Such pcm have an advantage due to minimal containment

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entropy as one of the states has a high disorder quite like the liquid state. Such PCM have an advantage due to minimal containment requirements. Solid to liquid transformations include storage in salt hydrates, and employ certain inorganic salts, which are soluble in water and form crystalline salt hydrates. Any latent heat thermal energy storage system should have at least following three components; i. a PCM in the desired temperature range ii. container for holding the PCM iii. a suitable heat exchanger for transferring the heat from the heat source to PCM and then from PCM to the working fluid or required point of use Latent heat storage systems are more expensive that the sensible heat storage materials, viz., water and rocks. The PCMs undergo solidification and cannot generally be used as heat transfer media in a solar collector system. Thus a separate heat transport medium is required, with a heat exchanger in between. Many PCMs have poor thermal conductivity; others are corrosive and require special containers. Due to the high cost of latent heat storage these systems are usually used only when; high energy density or high volumetric energy capacity is desired, the load is such that energy is required at a constant temperature or within a small range of temperature, and the storage size is small.
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22 3.13 Solar Thermal Applications (Quantitative analysis) Solar energy as thermal energy has several applications. The common applications in use are listed below; 1. water heating 6. space cooling and refrigeration 2. space heating 7. power generation and 3. distillation 8. solar pond 4. drying 5. cooking For each application, a variety of systems in use are described. A few numerical examples are also solved to show how systems can be approximately sized or alternatively how the performance of installed systems can be estimated. It may be noted that most of the above applications use one or more of the devices described in Sec. 3.2.1. It may also be noted that applications 1 to 5 use the heat energy collected from solar radiation directly, while applications 6 to 8 use the collected heat in thermodynamic cycles to obtain cooling in one case and work in the other. From an economic stand-point, applications which use the collected heat directly are obviously more attractive. 3.13.1 Water Heating Solar water heating is one of the most attractive solar thermal applications from an economic standpoint. In many countries of the world, it is already competing on equal terms with systems using other energy sources. In India, a large number of systems have been installed. Most of the systems use flat- plate collectors. It is cumulatively estimated that the total area of the flat-plate collectors in the systems installed in India till June 2006 is about 1.5 × 10 6 m 2 . The hot water is used for domestic purposes or for meeting the needs of industries and commercial establishments.
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