Numerical and experimental studies on heat transfer characteristics of thermal energy storage system packed with molten salt PCM capsules

摘要

In order to avoid intermittent energy supply problems, thermal energy storage system plays an important role in concentrated solar power plants. Thus, a significant focus has been given on the improvement of thermal energy storage systems from the past few decades. In this paper, the dynamic thermal performance of high temperature latent thermal energy storage system packed with spherical capsules is analyzed experimentally and numerically. The spherical capsules are encapsulated by sodium nitrate and air is used as heat transfer fluid. Transient two-dimensional continuous solid phase and effective packed bed models are developed and validated by comparing to the experimental results. Using these models, detailed characteristics of the heat transfer between the capsules and heat transfer fluid are analyzed. Parametric analyses are conducted to study the influence of mass flow rate, Stefan number, thickness and the thermal conductivity of the shell. The results indicate that the Stefan number plays a vital role on the total heat storage capacity due to sensible heat, and the shell properties of the capsule significantly influence the thermal performance of the system; the influence of the shell thickness increases (decreases) when the thermal conductivity of the shell is low (high). (C) 2015 Elsevier Ltd. All rights reserved.