Rheological properties of tetra-n-butylphosphonium bromide hydrate slurry flow

Abstract : Clathrate hydrate slurries can be considered as two-phase refrigerants due to their high energy densities. The heat of formation of many clathrate hydrates is higher than that observed for other phase change materials used in this field. The present work investigates the use of semiclathrate hydrates, formed from tetra-n-butylphosphonium bromide (TBPB) + water mixtures, as appropriate media for cold storage and distribution in refrigeration applications. Indeed, TBPB hydrates crystallize under atmospheric pressure and at temperatures around 281 K, which are suitable conditions for air-conditioning or refrigeration applications. In the present study, we focus on the rheological behaviour of TBPB hydrate slurry studied thanks to a dynamic loop and the application of Ostwald method. Volumetric flow rates and pressure drops are measured for hydrate fractions between 0 and 28.2 vol.%. The rheological properties deduced from these measurements were modelled using a semi-empirical Ostwald-de Waele law taking into account hydrate slurry fraction. Finally, the apparent viscosity of TBPB hydrate slurry was estimated from the model and a good agreement was found between our data and literature.