ARTICLE:

• DIRECT EXCHANGE AREAS FOR A RECTANGULAR BOX BY THE DIRECT DISCRETE-ORDINATES METHOD  download article

K. H. Byun
Department of Mechanical Engineering, Dongguk University, Seoul 100-715, Republic of Korea

Theodore F. Smith
Department of Mechanical Engineering, The University of Iowa, Iowa City, Iowa 52242, USA

ABSTRACT

The direct discrete-ordinates method (DSN) is applied to compute direct exchange areas (DEA) for rectangular box type enclosures. The discrete-ordinates weights and directions are derived using spherical coordinates. A gray absorbing and emitting medium is enclosed by black walls. A protrusion may exist in the system that alters the radiant exchange between some of the surfaces. The effects of optical thickness and the number of spatial and angular divisions on the accuracy of DEA results are studied. For given spatial and angular divisions, there is an optical thickness upper limit that ensures physically realistic results. Whether there is a protrusion in the system or not, DEAs for rectangular box type enclosures can be accurately obtained by using the DSN method within the optical thickness limit. If there is a protrusion in the system, additional spatial and angular divisions are needed than used for the no-protrusion case at the same accuracy. The results show the convergence characteristics with spatial and angular divisions. As optical thickness increases at a given spatial and angular division, the errors increase. For a given optical thickness, the errors are reduced as the number of spatial and angular division increases.

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