Effect of metal clusters on the absorption and emission spectra of high-density sodium vapors
The optical absorption spectra of high-density (1016–1019 cm−3) sodium vapors were studied in a broad spectral range (0.35–1.1 μm). The intensity of thermal radiation from sodium vapors was measured in the 2–3 μm wavelength interval. It is established that the effect of metal clusters can account neither for the observed structure of absorption spectra nor for the increased intensity of emission in the near-IR range reported in some works (in particular, for the emission spectra of high-pressure gas-discharge sodium lamps).
The double boundary layer model has been developed to study the behavior of film condensation heat transfer outside a horizontal tube in presence of air treated as a noncondensable gas. And the coupled heat and mass transfer on a smooth horizontal tube is numerically solved with the finite difference method. The local mass concentration of the noncondensable gas, the distributions of velocity and temperature in the boundary layers are presented and discussed. The numerical results have shown that the mass concentration and velocity of the noncondensable gas increase from the bulk mixture to the interface while the temperature decreases from the bulk mixture to the interface. Although the mass concentration of the noncondensable gas in the bulk mixture could be small, the reduction in average heat transfer coefficient is obvious. The comparisons of heat transfer coefficient show that the numerical predictions agree well with available experimental data.