Thermal Response During Rheological Transitions In Cyclopentane Hydrate-Forming Emulsions

Pipeline plugging by formation of clathrate hydrate is a problem which can result in flow interruption and equipment damage.  Hydrate formation in an emulsion occurs initially at the oil-water interface.   We study a water-in-oil emulsion system in which an atmospheric pressure hydrate former, cyclopentane, is contained in the oil. When hydrate forms, the polycrystalline shell forms a barrier limiting the rate of reaction of hydrate.   A mechanism of shell fracture in the hydrate system controlled by the stress imposed in the system is reported. Rheological properties of density-matched emulsions up to 40% water in a continuous oil are examined. We consider emulsions which form hydrate and non-hydrate forming systems, where ice is formed instead.   These have been investigated under various shear rates and shear stresses in conventional rheometers. The emulsions are quenched from room temperature to -7 C. At a constant shear rate of 100/s, the viscosity increase for the hydrate forming system is sharper and a significant heat generation rate is implicitly observed by a jump in temperature, when compared with the non-hydrate forming system as well as with a weakly sheared emulsion.  Yield stresses are found for sufficiently large internal phase (water) fraction. Regardless of the shear rate, the non-hydrate forming system does not experience a significant heat generation rate, indicating ice-forming emulsions are not a satisfactory model for the processes which induce plugging in hydrate-forming emulsions.