Automatically applied heat flux due to species flux

FliegenderZirkus · November 17, 2021, 11:12

The species solver supports three types of boundary conditions, here's a table from the manual:

Table 31: Properties of the Wall Species Option

Impermeable: Specifies the boundary as impermeable.
Specified Flux: Specifies a species flux at the boundary. The energy that is associated with the wall species influx or outflux is appropriately added.
Specified Value: Specifies a species mass fraction at the boundary.

I'd like to ask how the highlighted energy is calculated and what is the physical reasoning behind such a heat source/sink. I'm trying to model evaporation and am applying the latent heat of evaporation as heat flux profile, but this automatic heat due to species flux at a boundary seems to be superimposed to what I prescribe. To reproduce this just prescribe a species flux at a boundary and plot the boundary heat flux on the same boundary. The energy solver must be switched on. Thanks for any clues!

JBeilke · November 19, 2021, 07:08

When you remove a species ( for instance 10 droplets of water) at the wall, then you also loose the energy of the removed species in your flow domain.

FliegenderZirkus · November 19, 2021, 09:49

Would you say it's the enthalpy then, as in $\dot{Q} = \sum _i \dot{m}_i \cdot c_{p,i} \cdot \Delta T$ , whre i are all species? What would be the reference temperature though, 0 Kelvin? I also noticed there's a field function called ThermalDiffusionFluxEnergySource but I couldn't find any documentation on it.

JBeilke · November 22, 2021, 11:53

This look right. I expect, that ccm+ does this calculation automatically.

November 17, 2021, 11:12	Automatically applied heat flux due to species flux	#1
FliegenderZirkus Member Join Date: Nov 2019 Posts: 95 Rep Power: 6	The species solver supports three types of boundary conditions, here's a table from the manual: Table 31: Properties of the Wall Species Option Impermeable: Specifies the boundary as impermeable. Specified Flux: Specifies a species flux at the boundary. The energy that is associated with the wall species influx or outflux is appropriately added. Specified Value: Specifies a species mass fraction at the boundary. I'd like to ask how the highlighted energy is calculated and what is the physical reasoning behind such a heat source/sink. I'm trying to model evaporation and am applying the latent heat of evaporation as heat flux profile, but this automatic heat due to species flux at a boundary seems to be superimposed to what I prescribe. To reproduce this just prescribe a species flux at a boundary and plot the boundary heat flux on the same boundary. The energy solver must be switched on. Thanks for any clues!

November 19, 2021, 09:49		#3
FliegenderZirkus Member Join Date: Nov 2019 Posts: 95 Rep Power: 6	Would you say it's the enthalpy then, as in $\dot{Q} = \sum _i \dot{m}_i \cdot c_{p,i} \cdot \Delta T$ , whre i are all species? What would be the reference temperature though, 0 Kelvin? I also noticed there's a field function called ThermalDiffusionFluxEnergySource but I couldn't find any documentation on it. Last edited by FliegenderZirkus; November 19, 2021 at 11:39.

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November 19, 2021, 07:08		#2
JBeilke Senior Member Joern Beilke Join Date: Mar 2009 Location: Dresden Posts: 530 Rep Power: 20	When you remove a species ( for instance 10 droplets of water) at the wall, then you also loose the energy of the removed species in your flow domain.

November 22, 2021, 11:53		#4
JBeilke Senior Member Joern Beilke Join Date: Mar 2009 Location: Dresden Posts: 530 Rep Power: 20	This look right. I expect, that ccm+ does this calculation automatically.