Open Channel Flow
Closed pipe• Pump or fan driving force• No free surface Open channel• Gravity driving force• Free surface
Open channel
Irrigation Storm water collection Waste treatment Transport
Open channel
Prismatic channel Hydraulic radius• Rh = flow area/wetted perimeter
• Optimize for greatest flow at smallest wetted perimeter
Open channel
Flow determination• Empirical• Manning Equation• Weirs
Manning equation
USCS: cfs Q = (1.49/n)A Rh
2/3So1/2
Manning coefficient: n depends on channel surface smoothness
Weirs
Obstruction in flow channel Sharp-crested weirs Rectangular V-notch
Open Channel Lab
All data in USCS Obtain measurements for slope
calculations
Part 1
Flow valve wide open; allow flow to stabilize
Record flow meter value Record dimensions for Manning equation Install rectangular weir; obtain dimensions Install v-notch weir; obtain dimensions
Part 2
Adjust flow valve to reduce flow to about 50% of flow in Part 1
Repeat all measurements
Report
Data: dimensions and flow meter readings Results: calculated flows from Manning
Equation and two weirs Conclusions: compare flow meter readings
with those obtained from empirical equations