Rotating drop measurement

This second method does not lend itself to the development of quantitative correlations which are based solely on true physical properties of the fluids and which, therefore, can be measured in the laboratory. The prediction of heat transfer coefficients for a new suspension, for example, might require pilot-plant-scale turbulent-flow viscosity measurements, which could just as easily be extended to include experimental measurement of the desired heat transfer coefficient directly. These remarks may best be summarized by saying that both types of measurements would have been desirable in some of the research work, in order to compare the results. For a significant number of suspensions (four) this has been done by Miller (M13), who found no difference between laboratory viscosities measured with a rotational viscometer and those obtained from turbulent-flow pressure-drop measurements, assuming, for suspensions, the validity of the conventional friction-factor—Reynolds-number plot.11 It is accordingly concluded here that use of either type of measurement is satisfactory use of a viscometer such as that described by Orr (05) is recommended on the basis that fundamental fluid properties are more readily determined under laminar-flow conditions, and a means is provided whereby heat transfer characteristics of a new suspension may be predicted without pilot-plant-scale studies. 

The interfacial characteristics between an oil drop and aqueous mixed emulsifier solutions were studied with a spinning drop interfacial tensiometer. An interfacial layer was observed at the oil/aqueous phase interface, as evidenced by the formation of "tails" on the rotating drop. The length of these "tails" increased with spinning time and rotation speed. The interfacial tensions between styrene and aqueous mixed emulsifier solutions were unexpectedly high, 5 to 13 dynes/cm, whereas tensions in the range of 10 2 dynes/cm were measured between the "tails" and the aqueous solution. 

The spinning (rotating) drop method allows one to measure very small values of the interfacial tension at the liquid-liquid interface [23], Let us consider a tube filled with liquid into which a drop of another liquid of lower density is introduced (Fig. 1-16). Upon rotation of the tube around... 

Measurements of interfacial tensions of polymer melts were reviewed by Wu (55), Koberstein (65), and Demarquette (66). The measurements usually need long equilibrium time because of the high viscosities of polymer melts. The measurements can be divided into two groups static methods in which interfacial tension is calculated based on the equilibrium profile of the drops and dynamic methods that study the evolution of fiber or drop profiles with time. Static methods include pendant drop method, sessile drop method, and rotating drop method. Dynamic methods include breaking thread method, imbedded fiber method, and deformed drop retraction method. 

For example, the observed decrease in the shear viscosity with the addition of MAH and PENTA leads to lower pressure in the filling of the mold in the mold-injection operation. In fact, the injection pressure diminishes from 40,680 kPa for PET to 24,822 kPa in the system PET-clay-MAH (1 wt%) and to 13,790 kPa in the system PET-clay-PENTA under the same processing conditions. This corresponds to a threefold decrease in the viscosity. However, it is necessary to point out that the viscosity curves reported are built from simple shear rheometric flows. In the actual process operation, the fluid that fills the mold is subjected to a nonhomogeneous stress field, which is likely to develop slip at the walls and another complicated flow behavior [62]. In these circumstances, the in situ viscosity is probably lower than that measured in the rotational rheometer. Measurements of pressure drop versus flow rate made on the fluid that enters the mold would surely provide a more reliable value of the process viscosity, and hence a better evaluation of the effect of the nanoparticles on the flow behavior of PET. 

Fig. 4.4.4. The rotational velocity against applied voltage. The different symbols denote measurements on different drops. The angular velocity was noticeably less for drops which accidentally had dust particles attached to them (see the circles in the figure), but only the data for the fastest rotating drops were considered in the calculations. Between 3.5 and 5 V there was visible disturbance within the drop and measurements were not possible. At 5 V and above, the drop regained a uniform texture. (After reference 60.)...

Rotational flow in the forced vortex within the cyclone body gives rise to a radial pressure gradient. This pressure gradient, combined with the frictional pressure losses at the gas inlet and outlet and losses due to changes in flow direction, make up the total pressure drop. This pressure drop, measured between the inlet and the gas outlet, is usually proportional to the square of gas flow rate through the cyclone. A resistance coefficient, the Euler number Eu, relates the cyclone pressure drop Ap to a characteristic velocity v ... 

Only methods based on drop profiles are suitable for both surface and interfacial tension measurements. These include the pendant drop method [125-127], the sessile bubble or drop method [128, 129], and the rotating drop or bubble method [130, 131]. These methods are independent of the solid-Uquid contact angle but require accurate knowledge of the density difference across the interface. The demand of accurate density data becomes even greater when the two phases have similar densities. The rotating drop or bubble method is particularly suited for the determination of very low surface and interfacial tensions. 

Princen HM, Zia lYZ, Mason SG (1967) Measurement of interfacial tension from the shape of a rotating drop. J Colloid Interface Sci 23 99-107... 

From the fibre optic technique and pressure drop measurement it was proven that the FCC catalyst was fluidized at the impeller rotational speed of above 6300 RPM and somewhere above 10,000 RPM pneumatic transport could occur. The condition that favours the pneumatic transport was not desired because the catalyst could eventually become stuck at the upper grid. Therefore 7875 RPM, which corresponds to 75% of the motor speed on the speed controller, was taken as the normal operational speed of the impeller and falls in the well fluidized regime (see Figure 8 and 9). 

Interfacial tension (7,2) between immiscible liquids can, in principle, be measured by the same methods with which liquid/vapor surface tensions are mea-smed (Adamson, 1990). However, espedally for the measurement of fairly small 7,2 values, a few of these methods are better adapted for this particular purpose, e.g., the pendant drop-shape method (see above), the simpler, but less accurate dropnweight method (Adamson, 1990), and a few other methods using deformed interfaces, sudi as the rotating drop method (Vonnegut,... 

For very small values of 7, Vonnegut s (1942) rotating drop (or cylinder) method (which has been further elaborated upon by Princen et ai (1967)) is the most suitable. As a first approximation, the presence of a straight, flat meniscus at the interface between two liquids inside a vertical tube is an indication of a very low interfacial tension between two liquids. All the above methods are also applicable to measuring 7, using hanging drops, in air. 

The electrodes usually consist of mercury or deposited mercury or occasionally of inert solid material further, they are mainly of a stationary type (in the stripping step as the crucial analytical measurement, but not in the concentration step, where often the solution is stirred or the electrode is rotated). Considering the mercury, only exceptionally has a sessile mercury drop electrode (SMDE)91 or a slowly growing DME(drop time 18 min and phase-selective recording of stripping curve)92 been applied. Most popular are the hanging mercury drop electrode (HMDE) and the mercury film or thin-film electrode (MFE or MTFE). 

Electrode processes are often studied under steady-state conditions, for example at a rotating disk electrode or at a ultramicroelectrode. Polarog-raphy with dropping electrode where average currents during the droptime are often measured shows similar features as steady-state methods. The distribution of the concentrations of the oxidized and reduced forms at the surface of the electrode under steady-state conditions is shown in Fig. 5.12. For the current density we have (cf. Eq. (2.7.13))... 

Modifications of the conventional spinning drop tensiometer were required for operating at temperatures up to 200°C. Measurements carried out with heavy oil samples required the use of D20 instead of H20 to maintain a sufficient density difference between oil and water. For accurate measurements, considerable care must be used to ensure that heavy oil drops do not lag behind the rotation of the capillary tube in the tensiometer. Also, repeatability of measurements conducted with chemically ill-defined substances may be hampered by the inhomogeneity of the oil drops. 

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