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Direct and Diffused Radiation

Within SimScale, it is possible to model the radiation effects. This standard document explains the different types of radiations and the ones that SimScale incorporates for modeling.

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 like computers, or sources outside the domain, which is usually solar 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.

But what are the other radiation types and what do they mean?

Direct and Diffuse Radiation

The following two figures visually explain direct and diffused forms of radiation. While direct radiation is unidirectional diffused radiation operates in several directions.

direct radiation representation
Figure 1: Direct radiation is unidirectional.
diffuse radiation representation
Figure 2: Diffusive radiation is multidirectional.

Direct 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 as a point. This assumption can be made for many problems, however, the most common occasion is when dealing with solar radiation.

sun as a point source of radiation
Figure 3: Point source of radiation, typically solar radiation.

Assuming that the computational domain is located somewhere on the earth’s surface, we might say that radiation from the sun is directional from the point source. However, in practice, this is not true.

direct radiation getting diffused
Figure 4: Direct solar radiation can get diffused due to atmospheric interactions.

Direct solar radiation, after entering the earth’s atmosphere, might get diffused based upon cloud cover, particulate content, and other meteorological conditions that need to be considered.

SimScale Heat Transfer Support

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

TypeConvectiveConductiveDirect RadiationDiffuse Radiation
Heat Transfer
Convective Heat Transfer
Conjugate Heat Transfer
Coupled Conjugate Heat Transfer
Table 1: Heat transfer analysis types in SimScale supporting radiation.

Table 1 shows the current state of heat transfer support on the SimScale platform, this will be updated as support increases.

Last updated: June 30th, 2020

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