PCMs and ice slurries: PCMs: two recent applications

Phase-change materials (PCMs) can provide thermal storage which means that they can absorb thermal energy when they solidify and release it when they melt. This can be very useful to dampen temperature swings. PCMs are usually water-based and are either non-organic as in the case of sodium chloride, calcium chloride or ammonia, or organic, and usually alcohol-based, or wax, as in BASF's new Micronal phase-change capsules. These capsules were originally used in space exploration, for instance in astronauts' spacesuits, but also for soldier's garments. The innovation consists in applying this technique to interior plaster or plaster walls: Michael Guibault, a Marketing Manager for BASF's Construction Polymers business in North America claims that "the thermal capacity of a one-half-inch thick plaster layer with 30% Micronal is roughly equivalent to that of a six-inch thick brick wall." This can enable a reduction in air-conditioning and heating needs, and can also reduce energy costs and improve comfort. Cemagref, an institute based in the Paris suburbs, is currently working on a PCM application for refrigerator casings that could enable better food preservation and less risks in the case of power cuts: a refrigerator and freezer incorporating such materials could store enough thermal energy to maintain the temperature down for over 14 hours without requiring compressor operation. An experimental model has been designed: a 10-mm-thick plate containing a PCM was placed between the evaporator and an insulant. The initial tests demonstrated that the system had an 18 hours self-sufficiency and its COP was improved by 20%.The system should only entail easy and minor alterations to existing refrigerators.