Cascaded phase change materials in a packed bed thermal energy storage system: effect and solutions of filling void ratio with sensible heat materials

• Main Authors: Khor, Jun Onn, Romagnoli, Alessandro
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Conference or Workshop Item
• Language: English
• Published: 2021
• Subjects: Engineering::Environmental engineering; Engineering::Mechanical engineering; Thermal Energy Storage; Phase Change Material; Sensible Heat Storage; Void Ratio; Packed Bed; Cascaded Storage; Encapsulation Size; Storage Capacity
• Online Access: https://www.dubrovnik2019.sdewes.org/; https://hdl.handle.net/10356/152485
• Institution: Nanyang Technological University

In this paper, packed bed thermal energy storage consisting of three phase change materials cascaded in series is investigated. Phase change materials are macro-encapsulated in capsules with diameter ranged from 50 mm to 100 mm and placed in thermal storage tank with internal diameter of 1 m. With such encapsulation size, void ratios between 0.45 and 0.51 are recorded, depending on the diameter ratio of the tank internal diameter to the encapsulation outer diameter. Such void space contributes to no energy storage and wastes the volume of thermal storage tank. For packing of particles with two different sizes in a cylindrical tank, void ratio of as low as 0.20 has been recorded experimentally. Such concept is tested in this paper in which sensible heat thermal storage material with much smaller size is used to fill the void space in a macro-encapsulated phase change material thermal storage system to reduce the void ratio. Parametric analyses are then carried out based on (1) encapsulation size of the phase change materials, (2) updated void ratio of system after filling with sensible heat material and (3) phase change material storage capacity. Compared to the baseline case, cyclic efficiency of a thermal storage system increases by ≈ 13.5% with thermal storage capacity increase from 10 to 30 kWh, increases by ≈ 9.6% with reduction of encapsulation size from 100 mm to 50 mm (diameter ratio increases from 10 to 20) and increases by ≈ 13.2% if void ratio is reduced with solid sensible heat material to 0.30 and subsequently filled with heat transfer fluid. For the best case simulated (optimized with all three parameters), cyclic efficiency increases by ≈ 21.9% compared to the baseline case.