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Optimization of thermal performance in thermocline tank thermal energy storage system with the multilayered PCM(s) for CSP tower plants

Elfeky, K.E., Li, Xinyi, Ahmed, N., Lu, Lin, Wang, Qiuwang
Applied energy 2019 v.243 pp. 175-190
equations, heat transfer, latent heat, mathematical models, melting, melting point, solar energy, temperature, thermal energy
The current paper presents two parametric studies (inverse Stefan number and dimensionless temperature difference) to optimize the values of latent heat and melting temperature of multilayered phase change materials (MLPCM(s)) in thermocline tank for concentrating solar power (CSP) plants. Spherical capsules filled with PCM(s) of different thermo-physical properties are used to fill the bed region, and the molten salt is used as heat transfer fluid (HTF). The numerical model that has been developed uses the Dispersion-Concentric (D-C) equations. By using MATLAB, the governing equations are solved and validated against the experimental results. The results show that in the optimal configuration of the case (B), the values of InvSte number and dimensionless temperature (θm) are equal to 1.2 and 0.8 for the top PCM layer, respectively; 0.75 and 0.55 for the middle PCM layer, respectively; and 0.65 and 0.3 for the bottom PCM layer, respectively. Moreover, it is also found that to obtain the best design and distribution of temperature for a thermocline tank consisting of three layers of PCM, the top PCM layer should melts by ΔT = 55.4 °C below the HTF charging inlet temperature, the PCM layer at the bottom should solidifies by ΔT = 83.1 °C above HTF discharging inlet temperature.