No abstract

An effective method for handling turbulent fluctuations in temperature and in partial pressure of infrared-active gas is proposed in order to make a fairly accurate simulation within feasible calculation load in relation to radiative heat transfer in the large-scale hydrocarbon flame formed in industrial furnaces. As for the case of large-scale turbulent hydrogen flame in industrial furnace, an effective method for handling turbulent fluctuations has been proposed and verified in our previous papers. And yet, it's applicability to large-scale turbulent hydrocarbon flames has not been confirmed. In this paper, the abovementioned method is examined as to the applicability to hydrocarbon flames, and then, an improved method is proposed. In regard to the method proposed in our previous papers to reduce the enormous calculation load contingent on detailed non-gray analysis like line-by-line analysis, it's validity is easily confirmed not only for hydrogen flames but also for hydrocarbon flames. On the other hand, the method proposed in our previous paper for reducing the calculation load required for tracing turbulent fluctuation in temperature in great detail cannot give satisfactory results in relation to the large-scale hydrocarbon flame. So, in this paper, major attention is concentrated on the improvement of our method for reducing the calculation load associated with detailed trace of turbulent fluctuation. The assumption that temperature fluctuations of arbitrary two positions are independent from each other and the treatment of energy radiation associated with turbulent fluctuation are maintained also for hydrocarbon flames. In contrast, the treatment of fluctuating absorption is changed from the case of hydrogen flames. While the temporal mean amount of absorption is evaluated using the absorption coefficient at temporal mean temperature in the case of hydrogen flames, such value is evaluated using the temporal mean value of instantaneous absorptance. Validity of the improved method is examined on a model optical path imaging the typical course of radiative energy in large-scale industrial furnaces fueled by propane. It is indicated by examination that the error caused by improved method is satisfactorily smaller than that caused by entire disregard of turbulent fluctuation of temperature and gas composition. Moreover, this improvement related to the treatment of turbulent fluctuation is satisfactorily valid even if coupled with our efficient method for treating complicated spectrum of absorption coefficient.

Theoretical examinations based on absorption line databases were carried out about the influence of turbulence-radiation interaction on the radiative heat transfer arriving at the wall of large-scale industrial furnaces, where the re-absorption of radiative energy by combustion gas on its path toward objects to be heated cannot be neglected. In this study, the efficient and accurate calculation method for non-gray analysis and the effective method for handling turbulent fluctuations of radiation and absorption proposed in our previous paper were coupled. Combining the above coupled method and a governing equation solver for obtaining the spatial distribution of time-averaged values of temperature, concentration, velocity and so on, the heat transfer including radiation in large-scale industrial furnaces enveloping turbulent flames was able to be evaluated with sufficient accuracy equivalent to Line-by-Line analysis and with feasible calculation load. By applying this calculation technique to large-scale furnaces, it was found that negligence of turbulent fluctuation in numerical simulation gives rise to obvious change in heat flux distribution on the side wall and in the spatial distribution of time averaged temperature. In addition, change in the total amount of radiative energy arriving at side wall caused by negligence of turbulent fluctuations is fairly small compared with change observed in the case of a typical optical path indicated in our previous report.

The present study was conducted in order to clarify the effects of airflow turbulence on the spray combustion. Methanol was atomized with the two-fluid-type nozzle in order to generate the spray flame, and the turbulence characteristic of the flame was varied by inserting a mesh near the tip of the nozzle. Droplets in the spray flame were measured using a PDPA system in a reaction field, and changes in the turbulence characteristic were measured using a hot-wire anemometer in a no-reaction field in order to clarify the effects of turbulence on combustion behavior. Inserting a finer mesh promoted droplet evaporation and enhanced the dispersion characteristic. Regarding changes in the turbulence characteristic, the integral time scale increased and the energy spectrum decreased as the inserted mesh became finer. Based on the obtained results, we determined that a finer mesh causes vortexes to be more persistent and enhances the dispersion characteristic of the droplets.

Magnesium Fluoride is a hard and birefringent crystal with low refractive index and a wide transmission range. It is widely used in prisms and optical windows. We have studied the microwave properties of MgF 2 using a Hakki-Coleman dielectric resonator technique. The permittivity varies from 5.026 to 5.165 in the temperature range 15-295K and at a frequency of 32.9 GHz. The loss tangent varies from 1X10 -5 to 8X10 -5 when the temperature increases from 15 K to 295 K.