Electrochemical measurement of flow parameters in dilute solution

A new theoretical method is proposed in the electrochemical measurement to obtain therelationship between flow parameter and the electrode current under the existence of ion migration ef-fect.In this way the measurement of local mass transfer coefficient,wall shear stress and liquid veloc-ity are presented and the experiment results are also described.     

Analysis of dilute solid–liquid suspensions in turbulent stirred tanks

In this work, dilute suspensions of solid particles in stirred tanks are investigated by Particle Image Velocimetry measurements, which were specifically designed to determine the effects of the dispersed phase on mean velocity and turbulence levels of the continuous phase and the local solid–liquid slip velocity. In order to determine the effect of particle size and concentration, glass particles of narrow size distribution were selected; the particle content was increased stepwise up the maximum of 0.2 vol.%. Overall, moderate dampening of liquid turbulent fluctuations was found with the smaller particles, while turbulence enhancement was observed with the bigger ones. Continuous phase turbulence was found to affect the local map of the particle settling velocity, which was also discussed on the basis of a force balance analysis. The reduction of particle settling velocity due to free stream turbulence under specific conditions is confirmed.     

Gain studies of 1.3-μm dilute nitride HELLISH-VCSOA for optical communications

The hot electron light emitting and lasing in semiconductor heterostructure-vertical-cavity semiconductor optical amplifier (HELLISH-VCSOA) device is based on Ga_0.35In_0.65 N_0.02As_0.08/GaAs material for operation in the 1.3-μm window of the optical communications. The device has undoped distributed Bragg reflectors (DBRs). Therefore, problems such as those associated with refractive index contrast and current injection, which are common with doped DBRs in conventional VCSOAs, are avoided. The gain versus applied electric field curves are measured at different wavelengths using a tunable laser as the source signal. The highest gain is obtained for the 1.3-μm wavelength when an electric field in excess of 2 kV/cm is applied along the layers of the device.     

How does sequence length heterogeneity affect the dilute solution conformation of copolymers?

Sequence length heterogeneity (SLH) is defined as the change, as a function of copolymer molar mass (M), in the average number of continuous monomers of a given repeat unit. SLH can influence polymeric properties such as thermal stability, mechanical behavior, transparency, and the ability of copolymers to reduce interfacial surface tension. Here, we demonstrate the relation between SLH and the change as a function of molar mass of a dimensionless size parameter, the ratio of the viscometric radius and the radius of gyration, irrespective of chemical heterogeneity or molar mass polydispersity. Multi-detector size-exclusion chromatography (SEC) provides for a convenient method by which to experimentally establish this relation and, consequently, a method by which to determine whether SLH is present in a copolymer, whether the degree of randomness of a copolymer changes across the molar mass distribution (MMD), or whether two copolymers differ from each other in degree of randomness at a given M and/or across their MMDs. Results from our SEC and FT-IR measurements of block, random, alternating, and gradient copolymers of styrene (S) and methyl methacrylate (MMA) and their respective homopolymers agree with results from a probability theory based model of SLH in linear random copolymers. The multi-detector SEC method employs instrumentation available in most polymer separations laboratories and the relations developed should be applicable to copolymers other than the S-MMAs studied here.     

Chain stiffness and chain conformation of poly(α-methylene-γ-butyrolactone) in dilute solutions

The chain stiffness and local chain conformation of atactic poly(α-methylene-γ-butyrolactone) (PMBL), which is a side chain cyclic structural analog of poly(methyl methacrylate) (PMMA), with a weight-average molecular weight (M_w) ranging from 2.8 × 10³ to 2.6 × 10⁶ in N,N-dimethylformamide (DMF) and γ-butyrolactone (GBL) were characterized by size exclusion chromatography with a multi-angle light-scattering detector (SEC-MALS) and synchrotron radiation small-angle X-ray scattering (SAXS). Based on the Kratky-Porod worm-like chain model, the scattering functions and the M_w dependence of z-average root-mean-square radius of gyration <S²>_z^1/2 yielded the Kuhn segment lengths λ⁻¹, the diameter of the PMBL chains d, and the excluded-volume strengths in DMF and GBL. The local conformation of atactic PMBL in DMF and GBL were slightly larger than those of atactic PMMA, due to the presence of the conformationally rigid lactone ring structure.     

A filtration model for the flow of dilute,stable emulsions in porous media—I. Theory

Flow of dilute, stable emulsions in porous media is important in several oil recovery processes. Because underground media have relatively low permeabilities, the emulsion drop sizes may overlap the pore sizes. Hence, strong interaction occurs between the emulsion droplets and pore constrictions, and local flow redistribution occurs within the porous medium. To predict quantitatively how emulsions are transported in underground media, a theoretical model is required which correctly accounts for the interactions between the flowing droplets and the pore walls.In Part I of this work, we present a simplified filtration model describing the flow of stable, dilute emulsions in unconsolidated porous media. In the model, emulsion drops are captured in pores by straining and interception and, thus, reduce the overall permeability. Transient flow behaviour is characterized by there parameters: a filter coefficient, a flow-redistribution parameter and a flow-restriction parameter. The filter coefficient controls the sharpness of the emulsion front, the flow-redistribution parameter dictates the steady-state retention, as well as the flow redistribution phenomenon, and the flow-restriction parameters describes the effectiveness of retained drops in reducing permeability.Critical comparison is made between the new filtration theory and the current continuum—viscous and retardation models for emulsion flow in porous media. Only the filtration picture is able to explain all the experimental observations. Quantitative comparison between the filtration flow theory and experiment is presented in Part II.     

An empirical study on vortex-generator insert fitted in tubular heat exchangers with dilute Cu–water nanofluid flow

The heat transfer enhancement(HTE) in tubular heat exchangers fitted with vortex-generator(VG) inserts is experimentally investigated. The studied four parameters and ranges are: winglets-pitch ratio(1.33, 2.67, and 4),winglets-length ratio(0.33, 0.67, and 1), winglets-width ratio(0.2, 0.4, and 0.6), and Reynolds number(5200to 12200). The testing fluids are the water and Cu–water nanofluid at the volumetric fraction of 0.2%. The results obtained on HTE, pressure drop, and performance evaluation criterion(PEC) are compared with those for water in a smooth tube. It is found that the VG inserts with lower winglets-pitch ratio and higher winglets-length/width ratios present higher values of HTE and pressure drop. Over the range studied, the maximum PEC of 1.83 is detected with the Cu–water nanofluid inside the tube equipped with a VG insert at the winglets-width ratio of0.6 for the maximum Reynolds number, when the heat transfer rate and pressure drop are 1.24 times and 2.03 times of those in the smooth tube. Generalized regression equations of the Nusselt number, friction factor, and PEC are presented for the tubular heat exchangers with the VG inserts for both water and Cu–water nanofluid.It is concluded that the main advantage of the VG inserts is their simple fabrication and considerable performance, particularly at higher Reynolds number.     

Dispersion of water into oil in a rotor–stator mixer. Part 1: Drop breakup in dilute systems

Most previous studies of liquid–liquid dispersion in complex geometry are limited to turbulent flow at low continuous phase viscosity. In this study, a viscous continuous phase was employed over a range of flow conditions including both the laminar and turbulent regimes. Equilibrium drop size was measured for water dispersed into viscous food grade mineral oils in a batch Silverson L4R rotor–stator mixer. The influence of fluid viscosities and interfacial tension (by adding an oil-soluble surfactant) were examined. In order to isolate the effect of drop breakage from coalescence, Part 1 is limited to dilute conditions (water phase fraction, ? = 0.001). In the laminar regime, drop breakup was more likely due to a simple shear breakage mechanism than one for extension. Following Grace (1982), a semi-empirical drop size correlation was developed. For turbulent flow, the validity of the sub-Kolmogorov inertial stress model for correlating equilibrium mean drop size was verified. Surfactants were found to mostly decrease drop size by lowering interfacial tension. Except for laminar systems near the critical micelle concentration, where Marangoni stresses appear to play some role, the effect of surfactants on the drop size could be correlated using the equilibrium or static interfacial tension. The influence of water phase fraction and coalescence is considered in Part 2 ( Rueger and Calabrese, 2013) of this paper.     

Cyclic poly(dimethylsiloxane) via ring-closing dehydrocoupling of α,ω-dihydroxy-PDMS with α,ω-dihydrido-PDMS in dilute solution

Cyclic poly(dimethylsiloxane) (PDMS) was prepared from commercially available linear α,ω-dihydroxy-PDMS by a platinum-catalyzed dehydrocoupling of its chain ends with α,ω-dihydrido-PDMS in dilute solution. Ring closing was verified by MALDI-ToF mass spectrometry along with GPC, IR, ¹H and ²⁹Si NMR spectroscopy. Purification of the cyclic PDMS was achieved by inclusion complexation of linear byproducts with γ-cyclodextrin. Cyclic yields are ≥ 50% and the average molecular weight (M) closely reflects that of the linear starting material. Yields of large cycles, [(CH₃)₂SiO]_x where x > 6, are greater than those achieved by the traditional ring-chain equilibration route beginning with [(CH₃)₂SiO]₄ and [(CH₃)₂SiO]₅[1], and the M is greater than that obtained for the cyclic product obtained from base-catalyzed cyclodepolymerization of the same α,ω-dihydroxy-PDMS precursor [2].     

A filtration model for the flow of dilute,stable emulsions in porous media—II. Parameter evaluation and estimation

Part I of this work outlined a new theory, based on deep-bed filtration concepts, to describe the flow of dilute, stable emulsions in underground porous media. Here, in Part II, we quantitatively test the proposed theory against experimental data and we indicate how the filtration model parameters can be estimated from first principles.Comparison is made between the theory and data on transient permeability and effluent concentration for dilute, oil-in-water emulsions of mean drop-size diameters ranging from 1 to 10 μm and volume concentrations of 0.5–2.5% flowing in quartz sandpacks of 0.57–2.0 μm² permeability. The pH of the continuous aqueous phase is kept constant at 10. Filtration theory successfully represents the data, permitting unambiguous evaluation of the theoretical parameters.Procedures are described for a priori calculation of the filtration parameters from knowledge of the drop size and the pore-size and grain-size distributions of the porous medium. Good agreement is achieved between the experimentally determined parameters and their estimated values. Thus, the proposed filtration model provides a reliable tool for predicting emulsion flow behaviour in porous media.     

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.     

May the Knudsen equation be legitimately,or at least usefully,applied to dilute adsorbable gas flow in mesoporous media?

The question of applicability of Knudsen's equation to dilute adsorbable gas flow in mesoporous media was the subject of a recent debate between Ruthven et al. (2009), Ruthven (2010) and Bhatia and Nicholson, 2010, Bhatia and Nicholson, 2011. Here, we present a critique of the said debate and introduce new information of critical importance, which has nevertheless been disregarded by both sides thereof. It is pointed out that von Smolukowski's derivation leaves no doubt that Knudsen's equation is meant to apply to the limiting case of zero gas adsorption. In practice, this limit may be expected to be approached at high temperature/low gas adsorbability but the crux of the matter is (i) choice of the right transport parameter (in this case the “reduced permeability”) to provide a useful criterion of approach to the Knudsen limit and (ii) thorough study of the course followed by the said parameter in its approach to the said limit. In this light, we begin our review of the aforesaid new information with conventional surface flow theory, which can deal satisfactorily with higher and moderate, but not with the case of weak, adsorption (because the reduced permeability does not converge smoothly to the Knudsen limit). Even so, we show that it can provide a good answer to a significant question raised in the aforesaid debate. We continue with the more advanced (but still analytical) surface flow approach of Nicholson and Petropoulos (1973), which has provided a plausible physical mechanism for the experimentally observed passage of the reduced permeability through a minimum with rising temperature, in the weak adsorption region. It is shown here that the said experimental data constitute the first observations (including the “fine structure”) of what we have called “apparent or quasiKnudsen” (to avoid confusion with proper Knudsen) flow behavior, which is the central theme of the debate in question. We then pass onto a discussion on the confirmation of the above interpretation of quasiKnudsen-flow “fine structure”, as well as the identification of conditions favorable to the appearance of such flow in practice, afforded by the results of ab initio evaluation of dilute adsorbable gas flow, under suitable adsorption potentials, in model pores (and model pore networks) by and Petropoulos (1981, 1985) and Petropoulos and Petrou (1991).     

Removal of Cd(Ⅱ) from dilute aqueous solutions by complexation–ultrafiltration using rotating disk membrane and the shear stability of PAA–Cd complex

Removal of cadmium(Ⅱ) ions from dilute aqueous solutions by complexation–ultrafiltration using rotating disk membrane was investigated. Polyacrylic acid sodium(PAAS) was used as complexation agent, as key factors of complexation, pH and the mass ratio of PAAS to Cd~(2+)(P/M) were studied, and the optimum complexation–ultrafiltration conditions were obtained. The effects of rotating speed(n) on the stability of PAA–Cd complex was studied with two kinds of rotating disk, disk Ⅰ(without vane) and disk Ⅱ(with six rectangular vanes) at a certain range of rotating speed. Both of the rejection could reach 99.7% when n was lower than 2370 r·min~(-1) and 1320 r·min~(-1), for disk I and disk Ⅱ, respectively. However, when rotating speed exceeds a certain value,the critical rotating speed(n_c), the rejection of Cd(Ⅱ) decreases greatly. The distribution of form of cadmium on the membrane was established by the membrane partition model, and the critical shear rate(γ_c), the smallest shear rate at which the PAA–Cd complex begins to dissociate, was calculated based on the membrane partition model and mass balance. The critical shear rates(γ_c) of PAA–Cd complex were 5.9 × 10~4 s~(-1), 1.01 × 10~5 s~(-1),and 1.31 × 10~5 s~(-1) at pH = 5.0, 5.5, and 6.0, respectively. In addition, the regeneration of PAAS was achieved by shear induced dissociation and ultrafiltration.