We have been studying new organic hydrate phase change materials. It is well known that trimethylolehane (TME) has a soild-soild phase transition temperature of 81℃. Also,it generages a tetrahydrate compound. We found that its phase transition temperature could be controlled between 13℃ and 30℃ by adding small amounts of urea. This temperature s very suitable for use in air conditioning systems, passive solar systems, etc. We investigated its thermal properties and thermaldurabilities using a differential scanning calorimeter (DSC) and liquid chromatography (HPLC).
The melting point of PCM30 (the weight ratio was optimized on the basis of TME tetrahydrate) was 29.8℃ ,but phase-separation behavior was observed during heating-cooling cycles. The phase transition temperature of PCM30 decreased with the increasing addition of urea, and the final phase transition temperature was 13℃(PCM13).The durabilities of PCM30 and PCM13 were evaluated in a stainless steel (USU) sealed container. PCM30 was very stable in spite of its exposure to high temperature. On the other hand, PCM13 decomposed at the higher temperatures and the urea component changed to ammonia gas. However, at low temperatures of less than 25℃, the durability of PCM13 determined by kinetic calculations in the SUS sealed container was high enough for use as a latent heat storage material, even when it it is used for a long time. We found that the TME/water/urea mixture has a hign potential as a latent heat storage material when used for air conditioning systems and so on.