Hydrate nucleation rate scaling: the effects of system size and subcooling range

Understanding how gas hydrate nucleation rates scale with system size is essential for developing predictive models of hydrate blockage risk. Previous experimental work using the high pressure stirred automated lag time apparatus (HPS-ALTA) and a larger variant known as the Pipe-ALTA showed that nucleation rates measured in well-stirred systems could be reconciled when scaled by the gas water interfacial area. However, the geometries of these apparatus do not allow the three-phase contact line (TPCL) and the interfacial area to be varied independently, making it difficult to rule out the TPCL as the most appropriate scaling dimension. Here, new hydrate formation measurements are presented using two additional stirred ALTA configurations. The Cone-ALTA allows significant differential variation between interfacial area and TPCL through its conical geometry, while the Micro-ALTA can access higher subcoolings through its significantly reduced system volume. Induction time distributions were measured using these four different apparatus over subcoolings from 4 to 13.5 K and analysed within the framework of classical nucleation theory. Across the Cone-ALTA, Pipe-ALTA, and HPS-ALTA, nucleation rates are well reconciled when scaled by the gas water interfacial area, demonstrating that this property dominates system size scaling at lower subcoolings (ΔT < 8 K). At the higher subcoolings accessed in Micro-ALTA and ramped cooling HPS-ALTA experiments, the observed nucleation rate is determined by sites with larger energy barriers and higher areal densities. These results suggest that scaling hydrate nucleation rates across various system sizes requires a framework that accounts for different subcooling ranges.