ACUHS

Context

Montreal (1987) and Kyoto (1997) protocols regulate the use of classical refrigerants such as CFCs and HCFCs for their high ozone depletion potential and HFCs for their high global warming potential. The phase-out of such fluids is now a crucial point and replacement technologies are to be developed.
For refrigeration applications such as refrigerated display cabinets, the use of secondary refrigerant fluids arouse a great interest. The principle of such technology consists in using two different loops. The primary loop, of reduced dimensions and working with a classical refrigerant is set in a machine room. It exchanges heat with the fluid running in the secondary loop, which is responsible for the cold energy distribution. Therefore, this technology leads to a reduction of the total amount of classical refrigerant. Moreover, the latent heat of ice fusion provides a supplementary cold energy compared with single phase fluids. Lastly, this technology allows to product solid particles during the night—with the lowest energy costs—and store them until their distribution during the day. Ice slurries are well appropriate in the refrigeration field because of their low melting temperature. Concerning air-conditioning systems, a suitable phase-change material (PCM) should present a melting temperature within [+6°C; +12°C]. As it meets this property, the tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate seems to be a good candidate for this application field

Step 1 : Ph.D Work of Myriam Darbouret (2002-2005): In the refrigeration field, the use of ice slurries (suspensions of ice) as secondary refrigerant fluids is spreading. This technology could be extended to air-conditioning systems provided that one can propose a phase-change material (PCM) with melting temperature belonging to the range [+6°C; +12°C]. Aqueous solutions of tetra butylammonium bromide, which crystallise under atmospheric pressure and temperatures between 0 and +12°CC, into ice-like compounds (hydrates), seem to be good candidates for air-conditioning applications. The Ph.D work of Myriam Darbouret has focussed on the rheological properties of TBAB hydrates suspensions.

Step 2 : Ph.D Work of Jérôme Douzet (2007-2010) : Our air-conditioning system uses two different loops. The primary loop, of reduced dimensions, works with a classical refrigerant. The aqueous solution of tetra-n-butylammonium bromide (TBAB) replaces traditional secondary refrigerant fluids. The hydrates generator transforms the aqueous solution of TBAB into TBAB hydrates. The slurry is stored in an intermediate tank. The latent heat of hydrates fusion provides a supplementary cold energy compared with single phase fluids. Our technology allows to product solid particles during the night - with low energy costs - and to store them until their distribution during the day. We built a real size prototype, which stands both for a testing stand and for a life-size application

Step 3 : Ph.D Work of Pedro Brantuas(2009-2012) : The aim of this work is to modify an industrial prototype of air-conditionning based on phase change material (TBAB semiclathrates from an aqueous solution of tetra-n-butylamonium bromide) and to test a new concept of crystallizer. It is a gas bubbling reactor in which are formed TBAB-CO2 semiclathrates.