2-1
SECTION II CALCULATING FLOW
CIRCULAR CONDUITS
To calculate flow in circular conduits you need:
• The mean velocity from Section I.
• The depth of flow at the time of profile.
• The inside diameter of the conduit.
Outline
Calculating flow is outlined as follows:
• Calculate the level to diameter ratio (L/D).
• Identify the flow unit multiplier (K) (Table I, Pages 2-3 and 2-4).
• Square the diameter in feet.
• Calculate flow.
Calculate the Level/Diameter Ratio (L/D)
Ratio = L ÷ D
Where:
L is depth of flow in inches at time of profile.
D is inside diameter in inches.
L/D is the level/diameter ratio.
Identify Flow Unit Multiplier K
K 4 L/D Ratio in Table I on Pages 2-3 and 2-4.
Where:
K is the flow unit multiplier.
Find the appropriate L/D ratio in the L/D column and move to the right to the desired units column to
get the proper flow unit multiplier.
Comment:
The flow unit multiplier in Table I is only for circular conduits measured in feet. The multiplier was
derived using a one foot per second flow in a one foot diameter conduit as the model.
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