Menguc, MP
1993
Radiative Heat Transfer
Mengüç, M.P. and Webb, B.W.
Chapter 5, Fundamentals of Coal Combustion: For Clean and Efficient Use, (L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded by ACERC.
This chapter presents methods and data for reacting radiative heat transfer in coal combusting systems. The key factors to be considered in pulverized coal combustion have been outlined as 1) turbulent fluid mechanics, 2) gaseous turbulent combustion, 3) particle dispersion, 4) heterogeneous char reactions, 5) radiation heat transfer, 6) coal devolatilization, 7) ash/slag formation, and 8) pollutant formation. In most global coal combustion prediction methodologies, each of these facets is modeled separately, and then coupled with the others in a global prediction scheme. An intimate coupling exists between these different phenomena in a heterogeneous combustion system. The radiation transport lies at the very heart of this coupling, particularly since it is the dominant mode of heat transfer even in moderately scaled pulverized coal combustion systems. In this chapter, we concentrate on the fundamentals of radiation transfer and its application to pulverized-coal combustion systems.
1991
Effective Radiative Properties of Utah Blind Canyon Coal, Final Report
Mengüç, M.P. and Manickavasagam, S.
University of Kentucky and ACERC Report, August 1991. Funded by Pittsburgh Energy Technology Center.
The effective radiative properties of pulverized-coal particles have been obtained. Three different experiments have been carried out using narrow-size distribution of Utah Blind Canyon coal. In two of the experiments, the measurements were performed in situ without altering the particle morphology. For this purpose, a test cell was designed to generate a vertically downward coal flow. A CO2-laser nephelometer system was employed to obtain the scattering phase function of pulverized-coal particles at 10.6 µm. An inverse radiation analysis was followed to reduce the experimental data. Also, a Mercury-arc lamp monochromator system was used to measure the effective absorption coefficients of the same coals within the visible wavelength spectrum.
The results show that the "effective" scattering phase function of coal particles are highly forward scattering and show less sensitivity to the size than predicted from the Lorenz-Mie theory. The main reason for this is that the smaller size particles, which are always present in the coal cloud, contribute to scattering and absorption significantly. In addition to this, it was observed that in the visible wavelength range the coal absorption is not gray: at wavelengths about 440 and 550 nm, there is about 10% decrease in the absorption coefficient compared to the rest of the spectrum. This observation is especially important for the two-color pyrometry experiments used to determine particle temperatures.
The two experimental approaches followed in this study are unique in a sense that the physics of the problem is not approximated. The properties determined include all uncertainties related to the particle shape, size distribution, inhomogeneity and spectral complex index of refraction data. From these experiments, it is possible to observe the spectral behavior of coal radiative properties within the visible wavelength spectrum. However, the spectral range considered was not extensive.
In order to obtain radiative property data over a wider wavelength spectrum, additional experiments have been carried out using a Fourier Transform Infrared (FT-IR) Spectrometer. For this purpose, thin pellets were prepared by mixing coal particles with Potassium Bromide (KBr). The spectral measurements were performed over the wavelength range 2.5 to 20 µm. These results were interpreted to obtain the "effective" absorption efficiency factor of coal particles. The results clearly show that the coal/char radiative properties display significant wavelength dependency.
Menguc, MP
1993
Radiative Heat Transfer
Mengüç, M.P. and Webb, B.W.
Chapter 5, Fundamentals of Coal Combustion: For Clean and Efficient Use, (L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded by ACERC.
This chapter presents methods and data for reacting radiative heat transfer in coal combusting systems. The key factors to be considered in pulverized coal combustion have been outlined as 1) turbulent fluid mechanics, 2) gaseous turbulent combustion, 3) particle dispersion, 4) heterogeneous char reactions, 5) radiation heat transfer, 6) coal devolatilization, 7) ash/slag formation, and 8) pollutant formation. In most global coal combustion prediction methodologies, each of these facets is modeled separately, and then coupled with the others in a global prediction scheme. An intimate coupling exists between these different phenomena in a heterogeneous combustion system. The radiation transport lies at the very heart of this coupling, particularly since it is the dominant mode of heat transfer even in moderately scaled pulverized coal combustion systems. In this chapter, we concentrate on the fundamentals of radiation transfer and its application to pulverized-coal combustion systems.
1991
Effective Radiative Properties of Utah Blind Canyon Coal, Final Report
Mengüç, M.P. and Manickavasagam, S.
University of Kentucky and ACERC Report, August 1991. Funded by Pittsburgh Energy Technology Center.
The effective radiative properties of pulverized-coal particles have been obtained. Three different experiments have been carried out using narrow-size distribution of Utah Blind Canyon coal. In two of the experiments, the measurements were performed in situ without altering the particle morphology. For this purpose, a test cell was designed to generate a vertically downward coal flow. A CO2-laser nephelometer system was employed to obtain the scattering phase function of pulverized-coal particles at 10.6 µm. An inverse radiation analysis was followed to reduce the experimental data. Also, a Mercury-arc lamp monochromator system was used to measure the effective absorption coefficients of the same coals within the visible wavelength spectrum.
The results show that the "effective" scattering phase function of coal particles are highly forward scattering and show less sensitivity to the size than predicted from the Lorenz-Mie theory. The main reason for this is that the smaller size particles, which are always present in the coal cloud, contribute to scattering and absorption significantly. In addition to this, it was observed that in the visible wavelength range the coal absorption is not gray: at wavelengths about 440 and 550 nm, there is about 10% decrease in the absorption coefficient compared to the rest of the spectrum. This observation is especially important for the two-color pyrometry experiments used to determine particle temperatures.
The two experimental approaches followed in this study are unique in a sense that the physics of the problem is not approximated. The properties determined include all uncertainties related to the particle shape, size distribution, inhomogeneity and spectral complex index of refraction data. From these experiments, it is possible to observe the spectral behavior of coal radiative properties within the visible wavelength spectrum. However, the spectral range considered was not extensive.
In order to obtain radiative property data over a wider wavelength spectrum, additional experiments have been carried out using a Fourier Transform Infrared (FT-IR) Spectrometer. For this purpose, thin pellets were prepared by mixing coal particles with Potassium Bromide (KBr). The spectral measurements were performed over the wavelength range 2.5 to 20 µm. These results were interpreted to obtain the "effective" absorption efficiency factor of coal particles. The results clearly show that the coal/char radiative properties display significant wavelength dependency.