Head loss in sewer trash racks

Input data

Flow (Q)

Channel width (b)

Bar width (w)

Distance between bars (d)

Downstream water depth (yj)

Bar slope (𝝓)

Kirschmer β

Output data

Upstream velocity (Um)

Upstream energy (Em)

Upstream water depth (ym)

Downstream velocity (Uj)

Between bars velocity (U)

Downstream energy (Ej)

Head loss (Hf)

Water level difference (ym - yj)

Upstream depth at 50% obstruction (ym50%)

Upstream velocity at 50% obstruction (Um50%)

Upstream energy at 50% obstruction (Em50%)

Head loss at 50% obstruction (hf50%)

Between bars velocity at 50% obstruction (U50%)

Water level difference at 50% obstruction (ym50% - yj)

Description

Given the flow, channel geometry, and screen characteristics, this tool calculates the downflow water level if the upflow water level is known, or the upflow water level if the downflow water level is known. This is particularly useful in wastewater systems where trash racks are used to remove solids.

Failed to load imageHead Loss in Sewer Trash Racks Image

Available Calculation Methods

1. Downflow

Calculates the upflow water level, velocity, and energy, considering the known downflow water level.

Inputs:

Parameter
Unit
Description
Flow (Q)
m³/s
Inlet flow
Width (b)
m
Width of the channel
Trashrack width (W)
m
Thickness of the trashrack
Distance between trashracks (d)
m
Spacing between the trashracks
Downflow level (y)
m
Water level at downflow
Slope (º)
-
Slope angle of the trashrack
β - Kirschmer
-
Kirschmer coefficient

Outputs:

Parameter
Unit
Description
Upflow level (ym)
m
Water level at upflow
Upflow velocity (Um)
m/s
Flow velocity at upflow
Energy (Em)
J
Energy at the upflow
Velocity between bars (Ubb)
m/s
Flow velocity between bars
Head loss (Hl)
m
Head loss in the system

2. Upflow

Calculates the downflow water level, velocity, and energy, considering the known upflow water level.

Inputs:

Parameter
Unit
Description
Flow (Q)
m³/s
Inlet flow
Channel width (b)
m
Width of the channel
Trashrack width (W)
m
Thickness of the trashrack
Distance between trashracks (d)
m
Spacing between the trashracks
Upflow level (ym)
m
Water level at upflow
Slope (º)
-
Slope angle of the trashrack
β - Kirschmer
-
Kirschmer coefficient

Outputs:

Parameter
Unit
Description
Downflow level (y)
m
Water level at downflow
Downflow velocity (U)
m/s
Flow velocity at downflow
Energy (E)
J
Energy at the downflow
Velocity between bars (Ubb)
m/s
Flow velocity between bars
Head loss (Hl)
m
Head loss in the system

References

  • PESSOA, Constantino A. Tratamento de esgotos domésticos. 7. ed. Rio de Janeiro, ABES, 2014.