Gas Irradiation

mettler · August 31, 2023, 12:14

Hi -

I am trying to model gas irradiation for a laser. In my head I am picturing something very similar to a PIV system except the beads get super hot. I have a extremely tiny concentration of the atoms that are radiated that does not have any impact of the Cp/density etc of the main gas. The amount of time the gas is in front of the window where there LED light comes in is extremely small, but the radiation causes a very rapid heat up of the atom. I am thinking of using porous media to model it, but I am having some trouble coming up with the variables needed for the porous media flow since the porosity would be almost 1100%, and how to apply the input power to only the porous media. I don't think I can use a heat flux at the wall, since the atoms are all over the place but not at the wall at all.
I am interested in how much the gas heats up as a result of the irradiation. If anyone has another suggestion in how to model this, please let me know.

LuckyTran · September 1, 2023, 09:59

If all you care about is the temperature of the resulting gas then a simple volumetric heat source will do. The power of this heat source you can calculate with a napkin using the beam energy or intensity and absorption cross section of the particles.

mettler · September 1, 2023, 10:22

Quote:

Originally Posted by LuckyTran

If all you care about is the temperature of the resulting gas then a simple volumetric heat source will do. The power of this heat source you can calculate with a napkin using the beam energy or intensity and absorption cross section of the particles.

Thanks. That is a good idea, but I’m not sure if that would replicate what is going on. I do know the power input from the LEDs but the irradiated atom concentration in the gas is .000001, and those atoms are the only thing getting hot. The lab experiment shows about a 100k temp rise across the window.

I’ll try the volumetric case. When I did the steady-state temp rise calc I got roughly 100k, so maybe the volumetric way will work.

Thanks.

mettler · September 28, 2023, 14:21

I was able to do a great 2d model, but I can't get the volumetric heat source to work in 3d. I am only getting a very hot wall. I made a zone of the correct volume and applied a volumetric heat rate in the source. Any suggestions of what I missed would be appreciated.

thanks

August 31, 2023, 12:14	Gas Irradiation	#1
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	Hi - I am trying to model gas irradiation for a laser. In my head I am picturing something very similar to a PIV system except the beads get super hot. I have a extremely tiny concentration of the atoms that are radiated that does not have any impact of the Cp/density etc of the main gas. The amount of time the gas is in front of the window where there LED light comes in is extremely small, but the radiation causes a very rapid heat up of the atom. I am thinking of using porous media to model it, but I am having some trouble coming up with the variables needed for the porous media flow since the porosity would be almost 1100%, and how to apply the input power to only the porous media. I don't think I can use a heat flux at the wall, since the atoms are all over the place but not at the wall at all. I am interested in how much the gas heats up as a result of the irradiation. If anyone has another suggestion in how to model this, please let me know.

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September 1, 2023, 09:59		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	If all you care about is the temperature of the resulting gas then a simple volumetric heat source will do. The power of this heat source you can calculate with a napkin using the beam energy or intensity and absorption cross section of the particles.

September 28, 2023, 14:21		#4
mettler Senior Member Andrew Join Date: Mar 2009 Location: Washington, DC Posts: 211 Rep Power: 18	I was able to do a great 2d model, but I can't get the volumetric heat source to work in 3d. I am only getting a very hot wall. I made a zone of the correct volume and applied a volumetric heat rate in the source. Any suggestions of what I missed would be appreciated. thanks