Ash deposits decrease the boiler efficiency, reduce the generating capacity and cause unscheduled outages. The radiative heat transfer is the major heat transfer mechanism in utility boilers; thus, the ash deposit emissivity is critical to boiler efficiency and safety. This paper presents a radiative transfer model to predict the spectral emissivities of coal ash deposits. The model includes the effects of the microstructure, chemical composition and temperature. Typical ash deposit microstructures are generated using diffusion-limited aggregation (DLA). The radiative properties are then calculated using the Generalized Multiparticle Mie-solution (GMM). The combined GMM and DLA model predicts spectral emissivity better than the original Mie theory and Tien’s dependent scattering theory with the average relative difference between predicted results and experimental data decreasing from 17.7% to 8.1% for sample 1 and from 16.5% to 4.2% for sample 2. Maxwell-Garnett effective medium theory is used to calculate the ash deposit optical constants based on the chemical compositions to include the effect of chemical composition. Increasing temperatures increase the particle diameters and particle volume fractions and, thus, the spectral emissivities. The spectral emissivity ultimately remains constant and less than one. The homogeneous slab model gives the upper limit of the ash deposit spectral emissivity.
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ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology
July 14–19, 2013
Minneapolis, Minnesota, USA
Conference Sponsors:
- Heat Transfer Division
ISBN:
978-0-7918-5547-8
PROCEEDINGS PAPER
Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits
Yuan-Yuan Duan,
Yuan-Yuan Duan
Tsinghua University, Beijing, China
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Zhen Yang
Zhen Yang
Tsinghua University, Beijing, China
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Dong Liu
Tsinghua University, Beijing, China
Yuan-Yuan Duan
Tsinghua University, Beijing, China
Zhen Yang
Tsinghua University, Beijing, China
Paper No:
HT2013-17413, V001T01A005; 8 pages
Published Online:
December 21, 2013
Citation
Liu, D, Duan, Y, & Yang, Z. "Theoretical Predictions of Spectral Emissivity for Coal Ash Deposits." Proceedings of the ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. Volume 1: Heat Transfer in Energy Systems; Thermophysical Properties; Theory and Fundamental Research in Heat Transfer. Minneapolis, Minnesota, USA. July 14–19, 2013. V001T01A005. ASME. https://doi.org/10.1115/HT2013-17413
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