Difference between revisions of "Flow through perforated pipe"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
m
m
Line 1: Line 1:
Manufacturers of perforated pipe are often able to provide the open area per meter length.   
Manufacturers of perforated pipe are often able to provide the open area per meter length.   


<math>Q_{max, p}=L\times B\times C_{d}\times A_{o}\sqrt{2\cdot g\cdot \sum d}</math>
<math>\frac{Q_{max, p}=L\times B\times C_{d}\times A_{o}\sqrt{2\cdot g\cdot \sum d}}{1000}</math>
{{Plainlist|1=Where:<sub>d</sub>'' is the coefficient of discharge (0.61 for a sharp edged orifice),   
{{Plainlist|1=Where:<sub>d</sub>'' is the coefficient of discharge (0.61 for a sharp edged orifice),   
*''L'' is the length of perforated pipe (m)
*''L'' is the length of perforated pipe (m)
Line 16: Line 16:
<math>\frac{0.008\ m \times 0.0015\ m\times6}{0.03\ m }= 0.0024\ m^{2}/m</math>
<math>\frac{0.008\ m \times 0.0015\ m\times6}{0.03\ m }= 0.0024\ m^{2}/m</math>
Then the maximum flow rate per planter is calculated:
Then the maximum flow rate per planter is calculated:
<math>Q_{max, p}=8\times 0.5\times 0.61\times 0.0024\ m^{2}/m\sqrt{2\cdot 9.81\ m/s^{2}\cdot \sum 1.1\ m}=0.027\ m^{3}/s</math>
<math>Q_{max, p}=\frac{8\times 0.5\times 0.61\times 0.0024\ m^{2}/m\sqrt{2\cdot 9.81\ m/s^{2}\cdot \sum 1.1\ m}}{1000}=27\ L/s</math>

Revision as of 16:08, 25 February 2018

Manufacturers of perforated pipe are often able to provide the open area per meter length.

Where:d is the coefficient of discharge (0.61 for a sharp edged orifice),

  • L is the length of perforated pipe (m)
  • B is the clogging factor (between 0.5 to calculate a for matured installation and 1 to calculate a new perfectly performing BMP),
  • Cd is the coefficient of discharge (usually 0.61 for the sharp edge created by relatively thin pipe walls),
  • Ao is the total open area per unit length of pipe (m2/m),
  • g is acceleration due to gravity (m/s2)
  • Σ d is the total depth of bioretention components over the perforated pipe (m) (e.g. ponding/mulch/filter media/choker layer),


Example calculation[edit]

A part used roll of 100 mm diameter perforated pipe will be used for a stormwater planter project, where each planter will be 8 meters long. The initial design for the planters includes 750 mm depth of filter medium, 50 mm rock mulch, and a further ponding of 300 mm. Upon inspection the pipe is found to have perforations of 8 mm x 1.5 mm on six sides, repeated every 3 cm along the pipe. To calculate the maximum flow rate from each planter, first the open area of the pipe must be calculated in m2/m: Then the maximum flow rate per planter is calculated: