Fluent incident radiation problem

Michael Schwarz

Dear Fluent users,

enclosed you receive the collector model, with which we simulated the irradiation on a windowpane. The collector model consists of a rectengular-box, which is flowed through with air. The radiation falls through the windowpane on the rear wall. Thus the rear wall is warmed up and transfers the energy to the air flow. The following boundary conditions were set (see appendix).

Incident radiation on glas surface = 1000 W/m²

glas area = 1,8 m²

glas absorption coefficient band 1 = 32 1/m

band 2 = 200 1/m

velocity inlet = 0.2 m/s

After 350 iterations the simulation converged. The results are as followed (see appendix).

Inlet temperature = 300 K

outlet temperature = 310 K

glas temperature = 303 K

wand on backside = 314 K

flux report inlet/outlet = - 310 W intergral incident radiation on backside (absorbed energy) = +1788 W

energy balance = 1478 W

The energy balance is unfortunately not correct. The windowpane is impermeable for infrared radiation (Coeff=200 1/m). The absorber can therefore lose no energy to the environment by radiation. As a test we put the irradiation directly as a heat flux on the absorber and set the windowpane on diffuse. Now the air flow experiences a rise in temperature of about 80 K - this is realistic.

Can someone help me with this problem ??

Thanks for help, Michael Schwarz

Attachment:

File testfall_dsplan.cas

zone 2 (velocity_inlet.1): 0.024500012

zone 3 (pressure_outlet.2): -0.024499377

zone 4 (glasscheibe): 0

zone 5 (wandhinten): 0

zone 6 (wand_rechts): 0

zone 7 (wand_links): 0

zone 8 (wall): 0

zone 10 (default-interior): -1.1677017

net mass-flow: 6.35162e-07

zone 2 (velocity_inlet.1): 29.449089

zone 3 (pressure_outlet.2): -339.33804

zone 4 (glasscheibe): 0

zone 5 (wandhinten): 0

zone 6 (wand_rechts): 0

zone 7 (wand_links): 0

zone 8 (wall): 0

net heat-transfer: -309.88895

zone 2 (velocity_inlet.1): -11.843837

zone 3 (pressure_outlet.2): -33.356339

zone 4 (glasscheibe): 310.07889

zone 5 (wandhinten): -215.85818

zone 6 (wand_rechts): -16.41909

zone 7 (wand_links): -16.419128

zone 8 (wall): -16.041611

net rad-heat-transfer: 0.14069843

Integral Incident Radiation (glasscheibe): 1833.0248

Integral Incident Radiation (wandhinten): 1784.6536

Integral Incident Radiation (wand_rechts): 829.83936

Integral Incident Radiation (wand_links): 829.83936

Average Static Temperature (velocity_inlet.1): 300.06528

Average Static Temperature (pressure_outlet.2): 310.11212

Average Static Temperature (glasscheibe): 302.96265

Average Static Temperature (wand_links): 307.0737

Average Static Temperature (wand_rechts): 307.07373

Average Static Temperature (wandhinten): 314.14886