Thermal Stability of Nitrate-Based Form-Stable Thermal Storage Materials with In Situ Optical Monitoring

Abstract

Thermal energy storage (TES) is a developing technology with promising applications in renewable energy and waste heat recovery. In this study, we investigate the thermal stability of recently developed nitrate-based form-stable TES materials. Laser-induced breakdown spectroscopy (LIBS) is applied to monitor the release of the Na and K elements in nitrates through chemical decomposition exposing to a simulated high heat flow field, while morphology and thermal performance are characterized by typical ex situ methods. The results reveal that the compatibility between ceramic skeleton materials (SiO 2 and MgO) and phase-change materials (NaNO 3 and KNO 3 ) plays an important role in the thermal performance of composite phase-change materials (CPCMs). A one-step thermal decomposition reaction of SS (sodium nitrate and silicon dioxide composite) and PS (potassium nitrate and silicon dioxide composite) and a two-step decomposition of SM (sodium nitrate and magnesium oxide composite) and PM (potassium nitrate and magnesium oxide composite) are demonstrated by synchronous thermal analysis (STA). The onset temperature of decomposition (OTD) obtained from in situ LIBS measurements is significantly lower than that obtained from STA.

Novel Segmental Model for Predicting Bed-to-Tube Heat Transfer Coefficient in Gas–Solid Fluidized Beds

“…A mixture of 60 wt % sodium nitrate (NaNO 3 ) and 40 wt % potassium nitrate (KNO 3 ), known as solar salt, 2 is commonly used as the HTF and sensible thermal storage material in existing commercial demonstration CSP plants. However, the performance of the solar salt can degrade under the action of heat beyond its normal temperature range (230−581 °C), 3 which excludes it from the list of candidate HTFs for nextgeneration CSP technologies. Although supercritical carbon dioxide (sCO 2 ) 4 and liquid metals 5 pose little risk of thermal decomposition at target temperatures, the problem of the high cost of materials and equipment has not been effectively solved, which restricts their practical application.…”