Description: "Functions for convective heat transfer"

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## Buildings.HeatTransfer.Convection.Functions

Functions for convective heat transfer

### Information

This package contains functions that are used in the package Buildings.HeatTransfer.

### Package Content

Name | Description
--- | ---
windDirectionModifier | Wind direction modifier that is used to compute the wind-driven convective heat transfer coefficient
HeatFlux | Correlations for convective heat flux

## Buildings.HeatTransfer.Convection.Functions.windDirectionModifier

Wind direction modifier that is used to compute the wind-driven convective heat transfer coefficient

### Information

Function that outputs 1 if the incidence angle is below 100 degrees, and 0.5 otherwise. The implementation is once continuously differentiable in its input arguments.

See Buildings.HeatTransfer.Examples.ExteriorConvection for an example that uses this function.

Extends from Modelica.Icons.Function (Icon for functions).

### Inputs

Type | Name | Default | Description
--- | --- | --- | ---
Angle | azi |  | Surface azimuth [rad]
Angle | dir |  | Wind direction (0=wind from North) [rad]

### Outputs

Type | Name | Description
--- | --- | ---
Real | W | Wind direction modifier

### Modelica definition

function windDirectionModifier "Wind direction modifier that is used to compute the wind-driven convective heat transfer coefficient" extends Modelica.Icons.Function; input Modelica.SIunits.Angle azi "Surface azimuth"; input Modelica.SIunits.Angle dir(min=0, max=2*Modelica.Constants.pi) "Wind direction (0=wind from North)"; output Real W "Wind direction modifier"; protected constant Modelica.SIunits.Angle lee = Modelica.SIunits.Conversions.from_deg(100) "Angle at which the transition occurs"; constant Real cosLee = Modelica.Math.cos(lee) "Cosine of the angle at which the transition occurs"; algorithm // The wind direction is defined in TMY3 as dir=0 if from North, and 0 <= dir < 2*pi // Hence, we subtract pi to redefine dir=0 as wind coming from the south. // This simplifies the implementation since a surface azimuth is defined as azi=0 // if the surface is south-facing W:=Buildings.Utilities.Math.Functions.spliceFunction( pos=0.5, neg=1, x=cosLee-Modelica.Math.cos(azi+Modelica.Constants.pi-dir), deltax=0.05); end windDirectionModifier;