Turbulent flow behaviour of dilute polymer solutions in an annulus

An experimental study has been carried out to investigate the turbulent flow behaviour of dilute polymer solutions in an annulus. The polymers used are two grades of Separan, AP30 and MG500, both are known to exhibit drag reduction characteristics in turbulent pipe flow. Similar drag reduction phenomena have been observed in annulus flow. At a given Reynolds number, the friction factor decreases with increase in polymer concentration and appears to reach a minimum (or maximum drag reduction) at certain optimum concentration. An estimate of the critical wall shear stress, which marks the onset of drag reduction, is consistent with pipe flow results, suggesting that the critical value is independent of flow geometry and size. A lower drag reduction, achieved in an annulus in comparison with circular pipes, is attributed mainly to a diameter effect.     

Coalescence behaviour of gas bubbles in aqueous solutions of n-alcohols and fatty acids

Coalescence frequency and coalescence times of bubble pairs formed on two adjacent capillary tubes were determined in aqueous solutions of n-alcoho and fatty acids. The results show, that coalescence times of bubbles are proportional to the surface excess concentration of the solute. Coalescence ti increase with the polarity of the hydrophilic group of the solute, its chain length and the bubble size. Coalescence frequency decrease drastically fro 100% to 0% at a distinct solute concentration. The transition in coalescence behaviour occurs, if the coalescence times becomes greater than the availa contact times of the bubbles. The transition concentration therefore decreases with increasing rate of bubble formation.     

The coalescence of gas bubbles in dilute aqueous solutions

High speed cinematography was used to measure the lifetimes of thin aqueous films formed between nitrogen bubbles in dilute solutions of ammonium bromide, tetramethylammonium bromide, tetraethylammonium bromide, and tetra-n-propylammonium bromide. The bubbles were formed simultaneously on adjacent nozzles. Results were compared with film lifetimes calculated by a model proposed by Marrucci. This model assumes that the surface solute concentration is in complete equilibrium with the liquid solute concentration in the film, and that thinning occurs as solute diffuses into the film from the liquid outside the film. It is applicable where the dimensiordess concentration parameter crk²/γ is in the range of 0–10. Where crk²/γ is greater than 400, but where viscous effects can still be neglected, a model developed by Andrew, in which thinning is retarded by the slow diffusion of solute to the film surface, seems most applicable. With crk²/γ between 10 and 400, neither model predicts results adequately. Since the alkylammonium bromides are highly dissociated surface active salts, the decrease in internal pressure resulting from double layer repulsion could, in principle, be important. Such repulsion was considered within the framework of the Marrucci model, however, and was found to be generally small.     

The behaviour of vapour bubbles during growth at subatmospheric pressures

Initially, a growing vapour bubble is blown up due to an excess pressure. Continued bubble growth is governed by heat and mass diffusion.The combination of both mechanisms during the transition period may result in the occurrence of oscillations in the equivalent bubble radius. ExperimenExperimental data on the oscillations of growing and imploding vapour bubbles in water are in quantitative agreement with theoretical predictions.     

Behavior of gas bubbles in aqueous electrolyte solutions

A system was investigated in which a swarm of air bubbles was dispersed in aqueous electrolyte solutions. the salts used were: NaCl, NaBr, NaI, Na₂SO₄, Na₃PO₄ LiCl, MgCl₂, MgSO₄, CaCl₂, AlCl₃ and Al₂(SO₄₃. The effects of the salts on the interfacial area of dispersion and on the oxygen transfer coefficient were investigated at various salt concentrations. The results showed a definite dependence of the surface area of dispersion on the valence of the ionic species and salt concentrations. A very satisfactory correlation was obtained for all the salts with the use of ionic strength as the correlating parameter. The mechanism of the coalescence-preventing action of the salts was discussed and explained on the basis of ion—water interactions. The oxygen mass transfer coefficient was found to be only slightly dependent on the presence of electrolytes in the range of concentrations used in this work. The importance and possible practical application of the results were briefly discussed.     

Persistence of bubbles on inorganic salt solutions

The lifetime, t, of single bubbles on aqueous solutions of sodium chloride, sodium bromide, sodium sulphate, potassium chloride, magnesium chloride and two salt mixtures was determined. It was almost independent of the salt used, slightly increased with the concentration (e.g., 0·07, 0·09, 0·12 and 0·13 sec for 1·2, 3, 12 and 20% NaCl respectively and bubble diameters, d, between 0·007 and 0·19 cm), was not affected by d as long as this was between 0·002 and 0·06 cm, but was greater (1 sec) when d was 0·08–0·13 cm. The lifetime of mixtures exceeded that of the constituents. The absolute values of t were smaller than those recorded in the literature indicating the extreme sensitivity of bubble persistance to traces of impurities. The effect of d on t, so different from that in detergent solutions, is qualitatively explained.     

The potentiodynamic behaviour of copper in NaOH solutions

The potentiodynamic behaviour of Cu in different NaOH solutions at 25° C is studied paying particular attention to the anodic formation and cathodic reduction of the Cu(I) and Cu(II) surface species occurring during the electrochemical processes. The potentiodynamic response of the electrochemical interface is strongly dependent on the perturbation conditions and it reveals the complexity of the electrochemical reactions occurring there as well as the inter-relation of the processes taking place at different potentials. A reaction pathway to interpret the corresponding behaviour is advanced.     

The potentiodynamic behaviour of iron in alkaline solutions

The potentiodynamic behaviour of iron in alkaline solutions under carefully controlled perturbation conditions reveals that the overall electrochemical process is more involved than was thought earlier. The electrochemical characteristics of the systems are explained through a series of successive conjugated redox couples principally involving Fe(OH), Fe(OH)₂ and FeOOH as limiting stoichiometric species. The yield of soluble species such as either FeO^2?₂ or HFeO^?₂ increases with the pH. Ageing effects of reactants and products are also distinguished through the potentiodynamic E/I records.     

Diffusion in polymer solutions

Experiments using diffusion controlled electrolysis have been carried out in flow and in non-flow situations for the measurement of diffusivities in pure solutions and in solutions with polymeric additives. The non-flow cell was found to be unreliable and time consuming in operation and was not capable of yielding data on the effect of shear rate upon the diffusivity.The flow system gave results for pure solutions which were in agreement with previously published information and no effect of shear rate upon diffusivity was observed. With polymeric additives some solutions showed a significant decrease in diffusivity as the shear rate increased. Although more data are required to quantify this effect the results obtained do show the danger of using the common assumption of constant Dμ//T for such solutions.     

轮胎中夹带气泡的原因分析及解决措施

通过成立QC攻关小组,依据质量管理PDCA方法,利用相关质量工具对现状进行充分的调查与分析,明确轮胎制造过程中气泡类不合格产生的潜在因素,通过对轮胎制造成型过程中的流程分析,从生产全过程进行深入的研判,最终确定了气泡问题产生的主要原因。针对这些原因,通过优化工艺技术、完善车间管理制度、提升职工能力等措施开展质量改善活动,成品轮胎的气泡缺陷率持续下降,成品的合格率提高,产生了良好的经济效益和社会效益。     

Surface characteristics and surface behaviour of polymer carbons—V: Interaction of polymer carbons with bromine in aqueous solutions

Interaction of polymer charcoals with bromine in aqueous solutions results in the conversion of bromine into HBr and its fixation by the charcoals. The amount of bromine converted into HBr is related to the surface acidity of the char while the amount fixed depends upon the nature of the char and the history of its formation. PVDC and Saran charcoals adsorb appreciably larger amounts of bromine than PF and UF charcoals prepared at the same temperature. The adsorption decreases on outgassing the chars at 1000°C and the decrease is only slight in case of PVDC and Saran chars. The adsorption of bromine involves two different mechanisms. In case of the highly porous charcoals such as those of PVDC and Saran prepared by the carbonisation of oxygen free polymers, the adsorption of bromine occurs largely in pores. In the case of less porous charcoals such as those of PF and UF prepared by the carbonisation of oxygen containing polymers, the adsorption of bromine takes place partly by addition at the unsaturated sites and partly by substitution in place of bonded hydrogen.     

The concentration dependence of diffusion in semi-dilute polymer solutions

Dynamic light-scattering data for polystyrene fractions in a good solvent (benzene) and a theta solvent (cyclopentane, 20.4°C) are presented. They encompass a broad concentration interval in the semi-dilute range. These data are compared with those for the systems poly(ethylene oxide)/water and hydroxyethylcellulose/water. The entanglement network in these systems is reflected in part by the nature of the concentration dependence of the mutual diffusion coefficient and in part by the presence of a slow relaxation, information on which may be derived from the non-exponential autocorrelation function.     

The behaviour of MnO2 in strongly acidic solutions

Different MnO₂ samples were equilibrated with H₂SO₄ solutions of varying concentrations and the equilibrium concentration of dissolved Mn³⁺ determined experimentally. Leaching in strong acid appears to be a useful tool for characterizing different types of MnO₂ materials. The equilibrium concentration of dissolved Mn³⁺ showed a sharp drop above 9 M H₂SO₄. The crystal structure of MnO₂ was not affected by acid leaching and only a slight grain coarsening was observed.     

Mass transfer from single bubbles in aqueous solutions of surfactants

The constant volume technique developed by Calderbank has been used to measure mass transfer rates for single carbon dioxide bubbles (0.52 <d_o < 1.02 cm) in distilled water and in aqueous solutions of n-hexanol, n-heptanol and n-octanol.The addition of surfactants to water reduced the mass transfer coefficient. A model to estimate the mass transfer coefficient in aqueous solutions of surfactants has been proposed, where the effect of surfactants has been expressed by introducing the retardation coefficient which indicates the degree of the retardation of surface flow at the gas—liquid interface.     

Filtration of polymer solutions

An analysis of the viscous flow of time-independent non-Newtonian fluids in anisotropic compressible porous media has been conducted and applied to the problem of filtration of slurries in which the filtrate is non-Newtonian. The fundamental relationship formulated for filtration, which incorporates recent modifications of Tiller and Shirato, accounting for variations of the superficial velocity of the liquid and of the particles of the cake, associated with cake compaction, has been utilized in the analysis of constant pressure filtration. The efficacy of the concepts and relationships developed for constant pressure filtration in the interpretation and processing of experimental data is demonstrated with data collected in the constant pressure filtration of slurries of calcium carbonate in hydroxyethyl cellulose (Natrosol-250G) solutions.     

Multi-component diffusion in polymer solutions

In the present work a comprehensive methodology is proposed for calculating the Fickian diffusion coefficients in a multi-component solvents–polymer system as a function of the solvents self-diffusion coefficients, the constituent chemical potentials and the process conditions. This methodology is based on the application of well-established principles such as the Gibbs-Duhem theorem for diffusing systems along with the friction coefficient concepts. The case of constant friction coefficient ratios is re-examined leading to a screening of the existing theories for multi-component polymer systems. Finally, the described methodology is applied to the formamide–acetone–cellulose acetate (CA) system which is used in the asymmetric membrane manufacture. The acetone evaporation process from this system is studied as a one-dimensional numerical experiment. For this purpose, the evaporation process is modeled as a coupled heat and mass transfer problem with a moving boundary. The Galerkin finite element method is used to simultaneously solve the non-linear governing equations. All the model parameters were estimated from literature measurements leading to a fully predictive model. The model predictions are in excellent agreement with experimental data for polymer solution weight and surface temperature vs. time thus validating the applied methodology for the calculation of friction coefficients.     

Diffusion coefficient in polymer solutions

Molecular diffusivity of a solute in a solvent may be determined by measuring the extent of dispersion of solute in solvent flowing in a straight circular tube under the conditions of laminar flow. This simple and rapid method for determination of molecular diffusivity in aquous polymer solutions is discussed. Experimental results show a substantial reduction in the solute diffusivity with increase in polymer concentration.     

Diffusion in aqueous polymer solutions

The diffusion of Direct Blue 76 dye in aqueous dilute polymer solutions was studied using the capillary method. The polymer systems studied included dilute solution of carboxymethyl cellulose, poly(ethylene oxide), and polyacrylamide. It was found that the diffusion coefficient of Direct Blue 76 in carboxymethyl cellulose is higher than that in pure water, while in polyacrylamide and poly(ethylene oxide) solutions the value is lower than that in pure water. The diffusion coefficient of Direct Blue was found to decrease with increasing polymer concentration in case of poly(ethylene oxide) and polyacrylamide, while in case of carboxymethyl cellulose the diffusion coefficient increases with polymer concentration. The effect of temperature on the diffusion coefficient of Direct Blue 76 in the three polymers was found to obey the Arrhenius equation. The activation energy for diffusion of Direct Blue 76 in water, poly(ethylene oxide), polyacrylamide, and carboxymethyl cellulose was found to be 4.38, 7.7, 5.44, and 5 kcal, respectively, for polymer concentration of 0.25 g/l.