Title: Second-law thermodynamic analysis on premixed syngas flames

Authors: Yusen Liu; Jiajia Chen; Zeyan Qiu; Zhengwei Chen; Dong Han

Addresses: Key Laboratory for Power Machinery and Engineering, Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai, 200240, China ' Key Laboratory for Power Machinery and Engineering, Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai, 200240, China ' Key Laboratory for Power Machinery and Engineering, Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai, 200240, China ' Key Laboratory for Power Machinery and Engineering, Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai, 200240, China ' Key Laboratory for Power Machinery and Engineering, Ministry of Education, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai, 200240, China

Abstract: Exergy destructions in laminar premixed syngas flames, with varied fuel compositions and changed pressures, were numerically studied. Chemical reactions are found to be the dominant source for exergy destruction, followed by heat conduction and mass diffusion. As a result of the trade-off between the increased exergy destruction rates and narrowed flame thickness, the total exergy destruction increases by about 1% with hydrogen enrichment, but is nearly unchanged with pressure elevation. Specifically, with hydrogen enrichment, the exergy destruction from heat conduction decreases due to the narrowed flame thickness, whereas those from mass diffusion and chemical reactions increase because of higher diffusivity of H₂, H and H₂O and higher reactivity of H₂ than CO, respectively. In contrast, with pressure elevation, the higher temperature gradient and mole fraction gradients result in increased exergy destruction from heat conduction, but the exergy destruction from chemical reactions decrease due to the narrowed flame thickness.

Keywords: second law of thermodynamics; premixed flame; syngas; hydrogen.

DOI: 10.1504/IJEX.2020.108172

International Journal of Exergy, 2020 Vol.32 No.2, pp.174 - 185

Received: 24 Sep 2019
Accepted: 16 Dec 2019
Published online: 03 Jul 2020 *

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