Fundamental understanding of the interfacial behavior of molten salt based nanofluids on solid surfaces

The main issues of molten salts in concentrated solar power plants are their poor thermophysical properties and corrosion issues. To improve their properties nanoparticles are doped in molten salts. These suspended particles have an effect not only on the thermal, but also other properties such as viscosity and wettability, the latter having often been overlooked. In this work molten nitrate salts are doped with amorphous SiO$_2$ and graphite particles. A series of contact angle measurements are conducted to study the effects of nanoparticle concentration, composition, particle geometry, temperature and surface type. A small fraction of nanoparticles leads to a shift of the transition from non-wetting to wetting at higher temperatures. Furthermore, wettability studies on different surfaces provide insights into the physiochemical mechanism of molten salt corrosion. Molecular Dynamics simulations of the nitrate salts-based silica nanofluids are also conducted. Novel interatomic parameters are calculated for the molten nitrate salts as well as the α-SiO$_2$ and are used to predict the wetting behavior of the molten NaNO$_3$ and KNO$_3$ and their mixtures with and without a-SiO$_2$ nanoparticles, in order to provide a better understanding of the wetting behavior of molten salt based nanofluids

An integrated machine learning and metaheuristic approach for advanced packed bed latent heat storage system design and optimization

To tackle the challenge of waste heat recovery in the industrial sector, this research presents a novel design and optimization framework for Packed Bed Latent Heat Storage Systems (PBLHS). This features a Deep Learning (DL) model, integrated with metaheuristic algorithms. The DL model was developed to predict PBLHS performance, trained using data generated from a validated Computational Fluid Dynamics (CFD) model. The model exhibited a high performance with an R2 value of 0.975 and a low Mean Absolute Percentage Error ( <9.14% ). To enhance the ML model's efficiency and optimized performance, various metaheuristic algorithms were explored. The Harmony Search algorithm emerged as the most effective through an early screening and underwent further refinement. The optimized algorithm demonstrated its capability by rapidly producing designs that showcased an improvement in total efficiency of up to 85% over available optimized experimental PBLHS designs. This research underscores the potential of ML-integrated approaches in laying the groundwork for generalized design frameworks for TES systems, offering efficient and effective solutions for waste heat recovery

A comprehensive material and experimental investigation of a packed bed latent heat storage system based on waste foundry sand

The EU's industrial sector discards about 18.9% of its energy as waste heat, much of which has the potential for recovery. This study addresses the challenge by focusing on the advancement of latent heat thermal energy storage (LHTES) using phase change materials (PCMs) encapsulated within industrial waste foundry sand (WFS). WFS, a problematic by-product, is repurposed as a supportive matrix for NaNO3 and solar salt PCMs, tailored for effective integration into high-temperature industrial processes. The paper provides a thorough mechanical and thermal examination of the WFS-salt PCMs, highlighting their improved thermal stability, performance, and compatibility with direct thermal energy systems. The composite PCMs demonstrated melting points well-suited for industrial waste heat applications and achieved an energy density of 542.0 ± 8.3 kJ/kg for NaNO3 and 516.0 ± 4.5 kJ/kg for solar salt, An experimental cascade PBLHS, based on these CPCMs, with a capacity of 262 MJ, designed to mimic an industrial heat source at 450 °C, was systematically tested to assess its energy density and efficiency over repeated charging/discharging and free cooling cycles. Its overall system efficiency is found to be 68.5%. These findings position WFS-salt PCMs as a promising and environmentally beneficial approach to enhance industrial energy efficiency and utilisation

From waste to value:Utilising waste foundry sand in thermal energy storage as a matrix material in composites

Waste foundry sand (WFS) is a by-product of the casting industry, which poses increasing economic and environmental issues due to the costs associated with landfill maintenance and stricter environmental regulations. This study proposes a novel solution for WFS as a material for thermal energy storage. The approach involves blending WFS with NaNO3 and a proprietary additive, X, to fabricate a composite phase change material (CPCM). The CPCM is found to be structurally stable up to 400 °C, and an optimal composition with a mass ratio of NaNO3:WFS:X = 0.6:0.3:0.1 is achieved. This composition yields an energy storage density of 628 ± 27 kJ/kg, and an average thermal conductivity of 1.38 W/mK over the temperature range of 25–400 °C. The CPCM also exhibits good mechanical strength and a low coefficient of thermal expansion compared to NaNO3. Currently, only a small portion of WFS is recycled, most commonly in building applications. The CPCM presented in this study has the potential for medium-to-high temperature heat storage in waste heat recovery applications, offering a sustainable solution for upcycling WFS.</p

Fabrication of superhydrophobic metallic porous surfaces <i>via </i>CO₂ and water processing

Superhydrophobic surfaces are of paramount importance for a great number of applications ranging from heat transfer to medicine. However, their mass production is challenging from environmental and scaling points of views. This work proposes a simple, scalable, production method for superhydrophobic surfaces and porous materials. In particular, highly hydrophobic CH2/CH3-grafted copper is achieved via exposure to a high-pressure supercritical CO2 +H2O environment. The hydrophobicity was further reinforced by using hierarchical macro- nanoporous copper prepared by a simple templating-annealing method reaching a water contact angle of ~ 150◦ . The grafting is found to be durable in terms of ageing, abrasion and water impact. The superhydrophobic porous material is successfully used to separate oil emulsions from water. Molecular dynamics simulations are employed to investigate the underlying superhydrophobicity mechanisms further. We hypothesise that the obtained grafting results from a CO2 hydrogenation reaction. The proposed approach may pave the way for the mass use of superhydrophobic surfaces and porous materials for anti-corrosion, anti-icing, separation, batteries, sensors, electronic materials, etc

Phosphogypsum-Paraffin Composites for Low Temperature Thermal Energy Storage Applications

Phoshpogypsum (PG) is an environmentally hazardous industrial by-product of the fertilizer industry with an annual production of 300 Mt, with a utilization rate of only 15%. In this work, we propose a novel use-case for PG. The latter is combined with a commercial-grade paraffin to fabricate composite phase change materials (CPCMs), for thermal energy storage applications. CPCMs are fabricated following a comminution and sintering process. The fabricated materials exhibit a stable latent heat (75 J/g) after 96 cycles (25 to 100 &deg;C), with a maximum average specific heat capacity of 1.54 J/gK at 60% paraffin content. The thermal conductivity is found to be 75% higher than pure paraffin, while the energy storage density is only 14% lower