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چكيده انگليسي :

107 Evaluation of Entropy Generation in a Gaseous Flame by Considering the Effect of Radiative Heat Transfer Ali Emadi Andani a emadiandani@me iut ac ir Date of Submission 2013 01 14 Department of mechanical engineering Isfahan University of technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr M D Emami mohsen@cc iut ac ir Abstract Combustion of gaseous fuel is one of the main sources of power generation for various purposes A portion of chemical exergy of fuel is destroyed during the combustion process which reduces the exergy of system Entropy generation and exergy loss is evaluated in turbulent non premixed flames which have widespread use in practical burners Investigation is based on the local entropy generation due to viscous effects thermal conduction mass diffusion chemical reactions and radiation exchange Detailed chemical reaction and transport properties are considered to include intermediate reactions and species which lead to complete calculation of entropy generation due to mass diffusion and chemical reaction Turbulence chemistry interaction is considered using steady laminar flamelet model to precisely predict the reacting flow and species concentration Radiative heat transfer in combustion chamber is considered to investigate its influence on the flow field and its contribution on the exergy loss and irreversibility Discrete ordinates method which considers the directional effect of radiation paths is used to solve radiation field Weighted sum of gray gas model is used to consider the non gray behavior of combustion products Reacting flow and radiation field is solved using FLUENT commercial code Flamelet library is generated using FlameMaster open source code Entropy generation calculation is performed using a FORTRAN code developed in this study This code read extracted data from FLUENT and FlameMaster and calculates the entropy generation due to above mentioned phenomena s Results showed that thermal conduction is the main source of entropy generation and irreversibility such that more that 50 of irreversibility is due to thermal conduction Chemical reactions mass diffusion and thermal radiation are other source of entropy generation and irreversibility in order of enumeration while entropy generation due to viscous dissipation is negligible Entropy generation due to thermal radiation is not as important as other sources of entropy generation and generates only 1 3 of total entropy The second law efficiency for all investigated flames is near 50 means that about one half of incoming exergy is destroyed as a result of irreversibility Investigating the effect of combustion air showed that entropy generation decrease significantly by preheating combustion air which is mainly due to decrease of thermal conduction component of entropy generation By preheating combustion air contribution of thermal conduction decrease while the contribution of chemical reaction increase such that at high temperatures chemical reaction become that main source of entropy generation Also investigating the effect of fuel blend showed that entropy generation decrease with H 2 addition to the CH4 which is mainly due to decrease in entropy generation of chemical reactions while other sources of entropy generation remain nearly constant As a result contribution of thermal conduction on the entropy generation rate increases with H2 addition Key Words Combustion non premixed flame entropy generation radiation exergy irreversibility

عمادي انداني، علي

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