ReviewReview on thermal energy storage with phase change: materials, heat transfer analysis and applications
Introduction
Thermal energy storage (TES) in general, and phase change materials in particular, have been a main topic in research for the last 20 years, but although the information is quantitatively enormous, it is also spread widely in the literature, and difficult to find.
The work described below falls within an area of international interest as it deals with energy saving, the efficient and rational use of available resources and the optimum use of renewable energies. Within this framework, TES provides solutions in very specific areas:
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The time delay and available power between production or availability of energy and its consumption in receiving systems (solar energy, cogeneration, etc.)
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Security of energy supply (hospitals, computer centres, etc.)
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Thermal inertia and thermal protection
In the first case, applications related with the use of renewable energies are common, in particular the use of solar energy among others, although applications are also found in cogeneration equipment or in installations with reduced prices for electrical energy consumed during off-peak hours. Nowadays, security of energy supply is often achieved with extra equipment. The use of phase change materials (PCMs) could either avoid or reduce this extra equipment. As it will be seen later in this paper, thermal inertia and thermal protection is the area where the PCMs have achieved a higher penetration in the market.
This paper provides a review of studies dealing with TES using phase change materials. The material in this review has been arranged within the main areas of work:
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Phase change materials
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Heat transfer analysis
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Applications
The first two areas cover the two fundamental aspects to be studied in a thermal storage system, the material and the heat-exchanger, as is shown in Fig. 1.
Section snippets
Classification
In 1983 Abhat [1] gave a useful classification of the substances used for TES, shown in Fig. 2.
Among the most thorough references related with phase change materials, one can cite Abhat [1], Lane [2], [3] and Dincer and Rosen [4]. These contain a complete review of the types of material which have been used, their classification, characteristics, advantages and disadvantages and the various experimental techniques used to determine the behaviour of these materials in melting and solidification.
Theory and simulation
As regards the thermal gradient, information about the analysis of irreversibilities and the application of the second principle of thermodynamics can be found in articles by Strub [65] and Bejan [97], and a whole review in Chapter 9 of Dincer and Rosen [4]. Studies of these latter authors show that the use of exergy is very important in developing a good understanding of the thermodynamic behaviour of TES systems, and for rationally assessing, comparing and improving their efficiencies. In
Applications
Table 10 lists some of the different applications found in the literature. It should be pointed out that Dincer and Rosen [4] give a wide overview of different latent TES, cold TES and seasonal storage systems.
These applications can be divided into two main groups: thermal protection or inertia, and storage. One difference between these two substantial fields of application relates to the thermal conductivity of the substance. In some cases of thermal protection it is appropriate to have low
Summary
A review of TES using solid–liquid phase change has been carried out. The information obtained is presented divided into three parts: materials, heat transfer and applications. Materials used by researchers as potencial PCMs are described, together with their thermophysical properties. Commercial PCMs have also been listed. Different methods of thermal properties determination can be found. Problems in long term stability of the materials and their encapsulation are discussed. Heat transfer is
Acknowledgements
This paper was partially sponsored by the project P048/2000 of the Comunidad de Aragón, Spain.
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