## DescriptionðŸ”—

The humidityTemperatureCoupledMixed is a mixed coupled boundary condition for temperature to be used at the coupling interface between fluid and solid regions.

Various governing equations of this boundary condition are based on Bergman et al.[1].

The condition assumes a drop-wise type of condensation, whereby its heat transfer Nusselt number is calculated using:

$Nu = 51104 + 2044 (T - 273.15) \, \text{if} \, \, T > 295 \, \, \& \, \, T < 373$ $Nu = 255510 \, \, \text{if} \, \, T > 373$

The mass transfer correlation used is:

$h_m = D_{ab} \frac{Sh}{L}$

The Sherwood number is calculated using:

$Sh = 0.664 Re^\frac{1}{2} Sc^\frac{1}{3} \, \, \text{if} \, \, Re < 5.0E+05$ $Sh = 0.037 Re^\frac{4}{5} Sc^\frac{1}{3} \, \, \text{if} \, \, Re > 5.0E+05$

where:

Property Description
$$D_{ab}$$ Mass vapour difussivity
$$L$$ Characteristic length
$$Sh$$ Sherwood number
$$Re$$ Reynolds number
$$Sc$$ Schmidt number
$$Nu$$ Nusselt number

## UsageðŸ”—

The condition requires entries in both the boundary and field files.

### Boundary fileðŸ”—

<patchName>
{
type            patch;
...
}


### Field fileðŸ”—

On the fluid side:

<patchName>
{
// Mandatory entries
type            humidityTemperatureCoupledMixed;
mode            <word>;

// Optional entries
p               <word>;
U               <word>;
rho             <word>;
mu              <word>;
Tnbr            <word>;
qrNbr           <word>;
qr              <word>;
specie          <word>;
thicknessLayers <scalarList>;

// Conditional entries

// when 'thicknessLayers' entry is present
kappaLayers         <scalarList>;

// when 'mode' == 'constantMass'
thickness           <scalarField>;
cp                  <scalarField>;
rho                 <scalarField>;

// when 'mode' != 'constantMass'
carrierMolWeight    <scalar>;
L                   <scalar>;
Tvap                <scalar>;
liquid              <dict>;
thickness           <scalarField>;

// Inherited entries
...
}


On the solid side:

<patchName>
{
// Mandatory entries
type            humidityTemperatureCoupledMixed;

// Optional entries
p               <word>;
U               <word>;
rho             <word>;
mu              <word>;
Tnbr            <word>;
qrNbr           <word>;
qr              <word>;
specie          <word>;
thicknessLayers <scalarList>;

// Conditional entries

// when 'thicknessLayers' entry is present
kappaLayers         <scalarList>;

// Inherited entries
...
}


where:

Property Description Type Required Default
type Type name: humidityTemperatureCoupledMixed word yes -
mode Operation mode word yes -
p Name of pressure field word no p
U Name of velocity field word no U
rho Name of density field word no rho
mu Name of dynamic viscosity field word no thermo:mu
Tnbr Name of neighbour temperature field word no T
qrNbr Name of neighbour radiative heat flux field word no none
qr Name of radiative heat flux field word no none
specie Name of specie field word no none
thicknessLayers List of kappa-layer thicknesses scalarList no -
kappaLayers List of kappas corresponding to thicknesses scalarList conditional -
thickness Thickness field scalarField conditional -
cp Specific heat capacity field scalarField conditional -
rho Density field scalarField conditional -
carrierMolWeight Carrier molecular weight scalar conditional -
L Characteristic length of the wall scalar conditional -
Tvap Vaporisation temperature scalar conditional -
liquid Liquid properties dict conditional -

The inherited entries are elaborated in:

Options for the mode entry:

Property Description
constantMass Thermal inertia only
condensation Condensation only
evaporation Evaporation only
condensationAndEvaporation Simultaneous condensation and evaporation
• The correlation used to calculate Tdew is for water vapour.
• A scalar transport equation for the carrier specie is required, e.g. supplied via a function object or in the main solver. This specie transports the vapour phase in the main ragion.
• The boundary condition of this specie on the coupled wall must be fixedGradient in order to allow condensation or evaporation of the vapour in or out of this wall.
• There is no mass flow on the wall, i.e. the mass condensed on a face remains on that face. It uses a â€˜lumped massâ€™ model to include thermal inertia effects.
• With mode==condensation, when the wall temperature (Tw) is below the dew temperature (Tdew) condesation takes place and the resulting condensed mass is stored on the wall.
• With mode==evaporation, initial mass is vaporized when the wall temperature (Tw) is above the input vaporization temperature (Tvap).

## Further informationðŸ”—

Tutorial:

Source code:

API:

History:

• Introduced in version v1706