 24 mm, with 1.70<U/U_mf<3.20. Here U is the fluidizing velocity; U=U_mf at incipient fluidization. It was found that, for each sphere in a given bed, V=V_mf+C(U-U_mf): the constant C was up to 10 times larger for bubbling beds than slugging beds.The rise velocity at incipient fluidization, V_mf, is governed, for both types of bed, by the apparent viscosity of the incipiently fluidized bed. Therefore, Stokes's law was used to predict V_mf, but using an important modification: since each buoyant sphere appears to carry on its top a defluidized ‘hood’ of particles, Stokes's law was applied to the composite ‘particle’ consisting of the sphere plus its hood. Analysis of the measured V_mf then gave the volume of the hood, in agreement with direct measurements of it above a fixed cylinder in a two-dimensional bed. In addition, the analysis gave the apparent viscosity of the incipiently fluidized bed to be 0.66 Pa s, in excellent agreement with the estimate of Grace (Can. J. Chem. Eng. 48 (1970) 30) for similar sand.     

Mass transfer to a continuous moving surface of a sheet electrode

Correlations are presented for the rate of mass transfer to a continuous moving surface of a sheet electrode at nonzero velocities of the electrolyte bulk. The equations derived are valid for laminar flow, where the velocity of the moving electrode surface U_S and the velocity of the bulk phase U_∞ have the same direction, i.e. the criterion σ ≡ (U_∞ ? U_S)/(U_∞ + U_S) ranges from ? 1 to + The equations cover the Schmidt number range of 1–10 000 with an error less than 1.6% compared to the numerical solution of the Blasius and convectiv diffusion equations. The range of validity of these equations is shown graphically.     

Efficiency of a multistage process

By considering the Hausen stage efficiency E_H in the case of a cocurrent multistage process and a similar stage efficiency E_D in the case of a countercurrent multistage process, general relations giving the overall efficiency and the concentration profiles in both phases are derived. These relations are then extended to the limiting case of a continuous contact.     

Translocation dynamics of a semiflexible chain under a bias: Comparison with tension propagation theory

We study translocation dynamics of a semi-flexible polymer through a nanoscopic pore in two dimensions (2D) using Langevin dynamics simulation in presence of an external force inside the pore. We observe that for a given chain length N the mean first passage time (MFPT)〈τ〉 increases for a stiffer chain. By repeating the calculation for various chain lengths N and bending rigidity parameter κ _b we calculate the translocation exponent α (〈τ〉 ～ N ^α). For chain lengths N and bending rigidity κ _b considered in this paper we find that the translocation exponent satisfies the inequality α < 1 + ν, where is the equilibrium Flory exponent for a given chain stiffness, as previously observed in various simulation studies for fully flexible chains. We observe that the peak position of the residence time W(s) as a function of the monomer index s shifts at a lower s-value with increasing chain stiffness κ _b . We also monitor segmental gyration 〈R _g (s)〉 both at the cis and trans side during the translocation process and find that for κ _b ≠ 0 the late time cis conformations are nearly identical to the early time trans conformations, and this overlap continues to increase for stiffer chains. Finally, we try to rationalize dependence of various quantities on chain stiffness κ _b using Sakaue’s tension propagation (TP) theory [Phys. Rev. E 76, 021803 (2007)] and Brownian Dynamics Tension Propagation (BDTP) theory due to Ikonen et al. [Phys. Rev. E 85 051803 (2012); J. Chem. Phys. 137 085101 (2012)] originally developed for a fully flexible chain to a semi-flexible chain.     

Free coating of a Newtonian liquid onto a vertical surface

The entrainment of Newtonian liquid films onto a vertical surface which is continuously withdrawn from a bath of the liquid is considered. A new theoretical treatment is presented which is significantly different from previous theoreis and which predicts accurately the relationship between the dimensionless thickness parameter, T₀, and the Capillary Number, Ca, up to a value of Ca of 2. Experimental results have been obtained using a capacitance technique for film thickness measurement for a variety of Newtonian fluids with viscosities ranging from 0·006 to 2·06 N. sec m^?2.     

Lanthanide-Dependent Methanol Metabolism of a Proteobacteria-Dominated Community in a Light Lanthanide-Rich Deep Environment

This study investigated the occurrence and diversity of proteobacterial XoxF-type methanol dehydrogenases (MDHs) in the microbial community that inhabits a fossil organic matter- and sedimentary lanthanide (Ln³⁺)-rich underground mine environment using a metagenomic and metaproteomic approach. A total of 8 XoxF-encoding genes (XoxF-EGs) and 14 protein sequences matching XoxF were identified. XoxF-type MDHs were produced by Alpha-, Beta-, and Gammaproteobacteria represented by the four orders Methylococcales, Nitrosomonadales, Rhizobiales, and Xanthomonadales. The highest number of XoxF-EG- and XoxF-matching protein sequences were affiliated with Nitrosomonadales and Rhizobiales, respectively. Among the identified XoxF-EGs, two belonged to the XoxF1 clade, five to the XoxF4 clade, and one to the XoxF5 clade, while seven of the identified XoxF proteins belonged to the XoxF1 clade, four to the XoxF4 clade, and three to the XoxF5 clade. Moreover, the accumulation of light lanthanides and the presence of methanol in the microbial mat were confirmed. This study is the first to show the occurrence of XoxF in the metagenome and metaproteome of a deep microbial community colonizing a fossil organic matter- and light lanthanide-rich sedimentary environment. The presented results broaden our knowledge of the ecology of XoxF-producing bacteria as well as of the distribution and diversity of these enzymes in the natural environment.     

Fracture properties of a rigid polyurethane foam over a range of densities

Single edge notch fracture tests have been carried out on rigid polyurethane foam in the density range 32 to 360 kg/m³. Fracture properties were characterized in terms of the fracture toughness parameter (K_Ic), the critical strain energy release rate (G_Ic) and crack opening displacement (c.o.d.). The values of crack opening displacement lead to a proposed mechanism of crack propagation in foams of density greater than about 140 kg/m³.     

Parametric sensitivity of a CSTR

It is shown that the generalized sensitivity criterion recently developed in the context of thermal explosions and tubular reactors can be easily applied in the case of a CSTR as well. An illustrative example concerning sensitivity analysis of a single nth order irreversible exothermic reaction in a nonadiabatic CSTR is presented. A generalized region of parametric sensitivity is identified where the reactor temperature is parametrically sensitive simultaneously to all the input parameters. Asymptotic analysis for large heats of reaction is performed to investigate limiting behaviour, which leads to the classical Semenov limit in the case of large activation energies. It is shown that parametric sensitivity can occur even when unique steady states exist for all Damköhler number (Da) values. Furthermore, if operating conditions are chosen so as to avoid completely the possibility of parametric sensitivity for all Da, then the possibility of steady-state multiplicity is automatically avoided.     

Identification of a Pm4 Allele as a Powdery Mildew Resistance Gene in Wheat Line Xiaomaomai

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most destructive foliar diseases of wheat. In this study, we combined the bulked segregant RNA sequencing (BSR-seq) and comparative genomics analysis to localize the powdery mildew resistance gene in Chinese landrace Xiaomaomai. Genetic analysis of F₁ plants from a crossing of Xiaomaomai × Lumai23 and the derived F₂ population suggests that a single recessive gene, designated as pmXMM, confers the resistance in this germplasm. A genetic linkage map was constructed using the newly developed SNP markers and pmXMM was mapped to the distal end of chromosome 2AL. The two flanking markers 2AL15 and 2AL34 were closely linked to pmXMM at the genetic distance of 3.9 cM and 1.4 cM, respectively. Using the diagnostic primers of Pm4, we confirmed that Xiaomaomai carries a Pm4 allele and the gene function was further validated by the virus-induced gene silencing (VIGS). In addition, we systematically analyzed pmXMM in comparison with the other Pm4 alleles. The results suggest that pmXMM is identical to Pm4d and Pm4e at sequence level. Pm4b is also not different from Pm4c according to their genome/amino acid sequences. Only a few nucleotide variances were detected between pmXMM and Pm4a/b, which indicate the haplotype variation of the Pm4 gene.     

Break-up of a drop in a stirred tank

The drop break-up mechanism was studied in a stirred tank containing two immiscible liquids. The daughter drops formed by break-up of a single drop of known size were recorded photographically. From the experiments at constant agitator speed the following results were obtained. There is a critical drop size under which drops do not break up under given conditions. The break-up frequency increases approximately linearly with increase in drop volume. The number of daughter drops, v, is a random variable with a mean v > 2 which increases with the volume of the mother drop. The relative volume of a daughter drop has a β-distribution.     

Computational-fluid-dynamics study of a Kenics static mixer as a heat exchanger for supercritical carbon dioxide

The thermal efficiency of a Kenics^® KM static mixer used to pre-heat supercritical carbon dioxide, under high pressure conditions, is studied using computational fluid dynamics (CFD). A mesh sensitivity analysis is performed and the CFD model is validated against experimental results on heat transfer with conventional and supercritical fluids. Three turbulent models - standard k-?, RNG k-?, and k-ω - are employed to model the flow and heat transfer under high pressure conditions; the effects of large variations of the physical properties in the pseudo-critical region of the fluid are also studied. The RNG k-? model gives results that are closer to the experimental data than the other two turbulence models. The numerical results show that the static mixer has a thermal efficiency more than three times higher than that of a conventional empty pipe heat exchanger with similar heat transfer area.     

Formation of a FexSiyCz thin layer via PCV deposition of SiCN on a hot steel surface

In this work, it has been established that on steel plates heated to 600 °C, an Fe_xSi_yC_z layer forms during plasma chemical vapor deposition of SiCN ceramics. As a plasma-forming agent, hexamethyldisilazane was used in the deposition, from which a SiCN product was formed. The deposited ceramic film is heterogeneous and consists of regions where predominantly FeSi₂ or Fe_xSi_yC_z is present. The thickness of the film is~0.8 μm. An investigation of the degradation of the ceramic film in tap water and a 3% aqueous NaCl solution at 26 and 60 °C demonstrated that FeSi₂ corrodes first, and then Fe_xSi_yC_z corrodes. The process was also analyzed using electrochemical techniques.     

Effects of a water-retaining agent on the rheological behaviour of a single-coat render mortar

The effects of a water-retaining admixture on the rheological properties of a cement-based render mortar were studied. This agent, based on a cellulose ether compound, was introduced in contents up to 0.2 wt.%.Rheological behaviour was studied with a rheometer for mortars using two different speed profiles. First, the step profile allowed observing the variation of g and h parameters with the water-retaining agent content, g and h being directly related to yield stress and plastic viscosity. Second, the dwell profile allowed the study of the rheological behaviour variation with time, particularly the study of structural breakdown and reconstruction phenomena. These phenomena could be followed through the evolution of the hysteresis area in the flow curves. It was also possible to conclude that this admixture has a thickening effect except for low amounts (≤ 0.08%) and that it promotes structural breakdown together with a secondary effect of retarding the setting time.     

Simulation and experimental validation of a methanol burner

This paper presents a computational fluid dynamics model of a methanol burner. Special emphasis was placed on the study of the liquid atomization and combustion process. Linearized Instability Sheet Atomization (LISA model) was employed to simulate the fuel atomization process. Predictions of droplet diameters, droplet trajectories, temperatures and gas concentrations are presented and compared with an experimental database presented by Widmann and Presser in their work abenchmarkexperimentaldatabaseformultiphasecombustionmodelinputandvalidation. The predicted and simulated data were found to be in good agreement, however some discrepancies in the amount of unburned species were found probably related with the mechanism of combustion employed.     

Magnetic monitoring of a single particle in a prismatic spouted bed

In this work a non-intrusive measuring technique for continuous tracking of a magnetic marked particle during fluidization in a prismatic spouted bed is presented. The magnetic monitoring system provides besides the spatial coordinates x, y and z the orientation of the particle, whereby the trajectory, the velocity, the acceleration as well as the rotation of the particle are obtained. It will be demonstrated that the characteristic particle trajectories and particle velocity distributions in dependency of the gas throughput and of the bed mass can be detected in this type of spouted bed. Furthermore, a calculated particle velocity distribution obtained by a CFD continuum simulation will be favorably compared with a measured distribution.     

Electrophoresis of colloidal particles in a salt-free medium

A general theory for the electrophoretic mobility of dilute spherical colloidal particles in a salt-free medium containing counterions only is given. This theory assumes that each particle is surrounded by a spherical free volume, within which electroneutrality as a whole holds. It is shown that the mobility can be obtained from the balance between the Stokes drag for the case where the particle is uncharged and the pressure due to the excess counterion charge on the outer boundary of the free volume. The mobility μ is thus expressed as μ=Qexp(y(R))/D, where Q is the particle surface charge, D is the drag coefficient of the particle when uncharged, and y(R) is the scaled potential value at the outer boundary of the free volume.     

Free energy and confinement force of macromolecules in a slit at full equilibrium with a bulk solution

Nondilute athermal and theta solutions of nonadsorbing flexible macromolecules in equilibrium with repulsive slit-like pores were examined by the lattice Monte Carlo simulations. The free energy of confinement ΔA/kT and the force f/kT exerted by polymers on the slit were computed as a function of the slit width D in a wide range of bulk concentrations φ. The free energy and force profiles in nondilute solutions were found to deviate considerably from the ideal chain theory; the perturbation of chains by a presence of the slit walls were substantially reduced in nondilute solutions. The free energy and force functions appropriate for nondilute solutions were derived by fitting the simulation data. Further, the relative pressure p_I/p_E exerted by the nonadsorbing confined molecules on the slit walls was calculated. The depletion effect relevant to colloid stabilization was found in dilute solutions to be slightly weaker for excluded-volume chains than for ideal chains. The relative pressure equation was modified to cover semidilute solutions, by using the mean-field and scaling expressions of the osmotic pressure. Both the relative pressure p_I/p_E and the intra-slit concentration profiles φ_I(x) in tandem display a suppression of the depletion effect with increasing φ in simidilute solutions.     

Mass transfer from a freely moving single sphere to the dense phase of a gas fluidized bed of inert particles

Naphthalene spheres (particle diameter 2 <d_n < 20 mm) were vaporized in beds fluidized by air at a temperature of about 65°C. The bed material consisted of inert glass beads or alumina in the size range 100 <d_p < 700 μm. Mass transfer coefficients were measured by determining weight loss with time, as a function of d_n, d_p and the fluidization velocity U. The ratio d_n/d_p has been varied from 3 to 200. An interesting conclusion might be that there is no influence of the fluidization velocity on these transfer coefficients; they only depend on the minimum fluidization velocity U_mf. The empirical correlation ϵ_mf(j_D)_mfRe_mf^m=0.105 + 1.505 (d_n/d_p)^−1.05 with m = 0.35 + 0.29 (d_n/d_p)^−0.50, as a best fit of all the results, is accurate within 15%. At d_n/d_p = 1 it links up very well with the results of Hsiung and Thodos. For large values of d_n/d_p agreement with known results of mass transfer measurements between a fluidized bed and a wall or an object is good.     

Energy efficient control of a BTX dividing-wall column

Dividing-wall column (DWC) is considered nowadays the new champion in distillation, as it can bring substantial reduction in the capital invested as well as savings in the operating costs. This work presents the simulation results of energy efficient control and dynamics of a dividing-wall column (DWC). In order to allow a fair comparison of the results with previously published references, the case-study considered here is the industrially relevant ternary separation of the mixture benzene-toluene-xylene (BTX) in a DWC. Rigorous simulations were carried out in Aspen Plus and Aspen Dynamics. Several conventional control structures based on PID control loops (DB/LSV, DV/LSB, LB/DSV, LV/DSB) were used as a control basis. These control structures were enhanced by adding an extra loop controlling the heavy component composition in the top of the prefractionator, by using the liquid split as an additional manipulated variable, thus implicitly achieving minimization of energy requirements. The results of the dynamic simulations show relatively short settling times and low overshooting especially for the DB/LSV and LB/DSV control structures. Moreover, the energy efficient control proposed in this work allows the operation of DWC with minimum energy requirements or maximum purity of products.