This article reviews the latest updates and available features for our on-demand, CFD simulation software EXN/Aero, including multicomponent, evaporation and porous media conjugate heat transfer models. This latest update will particularly help those in the HVAC space.
The multicomponent feature applies where multiple fluids (components) make up a mixture. An example relevant to the HVAC sector would be moisture in the air; a two-component mixture where 'air' would be one component, and 'water vapour' would be the other. A user may have a source of water vapour (such as plants), and want to know how that moisture travels through the room. At each mesh location, the mass fraction of air and water vapour can be calculated and used to scale the bulk properties.
While users will be able to model water vapour in the air, it should be noted that condensation in air is a different thing. Users can however look to see where the water vapour mass fraction is approaching the dew point. It should also be noted that multicomponent and multiphase are two different things, albeit related. The hierarchy is that a simulation may have multiple phases and each phase may have multiple components. A key distinction here is that components all belonging to the same phase share velocity, pressure, temperature, etc. whereas each phase would have its own field for these values. Going back to the water vapour example, as long as the water stays as vapour it travels with the air, sharing the above fields. As soon as it condensates, the water droplets could move differently than the surrounding air, forming a stationary pool of liquid on a surface.
EXN/Aero offers two versions of this model, one that uses multicomponent and one that is single component (regular). In both cases the models calculate the evaporation on a surface, driven by the local temperature and concentration gradient. Multicomponent evaporation has particular relevance to the HVAC sector, for example when simulating an indoor pool. In this example the user would specify the pool surface as a boundary and water would evaporate from the surface based on the properties specified. In the multicomponent model the air above the pool would be simulated and the evaporation model would use the local water vapour saturation to determine evaporation from that part of the pool surface.
Multicomponent & Evaporation Model Combination
When the multicomponent model and evaporation are combined, one would end up with a HVAC model of the air above the pool showing humidity throughout the room. The user could then place equipment to best handle humidity and avoid high concentrations that could lead to mold.
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Porous Media Conjugate Heat Transfer
Conjugate heat transfer involves heat transfer from a solid to a fluid, like a heat sink in a computer giving heat to the surrounding air. Porous media CHT follows this same principle, but the solid and fluid overlap, say like a sponge that has solid (sponge) and air pockets intertwined. In the HVAC sphere, porous media CHT could benefit simulation of a filter in an air conditioner or heater unit.
The key factor in when to use porous media CHT versus regular porous media is that you expect a temperature difference between the porous lattice and the fluid passing through.
Porous Media Conjugate Heat Transfer in action.
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