Enthalpy settings - downdraught evaporative cooling
 

Hello Everyone,

Context:
I'm exploring a case of evaporative cooling in the courtyard of a building. On a hot day without any wind, I trying to test the airflow in the courtyard with a mist system at the top. Assuming that in dry conditions the evaporative cooling effect of water injected in the air could make the air temperature drop down10 C, the cooled air would induce a downdraught that would refresh the spaces.

Simulation :
I'm simulating using buoyantSimpleFoam + fvDom radiation + fvOptions (scalarSemiImplicitSource with injectionRateSuSp) + topoSet:
- topoSet to an arbitrary region at the top of the couryard that corresponds to a simplified injection of mist
- topoSet to set a 2m high box from the ground that simplifies all the internal gains (people, lighting, equipments)
- fvOptions to approximate the drop in temperature and the internal heat gains respectively from, that mist region and that internal gains box as sensibleEnthalpy or sensibleInternalEnergy
- fvDom to account for the surface temperatures

Problem:
I am really struggling to set the fvOptions correctly with the correct units and values of either enthalpy or internal energy (sensible or absolute). So far my reasoning remains at:
- for mist/sprinklers: I look at the Mollier Chart for a drop of 10 C when the dry air is at 30C, the enthalpy needed is 80 kj/kg, so I set "h (-80000 0);"
- for internal gains/heat: I have 72 W/m2 in a height of 2m so I set : 36 W/m3.


Questions:

1) Could clarify if I should use sensible or absolute, enthalpy or internalenergy ?
2) Considering my simplifications how can I set the values correctly?
3) Would you suggest that I change my simplifications for this case?


Thanks so much,
OLivier


scalarSemiImplicitSourceCoeffs
{
cellSet sprinklersP;
selectionMode cellSet;
volumeMode specific;
injectionRateSuSp
{
h (-80000 0);
}
}

heat
{
type scalarSemiImplicitSource;
active true;
scalarSemiImplicitSourceCoeffs
{
cellZone cellZone2;
selectionMode cellZone;
volumeMode specific;
injectionRateSuSp
{
h (36 0);
}
}
}