Rheological Study of Mixed Cyclopentane + CO2 Hydrate Slurry in a Dynamic Loop for Refrigeration Systems

The use of CO2 hydrates as phase change materials is promising for secondary loop refrigeration, as these compounds present adjustable dissociation temperature that can be higher than 273.15 K and have high enthalpy of dissociation. In the present work, by using various promoters, cyclopentane (CP) in this study, the formation pressure of hydrates may be significantly lowered than CO2 hydrates. For their application as a secondary refrigerant, the rheological properties of mixed CP + CO2 hydrate slurry need to be controlled. The flow properties of CP and mixed CP + CO2 hydrate slurries were studied in a dynamic flow loop at different cyclo-pentane contents ranging from 3 wt% to 15 wt%, using a capillary viscometer based on Rabinowitch and Mooney equation. Rheological parameters (viscosity, flow behavior...) related to these two slurries were compared. The experimental results demonstrate that CP and mixed CP + CO2 hydrates slurries exhibit a shear thinning behavior and the viscosity values vary between 3 and 12 mPa.s-1 at [100-1000 s-1] for CP hydrates slurries and between 2 and 10 mPa s-1 at [100-1200 s-1] for CP + CO2 hydrates slurries. CP hydrate and CP + CO2 hydrate slurry viscosity is close to that of TBPB hydrate and lower than that of CO2 hydrate. Moreover, mixed CP + CO2 have shown a time-evolution of the rheological behavior.