2023 Volume 49 Issue 3 Pages 79-87
Disodium hydrogen phosphate dodecahydrate is a latent heat storage material which is expected to be applied to indoor air conditioning and floor heating. However, because the dodecahydrate melt in the heat storage state does not nucleate easily even if it is cooled to a temperature below its melting point, it makes difficult to operate the latent heat storage system to release the stored heat at its melting point. In order to solve this supercooling problem, generally, nucleating agents are added. But, in spite of the many studies on the development of the agent thus far, their nucleation promoting abilities were still insufficient. In the present study, with the aim of extracting the physical properties necessary for functioning as a nucleating agent, the added reagents were fixed to sodium salts and the strength of their promoting abilities was investigated by thermal cycle experiments. As a result of examining the relationship between the strength of the promoting ability quantified by defining as a supercooling ratio and the acid dissociation constant of the anion, in the anion having a higher dissociation constant compared with the mono-hydrogen phosphoric ion constituting the dodecahydrate, it was found that the anion having a larger number of the dissociation constant exhibited a stronger promoting ability. In addition, as a mechanism for the appearance of the promoting effect, it was considered that the ionic environment in the dodecahydrate melt was destabilized due to the basic action of added anions, and the energy barrier for the nucleation was reduced.
