Emissivity
Emissivity
(OP)
Hello - I'm working through some transient thermal analysis and all seemed to be going well. I thought I had the radiosity solver cracked. The results I am getting are very reasonable.
However...
I set up my material properties as such:
MP,DENS,1,2000 !DENSITY [kg/m3]
MP,EMIS,1,0.8 !EMISSIVITY [-]
MPTGEN,0,15,300,200
MP,C,1,12.7,2.872,-0.00145,3.12E-7,-2.38E-11 !HEAT CAPACITY [J/kg.K]
MP,KXX,1,241.54,-0.241,1.088E-4,-2.144E-8,1.531E-12 !THERMAL CONDUCTIVITY [W/m.K]
Varying the emissivity has no effect on the solution. I've varied it 0 < EMIS < 1 but it doesn't make any difference.
Since I'm generating a number of temperatures and using C and KXX as polynomials to be evaluated at these temperatures do I need to do the same for EMIS? Or am I defining it wrongly somehow?
I'm convinced that changing the emissivity should affect the solution:
Power radiated = area * stefanBoltzmann * emissivity * Temp^4
Thanks for any advice!
H :)
However...
I set up my material properties as such:
MP,DENS,1,2000 !DENSITY [kg/m3]
MP,EMIS,1,0.8 !EMISSIVITY [-]
MPTGEN,0,15,300,200
MP,C,1,12.7,2.872,-0.00145,3.12E-7,-2.38E-11 !HEAT CAPACITY [J/kg.K]
MP,KXX,1,241.54,-0.241,1.088E-4,-2.144E-8,1.531E-12 !THERMAL CONDUCTIVITY [W/m.K]
Varying the emissivity has no effect on the solution. I've varied it 0 < EMIS < 1 but it doesn't make any difference.
Since I'm generating a number of temperatures and using C and KXX as polynomials to be evaluated at these temperatures do I need to do the same for EMIS? Or am I defining it wrongly somehow?
I'm convinced that changing the emissivity should affect the solution:
Power radiated = area * stefanBoltzmann * emissivity * Temp^4
Thanks for any advice!
H :)





RE: Emissivity
CODE
! Enclosure 1
sf,rad_1a,rdsf,0.950,1
sf,rad_1b,rdsf,0.900,1
! Radiation options
stef,5.67e-8
toffst,273.15
hemiopt,10
tunif,500
/solu
rsymm,,0,y ! For y-symmetry
rsymm,,0,z ! For z-symmetry
rsurf ! Create SURF252 elements on radiating surfaces
I found this link helpful: http
RE: Emissivity
I was using the following command later on in the script:
SFA,ALL,1,RDSF,0.8,1
so in fact it was just my stupid mistake of not realising I should change the emissivity value here, the MP,EMIS,1,0.8 command seems only to have an effect if I specify a range of emissivities and then tell SFA RDSF to use these.
Again, thank you for pointing out my massive oversight.
That document is a very good overview.