HEAT TRANSFER FOR FLOW OF AN ABSORBING, EMITTING AND ISOTROPICALLY SCATTERING MEDIUM IN A GRAY DIFFUSE WALL DUCT.

摘要

The purpose of this study is to examine the interaction of conductive, convective, and radiative heat transfer for a thermally developing gas flowing through a circular duct. The gas contains absorbing and emitting nongray gases and soot, and absorbing, emitting and isotropically scattering gray particles. Heat generation may also exist within the gas. The absorbing gases, soot, and particles have identical temperatures and velocities. The duct walls or deposit surfaces are opaque, gray, and diffusely emitting and reflecting. The radiative transfer analysis is formulated by the zone method with the weighted sum of gray gases model expressions to consider total as well as multi-dimensional aspects of radiation. Results are presented for both gray gas and non-gray gas cases. Gray gas cooling and heating cases for a prescribed wall temperature are studied for gas temperature profiles, wall Nusselt number, and heat exchanger effectiveness in terms of the Boltzmann number, gas conduction to radiation parameter, gas optical thickness, gas scattering albedo, and wall emittance. Non-gray gas results for wall and gas temperatures, wall heat flux, Nusselt number, and heat exchanger effectiveness are presented including the effects of gas heating or cooling, wall deposit, refractory wall, heat generation, and system size for prescribed wall temperature or wall heat flux distributions. Among the various variables, the results depend on the gas mean velocity, wall emittance, soot volume fraction, as well as particle extinction coefficient and albedo. The results are predicted by those for absorbing gases if both soot volume fraction and particle extinction coefficient are less than 10