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516 P. Kajitvichyanukul et al.
(b) Calculate the pressure drop
Using Eq. (10) to determine the pressure drop
Assume: m =1 10 3 Pa·s
Dp ¼ 1 mLVavg
2 D2 :
Dp ¼ 1 ð1 10
2
3Pa sÞ ð2mÞ ð0:32 m=sÞ
ð0:02 10 2mÞ 2 ;
Dp ¼ 8 10 3 Pa ¼ 0:08 10 5 Pa ¼ 0:08 atm:
The pressure drop is 8,000 Pa or 0.08 atm.
Example 2
Find the feed flow to the membrane unit if the water flux is designed as 5 10 -6 m 3 /m 2 ·h. The recovery
of the membrane unit is set at 80% and the surface area of the membrane is 30 m 2 .
Solution
1. Find the filtrate flow using Eq. (6)
Qp ¼
J ¼ Qp
;
Am
Qp ¼ Am
J ;
30 m 2
ð5 10 6 m 3 =m 2 sÞ ð3; 600 s=hÞ ;
Qp ¼ 1; 666:67 m 3 =s:
2. Find the feed flow to the membrane using Eq. (7)
R ¼ Qp
;
Qf
Qf ¼ Qp
R ;
Qf ¼ 1; 666:67 m3 =s
;
0:08
Qf ¼ 2;0833:38 m 3 =s:
The feed flow to the membrane unit is 2,0833.38 m 3 /s.