Transient Measurements of Temperature and Radiation Intensity in Spherical Microgravity Diffusion Flames

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76396/1/AIAA-2006-746-159.pd

Effect of fuel dilution by CO2 on spherical diffusion flames in microgravity

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76100/1/AIAA-2001-622-741.pd

Tunneling spectroscopy measurement of the superconductor gap parameter of MgB_2

Cryogenic scanning tunneling microscopy and magnetization measurements were used to study the superconducting properties of MgB_2. The magnetization measurements show a sharp superconductor transition onset at T_c = 38.5 K, in agreement with previous works. The tunneling spectra exhibit BCS gap structures, with gap parameters in the range of 5 to 7 meV, yielding a ratio of 2delat/KT_c ~ 3-4. This suggests that MgB_2 is a conventional BCS (s-wave) superconductor, either in the weak-coupling or in the `intermediate-coupling` regimeComment: accepted to PRB, revised versio

An experimental study of temperature and radiation characteristics of transient spherical diffusion flames in microgravity.

This thesis presents experimental research conducted to improve our understanding of flames in microgravity conditions. Of particular interest is to understand the effects of radiation heat loss and reabsorption because of their importance in flame extinction and implications for fire safety in low gravitational environments. Spherical diffusion flames were chosen for this study because they amplify the effect of radiation heat loss. Flames in microgravity naturally develop a spherical character due to diffusional symmetry, and consequently their one-dimensionality enables detailed models with chemistry and radiation. The focus of this microgravity diffusion flame study is to examine the effects of various diluents introduced on the fuel and oxidizer sides of a spherical diffusion flame. Characterization of the flame consisted of flame growth rate, temperature field, and spectral radiation emission measurements. Transient measurements were conducted at atmospheric pressure using a porous spherical burner aerodynamically supporting an ethylene diffusion flame in an oxidizing atmosphere. The effect of diluent on the fuel side of the reaction zone was investigated by comparing non-radiative N2 with a radiative diluent mixture including CO2 and He, while maintaining equivalent adiabatic flame temperatures. The influence of CO2 on the fuel side of the reaction zone reduced flame temperatures and inhibited soot formation. CO2 enhanced the heat release rate of the flames without contributing significantly to radiation reabsorption. The effect of diluent on the oxidizer side of the reaction zone was similarly investigated by replacing N2 in the oxidizer with CO2 and/or He. The influence of He on the oxidizer side initially increased heat release of the flame and decreased the flame temperature due to the enhanced thermal conductivity dominating the decreased thermal capacity of the mixture. The influence of CO2 on the oxidizer side also reduced flame temperatures and inhibited soot formation. However, the mechanisms by which CO2 affected the oxidizer were different from that of the fuel side. While CO 2 in the oxidizer similarly enhanced heat release from the flame, spectral radiation emission measurements showed significant radiation reabsorption effects. This study provides important implications for extinguishment mechanisms of flames in low gravitational environments.Ph.D.Applied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125572/2/3208290.pd