High temperature calorimetry and use of magnesium chloride for thermal energy storage

摘要

The primary objective of this study is to develop encapsulated phase change materials (EPCMs) capable of storing thermal energy at temperatures above 750 ℃. EPCM with magnesium chloride as phase change material (PCM) are considered here for application in concentrated solar power (CSP) systems. MgCl_2 is an effective storage medium because of its high melting temperature, 714 ℃, and high latent heat of fusion, 454 kJ/kg. A specialized calorimeter with requisite size and high temperature capability is designed and built to prove the storage capability of MgCl_2 EPCM. The calorimeter is also used to determine heat capacities for MgCl_2 in both liquid and solid states as well as its latent heat of fusion. Calorimetric tests for the thermal storage capacities of three MgCl_2 EPCM samples show excellent agreement with published data. Based on the measured properties, the latent heat of phase change can contribute about 84% of the storage capacity of MgCl_2 PCM for a 100 ℃ temperature swing bracketing the salt's melting point. Repeated thermal-cycles show sustained performance of MgCl_2 EPCM capsules with no discernible diminishment in storage capacity.