Specify these settings on the Solve dialog:
- Flow = On
- Heat Transfer = On
- Iterations to run = 200
- Specify a Gravity vector relative to the model coordinate system.
- Turbulence
- Flow in lighting applications is usually laminar or slightly turbulent.
- Click the Turbulence button on the Physics tab, and either select Laminar or the Mixing Length turbulence model.
- If the solution diverges within the first 100 iterations while run laminar, select the Mixing Length model, and restart the analysis from iteration 0.
- In addition to improved stability, the Mixing Length model provides a controlled level of turbulence that predicts slightly cooler temperatures than a completely laminar solution. These temperatures are often closer to values measured in physical testing.
Radiation
Radiation is a surface-to-surface heat transfer mode that requires a direct line of sight between surfaces. In many lighting analyses, radiation plays a significant role, and should not be neglected. Radiation can, however, significantly extend analysis times, and should be used carefully to ensure a balance between process efficiency and solution accuracy.
When to use radiation:
In lighting applications, radiation typically provides the greatest accuracy. Because of its impact on performance, it is not always warranted when conducting multiple design-level simulations. These are the two occasions within the simulation design process that radiation should be used:
- The initial design scenario. This is useful to help fully assess the thermal performance of the current design.
- The final design scenario. This is necessary to verify that the design parameters have been met, and that the device delivers the prescribed thermal performance.
Throughout the design process, focus on optimizing the design based on the conduction and convection solution. This provides a more conservative estimate. The final validation simulation should include radiation for a more accurate temperature solution.
The effects of radiation:
Radiation can make a significant impact on a simulation:
- For certain larger models, the inclusion of radiation can approximately double the solution time.
- Greater solution accuracy. Radiation provides the best fidelity prior to physical testing. Predicted temperatures when radiation is invoked are roughly 10-20% lower.
- Radiation can provide a stabilizing effect for some models.
To include radiation in the model:
- Apply a temperature boundary condition to the vertical surfaces of the enclosure. Use the same value as the inlet temperature boundary condition.
- Modify the emissivity of the air material to a more realistic value than 1.0.
- Save this material to a custom material database.
- This value is internally applied to the wetted surface of walls within the enclosure.
- In most situations, use an emissivity value of 0.3 unless the value is known. For materials with a black coating, specify an emissivity value of 0.8. Lenses typically have an emissivity value of 0.7 and a transmissivity value of 0.3.
- On the Physics tab of the Solve dialog, check Radiation.
For more about radiation...
Meshing |Results