Titan, Saturn's largest moon, is the only extraterrestrial body known to support stable liquid on its surface, in the form of seas and lakes that dot the polar regions. Many indications suggest that the liquid should be composed of a mixture of N 2 , CH 4 and C 2 H 6 . Recent RADAR observations of Titan's large sea, called "Ligeia Mare", have shown unexplained and ephemeral bright features, possibly due to rising bubbles. Here we report that our numerical model, when combined with experimental data found in the literature, shows that Ligeia Mare's bed is a favourable place for nitrogen exsolution. This process could produce centimeter-sized and radar-detectable bubbles.

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iscosity is an important transport property in process design and development. Knowledge of viscosity of pure liquids and of the liquid mixtures plays a key role in solving chemical engineering problems dealing with heat-transfer and masstransfer operations, and fluid-flow processes. Much effort has been directed towards the development of reliable models for correlating and predicting viscosities of pure nonpolar and polar liquids. However, there is still a lack of a sound theory for the accurate prediction of liquid viscosities within a wide Ž . range of temperatures and pressures Reid et al., 1987 . Furthermore, viscosity models based on similarities either with gas-like or solid-like behavior have not successfully been proven to yield values of liquid viscosity for pure liquids and Ž . mixtures as functions of temperature Chhabra, 1992 . Consequently, most of the viscosity models reported in the literature have been developed under semi-empirical and empirical considerations. Pertinent literature on viscosity models for pure liquids has been reviewed and evaluated by Przezdziecki Ž . Ž . Ž . and Sridhar 1985, Reid et al. 1987, Mehrotra 1991 , Mon-Ž . Ž . nery et al. 1995, Mehrotra et al. 1996 , and Poling et al. Ž . 2001 . A thorough review of the literature reveals that numerous empirical and semiempirical models have been published for viscosities of pure liquids with exponential viscosity-temperature functions receiving most of the attention. The corresponding states principle along with the Eyring's absolute rate theory are the most widely used approaches to represent the Ž . viscosity of pure liquids. Recently, Lei et al. 1997 presented a two-parameter model based on the Eyring's absolute rate theory for the correlation of the viscosity of pure liquids under saturated conditions. Their correlating results yielded an overall ADD of 1.51% in the representation of experimental liquid viscosities of 106 pure nonpolar and polar fluids. An important feature of the model proposed by Lei et al. is that, at a given temperature, the liquid viscosity can directly be computed from equilibrium properties such as vapor presCorrespondence concerning this article should be addressed to R. Macıas-Salinas. sure, heat of vaporization, and compressibility factors of the phases at equilibrium. Based on the two-parameter model of Ž . Lei et al. 1997 , the purpose of the present study is three fold. The first purpose is to make use of a well-known cubic equation of state to calculate all of the thermodynamic properties required in the model, thus enabling the simultaneous calculation of vapor-liquid equilibria and saturated liquid viscosity. The second purpose is to improve the correlation of liquid viscosity over a wider temperature range by modifying the functionality between the activation energy and the internal energy of vaporization, and, the third purpose is to extend the use of the model to the calculation of compressed Ž liquid viscosities at pressures larger than the saturation . point .

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