## 3 Results and Discussion  
### Study on Hydrate Slurry Dissociation Morphology  
Hydrate decomposition in a pipeline system was a micro-level process with lattice deconstruction and guest gas molecules' desorption. In detail, water molecules firstly were changed from the clathrate structure into a disordered and loose arrangement. Van der Waals forces between host water molecules and guest gas ones were then weakened, so that the gas molecules could escape from deconstruction lattices. Finally, these escaped guest molecules appeared in a dissolved or a free gas form on the surface or around the hydrate particles. Therefore, it was needed to distinguish the micro particle/droplet figures gathered by PVM, in order to identify bubbles, water droplets and hydrate particles. This was the basis to investigate the particles' interactions, chord length distribution, and the agglomeration mechanism during the decomposition. Figure 3 was a figure captured by the PVM of the slurry system with a few bubbles and water droplets. It can be seen that light spots (reflections of the laser light from PVM) appeared on the surface of the bubble rather than on that of droplets, due to the different optical properties of bubbles and droplets. With the aid of PVM, this paper obtained hydrate particles' definite morphological changes and aggregation characteristic. Figure 4 presents the particles' morphology and distribution at different time points in the process. Figure 4: _Cont._  
Figure 3: The distinction between gas bubbles and droplets. It can be analyzed from the above four figures as follows. In Figure 4a, before the hydrate dissociation, particles were relatively equally distributed in the system with irregular shapes. Hydrate slurry was easy to transport at this time point. In Figure 4b, at the beginning of the dissociation, lattice deconstruction and guest gas molecules' desorption happened on the surfaces of hydrate particles, leading to bright spots and even droplets on the surfaces. In Figure 4c, during the dissociation, hydrate particles would dissociate more thoroughly, resulting in better water wettability of the particle's surface, more water droplets, and larger agglomeration trend. In other words, it was easier for the \"secondary aggregation\" which could seriously impact the safety of hydrate slurry transportation and should be avoided in the transportation technology. In Figure 4d after the complete dissociation, lots of water droplets spread among the system. Yet their size would decrease with longer emulsification time (through the comparison of Figure 4d,e). This again shows that hydrate particles/droplets agglomerated during the decomposition. In a word, the morphology of hydrate particles or droplets would change with time during the hydrate slurry decomposition. In the dissociation, lattice deconstruction and guest gas molecules' desorption (captured as the light spots in the figures) did happen on the particles' surface. Hydrate particles, dissociating particles and water droplets coexisted in the system with further decomposition. This gave rise to various collision forms among them, increasing the aggregation strength (dissociation would cause the slurry destabilization). In the process, probability of hydrate particles to dissociation depended on the particle's shape and size, that was, different particles did not dissociate at the same time in the system. After the dissociation, the size of water droplets in the system was larger than that of the particle before the decomposition (through the comparison of  
Figure 4: Distribution of particles/droplets in the whole process of hydrate slurry dissociation (**a**–**e**). (**a**) Before hydrate slurry dissociation. (**b**) Beginning of hydrate slurry dissociation. (**c**) During hydrate slurry dissociation. (**d**) The complete dissociation. (**e**) The longer emulsification time after complete dissociation. Figure 4a,e).