Enzymic clarification is one of the most important techniques to enhance qualitative and quantitative characteristics of juice. The effects of the enzyme pectinase, incubation time, and temperature on rheo- logical characteristics of mango pulp was studied. It was found that enzyme treated mango pulp behaved like a pseudoplastic liquid and all variables had sig- nificant effects on rheological parameters of mango pulp (Bhattacharya & Rastogi 1998). Several authors studied the effect of pectinase on physico- chemical characteristics of fruit juice clarification and reported that all the variables had a significant effect on the viscosity of juices (Rai et al. 2004; Lee et al. 2006; Sin et al. 2006; Abdullah et al. 2007). Ahmed and Ramaswamy (2004) studied the effects of temperature, total soluble solid content, α-amylase concentration, and pH on rheological characteristics of papaya puree using the response surface method- ology. Several investigators reported that clarified and depectinated juices and their concentrates ex- hibit Newtonian flow behaviour (Ibarz et al. 1987, 1992a,b; Cepeda & Villaran 1999; Juszczak & Fortuna 2004). Several authors used Newtonian equation for describing rheologicalbehaviour of food products such as Pomegranate juice (Altan & Maskan 2005), Pekmez (Kaya & Balibagli 2002), Liquorice extract (Maskan 1999), however, certain juices with a low pulp content and soluble solid con- tent less than 30 o Brix also behave like a Newtonian
particle mixtures), and distilled water were prepared. Such mixtures were investigated in a standard rheometer with two different geometries, the parallel plates system and the vane rotor system, in order to distinguish disturbing effects. The vane geometry seems to be an appropriate rheometrical tool for quantitative evaluation of the rheologicalbehaviour of de- bris flow materials. Instead, by using the parallel plates sys- tem, only some qualitative ideas about their behaviour can be obtained. The comparison between the results of the two ge- ometry configurations allows checking the range of shear rate where there are no disturbing effects and misleading evalua- tions. In this range of shear rate all the tested debris flow mix- tures behave like a non-Newtonian fluid with a yield stress τ y that increases with solid volumetric concentration C v and
The effects of guar gum and lecithin concentrations (1, 0.75, and 0.5%wt) on the stability of oil in water emulsion were investigated. All emulsions can be stabilized at the studied concentrations of stabilizers. The samples tested by steady shear flow and dynamic viscoelasticity tests were carried out to characterize the rheologicalbehaviour of emulsions as influenced by concentration. Emulsions presented a non-Newtonian behaviour type with shear thinning and flow curves that could be described by the Carreau model. The dynamic viscoelastic properties characterized by an oscil- latory frequency sweep under small deformation conditions showed fluid-like viscoelastic behaviour. The interaction of the stabilizers in the mixture with each other at the interface appears to play a decisive role for the stabilization of emulsions.
ABSTRACT: Coal Water Slurries (CWS) are concentrated suspensions of coal particles in water and are used as fluid fuels. The rheological properties of Coal Water Slurries depend on a number of factors such as the type of coal, the solid content and its size distribution, the temperature, the pH and the presence of electrolytes and chemical additives. In the present study rheological behavior of Indian coal water slurry (CWS) was investigated using an Anton Parr RheolabQC rheometer. The objective of the current work was to determine the effect of concentration and additive on the rheologicalbehaviour of coal water slurries. It is observed that the coal water slurry exhibits shear thinning/thickening effects at low concentrations while at 50% Cw and above the slurry prepared from both coal samples consistently shows shear thinning behaviour. The increase of viscosity is found to be exponential with concentration. The viscosity is significantly affected by surfactant Triton X-100 which is observed to lower the viscosity at all selected dosages (i.e:0.5%-2.4% by weight of slurry).The optimal dosage is 1.5% of additive by weight of slurry. The maximum reduction in viscosity is about half at 1.5% additive dosage at 50% Cw of slurry. From work on surfactant loading it can be concluded that it might be possible to produce pumpable coal slurries at concentrations of 50% and above by adding suitable dispersant/additive at optimal dosage.
There are several methods designed for measurements of the rheologicalbehaviour of substances with different types of measurement geometry such as concentric cylin- ders, cone and plate or parallel plates (Vítěz and Severa, 2010). An extensive overview of the measurement tech- niques for rheological testing is given in the paper of Boger et al. (2009). Measurement of rheological properties was performed using this study was performed using an Anton Paar MCR 102 rheometer (Austria) with plate-plate mea- surement geometry. The diameter of the plate was 50 mm. The gap was set on the value of 0.5 mm. The gap was set with respect to the behaviour of the sample at a higher shear rate, when the liquid starts to leak out of measuring ves- sel. The constant shear test was performed at a value of the shear rate of 50 s -1 . A hysteresis loop test was performed at
All four plots are shown in the figure – box and whisker plots, scree plot, component weight plot, and scatterplot of component scores. The analysed datasets show normal dis- tribution at a significance level α = 0.05. Dependence of the rheological values (for example viscosity) is important to track from the viewpoint of rheology. The component weight plot shows dependences and similarities between the observed characters. From this plot, it is evident that viscosity does not exhibit any dependence or similarity to the other chemical values measured. This confirms the aforementioned hypothesis that rheologicalbehaviour is determined by the contents of many particles of various origins. It should be noted that the two com ponents com- pared explain approximately 68% of the total dispersion (Fig. 5). The scatterplot of the component scores represents relationships between the individual samples of wines (Fig. 6). It is possible to see that the white wines are located on the left side of the plot and the red wines are located on the right side of the plot. This suggests that the colour of wine is determined by chemical values.
A b s t r a c t. The rheologicalbehaviour of enzyme clarified depectinated Indian gooseberry juice and its concentrate was stu- died as a function of total soluble solids concentration in the range of 8.2 to 35.9°Bx and temperatures from 20 to 80°C using coaxial controlled stress rheometer up to a shear rate of 600 s -1 . The results indicated that the enzyme clarified gooseberry juice behaves like a Newtonian fluid with a viscosity ranging from 3.92 to 7.94 mPa s. The effect of temperature on viscosity of different concentration of juice was described by an Arrhenius type relationship (R >0.99). The activation energy for viscous flow was found to be in the range 4.34 to 5.37 KJ mol -1 depending upon the concentration of the juice. The activation energy of viscous flow on concentration was modeled by exponential equation (R>0.99). The effect of concen- tration on viscosity followed an exponential type relationship (R>0.98) at the temperature used.
The rheological behavior of the prepared emulsions was studied on a rotary viscometer "Brookfield" RV DV-II + Pro, equipped with an adapter for small samples, comprising a metal cylinder measuring with a water jacket SC4-13R and a cylindrical spindle with conical head SC4-27 (a length of the tube 33.02 mm and diameter 11.76 mm and total length of the working part 39.29 mm). The measuring cylinder had an internal diameter of 19.05 mm and a length of 64.77 mm. The upper conical part of the spindle should cover the test product. Therefore, during each experiment, the cylinder was filled with emulsion volume of 10.4 mL. Before the start of measurement, an insulating cap was placed on the neck of cylinder, and then began the preliminary experiments in order to specify the range of shear rates in which the measurements were possible to be done. The water jacket of the adapter for small samples was connected by flexible connections with ultra-thermostat "Zemail Horyzont", equipped with a contact thermometer with a range from 0 to 100 °C ± 0.1 and second control thermometer with the same scope. The measuring cylinder was filled with emulsion and then heated at four different temperatures (20, 25, 30 and 35 °C, respectively) for a period of 5 min. The selected temperatures were concerned with the storage and stability conditions of emulsions. After reaching the required temperature, an insulating cap was placed on the neck of the cylinder, and then the experiments can be started. An experiment was designed, during which the structural and mechanical properties of each emulsion were measured at 28 shear rates (D = 0.1 ÷ 1.02 s -1 ) determined during the preliminary experiments. Each experiment continued 42 min - the spindle rotated at every shear rates for the period of 90s at the end of which the viscometer registered a reading. The resulting data were used for constructing graphical dependencies between the shear stress and the shear rate which were used to define the rheological properties of the emulsion. The average values of the results from
As expected for biofluids, there is donor to donor variabil- ity, and, as a result, the measurements repeated with samples from different rabbit eyes and in different days, even under similar experimental conditions, present a significant variabil- ity. The oscillatory measurements show that G ' and G ' ' are higher in the gel phase measured 4 ± 1 h after dissection than right after dissection. Measurements with the gel phase (both right after dissection and 4 ± 1 h after the dissection) show that for all the frequencies, G ' is in average higher than G ' ', indi- cating that a solid-like behaviour dominates (Barnes 2000). For the liquid phase, both G ' and G' ' are lower than the gel phase, and the elapsed time after dissection does not seem to significantly influence the linear viscoelasticity of the fluid for the time frame investigated. Nevertheless, G ' is also higher than G ' ' for the range of frequencies tested and the fluid can be considered as a weak gel (Picout and Ross-Murphy 2003). We, however, still refer to it as liquid phase for consistency with previous works (Balazs and Denlinger 1982; Bishop 2000; Los et al. 2003; Sebag 1987). Similarly, Nickerson et al. (2008) showed that for variable frequency experiments, the broad plateau modulus region expected for gels occurs below ω = 5 rad/s. As such, we will base our analysis on values obtained for ω = 1 rad/s (see Table 2). Using the Cox-Merz rule (Manero et al. 2002), we can estimate the shear viscosity
Figure 1 shows that, for the Chlorella sp microalgae suspension obtained from different process conditions, their apparent viscosity has influenced the increase in the rotation frequency (which is directly proportional to shear rate) in all cases. On the other hand, during the implementation of the three repetitions for measuring viscosity, for the same process condition, it could be observed that the apparent viscosity values were not so close, which indicates that there is evidence that such suspension presents a certain thixotropy, i.e. their apparent viscosity decreased over time for a given rotation frequency, which is possibly due to the sedimentation of suspended particles. Such observation was evidenced by analyzing the degree of thixotropy of the Chlorella sp microalgae suspension: for all process conditions, the thixotropy index resulted in 0.5. These results are consistent with several authors works on algae suspensions in general: the same show the rheological behavior of shear-thickening fluid and an explanation for this behavior is that, as the shear stress increases, the interstitial fluid that lubricates the friction between the particles is unable to fill the spaces, due to an increase in the volume that often accompanies the phenomenon, where there is direct contact between the solid particles, thus causing the apparent viscosity increase . There are few studies that discuss the rheological properties of hydrocolloids, with the vast majority being undertaken on kappa-carrageenan [20, 21, 22, 23, 24].
Feedstock preparation for MIM is a crucial step since deficiencies in quality of the feedstock cannot be corrected by subsequent processing adjustments. Hence, it is important that the feedstock is homogeneous and free of powder-binder separation or particle segregation. Furthermore, the selection of binder and the formulation is important characteristics since it promotes the fluidity and rigidity of the feedstock especially during mixing, injection moulding and debinding [1-3]. Many binder systems have been developed in MIM with the aims of reducing cost and shorten the overall debinding time and at the same time maintaining shape integrity during the subsequent processing [3,4]. A new developed binder system consists of palm stearin shows a better rheological properties [5,6]. However the composition of palm stearin was achieving only 40wt.%. The advantages of this bio-polymer binder; palm stearin includes local natural resources and environmental friendly. Due to this consideration, this study investigate the influence of palm stearin content with the aim of using palm stearin as a based binder system. 2 EXPERIMENTAL PROCEDURES
The stability of three water-based slurries containing different loads of Al microparticles was measured by laser scattering. The slurries displayed a Newtonian behaviour and the evolution of viscosity over nine days was found to be constant. Ground surfaces of nickel were also wetted si- milarly irrespective of the Al content in the slurries (30, 40 or 50 wt%) thereby demonstrating that the 1/10 PVA/H 2 O water based slurries are adequate for spraying. After deposition and an-
Rheology provides a convenient and informative method for characterising the behaviour of polymer-based and colloidal sys- tems [72 e 76]. Meaningful measurements can be made on a wide range of ﬂ owable media (including solutions, suspensions, melts, gels, pastes and granular systems) under realistic conditions, using modest quantities of materials (i.e. consistent with the volumes of silk feedstock contained in the ducts of B. mori, other silkworms and reasonably large spiders). Moreover, in polymer-based systems, a suitable analysis of oscillatory measurements can yield information on chain entanglements, relaxation rates and molecular weight. In view of the role generally ascribed to interchain interactions, ﬂ ow- induced orientation and phase transformations, information of this type is considered to be germane for a complete understanding of
The rheological properties of starch pastes are determi- ned by various factors. The most important of them are the type and concentration of starch, the temperature of mea- surement and the method by which the paste is prepared ie the rate, time and temperature of heating, the way of stirring (Che et al., 2008; Jiang et al., 2011; Lagarrigue and Alvarez, 2001; Tattiyakul and Rao, 2000). A number of studies have already been devoted to investigating the rheological pro- perties of starch (Rao, 2007). It has found that corn starch dispersions heated at 80°C exhibit a non-Newtonian, shear- thinning flow with a tendency towards a yield stress, and show antithixotropy (Da Silva et al., 1998). The same re- search has revealed a relationship between the granule size distribution and the rheological properties of corn starch. Other authors have observed a similar behaviour in heated tapioca starch dispersions (Rao and Tattiyakul, 1999). The shear-thickening properties of starch dispersions was re- ported by Kim et al. (2002). The occurrence of anti- thixotropy connected with the formation of flow-induced structures has also been reported for modified corn starch (Tattiyakul and Rao, 2000) and waxy corn starch (Wang et al., 2010, 2011).
Heat stability tests only focus on the phase transition of the systems, from liquid to gel solid state while age thickening refers to the continuous change in rheologicalbehaviour of the system with time, eventually culminating in gelation. The author believes that the understanding of factors affecting heat stability can shed light on the age-thickening behaviour of dairy products, although previous authors have not drawn this parallel before. There are obvious differences between HCT and age thickening in milk systems, including temperature and solids content being the main variables. HCT is associated with less concentrated products which are subjected to higher temperature treatment. In addition, HCT is not a rheological measurement, as it does not investigate the relationship between shear stress and shear rate. It is speculated that a factor that gives rise to a lower HCT may increase the rate of age thickening, i.e. these two processes could be driven by similar mechanism/so
more stable rather than their metallic counterparts. The rheologicalbehaviour actually is affected by several main factors which include particle size and shape,temperature and particle concentrations. Based on previous studies, it is found that temperature give strong effect towards shear viscosity of nanofluids. For particle size, the viscosity will show tendency to depend on volume fraction when the size is decreased (Zhao et al., 2006). Meanwhile, nanofluids containing rod-like particles are likely to have high viscosity rather than spherical nanoparticles (Chen et al., 2009).
All samples show viscoelastic nature, suggesting that a combination of particle aggregation and shape effects is the mechanism for its high-shear rheologicalbehaviour, which is also supported by the thermal conductivity mea- surements [7,24,39]. G’ decreases after a certain critical strain, and G″ presents an overshoot phenomenon. Finally, the results of the frequency sweep show that the damping factor presents a maximum against frequency, corresponding to a continuous evolution with concentra- tion from viscous to elastic nature. This is an evidence of important aggregation and structural changes in the sam- ples, a subject still poorly studied that deserves further attention.
a function of the shear rate was due to the breakdown of structural units caused by hydrodynamic forces genera- ted during cutting (Grigelmo et al., 1999; Nurul et al., 1999; Valencia et al., 2013). High temperatures, such as T = 30, 40, and 50°C promoted the breakdown of weak interactions (hydrogen bonds) between macromolecules- macromolecules and macromolecules-water, obtaining a rheologicalbehaviour typical of liquid systems (Grigelmo et al., 1999). For the same temperature, the increase in SSC led to an increase in shear stress values caused by a high- er proportion in hydrated macromolecules and hydrogen bonding with the hydroxyl groups of solutes (Manjuantha Fig. 2. Time-dependent shear stress values at 20°C of vinasses
steep torrents and for immature debris flows allowed a good interpretation of the recorded data as well as parameters val- ues valid for stony debris flows. Only the hydrograph form and the photos of some deposits left in the field by the event allowed to discriminate the type of flow that took place. The behaviour of the water sediment flow that occurred on 4 Au- gust 2002 in the Moscardo Torrent should be considered a stony debris flow, with a rheologicalbehaviour that is by far different from debris flows occurred in 1991, 1993, 1996 in the same torrent and previously modeled. Different resis- tance laws (and rheological behaviours) may apply to differ- ent events for the same torrent, according to these evidences. This has implications both for science and engineering prac- tice, particularly in applying rheological models to evaluate mitigation measures or to create hazard maps.