Abstract
Low-resolution spectral absorptivities have been experimentally determined for water vapour, carbon dioxide and carbon monoxide in the near infra-red. The gases were contained in a "test" cell located within an electric furnace and surrounded by a pressure vessel containing inert nitrogen at the same pressure as the "test" gas. Thermal radiation from a Nernst filament enters and leaves the "test" cell and pressure vessel through infra-red transmitting windows, and the attenuated radiation is detected and analysed with respect to wavelength. The absorption bands studied were the 1.9 mum and 2.7 bands of water vapour, the 2.0 mum, 2.7 mum and 4.3 mum bands of carbon dioxide and the 2.35 mum band of carbon monoxide. Gas pressures were varied from 1 to 8 bar, temperatures from ambient (293K) to 900K and the mole fractions of the absorbing gas, in a mixture with nitrogen, ranged from 0.1 to 1.0. The radiation path length, as indicated by the length of the "test" cell, was 15.0 cm at ambient and 9-3 cm at all temperatures. Hence, absorber gas concentrations were 0.4 to 112 bar. cm.STP. Total absorptivity were calculated for all the absorption bands studied, and correlation equations developed to relate the band absorptivity with the gas partial pressure, total pressure, temperature and radiation path length. The accuracy and applicability of each of the correlations was determined as a result of comparisons with experimental data. The effects of mixtures of carbon dioxide and water vapour on spectral and band absorption have been commented on.