## 2 Literature Overview
The main assumptions of various models mentioned above include:  
-  Hydrate film having a homogeneous structure at the macroscopic level;  
-  Infinitely extending aqueous and guest-fluid phases and the interfaces between them;  
-  Spatially uniform hydrate film with thickness that does not vary with time;  
-  Hydrate crystal formation occurring only at the front of the hydrate film;  
-  The front temperature remaining constant at the three-phase equilibrium value;  
-  No advection occurring in either of the aqueous or guest-fluid phases. Based on experimental observations of important dynamic features such as hydrate film thickness as a function of time and comparison to their previous studies, [PERSON] and [PERSON] [19] have recently introduced two major interlinked assumptions: \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Hydrate Phase** & **1 st** & **2 nd** & **[PERSON] and** & **[PERSON]** & **[PERSON] and** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **This** \\
**Transition** & **Group** & **Group** & **[PERSON]** & **et al.** & **[PERSON]** & **et al.** & **et al.** & **et al.** & **et al.** & **Work** \\
**Characteristics** & **a** & **b** & **1997, 1998** & **1999** & **2001** & **(2001)** & **(2006)** & **(2017)** & **(2018)** & **Model** \\ \hline
**Score** & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 2 & 3 & 3 & 4 \\ \hline
**Phase transition** & & & & & & & & & & & \\
**thermodynamic control** & – & – & – & – & – & – & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline
**Phase transition** & & & & & & & & & & & \\
**mass transport kinetics** & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & – & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline
**Phase transition** & & & & & & & & & & & \\
**heat transport kinetics** & – & – & – & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline
**Irregular hydrate** & & & & & & & & & & & \\
**surfaces** & – & – & – & – & – & – & – & – & – & – \\ \hline
**Inhomogeneous (heteroge-)** & & & & & & & & & & & \\
**neous)hydrate** & & & & & & & & & & & \\ \hline
**Hydrodynamic level mass flow** & – & – & – & – & – & – & – & – & – & \(\surd\) \\ \hline
**Hydrodynamic level heat flow** & & & & & & & & & & \\ \hline
**Enthalpy changes** & – & – & – & – & – & – & – & – & – & \(\surd\) \\ \hline
**Changes in heat capacity** & – & – & – & – & – & – & – & – & – & \(\surd\) \\ \hline
**Changes in volume** & – & – & – & – & – & – & – & – & – & \(\surd\) \\ \hline \hline \end{tabular}  
* [PERSON] et al. [8], [PERSON] et al. [9], and [PERSON] et al. [10], b; [PERSON] et al. 1996 [12] and [PERSON] and [PERSON] 1997 [13].
* Scores are on a 0–5 scale based on the major aspects accounted for by each model; a model able to fully cover all the three aspects would be scored at 5. 4 (_). Hyphen indicates that the model in question ignores this aspect altogether; while (\(\surd\)) checkmark indicates that this aspect is accounted for, to a certain degree. The overall score reflects our opinion on the general comprehensiveness of the theoretical treatment as a whole.  
\end{table} 
Table 1: Properties needed for hydrate kinetic modeling, including details missing in hydrate phase transition models proposed by various research groups. Spatial non-uniformity of temperature at the film edge;  
A variation in the guest concentration on the aqueous-phase side (i.e., mole fraction of water/hydrate at the two-phase equilibrium over the film front surface). The most recent study in this overview, that of [PERSON] et al. [20], considered natural convective heat transfer along with the gas-liquid interface. Unlike the previous studies, this model does contain a quantitative relation between the hydrate film formation and experimental temperature. Their model also proposes a sub-cooling correlation and an assumption that heat exchange between gas and aqueous phases will not influence the diffusion of hydrate film.