Direct and Diffused Radiation

Radiation Types

In thermal simulations, the radiation sources we have to account for are radiation produced inside the computational domain, such as from hot components, or sources outside the domain, which is usually solar, produced by the sun and interfered with by the atmosphere. As mentioned in the SimScale documentation, only Diffuse radiation is supported, where radiation is omnidirectional, and this means some use cases are restricted.

Direct and Diffusion Radiation

Figure 1: Direct Radiation.

Figure 2: Diffusive Radiation.


Figure 1 and 2 show the two types of radiation, however, directional radiation is not physical where a source would emit radiation from a surface in one direction, therefore, in most physical cases, the diffusive radiation is dominant.


Considering the dominance of diffusive radiation in most cases, why worry about directional radiation? Directional radiation might be present (or at least the directional assumption) if there is a large heat source far enough away that we consider it a point. we might make this assumption for many problems, however, the most common occasion is when dealing with solar radiation.

Figure 3: point source of radiation, typically solar radiation.

Figure 4: Solar radiation arriving on the earth’s surface.


Assuming that the computational domain is located somewhere on the earth’s surface, we might then assure that radiation from the sun is directional from the point some source. However, this is not the case.

Figure 5: showing how direct solar radiation can cause diffuse radiation.


Figure 5 shows how direct solar radiation might be diffused based upon cloud cover, particulate content and other meteorological conditions which need to be considered.


SimScale Heat Transfer Support

SimScale has a range of thermal simulation types, but which support radiation?

Type Convective Conductive Direct Radiation Diffuse Radiation
Heat Transfer
Convective Heat Transfer
Conjugate Heat Transfer

Table 1: Heat transfer support.

Table 1 shows the current state of hat transfer support on the Sim scale platform, this will be updated as support increases.

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