Phase change materials are potentially able to store significant amounts of heat energy at almost constant temperatures, especially during the melting and freezing process. These materials enable us to design the individual thermal energy storage systems (TESS). However, several methods have been proposed to solve low thermal conductivity of PCMs, one of which is encapsulating the material in a heat-conducting membrane. In this research, non-welded steel capsules with unique sealing have been

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... nipulated. A Hermetic-Sealed Chamber is fabricated to investigate the heat transfer from a hot fluid to PCMs. The hot fluid is circulated through the spiral coil and Encapsulated PCMs are embedded in shell side. In two different test, static water and trapped air as intermediate fluids are used between the interior system's wall and the cylindrical capsules. The results show that during the heat storage period, combined heat transfer mechanism and mostly through radiation has played a pivotal role when using trapped air. On the other hand, in different flow regimes, a comparison between the total heat transfer coefficients of different tests show that in trapped air condition (Test 2), values of coefficients are almost 1 to 3 times greater than when the water is used (Test 1). Therefore, by considering case of trapped air and integrating this study with solar technologies as a heat source of hot fluid is an excellent way for building energy at any geographical locations.