Organic phase change materials for thermal energy storage

Abstract

Salt hydrate phase change materials used for thermal storage in space heating and cooling applications have low material costs, but high packaging costs. A more economic installed storage may be possible with medium priced, high latent heat organic materials suitable for low cost packaging, i.e. those that are insoluble in water and unreactive with air and some of the common packaging films. We have done a preliminary survey of 12 such organic materials with melting points in the range 10–43°C. Measurements of melting point, freezing point, and the latent heats of melting and fusion are presented. For distributed passive solar storages, butyl stearate, m.p. = 19°C, f.p. = 21°C, ΔH m = 120 J/g, current cost 55¢/lb, seem promising. For central storage, both vinyl strearate, m.p. = 27° C, f.p. = 29° C, †H m = 122 J/g , and mixtures of ethoxylated (C 11-C 15) linear alcohols, 30°C < m.p. < 41°C, 31°C < 40°C, 105 J/g < ΔH m < 134 J/g, current costs between 38¢/lb and 57¢/lb, for average molecular weights between 1080 and 1520, warrant further study. Isopropyl stearate, m.p. = 14°C, f.p. = 18°C, ΔH m = 142 J/g, should be considered as a “coolness” storage for desert regions. The other materials showed either supercooling or inappropriate melting points or lower latent heats than the 4 selected for further study.