| Solar energy is receiving a lot of attention now since it is a clean, renewable, and sustainable energy. Solar energy is used for space heating, power generation and other applications. A major limitation however is that it is available for only about 2,000 hours a year in many places. Therefore it is critical to find ways to store solar thermal energy for the off hours. Sensible heat of material has been used for storing thermal energy but due to material properties this type of thermal storage has limitations. Using encapsulated phase change materials is potentially a better way to store thermal energy. The present work deals with certain aspects of storing solar thermal energy in high temperature phase change materials with melting points above 400°C. The objective is the storage large amounts solar energy systems (∼2,400 MWh). Here two kinds of encapsulated particles are considered; Zinc encapsulated in Nickel and eutectic salt mixtures (72.2 mole% NaCl and 27.8 mole% MgCl2) in stainless steel encapsulation. Diffusion and phase change computations are reported here in the form of temperature profiles of the phase changing and encapsulated materials for spherical pellets. The time for heating and melting Zinc is significantly shorter than the storage times of several hours. Most calculations lend themselves to lumped capacitance method except for salt mixtures exposed to liquid heating/cooling that have large Biot numbers. As per expectations, the time for heat transfer is much shorter for liquid heat transfer media compared to those for gases. |
