Slit flow

A number of instruments are based on the extmsion principle, including slit flow and normal capillary flow (Table 6). These instruments are useful when large numbers of quality control or other melt viscosity test measurements are needed for batches of a single material or similar materials. When melt viscosities of a wide range of materials must be measured, rotational viscometers are preferable. Extmsion rheometers have been applied to other materials with some success with adhesives and coatings (10,161). 

One of the most common flows in polymer processing is the pressure driven flow between two parallel plates. When deriving the equations that govern slit flow we use the notation presented in Fig. 5.12 and consider a steady fully developed flow a flow where the entrance effects are ignored. 

Derive the equation for the steady state temperature profile in pressure driven slit flow with viscous dissipation. Assume a Newtonian viscosity model. 

The flow in many extrusion dies can be approximated with one, or a combination, of simplified models such as slit flow, Hagen Poiseulle flow, annular flow, simple shear flow, etc. A few of these are presented in the following sections using non-Newtonian as well as Newtonian flow models. 

Using the nomenclature presented in Fig. 6.12 and assuming a land thickness of h we can assume the land length to be described by slit flow and the manifold by the Hagen-Poiseuille flow with a variable radius as... 

Determine the velocity profile and traction profiles in a pressure driven slit flow of a Newtonian fluid. Use Ap =1000 Pa, //, =1000 Pa-s, h 1 mm and a distance from entrance to exit of 1000 mm. Solve the problem using isoparametric 2D quadratic elements and different gauss points, compare your solutions with the analytical solution for slit flow. 

Slit flow with a constant viscosity, r/ = p, (Newtonian),... 

Slit flow with an Arrhenius temperature dependent viscosity, rj(T), (Newtonian-Arrhenius),... 

Slit flow with a rate of deformation dependent viscosity, 77(7), (Carreau), and... 

Figures 11.15 and 11.16 compare the temperature and velocity profiles, respectively, for the steady-state, fully developed flow of the coupled flow-heat transfer pressure driven slit flow problem, using RFM and FDM. The agreement between the two solutions is excellent.

Upon exiting the die, the sheet extrudate will swell to a level determined by the polymer, the melt temperature, the die length-to-opening ratio, and the shear stress at the die walls. Additionally, flow instabilities will occur at values of the corrected shear stress at the wall, of the order of, but higher than 105 N/m2, as found by Vlachopoulos and Chan (58), who also concluded that, for PS, HDPE, and LDPE, the critical Sr in slits is 1.4 times higher than in tubes of circular cross section. Aside from these differences, the information presented in Section 12.1 and 12.2 applies to slit flow. 

The manifold and slit flows are treated independently, disregarding the disturbances in both flow fields as a result of the transition flow from the manifold to the slit, including entrance losses. To reduce the latter, tapered, wedge-shaped manifolds are used. 

Flow between two parallel stationary walls as a result of an applied pressure gradient is known as slit flow. It can be considered as the two-dimensional analog of capillary flow. This technique is used when studying practical industrial processes such as injection molding of plastics, for example, for bottle-pack lines. The shear stress is here calculated from ... 

Slit flow No Apent with wall-mounted pressure Edge effects with W/B > 5... 

The velocity profile V ix, y) must be determined. Suppose IT/// > 1 so that side-wall effects at x = 1T can be ignored. This limiting case is known as slit flow or flow between parallel plates. The velocity profile within the slit is... 

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