ABSTRACT
In the nomenclature of the process industries, a time-honored practice is to label the portion of heat transfer tubes which can "see" the flames from burners as the "radiant section" and the portion of the heat transfer tubes which cannot "see" the flames as the "convection" section. This nomenclature is convenient rather than completely correct, and it is so because of a number of factors. One factor is that the predominance of a particular heat transfer mechanism depends, principally, on the differential temperature level when the flow of the combustion gas heat-medium is low and the hot refractory surfaces can be "seen." Another is that, when flow of combustion gas is at a significantly high rate, the convective heat transfer portion of the total heat transfer increases greatly whether hot refractory can, or cannot, be "seen." Further, in process heat transfer, where heat becomes available because ofthe firing of fossil fuels, it is impossible to definitively separate the heat quantity as transferred by radiation from the heat quantity transferred by convection as total heat transfer is considered. This is to say that both heat transfer mechanisms contribute in any case of fossil fuels firing for useful heat transfer because there is always movement of combustion gases and there is always radiation. However, as predominant heat transfer sources are considered, it is quite convenient but actually incorrect to refer to one heat transfer area as radiant and the other portion of heat transfer area as convection.
