Modeling of a submerged flame porous burner/radiant heater
Abstract
Two unsteady mathematical.l models (i.e., one-dimensional and two-dimensional) of combustion/heat transfer within porous inert media (PIMs) and relevant phenomenological models have been developed and validated. The interaction between convection, conduction, radiation and fuel oxidation (combustion) occurring simultaneously in PIMs is considered in the models. A simple, highly-idealized radiation efficiency model is developed to assess the thermal performance of an ideal porous burner which yields the highest radiation efficiency. Two unit cell based models are developed to predict the effective thermal conductivity of porous materials. A unit cell model is developed in conjunction with the discrete ordinates ($S\sb{N})$ approximation for radiative transfer to predict the volumetric radiation characteristics of cellular ceramics. The volumetric heat transfer coefficients between cellular (reticulated) ceramics and a stream of air were measured using a single-blow transient experimental technique in conjunction with an inverse analysis. Experimental results are reported for five different reticulated ceramics having different mechanical structures. Volumetric Nusselt number correlations are developed in the form of $Nu\sb{v} = CRe\sp{m}$ for different porous materials based on the experimental measurements. The effects of the different characteristic lengths in defining both $Nu\sb{v}$ and Re on the correlations are discussed. A one-dimensional model accounting for the interaction of convection, conduction, radiation and chemical reaction in a porous radiant burner/heater is developed to predict the thermal performance of the burner. The porous radiant burner consists of two layers of cellular ceramics having different porosity and mechanical structure. The two flux radiation approximation was used for thermal radiation transfer in porous media. A study of effects of relevant parameters on the thermal performance of the porous radiant burner and comparison of predictions with experimental data are reported. An axisymmetric two-dimensional model accounting for transport of mass, momentum, heat, and species in radial and axial directions is developed to provide fundamental understanding of the transport phenomena relevant to porous radiant burners made from ported metals and ceramics. The complex "passage" geometry of porous media is replaced by a cylindrical tube in which combustion takes place. This enables treatment of the transport processes in the tube, heat conduction in the tube wall and surface radiation exchange to account for the conjugate effects. The model predictions are compared with available experimental data for the purpose of validating the model. Parametric calculations are performed to obtain a fundamental understanding of the phenomena.
Degree
Ph.D.
Advisors
Gore, Purdue University.
Subject Area
Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.