Measurement and Modeling of Particle Radiation in Coal Flames

This work aims at developing a methodology that can provide information of in-flame particle radiation in industrial-scale flames. The method is based on a combination of experimental and modeling work. The experiments have been performed in the high-temperature zone of a 77 kWth swirling lignite flame. Spectral radiation, total radiative intensity, gas temperature, and gas composition were measured, and the radiative intensity in the furnace was modeled with an axisymmetric cylindrical radiation model using Mie theory for the particle properties and a statistical narrow-band model for the gas properties. The in-flame particle radiation was measured with a Fourier transform infrared (FTIR) spectrometer connected to a water-cooled probe via fiber optics. In the cross-section of the flame investigated, the particles were found to be the dominating source of radiation. Apart from giving information about particle radiation and temperature, the methodology can also provide estimates of the amount of soot radiation and the maximum contribution from soot radiation compared to the total particle radiation. In the center position in the flame, the maximum contribution from soot radiation was estimated to be less than 40% of the particle radiation. As a validation of the methodology, the modeled total radiative intensity was compared to the total intensity measured with a narrow angle radiometer and the agreement in the results was good, supporting the validity of the used approach

Experimental Determination of Thermal Conductivity of a Lead- Bismuth, Eutectic-Filled Annulus

In order to obtain an accurate prediction of the thermal behavior of an annular fuel assembly (see MIT-NFC-PR-048 for a description of the rods), the thermal conduction of the region from the outside of the fuel capsule to the reactor coolant (within the test assembly) must be known. The effective thermal conductivity of this composite structure is dependent on the interaction of the parts via various physical phenomena, and therefore is difficult to infer accurately from the conductivity of the constituent materials. A mock-up of the annular fuel rod containment thimble was created to allow the conductivity of the annular lead bismuth eutectic-filled gap to be measured. An electric rod heater was used to provide temperatures similar to the in-core environment, and conductivity was determined based on thermocouple temperature readings at various points across the gap. A second series of experiments substituted a steel tube for the aluminum thimble, and used a bucket of stationary water as coolant. The purpose of these changes was to increase the temperature of the eutectic and achieve a larger melted fraction, while at the same time creating a large enough temperature drop across the gap to allow reliable measurements. A third series of experiments refined the setup and were able to produce more precise measurements of the thermal conductivity. The measured conductivities were between 4 and 8 W/m-K, much lower than the reported conductivity of the lead bismuth at about 10 W/m-K. The difference must be attributed to thermal resistances at the eutectic-aluminum and eutectic-steel interfaces. This, and the inherent difficulty of measuring the interface temperature due to the finite width of the thermocouples and the existence of sharp thermal gradients makes it difficult to further reduce the uncertainty in the measured conductivity

Atomic hydrogen concentration profiles at filaments used for chemical vapor deposition of diamond

Schäfer L, Klages C-P, Meier U, Kohse-Höinghaus K. Atomic hydrogen concentration profiles at filaments used for chemical vapor deposition of diamond. Applied Physics Letters. 1991;58(6):571-573.The quantitative determination of atomic hydrogen concentrations cH in the vicinity of hot filaments is performed with two-photon laser-induced fluorescence. The measurements yield atomic hydrogen concentration profiles up to 28 mm from the filament surface with a spatial resolution of about 0.5 mm. The nonequilibrium nature of the hydrogen dissociation on the filament surface results in a saturation of hydrogen concentration profiles C H([gamma]) for gas pressures above 10 mbar. Atomic concentrations in immediate vicinity of the filament are significantly lower than expected from thermodynamical calculations and depend on the filament diameter. Addition of methane results in a decrease of C H by more than 30% near the filament and a steeper C H([gamma]) dependence, demonstrating the accelerated consumption of H atoms by the presence of hydrocarbon species. H concentration profiles for Ta, Ir, and W filaments show a dependence on filament materials which might be taken into account when selecting filament materials for chemical vapor deposition of diamond

Gas phase synthesis of metal oxide monolithic catalysts for hydrocarbon deep oxidation

Bahlawane N, Premkumar A, Fehling K, Kohse-Höinghaus K. Gas phase synthesis of metal oxide monolithic catalysts for hydrocarbon deep oxidation. In: Gaigneaux EM, ed. Scientific bases for the preparation of heterogeneous catalysts. Studies in Surface science and catalysis. Vol 162. Elsevier; 2006: 625-632