Hydrate Film Growth on the Surface of a Gas Bubble Suspended in Water

Abstract

The lateral film growth rate of CH4, C2H4, CO2, CH4 + C2H4, and CH4 + C3H8 hydrates in pure water were measured at four fixed temperatures of 273.4, 275.4, 277.4, and 279.4 K by means of suspending a single gas bubble in water. The results showed that the lateral growth rates of mixed-gas CH4 + C2H4 hydrate films were slower than that of pure gas (CH4 or C2H4) for the same driving force and that of mixed-gas CH4 + C3H8 hydrate film growth was the slowest. The dependence of the thickness of hydrate film on the driving force was investigated, and it was demonstrated that the thickness of hydrate film was inversely proportional to the driving force. It was found that the convective heat transfer control model reported in the literature could be used to formulate the lateral film growth rate v(f) with the driving force DeltaT perfectly for all systems after introduction of the assumption that the thickness of hydrate films is inversely proportional to the driving force DeltaT; i.e., v(f) = psiDeltaT(5/2) is correct and independent of the composition of gas and the type of hydrate. The thicknesses of different gas hydrate films were estimated, and it is demonstrated that the thicknesses of mixed-gas hydrate films were thicker than those of pure gases, which was qualitatively consistent with the experimental result.

Heat Transfer Related to Gas Hydrate Formation/Dissociation

“…The further growth of hydrate is controlled by mass transfer of water or hydrate former through the film. Many experimental and/or theoretical studies on the growth of hydrate film have been carried out by several groups (Freer et al, 2001;Ma et al, 2002;Mochizuki and Mori, 2006;Mori, 2001;Ohmura et al, 2000Ohmura et al, , 2005Peng et al, 2007Peng et al, , 2008Peng et al, , 2009Saito et al, 2010Saito et al, , 2011Sun et al, 2007;Taylor et al, 2007;Uchida et al, 1999Uchida et al, , 2002, including the morphology of hydrate film, the growth rate of hydrate film, the thickness of hydrate film, the mechanism of hydrate film growth, and so on. However, so far it is still a controversial topic on the growth mechanism of hydrate film.…”

“…In addition, the assumptions adopted in this model, that is, the film front is in the water phase or one half in water phase and the other half in guest-fluid phase are too arbitrary. Therefore, Peng et al (2007) proposed another hydrate film model based on Mori's model. In their model, they assumed part of thickness x of hydrate film is in guest phase and another part of thickness x δ − is in water phase, as shown in Figure 3.…”

“…The value of x is guest composition dependent. (Peng et al, 2007), the thickness of hydrate film was assumed to vary with driving force inversely, i.e.,…”

“…The modified convection heat transfer model presented by Peng et al(2007), i.e., Equation 11, has been used to correlate the lateral growth rate of hydrate film of different crystal structures in wide temperature and pressure ranges (Peng et al, 2007(Peng et al, , 2009. It can be concluded that validity of Equation 11 is independent of the composition of hydrate former and the structure type of hydrates (Peng et al, 2007).…”

“…It can be concluded that validity of Equation 11 is independent of the composition of hydrate former and the structure type of hydrates (Peng et al, 2007).…”