OPTIMUM EFFICIENCIES AND PHASE-CHANGE TEMPERATURES IN LATENT-HEAT STORAGE-SYSTEMS

This paper presents an analysis of a class of latent heat storage syst ems (LHSS). The analysis is based on a lumped model (the basic model) that allows a broad class of LHSSs to be completely specified, with on ly two parameters and a set of operating temperatures, while still ret aining the main thermodynamic aspects associated with its operation. C haracterization of the performance in this manner permits the broad ba se application potential of such systems to be viewed. This modeling i s in contrast to most studies to date, which employ many parameters to include details of specific systems, and therefore obscure, to a grea t extent, this broad-based application potential. The basic model is l ater modified in three ways to analyze operating conditions that eithe r occur in practical units or are desirable for an improved operation of the units. The modifications include, first the consideration of th e LHSS as being formed by many independent phase-change material (PCM) capsules. Second, the possibility of having PCMs with different phase change temperatures filling the capsules. Third, the case when the PC M melts over a temperature range. The results indicate that the effici ency of the basic model represents a higher bound for the efficient op eration of LHSSs with negligible sensible storage capacity, and a sing le PCM. Using multiple PCMs within a LHSS results in higher efficienci es. These efficiencies set higher bounds for efficiency of any sensibl e or latent heat storage system, and also represent the only possibili ty for reversible operation of LHSS.