Rheological study on CO2 hydrate slurries for secondary refrigeration

Abstract

To help the fight against climate change, the Kigali deal has planned to eliminate hydrofluorocarbon’s use (HFC) in industrial systems. HFCs are powerful greenhouse gases with a high global warming potential. Moreover, HFCs are commonly used as a refrigerant within secondary refrigeration processes for cold production. A solution to limit their negative environmental impact would be to reduce the amount of HFC by using a phase change slurries (PCS) in the secondary loop. A PCS is composed of solid phase change particles (solid-liquid) in a liquid transportation phase. Clathrate hydrates are crystalline particles where gas molecules are trapped in water cages. Due to their high energy densities, hydrate slurries, in particular CO₂ hydrates, are relevant twophase secondary fluids because they enhance the energy efficiency of secondary refrigeration systems. In this study, the rheological behaviour of CO₂ hydrate slurries in various experimental conditions on a dynamic loop for cold distribution was investigated. An exhaustive state-of-the-art rheological study of hydrate slurries in aqueous solution has pointed out that hydrate slurries are non-Newtonian fluids. However, the rheological behaviour could be different for the same kind of hydrate slurry according to the literature. Moreover, the literature review also highlighted that the most used measurement method for the apparent viscosity is the capillary viscometer. We used a semi-empirical Herschel-Bulkley’s model for determining the apparent viscosity of the CO₂ hydrate slurry as a function of the hydrate slurry fraction. This work is primordial for designing and sizing a new efficient refrigeration system based on this innovative material.