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Studies on two-phase equilibria between the water-rich phase (L W ) and the gas hydrate phase (H) are important in understanding gas behavior in water at hydrate forming conditions for processes such as carbon dioxide sequestration and natural gas recovery. A new indirect method was developed in this study and applied for measurements of gas solubilities of carbon dioxide, methane, and ethane in aqueous solutions containing gas hydrates with and without sodium chloride. Effects of temperature, pressure, and salt concentrations on the solubility of these gases in the aqueous phase in equilibrium with the hydrate phase were investigated for P ) (10 to 20) MPa. Solubilities for these gases were found to increase as temperature increases. Methane and ethane were found to show a salting-out effect, whereas carbon dioxide showed a salting-in effect in hydrate forming conditions. Solubilities of methane and ethane decreased with pressure, but those of carbon dioxide showed very weak pressure dependence.

The solubility of carbon dioxide in three ionic liquids (ILs) under supercritical fluid condition was measured at pressures up to 32 MPa and at temperatures of 313.15, 323.15, and 333.15 K in a high-pressure view cell. The imidazolium-derivative ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]), and 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF 4 ]) were employed in this research. The effects of pressure, temperature, nature of anion and cation as well as the water content on the solubility of CO 2 in the ILs were investigated experimentally. The solubility of CO 2 in the IL was higher for the ILs with longer cationic alkyl group and for the ILs with lower anion polarity. The lower the water content or the lower the temperature as well as the higher the pressure, the higher was the solubility of CO 2 .

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The governing equation of acoustic wave propagation in a circular expansion chamber with mean flow and temperature gradient is solved. The circular chamber is divided into N segments and the flow speed and temperature are assumed to be constant in each segment. The solution is obtained in recursive form by applying the matching condition on the boundary of adjacent elements. The solution is verified by comparing it with the experimental results. The results demonstrate that the present theory can well predict the transmission loss of an expansion chamber which has offset, a twisting angle, mean flow, and temperature gradient.

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The noise of an automobile alternator generally increases with rotating speed. However, at some low rotating speeds, the alternator generates tonal noise in the frequency range of 1 to 3 kHz, which is the most irritating to the human ear. These tonal noises annoy the driver as well as passengers, especially at low speeds where background noise is relatively insignificant. Experiments were conducted to identify these noise sources by analyzing the noise and vibration signals. Modal tests were also performed using impact testing to study the modal vibrations of the stator. The source of tonal noises was identified as the magnetic noise which was caused by the strong alternating magnetic force on the stator. The magnetic noise increased abnormally at some specific rotating speeds when its frequency coincided with one of the modal frequencies of the stator.Volume 37/Number 1 31