### 8.2.1. Wall Treatment

The Rosseland approximation is not valid near walls. Therefore, a special boundary condition must be specified when heat conduction is comparable to radiation heat transfer. It has been proposed [24] that a temperature slip boundary condition should be in this region. From [24] the heat flux at the wall, is given by:

| (8–28)

where is the slip co-efficient, is the wall temperature and is the gas temperature at the wall. is computed as the solution of:

| (8–29)

where is given by:

| (8–30)

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