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# Radiative heating in NX thermal advanced

Valued Contributor

Hi everyone, one more problem that i can´t solve

Just trying to understand the basics on how this software calculates

My model:  A small heat source and a solid to be heaten on steady state condition

Boundary counditions: radiation (all) and radiative heating (solar, collimated and total power)

The weird part

When i set a thermal optical property for the solid which i want to heat up, i get the following scenarious

1) Solar absorptivity = 1 and on infrared properties, Transmissivity = 1 my solid gets hot

2) Solar Absorptivity = 1 and on infrared properties, Reflectivity = 1, solid doesn´t have it´s temperature changed.

As far as i know, if the absorption coefficient  is higher than 0, photons will be absorbed and a fraction will be reemited and the rest will be transformed in kinect energy. When the system  reaches thermal equilibrium, emissivity = absorption (Kirchoff Law)

So, i thought that with those boundary counditions, the following would happen

Boundary coundition: Spectrum Solar and total power of 300 W = a wavelength distribution of a 5000K (around 45% in visible light and 49 % in IR and 6% UV ) black body (sun) which provides 300 J/s of energy for my solid.  Solar absorptivity = 1 means everything will be absorbed and, since infrared emissivity = 0, 0 J/s can be emitted in IR zone. Conclusion: the solid should heat up, but on the simulation it remains in 20 C

Can anyone help me to understand how NX 10 deals with radiation?

Ps: already looked on documentation, couldn´t find the answer

2 REPLIES

# Re: Radiative heating in NX thermal advanced

Creator
Hi, carlosmeo. Can you send model files? I'll see settings and advise how to solve the problem.

# Re: Radiative heating in NX thermal advanced

Valued Contributor

Hi

Sorry, i managed to solve the problem

Sent an e-mail to mayahtt and got the answer on last friday

When you heat up a body with a radiative heating and use emissivity = 0, phisically the body would heat to a infinite temperature since it can only absorb heat. When i tried that on fluent, got a error message.

On Nx thermal, the body remains at room temperature. According to Maya, when you create that kind of problem, which has no sollution, the software just ignores the boundary counditions