An experimental and a theoretical investigation of combustion and heat transfer characteristics of reticulated ceramic burners
Abstract
Porous radiant burners are used in drying, preheating, curing and baking processes in the manufacturing industry. Most burners presently used are of the surface flame type. Burners with flames stabilized inside reticulated (cellular, foam) ceramics are expected to offer possible advantages over these burners. However, little knowledge is available about the operating characteristics and the structure of flames stabilized inside porous ceramic radiant burners. The objective of the present work is to investigate the global performance characteristics of the reticulated ceramic burners. A detailed study which includes the operating range, radiation efficiency, spectral intensity, exit gas temperature and velocity, and pollutant emission indices measurement has been carried out. Another objective is to study the flame structure of the submerged names by measuring the local gas temperature and species profiles. Results indicate that reticulated ceramic burners do offer a 30-40% gain in radiation efficiency and a wider operating range than the surface flame type burners. Local temperature measurements show an upstream motion of the flame at the higher firing rates revealing insights into the flashback problem. Local species measurements show that the submerged flame has a much broader reaction zone than the adiabatic laminar flat flame. Measurements are also conducted on a honeycomb ceramic burner of similar porosity. The limited flame stability range of this burner highlights the importance of the tortuous flow paths for flame stabilization in the reticulated ceramic burners. The present theoretical study involves asymptotic analysis using two approximations. The first method yields an equation that is mathematically similar to the adiabatic premixed flame propagation problem, and predicts within 15% of the experimentally observed flame speed. The second approximate analysis involves the treatment of radiation from the burner as a surface phenomenon. The solid phase and the gas phase energy equations are solved asymptotically. The predictions of flame position are within 20%, those for radiant efficiency are within 25%, and those of measured peak temperature are within 15% of the experimental data. Based on these results, the present simplified models can be used as engineering tools for radiant burner design.
Degree
Ph.D.
Advisors
Viskanta, Purdue University.
Subject Area
Mechanical engineering
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