Fully Developed Turbulent Flow Pressure Drops
In a number of engineering design calculations for turbulent ?ow, the shear rate range falls in region
(c) of Figure 3.9.4. Thus, power law relations are appropriate for such pressure drop calculations.
Hartnett and Kostic (1990) have investigated the various correlations which have appeared in the
literature for circular tubes and have concluded that for a circular tube the relation proposed by Dodge
and Metzner (1959) is the most reliable for pseudoplastic ?uids. It is given by
Viscoelastic Fluids
Fully Developed Turbulent Flow Pressure Drops
Viscoelastic ?uids are of interest in engineering applications because of reductions of pressure drop and
heat transfer which occur in turbulent channel ?ows. Such ?uids can be prepared by dissolving small
amounts of high-molecular-weight polymers, e.g., polyacrylamide, polyethylene oxide (Polyox), etc., in
water. Concentrations as low as 5 parts per million by weight (wppm) result in signi?cant pressure drop
reductions. Figure 3.9.8 from Cho and Hartnett (1982) illustrates the reduction in friction factors for
Polyox solutions in a small-diameter capillary tube. It is seen that at zero polymer concentration the
data agree with the Blasius equation for Newtonian turbulent ?ow. With the addition of only 7 wppm
of Polyox, there is a signi?cant pressure drop reduction and for concentrations of 70 wppm and greater
all the data fall on the Virk line which is the maximum drag-reduction asymptote. The correlations for
the Blasius and Virk lines as reported by Cho and Hartnett (1982) are
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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