Thermal properties of organic latent cold storage materials

Abstract

The thermal properties of organic compounds intended to be applied as latent cold storage substances were investigated by methods of analysis according to Tammann, and by DTA and DSC. Findings were made concerning the melting and solidification behaviour, subcooling, specific melting enthalpies and specific heat capacities of paraffin mixtures, low and high-molecular glycols, ethylenediamine hydrates and formamide. Ethylenediamines and ethylene glycol, with high storage densities of 200-300 MJ.m -3, appear to be promising cold storage substances if subcooling is reduced. Through the use of congruently melting lowmolecular glycols and formamide, storage densities of about 170 MJ "m-are obtained. Paraffin mixtures and hi_g3h-molecular glycols melt in wide ranges of temperatures and give values of about I00 MJ -m-, which are not relevant to cold storage units.At present, energy storing systems based on melting and solidification or lattice transformation processes, also called latent storage units, have been developed for a temperature range of about 0-1500 ~ [1]. The application of latent cold storage units in the fields of room air conditioning, cooling and frost protection has been achieved for conditions below room temperature. Especially mixtures of salt and water, paraffins, glycols, amines and clathrates with high specific melting enthalpies, inexpensive ness and ready availability are considered as cold storing substances. Among these substances, attention has so far been paid only to the salt-water systems. The relevant data on the substances which are required for the development of storage systems are essentially known in the literature [2][3][4][5]. In contrast, there is only incomplete information on organic latent cold storage substances. There is some knowledge of the thermoanalytical behaviour of nalkanes and paraffin fractions [4,[6][7][8], caprylic, acrylic and acetic acids [6,[8][9][10], polyethylene glycols [9,11,12] and some substance combinations such as ethylenediamine with dimethyl sulphoxide [13].