Jacek Różański

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.

Rheology and Structure of Emulsions and Suspensions

This article contains the results of experimental investigation of the rheological characteristics and structures of emulsions and suspensions. The emulsions had the oil volume fraction in the range from 0.1 to 0.4. The suspensions with nanoparticles are represented by suspensions of silica with concentrations from 1 to 4%. Paprika and coffee suspensions with concentrations of 5, 10, and 20% were studied. The material was subjected to rheological measurements using a concentric cylinder viscometer in the shear rate range of 16.2 to 1326s−1. A lot of food products are either in the form of emulsions or suspensions whose rheological and interfacial properties are important to achieve stability of the products. The rheology and structure analysis is very important from the point of view of flow, friction factors and Reynolds number for non-Newtonian fluids and food production processes. To characterize emulsions and suspensions, first the particle size distributions were made. The experiments presented have shown that the rheological characteristics of composite systems (emulsions and suspensions) depend on concentration and properties of dispersed phase. Concentration of dispersed phase has an effect on the character of the fluid. The fluid can have Newtonian character at low concentrations of dispersed phase. Above certain concentrations the nature of non-Newtonian fluid will appear. Emulsions have a polydisperse character. Emulsions with ϕ up to 0.4 show approximately linear increase of emulsion viscosity on the oil concentration. Silica represents suspension with aggregates, agglomerates or network formed. The increase in shear rate causes gradual destruction of the structure. The rheological behaviors confirm these processes. The paprika and coffee suspensions have non-Newtonian rheological properties. The suspensions have more and more non-Newtonian characteristics increasing particles concentration. The solid particles do not form structures. The correlation equation for rheological properties of systems studied has been shown. The results may be used for example to verify numerical models or comparisons with respect to similar fluids.

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.

Effect of surfactants and leaf surface morphology on the evaporation time and coverage area of ZnIDHA droplets

AimsThe aim of the study was to determine the effects of the addition of surfactants to ZnIDHA fertilizer on the area of leaf coverage and water evaporation time taking into account the morphology of leaf blades. The effect of three surfactants (polyglucoside, alcohol EO (ethylene oxide) and trisiloxane) on the size of the leaf coverage area and evaporation time was compared.MethodsAdaxial leaf surfaces of maize (Zea mays L. `Wilga`), wheat (Triticum aestivum `Adana-99`) and rapeseed (Brassica napus L. `F1`) were analyzed by scanning electron microscopy and laser scanning confocal microscopy. The contact angle for aqueous ZnIDHA solutions with and without the addition of surfactants was determined. Measurements of droplet evaporation time and area of leaf coverage were conducted at the relative humidity of 60±1%.ResultsThe adaxial surfaces of wheat and rapeseed leaves used in the study can be classified as highly non-wettable, whereas maize leaves are no-wettable. Out of the surfactants under study, the largest leaf coverage area was observed when adding the trisiloxane surfactant. Regardless of the surfactant used, the leaf coverage area decreased and the evaporation time increased for fertilizer droplets applied to the maize, rapeseed and wheat leaves.ConclusionsThis study demonstrated that the addition of surfactants to the fertilizer solution increases the wettability of the adaxial leaf surface and induces a strong capillary effect which determines the direction of spread of fertilizer droplets. In addition to the amount of trichomes and waxes, also the capillary effect has a significant impact on water evaporation time and the area of leaf coverage by fertilizer droplets.

Measuring Techniques and Potential Applications of Interface Rheology

Proteins, surfactants and some polymers adsorb spontaneously at the interface between their aqueous solution and a gas, solid, or liquid phase. The surface layer made this way is characterized by different mechanical properties from the bulk solution, which is determined by surface rheology. The surface layer can undergo dilatational deformation and shear. In general, it can be characterized by both viscous and elastic properties. Surface rheology allows understanding the interaction between molecules, change of molecular conformations or molecular aggregations and diffusion rate of molecules towards the surface layer. There are many publications in which attention is drawn to the possibility of a relationship between surface rheology and foam and emulsion stability. This chapter discusses basic measurement techniques used to determine rheological properties of the sur-face layer, examples of test results, and the potential possibility of their use in practice.

Applications and Properties of Physical Gels Obtained on the Basis of Cellulose Derivatives

Polymer physical gels have been used in numerous practical applications within food processing, chemical, cosmetics, pharmaceutical and agricultural industries. They may be obtained on the bases of synthetic and natural polymers. Natural polymers are easily biodegradable, hence their more extensive usage within the areas where synthetic polymers have been applied so far. The following chapter discusses basic properties and applications of physical gels obtained on the basis of cellulose derivatives. Additionally, it presents the application of rheology to examine the substances of this sort. The most widely known water-soluble cellulose derivatives include methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), and sodium carboxymethylcellulose (NaCMC). Despite the fact that the aforementioned polymers have been known for years, the research on their properties and the potential for new applications and usages are still being conducted.

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