Molecular Dynamics Studies on the Condensation Coefficient of Water

Abstract

Molecular dynamics (MD) simulations are carried out for water using two kinds of intermolecular potentials, the Carravetta−Clementi (C−C) model and the extended simple point charge (SPC/E) model, to understand the mechanism of interface mass transfer between liquid and vapor. Effects of different interface structures on the condensation process are investigated, and computational data on the condensation coefficient are presented. By changing incident conditions such as the translational and rotational energies of the incident molecules on the liquid surface, we find that the condensation coefficient of water primarily depends on the translational energy and the surface temperature, as is the case for a simple gas such as argon. The molecular exchange phenomenon caused by incident molecules has no marked influence on the condensation coefficient. A formula for the condensation coefficient is summarized as a function of the surface-normal component of the translational energy and the surface temperature. Also, relations between the surface structure and the condensation coefficient are discussed based on the transition state theory developed in our previous study. The paper demonstrates that the theory can explain the MD data very well, and it is concluded that the translational motion is important compared with the rotational motion, even for polyatomic molecules.

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“…The present formulation ensures that ∂K c /∂T K < 0, in accordance with experimental and theoretical studies (Tsuruta and Nagayama, 2004;Kon et al, 2014). Mathematically this present formulation of K c largely eliminates model instabilities by suppressing condensation relative to evaporation throughout the experiment and will be discussed in greater detail in a later section.…”

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“…More recent experiments, for temperatures between 238 and 298 K, have reduced the range to 0.01-1 (Beloded et al 1989;Hagen et al 1989;Shaw and Lamb 1999;Zagaynov et al 2000;Davidovits et al 2006), and Marek and Straub (2001) suggested that condensation coefficients less than 0.01 indicate contamination of the water surface. Molecular dynamics studies, for temperatures between 300 and 350 K, find the value of q c is close to unity (Morita et al 2004;Tsuruta and Nagayama 2004;Vieceli and Tobias 2004), a result that is at odds with many experiments. The reported values of q e also range from 0.01 to 1 (Eames et al 1997), and experimental challenges associated with determining q e again include surface contamination as well as accurate surface temperature measurements (Hickman 1965(Hickman , 1966.…”

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