Question

1. Wastewater flow through a bar screen with a flow rate of 8 m/s. The bars are 0.6 cm in thickness and 5 cm opening. Determine the velocity leaving the bars and the head loss through the bars. Assume bar screens are clean.

Answer 1

In order to find out the velocity through screen and head loss. We will use concept of continuity.

Continuity equation says that, rate of flow remains same after even after any cross sectional changes;. A1*V1=A2*V2

where A1, À2 are cross sectional areas of both section respectively

and V1, V2 are velocity at both the section respectively

According to the question, area of initial cross section is unknown, lets say A

Net area of the screen is calculated by the formula given below

A(net)= A[s/(s+t)]

where s= spacing between bars=5cm

t= thickness of bars=0.6 cm

So, A(net)=0.8928*A

Now let V1=velocity of approach= 8m/s

V2= velocity through net area

By the continuity equation;. A1*V1=A2*V2

A*8=0.8928*A*V2

V2=8.96 m/s

Now head loss is given by, assuming bar screens are clean Below formula works

H=0.0729[(V2)²-(V1)²]

H=0.0729*[8.96²-8²]

H=1.187 m