Air Ducts - Temperature, Pressure and Friction Loss

Temperature and air pressure influence on air ducts friction loss

Air ducts friction loss and pressure drop diagrams are normally made for air at Normal Temperature and Pressure (NTP) condition - with a temperature of 20 oC and a atmospheric pressure of 1 bar.

Influence of Temperature

The friction coefficient in the D'Arcy-Weisbach Equation increases with higher temperature but the coefficient will also be outweighed by the reduced pressure loss due to reduced density of the air.

  • the pressure loss in an air duct is reduced with higher temperature

With air temperature other than 20 oC - a "Temperature Compensating Coefficient" can be used to modify the pressure loss:

Δp = kt ΔpNTP         (1)

where

Δp = actual friction loss (pressure or head)

kt = Temperature Compensating Coefficient

ΔpNTP = friction loss at NTP conditions (pressure or head)

"Temperature Compensating Coefficient" for various air temperatures:

air ducts friction loss temperature compensation

Example - Air with Temperature 100oC

For air with temperature 100oC the "Temperature Compensating Coefficient" is approximately 0.83. So,

  • the pressure loss in air with temperature 100oC is approximately 83 % of the pressure loss in air at standard NTP conditions 20 oC

Influence of Pressure

If the actual pressure differ from atmospheric pressure (1 bar abs) - friction loss in air ducts should be compensated with a "Pressure Compensating Coefficient":

Δp = kp ΔpNTP         (2)

where

Δp = actual friction loss (pressure or head)

kp = Pressure Compensating Coefficient

ΔpNTP = friction loss at NTP conditions (pressure or head)

The "Pressure Compensating Coefficient" can be estimated for various pressures from the diagram below:

air ducts friction loss pressure compensation

  • 1000 mbar = 1 bar = 105 Pa (N/m2) = 0.1 N/mm2 = 10,197 kp/m2 = 10.20 m H2O = 0.9869 atm = 14.50 psi (lbf/in2) = 106 dyn/cm2 = 750 mmHg

Related Topics

  • Ventilation - Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

Related Documents

Tag Search

  • en: air ducts friction loss temperature pressure
  • es: conductos de aire a presión a temperatura pérdida por fricción
  • de: Luftkanäle Reibungsverluste Temperatur Druck

Search the Engineering ToolBox

- "the most efficient way to navigate!"

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!

close