Coupled effects of slurry rheology, heat transfers, and thermodynamics on performance of secondary refrigeration loops in steady-state operation.

Because of major global warming concern (refrigerant leaks in large direct refrigeration systems), secondary refrigeration should develop in the next future, especially when using slurries with strong energetic density. With gas-hydrate slurries the fusion temperature can be modified via the gas pressure; this is a new feature. In order to thermodynamically revisit the question, a numerical model of secondary refrigeration loops in steady-state operation has been developed. It includes the cooling unit, the heat-exchangers, the pumps, heat-dissipation's, and non-Newtonian effects on pressure drops and heat transfers. The whole system is sized while accounting for engineering constraints: prescribed cooling power, prescribed total heat-transfer areas, imposed degree of turbulence in the slurry flow so that crystal deposition and blockage are prevented while keeping acceptable pressure drops. CO2- and mixed CO2+TBPB hydrates, are compared to usual ones in terms of global electricity consumption and exergy losses. Global energetic performance mostly depends on fusion temperature of the slurry.