Ultrasonic Absorption and Relaxation Times in Nitrogen, Oxygen, and Water Vapor

Abstract

The absorption coefficient α is measured in nitrogen, oxygen, and water vapor by a direct traveling‐wave method that employs a pulse modulated signal of about 65 kc/sec. The apparatus used is a modification of that previously reported by C. Ener, O. Herbjørnsen, Y, Fujii, and L. Nyborg. The rotational relaxation times in nitrogen and oxygen for 22°C and 1 atm are obtained as (7.6±0.6) × 10⁻¹⁰ to sec for nitrogen and (5.1±0.4) × 10⁻¹⁰ sec for oxygen. The coefficient α in water vapor is measured for temperatures between 42° and 183°C and over the range of angular frequency/pressure from 1 to 50 Mc/sec/atm. Part of the observed excess absorption is probably due to rotational relaxation, but the larger part, especially at the higher temperatures, is considered to be due to vibrational relaxation. On the latter assumption, calculation of the relaxation time yields a value of the order of 1.5 × 10⁻⁸ sec. This is of the same order of magnitude as that reported by other observers for higher temperatures.