Effects of drag reducing polymers on initiation of atherosclerosis

Results from two pilot studies using White Carneau pigeons on high cholesterol diets have demonstrated substantial reduction in arterial plaque accumulations when the birds were periodically injected with dilute aqueous solutions of a drag reducing polymer (Separan AP-30) so as to maintain circulating blood concentrations of approximately 60 ppm. Initiation of arterial plaque formation may be fluid-mechanically motivated such that regions subjected to fluid turbulence, rapidly developing boundary layers, and alternate separation and reattachment, arc; the most prone lo attack. Viscoelastic fluid response, as seen in drag reducing media, is known to alter such phenomena. Comparative documentation of plaque deposition in experimental as well as control birds shows significant differences in both the aortas and coronary arteries, at optical magnifications from 20 to 15000X.     

Roles of drag reducing polymers in single- and multi-phase flows

It has become a well-known fact that finding sustainable solutions to the unavoidable high pressure losses accompanying pipeline flows to increase the pumping capacity without necessarily adding more pump stations is inevitable. Polymers, as one of the drag reducing agents which have been found to offer such an economic relieve, is the most widely investigated and most often employed in industries because they can produce drag reduction up to 80% when they are added in minute concentrations. In addition, polymer additives modify the flow configurations of multiphase flows to such an extent that stratification of individual phases is enhanced thereby making the separation of the phases at the fluid destination much easier. The achievements so far made and the challenges facing the use of polymers as drag reducers in turbulent single and multiphase flows are comprehensively reviewed. This review discusses the experimental studies of the effects of polymer additives in turbulent flows, the analytical studies, and the proposed models as well as the suggested mechanisms that explain the drag reduction. Likewise, specific areas of interest in the review include phenomena of drag reduction by polymers, factors influencing the effectiveness of the drag reducing polymers, methods of injecting the polymers into the base fluids, degradation of the polymers and industrial applications of polymers as drag reducing agents. The current and future research interests are also addressed. Although finding reveals that there are quite a lot of research in this area, most of the experimental and theoretical works are devoted to single phase flows while the remaining ones are mostly directed towards gas–liquid flows except in very recent time when investigation into the use of polymers in liquid–liquid flows is being focused. Despite this voluminous works on drag reducing polymers, there are no universally accepted models and hence the mechanisms of drag reductions by polymers.     

Generalized correlation for friction loss in drag reducing polymer solutions

The definition of the pipe flow friction factor has been extended to include the effect of fluid viscoelastic properties on energy dissipation in turbulent tube flow. The resulting friction factor includes a characteristic fluid relaxation time, which can be determined directly from rheological measurements, and reduces to the usual Fanning friction factor for inelastic fluids. The use of this more general friction factor enables turbulent tube flow data for both fresh and shear degraded “concentrated” drag reducing polymer solutions of various concentrations in various tube sizes to be correlated by the usual f vs. N_Re relation for Newtonian fluids in smooth tubes.     

Inhibition of diffusion controlled corrosion in pipelines by drag reducing polymers under turbulent flow conditions

The effect of adding carboxymethylcellulose drag reducing polymer on the rate of corrosion of aluminium tube through which sodium hydroxide solution flows, was studied by a weight loss technique. The variables studied were solution flow rate and polymer concentration. Reynolds number and polymer concentration were varied over the range 3500 to 30 000 and 10 to 500 ppm, respectively. Polymer addition was found to decrease the rate of corrosion by a maximum of 63% depending on polymer concentration and Reynolds number.Nomenclature Re Reynolds number - Solution density - d tube diameter - u solution viscosity     

High performance size-exclusion chromatography of anionic polymers in aqueous solutions

The applicability of high performance size-exclusion chromatography was tested for anionic polymers with a new type of column. It was found that a solvent salt concentration of 0.1M and an elevated temperature (60°C) prevented adsorption of the polystyrene sulfonate standards on the column packing. The calibration curve and the effect of the concentration on the retention volume remained, however, colum-dependent. We concluded also that the use of the column was restricted to the linear range of the calibration curve and to concentrations below 1 mg mL^?1 for the highest molecular weight standards. The influence of the flow rate (below 1 mL min^?1) on the retention volume was negligible. The main cause of errors when the universal calibration technique is used originated in the experimental determination of the intrinsic viscosities of the standards. The combination of the errors on the viscosity and on the experimentally determined retention volume easily introduced an error of 15% on the determined molecular weight of the sulfated polysaccharide k-carrageenan. The use of the universal calibration method for an exact molecular weight determination of anionic natural polymers is therefore still questionable.     

A rheological study of laminar–turbulent transition in drag reducing polymeric solutions

Presented herein are the studies of laminar–turbulent transition in micropolar and power law fluids flowing in a circular pipe. For some parametric values of micropolar and power law fluids, both depict the drag reducing properties. The parametric values of these representations have been obtained from the experimental results of Mc-Comb. It has been observed that, in both the cases, as the drag-reducing property in the solution increases, the first transition point moves towards the walls of the pipe. It is also observed that the onset of early turbulence phenomenon occurs for the drag-reducing polymeric solutions.     

Degradation of polyacrylamide molecules in aqueous solutions by high-speed stirring

It has been observed that the viscosity of polyacrylamide (PAM) solution decreased with an increase in high-speed stirring time. The viscosities of PAM solutions decrease initially and then remain constant as the stirring time is increased. The final values depend on the stirring speed. This decrease was assumed to be due to a change in the dissolved state and/or the degradation of PAM molecules. It was discovered through experimentation that the molecular weight decreased, implying that the PAM molecules were degraded.     

Degradation of aqueous DEA solutions in a heat transfer tube

To study the degradation of aqueous diethanolamine (DEA) solutions in heat transfer equipment, DEA solutions were passed through a coiled heat transfer tube (2.032 mm ID, 3.175 mm OD, 4.8 m long) immersed in a constant temperature bath. The operating conditions were: DEA flow rate 0.011 to 0.0172 L/s, DEA concentration 20 to 40 wt%, DEA temperature 60 to 200°C, CO₂ partial pressure 1.38 to 4.18 MPa. The degradation rate was found to increase with temperature, DEA concentration and CO₂ partial pressure; it decreased slightly with solution flow rate. The degradation was accompanied by the formation of a fouling deposit. A simple mathematical model is presented for predicting DEA degradation.     

Degradation of polymers during aerosol formation from antimisting polymer solutions

Degradation of polyisobutylenes as a consequence of spraying jet-fuel solutions of these polymers was studied as a function of polymer molecular weight and concentration and the spray conditions. Assessment of the degradation was made by measuring the maximum ductless siphon height h^* for sprayed samples and comparing this with prespray values. Two polymers, L-160 from Exxon and B-288 from BASF ( M _v = 4.1× 10⁶ and 11.9 × 10⁶), were studied to concentrations of 3000 and 2000 ppm, respectively. Degradation was found to be extremely sensitive to the air speed used in wind-shear spraying, above a critical value of approximately 30–40 m/s. At the highest air speed employed, 135 m/s, degradation was so severe that h^* values were reduced nearly to Newtonian (solvent) values, for all concentrations of both polymer additives. The implications of these results are important for designing effective antimisting fluids.     

Mesoglobules of thermoresponsive polymers in dilute aqueous solutions above the LCST

The colloidal stability and characteristics of particles formed by homopolymers of poly(N-vinyl caprolactam), poly(N-isopropyl acrylamide) and poly(vinyl methyl ether) in dilute aqueous solutions above the lower critical solution temperature, LCST, was followed by means of dynamic and static light scattering. Depending on the solution concentration, the homopolymers precipitate or form stable dispersions of monodisperse spherical particles. To obtain colloidally stable aggregates, also called mesoglobules, no stabilising agent was added. The stability of the mesoglobules upon time and dilution at temperatures above the LCST suggests that the particle surfaces possess a hydrophilic character. The size of the formed particles depends on the concentration and the heating rate of the solutions. However, internal structure and shape of mesoglobules are affected neither by the way, how the mesoglobules were prepared, nor by molar mass of individual macromolecules. Mesoglobules of PNIPAM obey the M∝R^2.7 scaling law. Origin of stability of the dispersions vs. expected precipitation is discussed.     

Correlation of carbon nanotube dispersability in aqueous surfactant solutions and polymers

In order to assess the dispersability of carbon nanotube materials, tubes produced under different synthesis conditions were dispersed in aqueous surfactant solutions and the sedimentation behaviour under centrifugation forces was investigated using a LUMiFuge stability analyzer. The electrical percolation threshold of the nanotubes after melt mixing in polyamide 6.6 was determined and the state of dispersion was studied. As a general tendency, the nanotubes having better aqueous dispersion stability showed lower electrical percolation threshold and better nanotube dispersion in the composites. This indicates that the investigation of the stability of aqueous dispersions is also able to give information about the nanotubes inherent dispersability in polymer melts, both strongly influenced by the entanglement and agglomerate structure of the tubes within the as-produced nanotube materials.The shape of the nanotubes in the aqueous dispersions was assessed using a SYSMEX flow particle image analyzer and found to correspond to the shape observed from cryofractured surfaces of the polymer composites.     

Pipeline scale-up in drag reducing turbulent flow

Models available in literature for predicting drag reduction scale-up are inadequate as they have been successful only over a narrow range of diameters. A new scale-up model is presented which equates dampening of turbulent velocity fluctuations by drag reducing additives to a reduction in the Prandtl mixing length. Flow and pressure drop data from a laboratory scale pipe along with shear viscosity measurements are sufficient to predict drag reduction scale-up in bigger diameter pipes. Using this approach, scale-up was successfully predicted over a diameter range of 7 to 154 mm for a surfactant-water system and 26.6 to 1194 mm for a polymer-oil system.     

Bubble drag in contaminated non-newtonian solutions

The motion of a bubble in an infinite fluid is examined in the case where the surrounding fluid is non-Newtonian and contains impurities. An expression is developed for the drag force as a function of the shear-thinning character as well as of the concentration of surfactant of the fluid. The obtained expression for the drag force correlates quite nicely with experimental data for small bubbles.     

Synthesis and swelling behaviour of hydrophobically modified responsive polymers in dilute aqueous solutions

New series of associating polymers were synthesised in order to investigate opposite behaviours of hydrophobically modified water-soluble polymers and thermoresponsive water-soluble polymers carrying LCST stickers. On the basis of a poly(acrylic acid) backbone, amino-terminated poly(N-isopropylacrylamide), poly(ethylene oxide-co-propylene oxide) and/or dodecyl chains were grafted following a reaction of condensation activated by carbodiimide. Two homologous series of well-defined single grafted and double grafted copolymers were obtained, with double grafted chains containing both C12 and LCST grafts. The dilute solution properties of these copolymers were carefully studied by capillary viscometry. At low salt concentration and below the LCST of the grafts, the swelling properties of macromolecular chains are controlled either by intramolecular associations between hydrophobes, excluded volume effect exerted by hydrophilic grafts or by a balance between these opposite interactions. The deswelling of macromolecular chains, induced by hydrophobic interactions, is amplified at higher ionic strength and more particularly above the transition temperature of the side chains.     

Degradation characteristics of IrO2-type DSA in methanol aqueous solutions

In this paper, a comparative study has been done on the long-term stability and deactivation characteristics of IrO₂-type DSA^® in acidic solutions with the absence and the presence of methanol compound, respectively. The long-term stability is evaluated by accelerated lifetime tests. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements are carried out on the electrodes before and after deactivation, by which the failure characteristics of Ti-supported oxide electrodes are deduced. The service life is found to increase and then decrease with increasing the calcination temperature of the as-prepared electrodes; on the other hand, the lifetime is obviously shortened by the addition of methanol into the testing solution. The latter phenomenon can be interpreted by more severe dissolution of titanium base and active oxide layers in methanol-involved solution than in blank one. But the former one (temperature-dependent lifetime) cannot be simply explained by the progressive enhancement of stability of active IrO₂ layer with the heating temperature, as concluded from the continuous decrease in change rates of crystalline orientation, unit cell volume and microstrains of oxide layers with the temperature, after the deactivation. SEM observation shows a coating peeling off within the oxide layer and the total delamination of oxide coating at the metal/oxide interface of samples prepared at high temperature after the failure, due to the low coating adhesion. The ease of mechanical loss of oxide layer is considered as one of the main reasons for rapid deactivation of Ti/IrO₂ electrodes prepared at high temperature, although the oxide layer itself in these electrodes is chemically stable enough.     

减阻剂的研究现状及应用

介绍了减阻剂的国内外研究与应用现状,综述了减阻剂的生产工艺,并对减阻剂今后发展方向提出了建议。     

Degradation of drag-reducing polymers

A simple, fixed-head flow device was used to characterize drag reduction by polymers in water. Using a parallel flow of water as a reference system, the Reynolds numbers ranged from 8600 to 12,000. The degradation of poly(ethylene oxide) and polyacrylamide during turbulent flow of dilute solutions (1 to 50 g/kl) was measured in terms of friction-reducing effectiveness. Poly(ethylene oxide) decreases in effectiveness more rapidly than polyacrylamide in a recycling test.