functionpowerLaw
Information
This model describes the mass flow rate and pressure difference relation of an orifice in the form
V = k sign(Δp) |Δp|m
where V is the volume flow rate, k > 0 is a flow coefficient Δ p is the pressure drop and m ∈ [0.5, 1] is a flow coefficient. The equation is regularized for |Δp| < Δpt, where Δpt is a parameter. For turbulent flow, set m=1 ⁄ 2 and for laminar flow, set m=1.
The model is used for the interzonal air flow models.
Implementation
For |Δp| < Δpt, the equation is regularized so that it is twice continuously differentiable in Δp, and that it has an infinite number of continuous derivatives in m and in k.
If m is not a function of time, then a, b, c and d can be pre-computed. In this situation, use Buildings.Airflow.Multizone.BaseClasses.powerLawFixedM, which allows to compute these values outside of this function, for example as parameters of a model.
Inputs
| Type | Name | Default | Description |
|---|---|---|---|
| Real | k | Flow coefficient, k = V_flow/ dp^m | |
| Modelica.SIunits.PressureDifference | dp | Pressure difference | |
| Real | m | Flow exponent, m=0.5 for turbulent, m=1 for laminar | |
| Modelica.SIunits.PressureDifference | dp_turbulent | 0.001 | Pressure difference where regularization starts |
Outputs
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.SIunits.VolumeFlowRate | V_flow | Volume flow rate |
Revisions
-
January 22, 2016, by Michael Wetter:
Corrected type declaration of pressure difference. This is for #404. -
August 12, 2011 by Michael Wetter:
Reimplemented model so that it is continuously differentiable. - July 20, 2010 by Michael Wetter:
Migrated model to Modelica 3.1 and integrated it into the Buildings library. - February 4, 2005 by Michael Wetter:
Released first version.