Drag Reduction Additives

Drag reduction is caused by the viscoelasticity of polymer solutions (61). PIB is oil soluble and is thus interesting as a drag reducing additive for the transport of crude oil in pipelines (62). 

Universal drag reduction curves can be obtained in several ways, for example, by normalizing the hydrodynamic volume fraction of the polymer in solution (63). Further, a three-parameter empirical relationship between the drag reduction and concentration has been introduced (64). 

The effects of the concentration of PIB on drag reduction in different solvents have been investigated (65). Viscosity measurements of PIB with different molecular weights in two solvents, namely cyclohexane and xylene showed that a universal drag reduction equation can be used in order to describe the behavior. 

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Gas hydrate inhibitors. Gas hydrates, solid water clathrates containing small hydrocarbons, are problematic for oil and gas production because they can precipitate and cause line blockage. Simple cationic surfactants containing at least two butyl groups were previously developed to inhibit formation of gas hydrate precipitates in gas production lines [87]. However, similar to the situation with cationic drag reduction additives, poor toxicity profiles prevent widespread commercial acceptance. Ester quaternaries with structures somewhat similar to those used in fabric care have been claimed as hydrate inhibitors [88 ]. Additionally, certain alkylether quaternary compounds, e.g. C12-C14 alkyl polyethoxy oxypropyl tributyl ammonium bromide, were shown to have hydrate inhibition properties [89]. 

Zhang, Y, Correlations among surfactant drag reduction, additive chemical structures, rheological properties and microstructures in water and water/co-solvent systems, Ph.D. dissertation, Ohio State University, Columbus, 2005c. 

Polysaccharides, along with guar gum and xanthan gum, comprise an important class of drag reduction additives (Fig. 22a) [194]. They are fairly shear stable but not as effective as PEO and PAM. So grafting synthetic polymers onto the backbone of polysaccharides was popular in the late 1980s. Singh and co-workers... 

Recently, Inaba and co-workers (173) pointed out that it is possible to reduce the pumping power, to downsize the transport system, and to decrease the heat loss to environment by using surfactant water solution as a thermal energy transport medium. The environmental pollution caused by discarding the used surfactant solution has become a serious problem. It is required that the new additive have the same flow drag reduction effect as surfactant solution, and also that little environment load be used. They used pulp fiber as the new type of flow drag reduction additive in a circular pipe. The pulp fiber consists of a... 

The presence of small amounts of dissolved polymer can alter sizably the aerosol particle dimensions when the solutions are sprayed. This antimisting property has received special attention in an effort to develop additives for jet fuel to prevent accidental ignition following crash landing. As in drag reduction, the polymer... 

The effect of polymer additives on turbulent flow is at the origin of the important phenomenon of drag reduction and has found other industrial applications such as oil recovery and antimisting action. Drag reduction in dilute polymer solutions... 

Loitsianskii LG (1966) Mechanics of liquid and gases. Pergamon, Oxford Lumley JL (1969) Drag reduction by additives. Ann Rev Fluid Mech 1 367-384 Ma HB, Peterson GP (1997) Laminar friction factor in microscale ducts of irregular cross section. Microscale Thermophys Eng 1 253-265... 

A. Gyr and H.-W. Bewersdorff, Drag reduction of turbulent flows by additives, Kluwer Academic Publishers, Dordrecht (1995). 

A drag reduction of up to 48% was achieved. In addition, a reduction of corrosion occurred [1197],... 

A polymer of the polyacrylamide type was injected as a 0.5% solution from an axially-placed nozzle at the bellmouth entrance. The experiments showed that the central thread provided drag reduction almost equivalent to premixed solutions of the same total polymer concentration flowing in the pipe. Overall concentrations of 1, 2, 4, and 20 ppm were used. Moreover, the effects were additive 2 ppm thread overall concentration plus 2 ppm premixed gave drag reductions equivalent to 4 ppm of either type. Reynolds numbers of up to 300,000 were investigated. In other experiments, a number of different polymer fluids were injected on the centerline of a water pipe-flow facility [857]. Two distinct flow regions were identified ... 

Experiments have been conducted to investigate the effect of a soapy industrial cleaner on reducing the skin friction of a Jordanian crude oil flowing turbulently in pilot-scale pipes of different sizes. Experiments showed that a concentration of only 2 ppm of the chemical additive injected into the crude oil line caused an appreciable amount of drag reduction [1165]. The effects of additive concentration and pipe diameter on drag reduction have been investigated. 

Zakin, et al. "Variables Affecting Drag Reduction by Nonionic Surfactant Additives," Chem. Eng. Commun.. 1983, 23, 77 88. 

Drag reduction decreases with flow time — which is in most application undesirable — and is obviously caused by a degradation of the polymer chain. Degradation of polymeric additives in turbulent flow cannot be easily understood on the basis of present knowledge, i.e., predictions towards the onset of chain scission cannot yet be made. These difficulties can be attributed, on the one hand, to the complex fluid structure and, on the other hand, to the fact that both shear and tensile stresses act simultaneously in turbulent flows. 

In the area of hydrodynamics the term drag reduction has become a familiar name for characterizing the reduction of friction in turbulent flow through pipes. This is not caused by an improvement in the wall properties as this would only lead to a decrease in friction of a few percent. It is possible, however, to reduce the degree of friction in turbulent flow by a considerable extent, if small amounts of a suitable additive in a concentration range of only a few parts per million by weight are used a reduction in friction of 80 percent can be reached. A tremendous change in the flow field will result, while turbulent flow still remains. 

The first reports on the drag reduction phenomenon are found in publications by Blatch (1906), Forrest (1931), as well as by Brautlecht (1933), who measured the flow behaviour of paper pulps. In independent studies made by Mysels (1949) and Toms (1948) this phenomenon was observed in the turbulent flow of gasoline in pipes when aluminum soaps were added and, in Toms experiments, when polymethylmethacrylate in monochlorobenzene was used. The reduction of friction is therefore often termed the Toms effect . This flow behaviour is also known in the literature as the Non-Newtonian- , visco-elastic- , Texas- or Texas-Toms-effect , due to the contributions made by Texan researchers. It is also more generally known, and this term will be used in this paper exclusively, as the drag-reduction effect of flow additives. 

The non-ionic surfactants have an advantage over all the drag-reducing additives studied so far. They are both mechanically and chemically stable, do not precipitate in the presence of calcium, and hence can be used in all impure waters, sea water, brackish water, or concentrated brine solutions. They have an excellent potential for drag reduction at high temperatures. 

Therefore, when dealing with polyelectrolytes, countless Mark-Houwink relationships must be established. This shows the increasing problems of simple molecular weight determinations on charged systems (for more details, see Kulicke. Horl (1985)). Thus, the molecular weight determination of polymer molecules or additives is an important fact in the drag reduction area. Molecules or particles which are effective have molecular weights above 105 g/mol (the polymer backbone chains should be linear, flexible, and unbranched). 

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