Index of content:
Volume 22, Issue 6, December 1978
Velocity Field Rearrangement in Stagnation Flow Leading to Diverging Radial Flow Between Parallel Plates22(1978); http://dx.doi.org/10.1122/1.549490View Description Hide Description
Velocity field rearrangement in tube flow followed by stagnation flow and diverging radial flow between parallel plates has been investigated with a polypropylene melt and composites of solid glass beads in a polypropylene melt. The tube axis was aligned normal to the parallel plates, creating a stagnation flow at the inlet to the diverging flow channel. Pigmented tracer elements, placed at precise locations in the tube, illustrated flow patterns which were recorded on 16 mm movie film. After an analysis of the film, the diagonal components of the rate‐of‐deformation tensor were computed at several different positions in the flow channel. From the sign and relative magnitude of the diagonal components the basic types of extensional flow were identified. The flow behavior of the polypropylene and the bead‐filled polypropylene in the complex channels is essentially the same despite large differences in the rheological and physical properties of the composites. Although the tracer technique needs to be refined for stagnation flows, the reduced tracer data show that the inlet effects associated with the complex stagnation flow extend from the stagnation point a distance of 5–10 times the plate separation. The flow in this region is a combination of shear and complex extensional flows. Beyond this inlet region the flow is somewhat less complex and can be described as a combination of planar extension and simple shear.
22(1978); http://dx.doi.org/10.1122/1.549491View Description Hide Description
The Regularization‐Quadratic Programming (RQP) method is used to circumvent the inherent ill‐posedness of integral equations of the first kind found in the theory of linear viscoelasticity. The ability of this method to detect sharp “cutoffs” in a relaxation spectrum is investigated. Finally, the method is applied to standard master curve polyisobutylene data in order to substantiate the ability to reliably predict sharp boundaries and the overall spectrum shape. The results are very encouraging since no prior assumptions were made as to the functional shape of the sought‐after relaxation spectrum.
22(1978); http://dx.doi.org/10.1122/1.549492View Description Hide Description
The flow behavior of both highly flocculated and dispersed kaolin suspensions has been studied using a capillary tube viscometer and two horizontal pipeline test loops. These facilities enabled wall shear rates to be varied from 30 to Experiments were carried out in which volumetric solids concentrations ranged from 8.6 to 23.4% for the flocculated suspensions, and from 23.4 to 38.7% for the dispersed suspensions. Over the shear rate range the rheograms for laminar flow of the flocculated suspensions followed the Ostwald‐de Waele power law model, while for the higher shear rate range the Bingham plastic model fitted slightly better. Since the high shear rate range was obtained using the capillary tube viscometer, it was concluded that great care must be exercised when scaling up from capillary tube data to pipeline installations, in which the wall shear rate rarely exceeds The dispersed kaolin suspensions were essentially Newtonian, but at the highest solids concentration a measurable degree of shear‐thickening behavior was observed. Results for turbulent flow of the flocculated material are in good agreement with those obtained for similar systems by Kemblowski and Kolodziejski (1973), who have already shown that Dodge and Metzner's equation (1959) for the friction factor of a power law material is not applicable.
22(1978); http://dx.doi.org/10.1122/1.549493View Description Hide Description
A summary is given of certain theoretical predictions of the tensile stress in suspensions of oriented rigid fibers in nonlinear materials exhibiting fluidlike power law shear behavior. The theory is compared with experimental creep data of Street (1971) for a lead matrix containing phosphor‐bronze fibers, and also with the extensional flow data of Chan et al. (1977) for polymer melts containing chopped glass fibers. In the first instance, the agreement is satisfactory, whereas in the latter it is only qualitative, suggesting a need for further work.
22(1978); http://dx.doi.org/10.1122/1.549494View Description Hide Description
A fixture consisting of a bob and a special cup was developed to ease the charging of polymer melt to the gap of a concentric‐cylinder rheometer. Dynamic measurements with the improved rheometer for two polyolefins below melt temperatures were compared with results obtained on the Rheovibron and the torsion pendulum. Shear moduli were generated for polypropylene, polyethylene,and poly(vinyl chloride) melts by oscillating the bob in the axial mode at amplitudes effecting relatively large strain. Bob oscillations in the rotational mode were also investigated. The phase angles and complex shear moduli differed slightly for different modes of oscillation. At strains of 9%, the time‐temperature shift factor remained constant throughout the test‐frequency range for an isotactic polypropylene. However, increased with increasing frequency for strains of 98%. A time‐strain shift factor, was found to satisfactorily superimpose polypropylene moduli data generated at high and low strain levels.
22(1978); http://dx.doi.org/10.1122/1.549495View Description Hide Description
Drag reduction in turbulent pipe flow by means of boundary and centerline injection of long hairlike fibers has been investigated. Experiments have been conducted at various main flowReynolds numbers as well as at various injection rates of the fiber suspensions. The occurrence of drag reduction was observed even with a trace quantity of the fibers. Comparison of the two modes of fiber injection indicates that elongated fibrous elements are more effective as drag reducers when they are present in the outer region of the turbulent core. Measurements of the mean velocity profiles with both modes of injection indicate that the drag reduction can be attributed to a reduction in the momentum transfer ability of the suspensions in the turbulent core.
22(1978); http://dx.doi.org/10.1122/1.549503View Description Hide Description