Experimental determination of sound velocity in liquefied propane-butane gas mixture (LPG)

In this article, experimentally determined values of sound velocity in LPG in a temperature range (–23...+55) °C are presented. The measurements were taken using two industrial LPG samples in a standard five liter pressurized gas tank. The propagation time of a ultrasonic signal with the frequency of 0.7 MHz was measured. To increase the accuracy of measurement, a pulse-phase method was applied in our measurement system. The propagation time of the acoustical signal through the LPG was measured by filling the mesurement interval with pulses of 100 MHz frequency. The propagation of ultrasonic signal through the walls of the tank was eliminated by applying a special method. Measurements showed that the amplitude of the signal, which has propagated through the LPG, has attenuated by about 30% in the selected temperature range. The curve of sound velocity for LPG, with 71.74 % of propane, is below the curve for LPG with 27.80 % propane. At the temperature of 20.0 °C, sound velocities in the samples are 810.16 m/s (sample with 71.74 % of propane) and 840.31 m/s (sample with 27.80 % of propane). The sound velocity in the previously mentioned temperature range is close to linear dependence versus temperature. The sound velocity differences in industrial LPG samples with different propane-butane ratios can be used to develop a method to determine the composition of LPG, in which this ratio is unknown.