Calcium Chloride Hexahydrate/Diatomite/Paraffin as Composite Shape-Stabilized Phase-Change Material for Thermal Energy Storage

Abstract

In this work, the calcium chloride hexahydrate/diatomite/paraffin composite phase-change material (PCM) was fabricated by impregnating calcium chloride hexahydrate into diatomite and further coating with paraffin. Scanning electron microscope (SEM) results showed that the hydrated salt could be impregnated into a diatomite well and the paraffin could be coated on a diatomite surface. The Fourier transform infrared spectroscopy (FT−IR) demonstrated that no chemical interactions were found between calcium chloride hexahydrate and diatomite matrix except that of hydrogen bonds. The melting and crystallizing enthalpy of the coated composite PCM are 108.2 and 98.5 J/g, respectively. The supercooling of hydrated salts was weakened due to the nucleation positions on the huge surface of diatomite and the coating effect of the paraffin, and phase segregation was eliminated in 100 cycles by microvolume effect in the pores of the diatomite. Additionally, coated composite PCM and composite PCM exhibited better thermal stability and reliability than hydrated salts due to the interactions of hydrated bonds, the capillary force and the surface tension as well as the coating of the paraffin. After the 100 cycles, the melting and crystallizing enthalpy of coated composite PCM declined to 106.2 and 93.8 J/g from 108.2 and 98.5 J/g, dropping by 1.8% and 4.8%, respectively. The coated composite PCM with well thermal properties, thermal reliability, and chemical stability was a promising PCM candidate for heat-energy storage applications.

Development of a new methodology for validating thermal storage media: Application to phase change materials

“…Chemical degradation of PCMs is reported in several papers under the name of thermal stability studies . In all of them, TGAs are performed under inert atmosphere (N 2 or Ar) at a single heating rate (normally 10°C/min) in order to obtain the temperature limit for the beginning of PCM degradation.…”

“…According to this review, most tested PCMs are intended for storage applications at temperatures below 100°C. Those PCMs include pure substances, eutectic mixtures, and composites that undergo either solid‐liquid or solid‐solid phase transitions. In contrast, only few stability studies have been found for PCMs intended to temperature applications above 100°C.…”

“…In order to perform cycling tests, some authors used differential scanning calorimetry (DSC), whereas the majority used set‐ups adapted and/or designed on purpose. Those set‐ups included thermostatic chambers, thermal water baths, electric hot plates with temperature control, weathering chambers, ovens with controlled heating, and, in few cases, also with a cooling control .…”

Preparation and performances of palmitic acid/diatomite form‐stable composite phase change materials

“…In recent years, with the aim to avoid leakage, researchers have developed various methods to encapsulate PCMs, such as direct adsorption, capsulation, and sol‐gel method . The direct adsorption method is commonly to use porous materials as carriers, such as expanded graphite, perlite, montmorillonite, bentonite, and diatomite .…”

Modification on hydrated salt‐based phase change composites with carbon fillers for electronic thermal management

“…There into, inorganic PCM have some attractive properties such as larger latent heat density, higher heat conductivity, and lower material cost compared with organics. However, phase separation and supercooling are two severe problems of hydrated salts for technical application . The conventional methods to solve above problems are utilization of thickening and nucleating agents .…”