| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Andersson, Klas, 1977-, et al.
(författare)
-
Radiation intensity of lignite-fired oxy-fuel flames
- 2008
-
Ingår i: Experimental Thermal and Fluid Science. - 0894-1777. ; 33:1, s. 67-76
-
Tidskriftsartikel (refereegranskat)abstract
- The radiative heat transfer in oxy-fuel flames is compared to corresponding conditions in air-fuel flames during combustion of lignite in the Chalmers 100 kW oxy-fuel test facility. In the oxy-fuel cases the flue-gas recycle rate was varied, so that, in principle, the same stoichiometry was kept in all cases, whereas the oxygen fraction in the recycled flue-gas mixture ranged from 25 to 29 vol.%. Radial profiles of gas concentration, temperature and total radiation intensity were measured in the furnace. The temperature, and thereby the total radiation intensity of the oxy-fuel flames, increases with decreasing flue-gas recycle rate. The ratio of gas and total radiation intensities increases under oxy-fuel conditions compared to air-firing. However, when radiation overlap between gas and particles is considered the ratios for air-firing and oxy-fuel conditions become more similar, since the gas-particle overlap is increased in the CO2-rich atmosphere. A large fraction of the radiation in these lignite flames is emitted by particles whose radiation was not significantly influenced by oxy-fuel operation. Therefore, an increment of gas radiation due to higher CO2 concentration is not evident because of the background of particle radiation, and, the total radiation intensities are similar during oxy-fuel and air-fuel operation as long as the temperature distributions are similar.
|
|
| 5. |
- Andersson, Klas, 1977-, et al.
(författare)
-
Radiation Intensity of Propane-Fired Oxy-Fuel Flames: Implications for Soot Formation
- 2008
-
Ingår i: Energy & Fuels. ; 22:3, s. 1535-1541
-
Tidskriftsartikel (refereegranskat)abstract
- The changes in the soot-related radiation intensity between two different oxy-fuel flames and an air-fired flame were investigated in a 100 kW oxy-fuel test unit firing propane. The oxy-fuel test cases with 21 and 27 vol % O2 in the recycled flue gas (RFG) were run with different amounts of dry RFG, which in principle only consisted of CO2 from combustion and some excess O2. The stoichiometric oxygen-to-fuel ratio was kept at 1.15 in all cases. Total radiation intensity was measured with a narrow angle radiometer. Temperature and gas composition measurements served as inputs to computations of gas radiation. A comparison of the computed gas radiation with the measured total radiation intensity enabled estimation of the radiation related to soot. Clear differences were observed in the amount of soot formed in the two oxy-fuel flames (also compared to the air flame). In the oxy-fuel flame with 21 vol % O2 in the RFG, soot formation is almost completely suppressed, but when the total flow through the burner is reduced by about 20% (by volume) (i.e., from 21 to 27 vol % O2 in the RFG), the amount of soot present in the flame becomes significant. This change in soot volume fraction affects the radiation emitted from the flames; images of the flames qualitatively confirm these differences in the flame luminosity. Thus, carbon dioxide not only increases the gas radiation, but it can also drastically influence soot formation and the radiation originating from soot during oxy-fuel combustion.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Bergenblock, Tobias, 1972-, et al.
(författare)
-
Averaging of particle data from phase Doppler
- 2006
-
Ingår i: International Journal of Multiphase Flow. ; 32, s. 248-268
-
Tidskriftsartikel (refereegranskat)abstract
- A novel post-processing algorithm is proposed to correct statistical bias observed in the treatment of time series obtained by a phase Doppler anemometer (PDA) at flow locations with variable particle velocity and concentration. Extensive properties of each validated particle are weighted with their inverse measuring (validation) volume to account for the procedure of particle sampling and fluctuations in the particle concentration. To compensate for the short characteristic length of the validation volume, the properties of particles are expressed by properties of fields of particle groups, using a local averaging time. A window shift and a decorrelation scheme are applied on the fields to increase their frequency resolution. This algorithm has been tested on numerical time series, provided by an Eulerian/Lagrangian code representing a gas/solids flow past a bluff body. Moments and spectral estimates of concentration and velocity of particle groups were successfully validated by the numerical simulation using the PDA data algorithm and control volume averaging. The control volume was much larger than the PDA validation volume, but the centre positions of the two volumes were identical.
|
|
| 10. |
- Bergenblock, Tobias, 1972-, et al.
(författare)
-
Experimental estimation of particle flow fluctuations in dense unsteady two-phase flow using phase Doppler anemometry
- 2007
-
Ingår i: International Journal of Multiphase Flow. ; 33, s. 849-872
-
Tidskriftsartikel (refereegranskat)abstract
- A recently proposed and successfully validated post-processing algorithm is extended to treat particle data obtained by a phase Doppler anemometer (PDA) in dense, fluctuating, low-speed, two-phase flow. In such a flow, Doppler signals may be noisy and split, since particles have long residence times in the measurement volume. A novel time average based on the measured burst lengths is proposed to estimate the cross-sectional area of the measurement volume. This time average accounts for the possible split of a noisy Doppler burst, and it provides a more general description of the measurement volume than the conventional ensemble average. The extended post-processing algorithm was tested on experimental time series obtained in a circulating fluidized bed and the algorithm was compared to conventional treatment of the particle data by a commercial PDA processor. The conventional processing strongly overestimates the vertical mass flux integrated over the cross-section. In contrast, time-mean and fluctuations of mass flux, particle volume concentration, and particle velocity are reliably estimated employing the proposed algorithm, with continuity check parameters in succeeding particle data, as well as with a particle velocity filter to estimate the size of the probe volume, applying a two-component PDA in a three-dimensional flow.
|
|
