Friction factors for transitional and turbulent conditions
Though turbulent flow conditions are encountered less frequently with
polymeric non-Newtonian substances, sewage sludges, coal and china clay
suspensions are usually all transported in the turbulent flow regime in large
diameter pipes. Therefore, considerable research efforts have been directed at
developing a generalised approach for the prediction of the frictional pressure
drop for turbulent flow in pipes, especially for purely viscous (power-law,
Bingham plastic and Herschel–Bulkley models) fluids. Analogous studies for
the flow of visco-elastic and the so-called drag-reducing fluids are somewhat
inconclusive. Furthermore, the results obtained with drag-reducing polymer
solutions also tend to be strongly dependent on the type and molecular weight
of the polymers, the nature of the solvent and on the type of experimental set
up used, and it is thus not yet possible to put forward generalised equations for
the turbulent flow of such fluids. Therefore, the ensuing discussion is restricted
primarily to the turbulent flow of time-independent fluids. However, excellent
survey articles on the turbulent flow of visco-elastic and drag-reducing systems
are available in the literature [Govier and Aziz, 1982; Cho and Hartnett, 1982;
Sellin et al., 1982].
In the same way as there are many equations for predicting friction factor for
turbulent Newtonian flow, there are numerous equations for time-independent
non-Newtonian fluids; most of these are based on dimensional considerations
combined with experimental observations [Govier and Aziz, 1982; Heywood
and Cheng, 1984]. There is a preponderance of correlations based on the
power-law fluid behaviour and additionally some expressions are available for
Bingham plastic fluids [Tomita, 1959; Wilson and Thomas, 1985]. Here only
a selection of widely used and proven methods is presented.
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 .
|