constantCoefficient
wall
floor
ceiling
raleigh
BaseClasses
| Name | Description |
|---|---|
| constantCoefficient
| Constant convective heat transfer coefficient |
| wall
| Free convection, wall |
| floor
| Free convection, floor |
| ceiling
| Free convection, ceiling |
| raleigh
| Raleigh number with smooth transition to lower limit |
| BaseClasses
| Base classes for convective heat transfer coefficients |
h=hCon, where hCon=3 is a default input argument.
The convective convective heat flux is
q_flow = h * dT,
where dT is the solid temperature minus the fluid temperature.
Extends from Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux (Partial function for convective heat flux).
| Type | Name | Default | Description |
|---|---|---|---|
| TemperatureDifference | dT | Temperature difference solid minus fluid [K] | |
| CoefficientOfHeatTransfer | hCon | 3 | Constant for convective heat transfer coefficient [W/(m2.K)] |
| Type | Name | Description |
|---|---|---|
| HeatFlux | q_flow | Convective heat flux from solid to fluid [W/m2] |
function constantCoefficient
"Constant convective heat transfer coefficient"
extends Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux;
input Modelica.SIunits.CoefficientOfHeatTransfer hCon = 3
"Constant for convective heat transfer coefficient";
algorithm
q_flow :=hCon*dT;
end constantCoefficient;
h=1.3*|dT|^0.3333,
where dT is the solid temperature minus the fluid temperature.
The convective convective heat flux is then
q_flow = h * dT.
Extends from Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux (Partial function for convective heat flux).
| Type | Name | Default | Description |
|---|---|---|---|
| TemperatureDifference | dT | Temperature difference solid minus fluid [K] |
| Type | Name | Description |
|---|---|---|
| HeatFlux | q_flow | Convective heat flux from solid to fluid [W/m2] |
function wall "Free convection, wall" extends Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux; algorithm q_flow := sign(dT)*1.3*abs(dT)^1.3333;end wall;
h=k*|dT|^0.3333,
where
k=1.51 if the floor is warmer than the fluid,
or k=0.76 otherwise, and where
dT is the solid temperature minus the fluid temperature.
The convective convective heat flux is then
q_flow = h * dT.
Extends from Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux (Partial function for convective heat flux).
| Type | Name | Default | Description |
|---|---|---|---|
| TemperatureDifference | dT | Temperature difference solid minus fluid [K] |
| Type | Name | Description |
|---|---|---|
| HeatFlux | q_flow | Convective heat flux from solid to fluid [W/m2] |
function floor "Free convection, floor" extends Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux; algorithm q_flow := if (dT>0) then 1.51*dT^1.3333 else -0.76*(-dT)^1.3333;end floor;
h=k*|dT|^0.3333,
where
k=1.51 if the fluid is warmer than the ceiling,
or k=0.76 otherwise, and where
dT is the solid temperature minus the fluid temperature.
The convective convective heat flux is then
q_flow = h * dT.
Extends from Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux (Partial function for convective heat flux).
| Type | Name | Default | Description |
|---|---|---|---|
| TemperatureDifference | dT | Temperature difference solid minus fluid [K] |
| Type | Name | Description |
|---|---|---|
| HeatFlux | q_flow | Convective heat flux from solid to fluid [W/m2] |
function ceiling "Free convection, ceiling" extends Buildings.HeatTransfer.Convection.Functions.HeatFlux.BaseClasses.PartialHeatFlux; algorithm q_flow := if (dT>0) then 0.76*dT^1.3333 else -1.51*(-dT)^1.3333;end ceiling;
RaMin is used to transition
to a lower limit for the Raleigh number.
This is helpful to avoid a Raleigh number of zero or
to avoid an expression for a convection coefficient that
has an infinite derivative near zero, i.e., if h=f(Ra(1/2)).
| Type | Name | Default | Description |
|---|---|---|---|
| Length | x | Layer thickness [m] | |
| Density | rho | Mass density [kg/m3] | |
| SpecificHeatCapacity | c_p | Specific heat capacity [J/(kg.K)] | |
| DynamicViscosity | mu | Dynamic viscosity [Pa.s] | |
| ThermalConductivity | k | Thermal conductivity [W/(m.K)] | |
| Temperature | T_a | Temperature of surface a [K] | |
| Temperature | T_b | Temperature of surface b [K] | |
| Real | Ra_min | Minimum value for Raleigh number |
| Type | Name | Description |
|---|---|---|
| Real | Ra | Raleigh number |
function raleigh "Raleigh number with smooth transition to lower limit" input Modelica.SIunits.Length x "Layer thickness"; input Modelica.SIunits.Density rho "Mass density"; input Modelica.SIunits.SpecificHeatCapacity c_p "Specific heat capacity"; input Modelica.SIunits.DynamicViscosity mu "Dynamic viscosity"; input Modelica.SIunits.ThermalConductivity k "Thermal conductivity"; input Modelica.SIunits.Temperature T_a "Temperature of surface a"; input Modelica.SIunits.Temperature T_b "Temperature of surface b"; input Real Ra_min "Minimum value for Raleigh number"; output Real Ra "Raleigh number"; protected Modelica.SIunits.TemperatureDifference dT "Temperature difference"; algorithm dT :=abs(T_a - T_b); Ra := rho^2*x^3*Modelica.Constants.g_n*c_p*dT/((T_a+T_b)/2*mu*k); Ra := Buildings.Utilities.Math.Functions.smoothMax(x1=Ra, x2=Ra_min, deltaX=Ra_min/10);end raleigh;