No abstract

To examine the contributions of different types of aromatics, the volume swell of nitrile rubber O-rings was determined in aromatic-free synthetic JP-5 fuel and in synthetic JP-5 fuel blended with selected aromatics. Additionally, partition coefficients between the O-ring and fuel phases were measured for the fuel and aromatic species. Volume swell was measured using an in situ optical dilatometry technique that provided temporal data, while partition coefficients were measured using direct thermal desorption GC-MS analysis of swollen O-ring samples. For the hydrocarbons studied, the data indicate a correlation between partition coefficient and volume swell. The propensity to swell nitrile rubber was found to increase with the polarity and hydrogenbonding character of the aromatics, suggesting that swelling of nitrile rubber requires disrupting the attractive forces between cyano groups on adjacent polymer chains and replacing them with cyano group-aromatic interactions. Volume swell was also found to decrease with increasing molecular weight.

No abstract

Digital particle image velocimetry (DPIV) has been used to examine the flow field in a vessel agitated by an axial-flow impeller in turbulent operation. Both a pitched-blade turbine and a high-efficiency impeller were studied. Time series analysis indicates that the flow field is not steady; rather, it is subject to transients with frequencies well below the blade passage frequency (periods ranging from 40 to over 300 impeller revolutions have been observed). This result has important implications for computational modeling because current descriptions of agitated vessels are based upon time-averaged flow fields with superimposed turbulence. This modeling approach may not accurately capture the mixing associated with the low-frequency phenomena observed in this study.