Supersonic Effects of Water Vapor in CO2 and Their Relation to Molecular Vibrations

Abstract

Acoustic interferometer measurements at approximately 28°C and atmospheric pressure were made from which the velocity and the absorption in CO2 were computed. Various H2O-concentrations were used with each frequency, covering the range 284 to 1595 kc/sec. At each frequency, μ (the absorption per wave-length) rises with increasing humidity to a maximum of about 0.28 and then drops slowly, but with the lower frequencies it also passes through a shelf or minor peak before saturation is reached. As the first absorption peak is approached the velocity drops about 10 m/sec. and a 1-m/sec. drop occurs near the minor peak. As the frequency is increased the critical H2O-concentration hm is increased also but at different rates for the two peaks. For the major peak fm = [60+8(10)4h] kc/sec. for the minor peak fm′ = [50+2(10)4h′] kc/sec. Thus the average lifetime of a quantum of vibrational energy is decreased rapidly with humidity. These facts are presented as graphs. They are also correlated with results by other investigators, none of whom has observed a minor absorption peak and dispersion region. Most of these facts are represented quite accurately by theory, the results of which are included.

Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature

“…The estimation of c vib was thus based on the gas values for the vibrational frequencies 34 , and assumed to be pressure independent.…”

“…The presence of a thermal relaxation in gaseous and liquid CO 2 is a long-known and well documented phenomenon 34,35,36 . The relaxation frequency ω r was found to be a linear function of density in the gas phase, whereas it increases more rapidly in the liquid.…”

“…As a consequence, for ωτ v ∼ 1 the sound velocity goes from its low-frequency ("static") value v 0 s to an unrelaxed value v ∞ s . The presence of a thermal relaxation in gaseous and liquid CO 2 is a long-known and well documented phenomenon 34,35,36 . The relaxation frequency ω r was found to be a linear function of density in the gas phase, whereas it increases more rapidly in the liquid.…”

“…To our knowledge, there are no data on the vibrational frequencies of the fluid in our P − T range; however, the measurements made on solid I showed that these modes are very weakly pressure and temperature dependent 40,41,42 , which should also be valid for the fluid. The estimation of c vib was thus based on the gas values for the vibrational frequencies 34 , and assumed to be pressure independent.…”

Sound

“…To test the instrument the velocity in ethylene was measured both in it and in one in which the reflector moves, namely, the variable-path type of instrument. Pielemeier, Saxton and Telfair (1940) have derived both the velocity and absorption coefficients in carbon dioxide, with which various percentages of water vapour were mixed, over the range of frequency 284 to 1595 kc./sec. As the humidity is increased, the absorption per wave-length rises to a maximum of about 0.28 and then diminishes.…”