Abstract:
The computation of sound speeds in nitrogen, oxygen, and methane was performed with two methods. Results from the traditional method that relied on virial coefficients B and their temperature derivatives T dB/dT, T[sup 2] d[sup 2]B/dT[sup 2], were compared with those given by a simplified method. At a pressure of 101.325 kPa, and at a temperature of -10 (degrees)C, the maximum sound speed deviations between the two methods are within 0.2% and -0.4% for nitrogen and oxygen, respectively. For methane, at the above pressure, and over the temperature range from zero to 450 (degrees)C, the maximum deviation is 1.2%. For the above gases, the sound-speed deviations between the methods are largest at low temperatures. It can be shown that by modifying the numerical values of the virial coefficients and their temperature derivatives, the sound-speed deviations between the two methods can be reduced substantially. For nitrogen, when B, T dB/dT, and T[sup 2] d[sup 2]B/dT[sup 2] are modified by multiplication factors of -0.1, 0.55, and 0.7, respectively, the difference between the sound speeds obtained with the two methods decreases to less than (plus or minus)0.05%. It is noted that the sign of the numerical value of B is reversed. Uncertainties of the results obtained with both methods were examined.