COUPLED THERMAL RESPONSE OF OBJECTS AND PARTICIPATING MEDIA IN FIRES AND LARGE COMBUSTION SYSTEMS

Abstract

When an object is subjected to a flowing, participating medium at a different temperature, such as a flame, the thermal response of the object and the surrounding medium becomes coupled. The differences inherent in treating the medium as a blackbody at some approximate temperature as opposed to a participating medium are assessed and quantified in this work by solving the transient, coupled, radiation, and conduction heat transfer problem for the flow of an absorbing and emitting medium adjacent to a vertical flat plate. The results are presented in terms of nondimensional parameters and include both average and local heat fluxes as a function of time. Early in the transient, a reduction in net heat flux of up to 65% was observed by accounting for absorption and emission in the medium. Accordingly, a longer time is required for the object to reach an equilibrium temperature (up to 100% for values of the radiation parameter, N_rad', of 5.0) than is predicted using the blackbody assumption. For radiation Biot numbers greater than 5 or values of N_rad', less than ⁻², the differences inherent in the two approaches are negligible, and the blackbody assumption is valid.