Effect of Load Thickness on Fuel Economy

When heating material of low absorptivity (and emissivity) and high conductivity (such as aluminum), the stock thickness does not affeet fuel eeonomy. However, for a material such as steel (high absorptivity, but low thermal conductivity), the load thickness has a major effect on fuel economy because (a) the surface will be hotter than the interior, and (b) the poc must leave with a higher temperature. Of course, if the loads were left in the furnace longer in hopes of lowering the gas throwaway temperature, the production rate would drop. 

If the load material is easily oxidized, other factors enter. Scale has a higher absorptivity than bright metal thus, in the initial stages of heating, it promotes heat 

Fuel economy calculations are more complex for multizone furnaces, including rotary furnaces—side fired, roof fired, or longitudinally fired—with or without baffles between zones. (See sec. 2.6, 3.4, 3.5.) With thick loads, load placement is more critical. (See sec. 3.5, 6.9, 6.10.) 

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