Shear rotating disk flow

Stable interchain complexation at around neutral pH in very dilute solution (1.9 X 10 " M) under a high shear rotating disk flow (used for drag reduction measurements). Drag reduction (DR) of the PAA decreased sharply depending on the shear rate and time but without causing turbidity in the solution [5]. Such behavior is sensitive to the external conditions. 

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. 

Hydrodynamic boundary layer — is the region of fluid flow at or near a solid surface where the shear stresses are significantly different to those observed in bulk. The interaction between fluid and solid results in a retardation of the fluid flow which gives rise to a boundary layer of slower moving material. As the distance from the surface increases the fluid becomes less affected by these forces and the fluid velocity approaches the freestream velocity. The thickness of the boundary layer is commonly defined as the distance from the surface where the velocity is 99% of the freestream velocity. The hydrodynamic boundary layer is significant in electrochemical measurements whether the convection is forced or natural the effect of the size of the boundary layer has been studied using hydrodynamic measurements such as the rotating disk electrode [i] and - flow-cells [ii]. 

In order to calculate the thin film viscosity with Eq. (15), the flow-activation entropy near the surface is also needed. An experimental flow-activation entropy is calculated from the spin-off data with Eqs. (15) and (19) as follows. The experimental vj vs. h is determined from the dh/dt during air shear induced flow on a rotating disk. Eq. (19) is then solved for AS vis versus h using Eq. (19) for AE -. Below 2.3 nm, — 1.9kJ/mol, which corresponds to the critical configurational entropy change for flow (-/ ln2 - 5.76J/mol-K). 

Shear Stress Sensors, Fig. 8 Schematic of a static calibration apparatus (a) using a rotating disk and (b) long, high aspect ratio smooth channel flow... 

Figure 5.7.2a illustrates the eccentric rotating disk (ERD) geometry (recall Exercise 1.10.7 and Example 2.3.1). A sample is placed between two disks that rotate at the same angular velocity but about offset or eccentric axes. Surface tension holds the sample between the disks. The flow between these eccentric rotating disks results in a shearing motion, with material elements moving in circular paths with respect to each other. A coordinate system r, j, z that rotates with the lower disk (Figure 5.7.2b) can describe the relative motion between particles (Figure 5.7.2c). The deformation is seen to be of constant magnitude, but continually changing direction.

The unsuitable nature of many commercial instruments which are in common use clearly illustrates the confusion prevalent in the field of viscometric measurements. Many instruments measure some combination of properties which depend only partly on the fluid consistency since the flow is not laminar. In others the shear rates are indeterminate and the data cannot be interpreted completely. Examples of such units include rotational viscometers with inserted baffles, as in the modified Stormer instruments in which the fluid flows through an orifice, as in the Saybolt or Engler viscometers instruments in which a ball, disk, or cylinder falls through the fluid, as in the Gardiner mobilometer. Recently even the use of a vibrating reed has been claimed to be useful for measurement of non-Newtonian viscosities (M14, W10), although theoretical studies (R6, W10) show that true physical properties are obviously not obtainable in these instruments for such fluids. These various instru-... 

The velocity field between the cone and the plate is visualized as that of liquid cones described by 0-constant planes, rotating rigidly about the cone axis with an angular velocity that increases from zero at the stationary plate to 0 at the rotating cone surface (23). The resulting flow is a unidirectional shear flow. Moreover, because of the very small i//0 (about 1°—4°), locally (at fixed r) the flow can be considered to be like a torsional flow between parallel plates (i.e., the liquid cones become disks). Thus... 

The activity inside the pump volute incurs several losses first is the backflow of the flow that had aheady been acted upon but is shpping back into the suction eye of the impeller or, in general, toward the suction side of the pump. Because energy had already been expended on this flow but failed to exit into the discharge, this backflow represents a loss. The other loss is the turbulence induced as the impeller acts on the flow and swirls it around. Turbulence is a loss of energy. As the impeller rotates, its tips and sides shear off the fluid this also causes what is called disk friction and is a loss of energy. All these losses cause the inefficiency of the pump is these losses. 

This implies that mass transfer by shear and by diffusion scales flow in proportion with disk area, while keeping rotational speed constant. If, however, convective transport due to surface waves is included the rotational speed is reduced as disk size is increased and... 

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