Numerical Modelling of Radiative Heat transfer in Flameless and Conventional Combustion

 

 

Summary of the MSc Thesis of Soheila Riahi, presented on November, 23, 2012

Supervisor: Prof. Dr. D.J.E.M. Roekaerts

Thermal efficiency and amount of pollutants in flue gases are main concerns in the scientific research of combustion. Combustion in highly diluted condition ‘flameless combustion’ is considered to be an alternative due to its advantages of higher thermal efficiency and lower rate of pollutant emission. Different aspects of conventional and flameless combustion have been objectives of many recent researches. Radiation and convection heat transfer are important modes of heat transfer in combustion. There are claims of higher rate of heat transfer, namely radiation heat transfer, in flameless combustion in the related literature.

This work aims to investigate the rate of radiation heat transfer and its ratio to the convection heat transfer in the two modes of combustion. Numerical computation using Reynolds Averaged Navier Stokes (RANS) models for turbulence, Eddy Dissipation Concept (EDC) model for turbulence chemistry interaction, Discrete Ordinate (DO) model for radiation and Weighted Sum of Gray Gases (WSGG) model for radiative properties, as implemented in the commercial software, FLUENT 12.0, is used to compare different cases in a lab scale furnace. Results are compared to the experimental data of the lab scale furnace from Mons University [1] and also other investigations from literature.

The results of this study show higher rate of total heat transfer to the cooling medium and lower rate of waste energy through the flue gases in the cases of 10% and 20% excess air of flameless combustion, compared to the conventional combustion. However, the radiation heat transfer to the cooling medium still is higher in the conventional cases. The ratio of radiation to the convection heat transfer is 5 and 2.5 in the flame and flameless modes, respectively. Furthermore, the ratio of the radiation heat transfer to the convection heat transfer is effected by the ratio of the area of high temperature walls to the projected area of high temperature zone in a furnace. Thereby the latter ratio might be a key parameter, leading to the ratio of the radiation to the convection heat transfer in different modes of combustion.

[1] Lupant D., Experimental and Numerical Investigation of Flameless Combustion of Natural Gas in a 30 kW Capacity Lab Scale Furnace, PhD Thesis, University of Mons, 2011.

Publications on results of the project:

S. Riahi, D.J.E.M. Roekaerts and D. Lupant, Numerical comparative study of heat transfer in flameless and conventional combustion in a 30kW furnace, In: Proceedings of the European Combustion Meeting, Lund, 2013, 6 pages, to be published

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