Q

where A = bed area of solids in the equipment.

Important considerations in the application of the foregoing equations are:

1. Since the temperature of the emitter is generally known (preselected or readily determined in an actual operation), the absorptivity value er is the unknown. This absorptivity is partly a measure of the ability of radiant heat to penetrate the body of a solid particle (or a moisture film) instantly, as compared with diffusional heat transfer by conduction. Such instant penetration greatly reduces processing time and case-hardening effects. Moisture release and other mass transfer, however, still progress by diffusional means.

2. In one of the major applications of radiative devices (drying),

TABLE 11-10 Normal Total Emissivity of Various Surfaces

A. Metals and Their Oxides

TABLE 11-10 Normal Total Emissivity of Various Surfaces

A. Metals and Their Oxides

Surface

t, o F.*

Emissivity*

Surface

t, o F.*

Emissivity*

Aluminum

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