Laser-modulated particulate (soot) incandescence has been studied by measuring the laser-driven particle surface temperature in a propane diffusion flame as a function of laser focal flux. The experimental results display fair agreement with an analytical model of the process. Quite importantly, the absolute incandescence level displays a saturation behavior with increasing laser pulse energy. For laser Raman scattering diagnostics, this behavior means that the S/N ratio will increase with increasing laser flux level. Thus, for highest S/N ratio, it is preferable to operate at the highest possible flux short of gas breakdown and/or optical-component damage levels.
For rarefied gases the collision frequency of the Krook kinetic equation is expressed as the sum of wall and gas collision frequencies. Effective transport coefficients arise from the Chapmanâ€”Enskog theory, and are similar to those proposed by other methods. The transport of either energy, momentum, or mass is analysed for several geometries. Profiles of temperature, velocity, and concentration, which involve jump and slip at the wall, are derived, and accommodation effects are included. The expressions have the proper limits for the continuum and free-molecule regimes, and compare well with other theories and experimental data for transition regime. Heat conduction formulas apply to polyatomic gases. Plane, concentric cylinder, and spherical geometries are considered.
Optical Constants of Soot and Their Application to Heat Flux Calculations Data on the roorn temperature optical constants of soot are present.ed for the wavelength regions 0.4-0.8 micro m and 2. 7 -10.0 micro m Dispersion formlas are developed for interpolating the data between 0.8 and 2.5 micro m. The results are used to calculate the spectral absorption coefficient and the locall emissivties of soot suspensions. It is shown that the correct values of the optical constants are neeeded in thc use of light-scatterirrg techniques for the measurement of the soot concentration but that uncertainties introduced in flux calculations by use of approximate values of the optical constants are not greater than those inlroduced hy the present uncertainties in the valucs of the soot concentration