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 cyclopentane 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.