Disc-shearing device

To measure the adhesion strength of bacteria, it is necessary to remove them from the surface. Weiss (1961) measured bacterial adhesion by allowing cells to settle onto a glass surface of a sealed chamber, and then counting them with the aid of a microscope. After a period of incubation the chamber was turned upside down, the unattached cells fell from the surface and the remaining attached cells were recounted. This adhesion number method is purely observational, as it does not measure adhesion directly. Weiss also described a disc-shearing device,... 

An example of a simple, direct-shear device is shown in Fig. 6.79. In this brake MR fluid is located between the faces of the disc-shaped rotor and the... 

Contrary to RPBRs, in SDRs, intensified heat transfer presents the most important advantage. Liquid reactant(s) are fed on the surface of a fast rotating disk near its center and flow outward. Temperature control takes place via a cooling medium fed under the reaction surface. The rotating surface of the disc enables to generate a highly sheared liquid film. The film fiow over the surface is intrinsically unstable and an array of spiral ripples is formed. This provides an additional improvement in the mass and heat transfer performance of the device. 

Rotating disc systems have also been described as efficient devices to overcome flux limitation due to matter deposit on membrane surface during cross-flow filtration [40]. The problem of erosion of a macroscopic particle solid deposit on a rotating disc membrane has been quantified by Aubert et al. [41]. The influence of the transmembrane pressure, the thickness of the initial deposit and the pore size on the critical shear stress have been investigated and described by empirical fits. It results from this study that fouling is more efficiently eliminated at high Ap and large pore size. 

Rotational speeds are very low, in most cases ranging between 50 and 200 RPM. The low-speed hydraulic motors develop very high torques on the shafts, providing considerable shearing power to the cutting discs. This power makes shear shredders effective in difificult-to-cut materials. This equipment has been used to shred materials such as metals, truck and car tires, wood, pallets, bulky objects, and electrical and electronic devices, for example, in relatively coarse particle size. On the contrary, they are not capable of shredding materials into fine size (less than 10 mm). The main advantage of shear shredders is that... 

Trimming of plastics, if not performed correctly, can be damaging to formed parts and slow down or stop the output. Tools for trimming include shear discs, steel rule dies, and saws. The cutting action can be done with the usual punch press, as well as press brakes and other devices. Punch and... 

Brookfield viscosimeters also belong to the group of rotational viscosimeters. In contrast to the devices described earlier, this viscosimeter does not generate a defined shear field. The Brookfield viscosimeter consists mainly of a disc or a pin that is rotating with a defined velocity in the sample fluid. The torque that is required to achieve this rotational speed directly yields a viscosity through comparison with a calibration fluid. The range of measurable viscosities can be adjusted by variation of the disc geometry. 

Laminar flow devices are commonly used to characterize cell adhesion, and include rotating disc, parallel-plate (and variants), and radial-flow devices. These devices all employ tangential fluid flow to exert hydrodynamic drag and torque on adherent cells [98]. Among the different devices, the parallel-plate flow chamber (Figure 34.5a) is described most extensively, and has been used primarily to characterize cell and tissue phenomena under a well-defined hydrodynamic shear stress, r. Here, r can be predicted from fluid mechanics. 

The rotating disc differs from laminar flow chambers in that a motor is used to put the cell-seeded substrate in motion, rather than a pressure gradient to put the fluid in motion [47,107,108] (Figure 34.6). An advantage of this device is that generates a shear stress, r, that varies linearly with radial position, r, by... 

Reutelingsperger, C.P.M., van Gool, R.J.G.,Heinjen, V. et al.,The rotating disc as a device to study the adhesive properties of endotheKal cells under differential shear stresses, J. Mater. Sci., Mater. 

In this device, shown in Fig. 6-3, two disc-shaped samples are periodically sheared between flat surfaces inside a thin cylindrical driving tube and a heavy. 

All the dynamic measurements thus far mentioned furnish the complex Young s modulus in the fiber direction. The shear modulus at right angles can be measured by torsional vibrations of the fiber itself, using a light crossbar or disc to provide the amount of inertia for a compound oscillating system in forced or free vibration. An example is shown in Rg. 7-7, where the forced vibrations are driven by an electrostatic device. Here the analog of equation 13 of Chapter 6 is ... 

Oscillatory shear experiments using, for example, cone-and-plate devices constitute the third main group of viscometric techniques. These techniques enable the complex dynamic viscosity rj ) to be measured as a function of the angular velocity (cu). The fundamental equations are presented in section 6.2 (eqs (6.22H6.27)). Another arrangement is two rotating parallel excentric discs by which the melt is subjected to periodic sinusoidal deformation. 

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