Gasdichtemessung mittels Akustischer Methode / Gas density measurement by an acoustic method

Abstract

Eine Methode zur Dichtebestimmung von Gasen wurde entwickelt, bei welcher das zu untersuchende Gas von einer Schallquelle erregt, und der erzeugte Druck von einem nahen Mikrofon gemessen wird. Man kann zeigen, daß dieser Druck der Gasdichte proportional ist. Schon die mit einer einfachen Versuchsanordnung durchgeführten Messungen ergaben Dichtewerte mit einer Präzision von 0-2% für Dichten über 0,7 kg m~3, die nach einer empirischen Korrektur für alle Dichten gilt. Diese Korrektur verkleinert auch den Fehler der Dichtebestimmung für Dichten über 0,7 kg m -3 auf weniger als 0,2%. Es lassen sich nach dieser Anordnung sehr einfache Dichtemesser sowohl als Industriegeräte und wahrscheinlich auch als Laborgeräte für breite Temperaturund Druckbereiche herstellen.A methodfor the measurement of gas densities has been developed. The gas is exited by a source of sound and the resulting dynamic pressure measured by a microphone nearby. It can be shown that this pressure is proportional to the gas density. Even measurements made with a crude setup yielded results with the precision of 0-2% for densities above 0,7 kg m~3, and with an empirical correction for all densities. This correction also reduces the error of the density determination for densities above 0,7 kg m~3 to less than 0,2% o . Thus it will be possible to construct very simple instruments for industrial and probably laboratory use for a wide range of temperatures and pressures.

Refractometry and gas density

“…For comparison with these experimental values, the theoretical dispersion of helium is calculated with the Lorenz-Lorentz formula (5) and Bhatia and Drachman's [87] ab initio atomic polarizability results: α rel = 1.383 160 981 + 0.385 530 216ω 2 + 0.127 538 95ω 4 +0.045 731 14ω 6 (11) in reduced atomic units and where ω is the angular frequency in reduced Rydberg units. Non-ideal gas behaviour is accounted for with a value for B R = −0.068(10) cm 6 mol −2 (the refractivity virial coefficient in (5); experiment: [93] at λ = 633 nm), together with the equation-of-state virial coefficients, B and C, discussed in section 5.1.…”

“…This discrepancy of about +0.01 × 10 −6 above the corresponding theoretical curve, noted by Leonard [91], Pendrill [19] and Bhatia and Drachman [87] and remaining even with later data, may be explained by using an absolute temperature of 273 K rather than 273.16 K, but the latter value is quoted explicitly in Leonard's compilation, in accord with the IPTS-68 temperature scale applicable at the time. The theoretical values used here in these comparisons with experiment are based on Bhatia and Drachman's [87] values for the dispersion terms in (11), while adopting the more recent estimate of 1.383 191(2) au [86,88] for the static atomic polarizability. The uncertainty limits on the theoretical values are (conservatively) calculated from the difference between the two theoretical estimates of the static polarizability.…”

“…Various methods may be employed to measure gas density, including equation-of-state gas parameter (pressure, temperature, etc) determination [7], vibrating tube densimeters [10], acoustics [11,12] as well as the weighing of buoyancy artefacts [8,9,[13][14][15][16].…”