Thermal and Exergy Assessment of a Micro Combustor Fueled by Premixed Hydrogen/Air under Different Sizes: a Numerical Simulation

In this work, a numerical study has been carried out in order to investigate the effects of a micro combustor size on the exergy and energy efficiencies of a premixed hydrogen/air for a micro thermophotovoltaic system. For this purpose, six combustors in different sizes are designed, in which geometry dimensional size gradually reduced. The effects of the combustor size on the entropy, exergy, radiation power, and energy conversion efficiency are investigated. Also, mean and uniform wall temperature are discussed. In order to compare the entropy generation of each micro combustor, a dimensionless entropy generation rate is defined. The hydrogen/air combustion with 9 species and 19 reversible elementary reactions were simulated by using the Eddy Dissipation Concept (EDC) model. Results indicate the micro-combustor geometry size has important effects. A reduction of the combustor geometry size dimensionality causes an increase in average wall temperature and makes it uniform. Moreover, by decreasing micro combustor size, the radiation power efficiency increases from 41.96 to 45.62% and total energy conversion efficiency from 6.46 to 7.02%. The highest exergy efficiency, 38.63%, is achieved in the smallest micro combustor while the minimum exergy efficiency 33.22%, is obtained in the largest micro combustor.