Hello ,

**The Solar Ray Tracing Model**

The solar load model’s ray tracing algorithm can be used to predict the direct **illumination energy source** that results from **incident solar radiation**. It takes a beam that is modelled using the **sun position vector** and **illumination parameters**, applies it to any or all wall or inlet/outlet boundary zones that you specify, performs a **face-by-face shading analysis** to determine well-defined shadows on all boundary faces and interior walls, and **computes **the **heat flux on the boundary faces** that results **from** the **incident radiation**. The solar ray tracing model **includes only boundary zones that are adjacent to fluid zones** in the ray tracing calculation. In other words, **boundary zones** that are attached to **solid zones are ignored.** The resulting heat flux that is computed by the solar ray tracing algorithm is coupled to the **ANSYS FLUENT** calculation via a source term in the energy equation.

**DO Irradiation Model**

The solar load model’s discrete ordinates (DO) irradiation option provides you with an easy means of applying a **solar load directly** to the **DO model**. Unlike the ray tracing solar load option, the DO irradiation method **does not compute heat** **fluxes** and **apply them as heat sources to the energy equation**. Instead, the **irradiation flux is applied directly to semi-transparent walls** (which you specify) as a boundary condition, and the **radiative heat transfer** is derived from the solution of the **DO radiative transfer equation**.

I hope now you would have understood the physics and the difference between the two models. Hope this helps you to solve your problem.

Thanks