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Ducts Modules

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CALCULATOR MODULE : Dimensionless Relative Roughness Number   ±

Calculate the dimensionless relative roughness or roughness number for pipes and rectangular ducts.

`rr = (ir) / (ID) `

where :

rr = relative roughness or roughness number
ir = surface roughness
ID = pipe inside diameter

For rectangular ducts the hydraulic diameter is used

`ID = 2 w h / (w + h) `

where :

ID = hydraulic diameter
w = duct width
h = duct height

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CALCULATOR MODULE : Dimensionless Reynolds Number   ±

Calculate the dimensionless Reynolds number for pipes, rectangular ducts and general flow.

The Reynolds number approximates the ratio of kinetic energy over viscous drag loss.

`Re = ρ V L / μ = V L / ν `

where :

Re = Reynolds number
ρ = fluid density
V = fluid velocity
L = characteristic length
μ = dynamic viscosity
ν = kinematic viscosity = μ / ρ

At low reynolds numbers the flow is laminar. At high Reynolds numbers the flow is turbulent. The characteristic length is a defining length dimension. For pipelines the inside diameter is used as the characteristic length. For rectangular ducts the hydraulic diameter is used as the characteristic length.

`ID = 2 w h / (w + h) `

where :

ID = hydraulic diameter
w = duct width
h = duct height

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CALCULATOR MODULE : Liquid Rectangular Duct Pressure Loss   ±

Calculate single phase liquid flow in a rectangular duct.

The Moody diagram is valid for rectangular ducts provided that the Reynolds number is calculated from the hydraulic diameter (equal to four times the cross section area divided by the perimeter). The Darcy friction factor can be calculated from the Moody diagram using either the Hagen-Poiseuille laminar flow equation, the original Colebrook White equation or the modified Colebrook White equation. The minor loss K factor is used to account for pipeline fittings such as bends, tees, valves etc.. Change flow coefficient units on the setup page (Av, Kv, or Cv).

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CALCULATOR MODULE : Low Pressure Air Pressure Loss From The Moody Diagram   ±

Calculate pressure loss for low pressure air circular and rectangular ducts using the Moody diagram.

The calculators use the Darcy-Weisbach pressure loss equation. For low Reynolds numbers Re < 2000, the fluid flow is laminar and the Darcy friction factor should be calculated using the Hagen-Poiseuille laminar flow equation. For high Reynolds numbers Re > 4000, the fluid flow is turbulent and the Darcy friction factor should be calculated using one of the turbulent flow equations. In the transition region 2000 < Re < 4000, the flow is unstable and the friction loss cannot be reliably calculated.

Minor losses can be entered as either a K friction factor, a length, or length over diameter ratio. The minor losses are used to account for pipeline fittings such as bends, tees, valves etc.. :sg:For air the gas specific gravity SG = 1.0. For low pressure air the compressibility factor is assumed equal to one.

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CALCULATOR MODULE : Gas Rectangular Duct Pressure Loss   ±

Calculate single phase gas flow in a rectangular duct.

The Darcy friction factor can be calculated from the Moody diagram using either the Hagen-Poiseuille laminar flow equation, the original Colebrook White equation or the modified Colebrook White equation. The Moody diagram can be used for rectangular ducts if the Reynolds number is calculated from the hydraulic diameter (equals four times the cross section area divided by the perimeter). Minor losses can be calculated using either the K factor, an equivalent length, equivalent diameters, or the flow coefficient. Change flow coefficient units on the setup page (Av, Kv, or Cv).

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CALCULATOR MODULE : Compressible Flow Pressure Loss Factor   ±
CALCULATOR MODULE : API 520 Darcy Friction Factor   ±

Calculate API 520 Darcy friction factor and pressure loss factor for single phase liquid and single phase gas.

The Darcy friction factor can be caclulated from either the Moody diagram or the Von Karman rough pipe equation (API 520 Annex E).

At high Reynolds numbers the Moody diagram friction factor is fully turbulent and is dependent on the pipe roughness only. The pressure loss factor (fLe/ID) includes minor losses. Minor losses can be entered as either a K factor, an equivalent added length, or an equivalent added length over diameter ratio.

Reference : API 520 Sizing, Selection And Installation Of Pressure Relieving Devices (2014)

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