Sylwia Różańska

DRAG REDUCTION EFFECT IN PIPE SYSTEMS AND LIQUID FALLING FILM FLOW

In this paper the most important literature data on polymer and surfaceactive additives effect on flow drag reduction and heat transfer effect in pipeline systems, as well as on liquid film flow characteristics, are presented. Previous published reviews by Gyr and Bewersdorff [1995], Choi [2000] and Graham [2004] were concerned with drag reduction effects in polymer solutions, and drag reduction effects in surfactant solutions were reviewed by Zakin et al. [1998]. The authors of the present review paper limited themselves to review important issues related to drag reduction effect and heat transfer in turbulent flows without phase change. Special attention was directed to elaborate the similarities and differences of drag reduction in high-molecular polymers and surfactants solutions, which relate to the flow phenomena and the associated heat transfer in straight tubes, coils and in falling films. It has been underlined that despite the large amount of research, which includes applications of modern measurement techniques to study turbulence phenomena and the Theological characteristics, the details of the drag reduction and heat transfer mechanisms are still not well understood. In the experimental studies performed in the last years with mixed drag reducers systems (polymer/surfactant, surfactant/surfactant), it has been shown that the presence of other surfactants or polymer in drag reducing surfactant systems causes an increase of the system stability and of the temperature range in which the additives are most effective. Perhaps the zwitterionic surfactants with special additives have the potential to become very useful in the future. It has been shown that another important issue for future research is finding drag reducing systems for long-distance transport of non-polar fluids, taking into account changeable environment temperature conditions.

Extensional viscosity measurements of concentrated emulsions with the use of the opposed nozzles device

This paper presents results of experimental studies on the apparent extensional viscosity of emulsions. The apparent extensional viscosity measurements were carried out with the use of a customized rheometer which utilizes stagnation flow between two opposing nozzles. Apparent extensional viscosity was determined for emulsions containing 60, 70 and 74 vol.% of dispersed phase. The emulsions were produced using a homogenizer equipped with different dispersing endings that resulted in emulsions characterized by different droplet sizes. The experimental results show that the value of apparent extensional viscosity of the emulsion is significantly influenced by the droplet size and by the concentration of dispersed phase. Apparent extensional viscosity as well as shear viscosity of the emulsions increases with the increase of the dispersed phase concentration and with the decrease of the droplet diameter. It has also been observed that the decrease in the diameter of droplets increases the ratio of the apparent extensional viscosity to the shear viscosity, known as the Trouton ratio.

Extensional flow of carboxymethylcellulose sodium salt measured on the opposed-nozzle device

ABSTRACT The study presents results of the shear viscosity and apparent extensional viscosity measurements performed for semidilute solutions of carboxymethylcellulose sodium salt with two different average molecular weights and three different degrees of substitution, in distilled water and with the addition of NaCl. An increase in the weight average molecular weight of Na-CMC triggers a rapid increase in the apparent extensional viscosity and the Trouton ratio. Another finding was that the values of the apparent extensional viscosity and the Trouton ratio rose with a decrease in the degree of substitution, which can be attributed to the presence of interchain hydrogen bonds. The addition of NaCl to the Na-CMC solutions induces a reduction in the apparent extensional viscosity and the Trouton ratio, which can be linked to a change in the configuration of the polyelectrolyte chain.

Extensional Flow of Polymer Solutions Through the Porous Media

The flow through porous media plays an important role within several areas of science. In many real processes in which the channels undergo continuous expansion and contraction, fluids are subjected not only to shearing but also to stretching. Such examples are the fluid flows through the plate heat exchangers, the porous beds and gaps of rock during crude oil extraction. Typically, pure and/or extensional flow is often required in many practical situations. Most often, we are dealing with the so-called mixed flow, where the deformation rates have parallel and perpendicular components to the flow direction. Solutions of high molecular weight polymers exhibit considerable differences in extensional and shear flow behaviors, and the ratio of extensional viscosity to shear viscosity can be as much as 100 times higher. In case of the flexible polymer solutions through porous media is the increase in flow resistance obtained beyond a critical flow rate. That increase has been attributed to the extensional nature of the flow field in the pores caused by the successive expansions and contractions. Such solutions exhibit strain hardening in extension. In case of the polymer solutions with semi-rigid and rigid chain structures, only the extent strain thinning region can be observed.

Właściwości reologiczne warstwy powierzchniowej cieczy wybranych piw komercyjnych

S t r e s z c z e n i e W pracy przedstawiono wyniki badan reologicznych warstw powierzchniowych piw: Debowe Mocne, Tyskie Gronie, Żywiec oraz Warka Strong w przeplywie oscylacyjnym. Uzyskane zalezności miedzyfazowego modulu zachowawczego Gs’ i miedzyfazowego modulu stratności Gs” w funkcji czasu mialy przebieg charakterystyczny dla rozcienczonych wodnych roztworow bialek. We wszystkich uzytych w badaniach piwach wartości obu modulow wzrastaly, a po pewnym charakterystycznym dla danego rodzaju piwa czasie dochodzilo do ich przeciecia na wykresie. Wyniki pomiarow oscylacyjnych świadczą o tym, ze w warstwach powierzchniowych piw dochodzilo do uformowania sie struktury sieciowej. Bardzo dlugi czas formowania sie tej struktury jest dowodem, ze w jej tworzeniu wazną role odgrywaly zawarte w piwach bialka. Zaobserwowano takze, ze najbardziej stabilna piana wystepowala na powierzchni piwa Żywiec. Zmierzone wartości miedzyfazowych modulow Gs’ i Gs” tego piwa byly najwyzsze. Wyniki te wskazują, ze istnieje związek miedzy wlaściwościami reologicznymi warstwy powierzchniowej piwa a stabilnością piany. Slowa kluczowe: piwo, wlaściwości reologiczne, powierzchnia miedzyfazowa, warstwa powierzchniowa, piana