In many practical situations involving the flow of polymer melts through dies
and along channels, the cross-sections are tapered. In these circumstances,
tensile stresses will be set up in the fluid and their effects superimposed on
the effects due to shear stresses as analysed above. Cogswell has analysed this
problem for the flow of a power law fluid along coni-cylindrical and wedge
channels. The flow in these sections is influenced by three factors:
(1) entry effects given suffix O
(2) shear effects given suffix S
(3) extensional effects given suffix E
Each of these will contribute to the behaviour of the fluid although since each
results from a different deformation mode, one effect may dominate depending
on the geometry of the situation. This will be seen more clearly later when
specific design problems are tackled.
(a) Flow in Coni-Cylindrical Dies
Consider the channel section shown in Fig. 5.8(a) from which the element
shown in Fig. 5.8(b) may be taken.
(i) Pressure Drop Due to Shear, Ps
Assuming that the different modes of deformation are separable then considering
equilibrium of forces in regard to the shear stress only, gives
d Ps. 7rr 2 = 2zrr d l sec 0- r cos 0
2r
d e s = -r- . dl (5.38)
In many practical situations involving the flow of polymer melts through dies
and along channels, the cross-sections are tapered. In these circumstances,
tensile stresses will be set up in the fluid and their effects superimposed on
the effects due to shear stresses as analysed above. Cogswell has analysed this
problem for the flow of a power law fluid along coni-cylindrical and wedge
channels. The flow in these sections is influenced by three factors:
(1) entry effects given suffix O
(2) shear effects given suffix S
(3) extensional effects given suffix E
Each of these will contribute to the behaviour of the fluid although since each
results from a different deformation mode, one effect may dominate depending
on the geometry of the situation. This will be seen more clearly later when
specific design problems are tackled.
(a) Flow in Coni-Cylindrical Dies
Consider the channel section shown in Fig. 5.8(a) from which the element
shown in Fig. 5.8(b) may be taken.
(i) Pressure Drop Due to Shear, Ps
Assuming that the different modes of deformation are separable then considering
equilibrium of forces in regard to the shear stress only, gives
d Ps. 7rr 2 = 2zrr d l sec 0- r cos 0
2r
d e s = -r- . dl (5.38)
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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