Measurement Of Speed Of Sound In Carbon Dioxide Near The Critical Region With Cylindrical Resonator

Carbon dioxide is one of the most important green-house gases. The technology which focuses on carbon dioxide capture and storage is considered the direct and effective method to mitigate climate change. In the future, carbon dioxide capture and storage will contribute to reduce carbon emission in China. Also, as an environment-friendly natural substance, carbon dioxide is substitute for CFCs substance in application of refrigerant. This way will reduce the destruction speed in ozone layer. Compared with HFCs substance, the greenhouse effect caused by carbon dioxide is much smaller. Thus with good engineering application, the thermophysical properties of carbon dioxide are crucial basis for industrial applications. However, precision experimental data of the speed of sound in gaseous carbon dioxide is very limited. In this thesis, speed of sound measurement system for gases at high pressures was built. The new system including cylindrical resonator, pressure vessel, frequency measurement system, temperature measurement system, pressure measurement system, gas filling system and the vacuum system can be used to measure speed of sound in gases at temperature from220K to440K and pressures high to6MPa. Based on first-order acoustic perturbation theory, the key issues in measuring speed of sound in gaseous were researched.The fixed-length cylindrical resonator was used in the measurement. The piezoelectric transducer replaced traditional condenser microphone to improve the signal-to-noise ratio in the frequency measurement. Using the minimum inside-diameter ducts made the disturbance of the sound field being greatly reduced, and achieved the optimization design of the ducts. The structure of a long rod standard platinum resistance thermometer which can be inserted in the outer wall of the resonance was designed to meet the real-time temperature measurement under high pressure. This method improved the reliability of the temperature measurement. Further, high-pressure vessel is designed to create an isobaric environment for acoustic sensor. This way greatly expanded the range of pressure measurement. Automatic control of the temperature, pressure, frequency measurement, as well as data acquisition and processing were achieved by Lab View.Resonance frequencies of CO2were measured at temperature of263to333K and pressure up to6MPa. Based on the acoustic perturbation theory, the boundary layer effect, shell motion, perturbation from ducts and vibration relaxation were analyzed which are main effects. According to the speed of sound in Ar and corrected resonance frequency, calibrated the resonator length and radius with a relative method, then speed of sound in gaseous carbon dioxide could be calculated by theoretical formula. The accurate speed of sound experimental data showed a0.01to0.02%discrepancy with the international standard equation of state for carbon dioxide. Also the present results will provide the basic data for establishment of new equation. In the light of thermodynamic equation, the acoustic virial coefficients and ideal-gas specific heat capacity were calculated which are in good agreement with reference values.