Secondary two-phase fluids are suspensions of solid crystals. Thanks to the melting latent heat, they present a great interest for cold transportation. Moreover, they are a mean of reducing the amount of classical refrigerant. In the refrigeration field, ice slurries are already used. The goal is now to extend this technology to other temperature ranges suitable for other applications like freezing or air-conditioning (ACUHS project).
For an air-conditioning application, a TBAB (Tetra-ButylAmmonium Bromide) aqueous solution is studied. Under atmospheric pressure and for positive temperatures, this solution crystallizes into ice-like compounds named “hydrates”. First, the physical properties of the aqueous solution and its crystallisation conditions were studied. Two different types of hydrates can appear.
The goal of the experimental set-up is to study the rheological behaviour of two-phase fluids. Slurries are made in brushed-surface heat exchanger and pumped into pipes where flow rates and pressure drops are measured.
The rheological behaviour of TBAB hydrates slurries can be described using a Bingham fluid model. We highlight that the two rheological parameters, which are the apparent viscosity and the yield shear stress, depend on the volume fraction of crystal of course, but also on the hydrate type, and on the initial concentration of the solution. The yield shear stress is interpreted as the consequence of the Van der Waals inter-particle interaction forces.
Finally, possible stratification effects are modelled with a finite difference method. The principle is to calculate particle concentration and velocity profiles following the flow of the slurry. Calculations are validated with experimental velocity profiles published by P. Reghem (2002). This model underlines the influence of the particle distribution in the pipe on pressure drops.