5 research outputs found
Statistical Analysis of Supercooling in Fuel Gas Hydrate Systems
The recently developed high pressure automated lag time
apparatus (HP-ALTA) was applied to the study of the formation and
growth of interfacial gas hydrate films for three gases; methane (C1),
90% methane/10% propane gas mix (C1/C3), and synthetic gas mix (SGM).
The effects of gas pressure and cooling rate were studied for each
gas. Some degree of supercooling was observed in all cases. The probability
distributions of formation temperature (<i>T</i><sub>f</sub>) were often found to be bimodal, due to the formation of either
gas hydrate or ice in sequential experimental runs. The width of the <i>T</i><sub>f</sub> distribution of ice was about 3–4 K.
In contrast, the width of the <i>T</i><sub>f</sub> distribution
of gas hydrates was about 20 K which reflects the importance of mass
transfer (gas diffusion) processes in nucleation. Differences in hydrate
and ice nucleation probability distributions were observed for different
gases, reflecting differences in both thermodynamic equilibrium phase
behavior
and hydrate formation mechanisms. For all gases studied, <i>T</i><sub>f</sub> generally increased with increasing gas pressure. A
minimum threshold pressure for hydrate formation was observed, with
magnitude decreasing in the order C1 > SGM > C1/C3. The effect
of cooling rate on gas hydrate nucleation probability was also studied.
The median of the distribution of <i>T</i><sub>f</sub> (<i>T</i><sub>f50</sub>) was found to decrease with an increased
cooling rate, consistent with the increases in effective induction
time as samples were cooled more slowly. Our results clearly highlight
the value in collecting large data sets which can be used to assemble
probability distributions when studying intrinsically stochastic processes
such as gas hydrate nucleation and growth