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# المحاضرة 4-4

الكلية كلية الهندسة     القسم  الهندسة البيئية     المرحلة 4
أستاذ المادة محمد عبد مسلم عبد الله الطفيلي       04/07/2018 08:47:51
For the second iteration, assume a settling velocity value of 0.109 m/s, and calculate the Reynolds number. Use the Reynolds number to determine the drag coefficient, and use the drag coefficient in Newton s equation to find the settling velocity.

N_R=(0.85 (0.109 m/s)(0.5 x ?10?^(-3) m))/((1.003 x ?10?^(-6) m^2/s) )=46.19

C_d= 24/(46.19)+ 3/?(46.19)+0.34=1.3

v_(p(t))=?((4 g)/(3 C_(d ) ) (S g_p-1) d_p ) =?((4 (9.81 m/s^2 )(2.65-1)(0.5 x ?10?^(-3) m))/(3 x 1.3)) =0.091 m/s
Because the settling velocity used to compute the Reynolds number agrees with the settling velocity value from Newton s equation, the solution approach has been confirmed.

Idealized discrete Particle Settling

In the design of sedimentation basins, the usual procedure is to select a particle with a terminal velocity v_c ( Surface Overflow Rate SOR ) and to design the basin so that all particles that have a terminal velocity equal to or greater than v_c will be removed. The rate at which clarified water is produced is equal to:
?Q=A v?_c
Where :
Q = flowrate, (m3/s)
A = surface area of the sedimentation basin, (m2)
v_c= particle settling velocity, (m/s)

Rearranging yields:

? v?_(c ) (SOR)= Q/A (m3/m2.d)

Thus the critical velocity is equivalent to the overflow rate or surface loading rate. A common basis of design for discrete particle settling recognizes that the flow capacity is independent of the depth.
For continuous flow sedimentation, detention lime should be such that all particles with the design velocity v_c will settle to the bottom of the tank. The design velocity, detention time, and basin depth are related as follows:

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 .