Viscosity rotational modes

The relative viscosity rj and storage modulus G were determined by Cirkel and Okada in experiments using a rheometer in oscillatory rotational mode and Couette sample geometry as a function of Nafion volume fraction, cp, and angular frequency, a>, for the acid and sodium forms at 25 °C. Parallel experiments... 

In rotational mode, the following expressions can be used to determine the apparent viscosity and the normal stress from the measurement of the torque on the fixed bottom plate (Bird et al, 1987)... 

The only gross mode that is normally observed is the rotational n = 2 instability. The observed stable period before the mode onset is consistent with the FRC increasing in angular velocity until it crosses a threshold for instability predicted by a Vlasov fluid code. The angular acceleration could be due to an external torque perhaps applied by plasma outside the separatrix through viscosity.Another cause of acceleration could be net angular momentum carried by particles diffusing across the separatrix. This particle loss model predicts that the onset of the instability should occur when about half the particles are lost. This prediction is consistent with the experiment. Since the external torque or other sources of rotation are also possible, better correlation between experiment and theory is needed to properly understand this issue. However, if the FRC stable period Xg (time before mode onset) continues to scale with the time required to lose half the particles, then particle transport, not the rotational mode, will limit the reactor potential of the FRC. 

Rheometric Scientific markets several devices designed for characterizing viscoelastic fluids. These instmments measure the response of a Hquid to sinusoidal oscillatory motion to determine dynamic viscosity as well as storage and loss moduH. The Rheometric Scientific line includes a fluids spectrometer (RFS-II), a dynamic spectrometer (RDS-7700 series II), and a mechanical spectrometer (RMS-800). The fluids spectrometer is designed for fairly low viscosity materials. The dynamic spectrometer can be used to test soHds, melts, and Hquids at frequencies from 10 to 500 rad/s and as a function of strain ampHtude and temperature. It is a stripped down version of the extremely versatile mechanical spectrometer, which is both a dynamic viscometer and a dynamic mechanical testing device. The RMS-800 can carry out measurements under rotational shear, oscillatory shear, torsional motion, and tension compression, as well as normal stress measurements. Step strain, creep, and creep recovery modes are also available. It is used on a wide range of materials, including adhesives, pastes, mbber, and plastics. 

The DTO model ignores the overall translations and rotations of the molecule as a whole and refers only to internal vibrational modes. It is therefore incapable of explaining on its own the viscosity of dilute polymer solutions. The enhanced viscosity of dilute polymer solutions is undoubtedly due to a hydrodynamic damping of the polymer as a whole as it translates and rotates in the shear field. This was very well described by Debye (21). We should point out that the Debye viscosity is alternatively derivable from the RB theory. 

The properties and composition of the hydrolysate are greatly affected by the hydrodynamic mode of the process. Thus, increasing the number of agitator rotations from 300 to 1000 per minute raises dimethylcyclosilox-ane content from 28 to 43% and at the same time visibly reduces the acidity and viscosity of the hydrolysate. 

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