Evaluation of Formate Salt PCM’s for Latent Heat Thermal Energy Storage

Samuel Gage,Craig Turchi,Prashant Sharan,Judy Netter

doi:10.3390/en14030765

Samuel Gage, Craig Turchi + Show 2 more

Open Access

https://doi.org/10.3390/en14030765

Copy DOI

Abstract

This work examines formate salts as potential phase change materials (PCMs) for middle-high temperature (≤250 °C) latent heat thermal energy storage applications. The thermophysical properties of three formate salts were characterized: pure sodium formate and binary blends of sodium/potassium formate and sodium/calcium formate. The stability of formate PCM’s was evaluated by thermal cycling using differential scanning calorimetry where sodium formate and sodium/potassium formate appeared stable over 600 cycles, while sodium/calcium formate exhibited a monotonic decrease in heat of fusion over the test period. A longer test with sodium formate led to gas release and decomposition of the salt. FTIR analysis of the PCM showed degradation of formate to oxalate. T-history experiments with 50-g PCM quantities demonstrated a bulk supercooling of only 2–3 °C for these salts. Thermal conductivity enhancement of over 700% was achieved by embedding aluminum in the solid PCM. Finally, mild carbon steel was immersed in molten sodium formate for up to 2000 h. Sodium formate was found to be non-corrosive, as calculated by mass loss and confirmed by cross-sectional high-resolution microscopy. FTIR analysis of the PCM after 2000 h shows oxidation at the free surface, while the bulk PCM remained unchanged, further indicating a need to protect the formate from atmospheric exposure when used as a PCM.

Highlights

Industry is a major source of global carbon emissions and accounts for nearly 30% of the world’s annual energy consumption
A recent study found that while 90% of industrial process heat is currently provided by fossil fuels, over 50% of heat demand is for temperatures of 300 ◦ C or below [1]
The absolute latent heat of fusion was measured for each formate phase change materials (PCMs) (Table 1)

Summary

Introduction

Industry is a major source of global carbon emissions and accounts for nearly 30% of the world’s annual energy consumption. Fossil fuel demand is often driven by the need for industrial process heat. A recent study found that while 90% of industrial process heat is currently provided by fossil fuels, over 50% of heat demand is for temperatures of 300 ◦ C or below [1]. Solar thermal technology offers industry a more sustainable alternative thermal source, which may significantly reduce carbon emissions. Solar thermal energy is often associated with electricity generation using high temperature concentrating solar power (CSP). Solar thermal energy for industrial process heat can be a much simpler and cheaper process compared to electricity production, as the heat can be efficiently utilized without heat-to-electricity conversion losses associated with electricity generation [2]

Methods

Results

Conclusion