This paper compares and scrutinizes the characteristics of radiation element method by ray emission model (REM 2 ) and discrete ordinates interpolation method (DOIM). A threedimensional radiative heat transfer problem is solved within a rectangular enclosure containing absorbing, emitting, nonscattering medium with temperatures given as a sine function. The calculation results are validated with the zonal results and the analytical solution. Generally, the calculation results agree well with

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... exact solution. However, when the optically thickness is much larger than unity, the zonal and REM 2 results overestimate the heat source strength and wall heat flux, and when it is small, DOIM results underestimate them. The reasons and remedies are carefully discussed.