Thermal Energy Storage Medium Research Articles

Influence of Different Melting Points of Phase Change Material on Photovoltaic Phase Change Materials System Performance: An Energy, Exergy, and Environmental Point of View

The photovoltaic (PV) module extracts and converts solar irradiation energy into electrical power in a sustainable and renewable manner. The substantial upswing in the temperature of the PV panel occurs while conversion predominantly impacts its performance and reduces efficiency. To resolve this issue, three different organic phase‐change materials (PCMs), OM29, OM35, and OM42, are proposed for cooling the PV panel as a thermal energy storage medium. The energy and exergy performance of PV panels with and without PCM are compared through experimental investigation to study the influence of different melting points of PCM with reference PV system (PVr). It is identified that the average PV panel temperature can be significantly reduced by incorporating PCM materials (OM29, OM35, and OM4), which are 12.7%, 21.53%, and 17.71% lower than the PVr system. The average electrical efficiencies of PV‐PCM–OM29, PV‐PCM–OM35, and PV‐PCM–OM42 are 10.96%, 10.77%, and 11.66%, which are 4.07%, 6.38%, and 4.91% higher than PVr system. Similarly, the average exergy efficiency is 4.62%, 5.06%, and 5.57% higher. The incorporation of PCM (OM29, OM35, and OM4) as a cooling mechanism effectively mitigates the CO2 3.70, 5.67, and 4.46 tons of CO2 throughout its lifetime and contributes to the sustainable development goal 7.

Predicting thermophysical properties of molten salts in the MgCl2-NaCl-KCl-LiCl system with a shell-model potential

Ternary eutectic salts composed of MgCl2, NaCl, and KCl, referred to as MNK salts, have recently emerged as promising candidates as high-temperature heat transfer fluids and thermal energy storage media. In this study, we performed classical molecular dynamics (MD) simulations to predict the densities, specific heat capacities, viscosities, and ionic self-diffusivities for MNK salts over a wide temperature range. The impact of LiCl additive on their thermophysical properties was also investigated. To capture the electronic polarization of Cl anions by neighboring cations, we developed a novel shell-model potential using the force-matching method and a dataset of ab initio calculated interatomic forces. Our extensive MD simulations predict structure and properties for pure salts and binary/ternary salt mixtures in the MgCl2-NaCl-KCl-LiCl system in overall good agreement with available experimental and theoretical data, which corroborates the accuracy and reliability of our developed potential.

Dynamic Modeling of a Concentrating Solar Thermal Plant With a Packed Bed Energy Storage

The Air-packed bed system is a cost-competitive concentrating solar thermal system that employs air as the heat transfer fluid and a solid packed bed as the thermal energy storage medium. The thermocline behavior of the packed bed plays an important role in the performance and operation of the system, so a dynamic model of the TES is needed to evaluate the design and performance of the system. A high-fidelity first-principle TES model is often too computationally expensive to incorporate into a larger system model for simulation and optimization at an annual time scale. Here, we develop in Modelica a system model for a CST concept plant with a reduced order TES model to ensure the necessary thermocline fidelity while maintaining suitable computational performance. The validity of the reduced order model is quantified both against simulation results from a first-principle finite-difference model and against real-world test data taken at the Heliogen Test Facility in Lancaster, CA. The thermocline fidelity and computational performance of the system model are then demonstrated with an annual simulation run of the concept air-packed bed plant.

Electrochemical impedance study of corrosion of pure Ni, Fe, Cr, and Fe‐5Cr alloy in molten nitrides

AbstractMolten nitrates or nitrate–nitrite mixtures have been used as heat transfer fluid as well as thermal energy storage medium in concentrated solar power plants and other industrial applications. However, containment materials in contact with these molten salts are subjected to molten salt corrosion, which has been a concern over the years. In this investigation, the corrosion behavior of pure Ni, Fe, Cr, and Fe‐5Cr alloy (in weight percent) has been examined at 400°C in molten nitrates using electrochemical impedance spectroscopy and gravimetric tests. It is shown that Ni, Fe, and Fe‐5Cr exhibit mass gain, with the best corrosion resistance for Ni followed by Fe‐5Cr and Fe, while pure Cr goes through fast dissolution, forming hexavalent chromium product K3Na(CrO4)2. The increase of salt basicity from Solar Salt to Hitec could accelerate the dissolution of Cr. Nevertheless, the formation of an inner Cr‐containing scale could still offer the alloy good protection because the external insoluble Ni or Fe oxides can protect it from dissolution.

Flexible insulating phase change composite film with improved thermal conductivity for wearable thermal management

Phase change materials (PCMs) are extensively employed as media for thermal energy storage and temperature regulation due to their remarkable capacity to absorb or release significant amounts of latent heat at constant phase transition temperatures. However, the inherent low thermal conductivity, solid-state rigidity and electric insulation issues of PCMs greatly limit their practical applications in the field of wearable thermal management of flexible electronic devices. Herein, we have developed a flexible composite PCM film with improved thermal conductivity by incorporating paraffin wax (PW) with a porous structure of polyvinylidene fluoride-boron nitride (PVDF-BN) film as a substrate. Remarkably, the composite film exhibits outstanding electric insulation properties and excellent cycle stability, further enhancing its suitability of thermal management in wearable electronics for safe and long-term applications. The obtained flexible composite PCM film exhibits a superior melting enthalpy of 105.63 J·g−1, along with a 200% improvement in thermal conductivity compared to the pure PW. Furthermore, this flexible composite film can not only retain its remarkable flexibility at room temperature but also demonstrate attractive shape recovery capabilities during phase transition process. The flexible insulating PCM film developed in this work may hold substantial promise for applications in the field of wearable thermal management for next-generation electronic devices.

Thermal Stability and Performance Evaluation of Hitec Molten Salt for High-Temperature Energy Storage Applications

The quest for advanced materials in thermal energy storage (TES) has become paramount in a world grappling with pressing demands for sustainable and reliable energy solutions. Among these materials, molten salts have emerged as up-and-coming contenders, owing to their exceptional thermal properties and wide operational temperature ranges. HITEC, a eutectic blend of sodium nitrate, sodium nitrite, and potassium nitrate, distinguishes itself as a superior choice due to its unique amalgamation of favorable thermal characteristics. This comprehensive review delves into the thermal properties of HITEC molten salt and its manifold applications in thermal energy storage, illuminating its potential as a pivotal element in addressing contemporary global challenges. The review examines HITEC's specific heat capacity, thermal conductivity, and thermal stability, presenting critical insights into its efficacy as a TES medium. Such comprehension fosters the advancement of Sustainable Development Goal 7. The article explores strides made in HITEC-based TES systems, underscoring inventive engineering approaches and burgeoning technologies that bolster progress towards Sustainable Development Goal 9. Furthermore, the article discusses challenges associated with HITEC molten salts, such as corrosion and material compatibility issues, and investigates ongoing research efforts to overcome these limitations. A comparative evaluation of HITEC with other molten salt mixtures elucidates its competitive advantages. This review consolidates knowledge about HITEC molten salt for thermal energy storage applications, providing valuable perspectives for researchers, engineers, and policymakers dedicated to advancing sustainable energy technologies. The review underscores the pivotal role of HITEC molten salt in advancing thermal energy storage technologies, directly influencing the achievement of several SDGs.

Graphene oxide – adipic acid nanocomposites for thermal energy storage: Assessment of thermophysical properties and energy storage performance

Adipic acid is one of the organic phase change materials with a melting temperature greater than 150 °C and a freezing point greater than 140 °C, making the same a suitable thermal energy storage medium for near-atmospheric pressure steam generation. This work attempts to alleviate the rate limitation posed by the lower thermal conductivity of adipic acid by adding graphene oxide (GO) nanostructures at lower concentrations such that the energy storage capacity is not severely affected. The resultant GO – adipic acid composites (0–2 wt% GO) were characterized in terms of latent heat for phase change, specific heat and thermal conductivity. The composite containing 1 wt% GO exhibited a 16 % enhancement in thermal conductivity with a 3.4 % reduction in latent heat and 3.6 % reduction in specific heat. The impact of GO addition on the solidification rate was remarkable, with a 44 % enhancement in overall heat transfer coefficient during the initial solidification phase, when solidification was carried out in thermal contact with a constant temperature heat transfer fluid (oil bath). Thus, the present work clearly demonstrates the intensification of heat transfer during the discharge cycle of a thermal energy system with 1 wt% GO-Adipic acid composite as the thermal energy storage medium.

Analysis of heat charging and release processes in cascade phase change materials energy storage floor heating systems: Performance evaluation

To address the issues of high energy consumption, significant temperature fluctuation and low heat release efficiency in conventional energy storage floor heating systems, this study proposes a novel solution known as the cascade energy storage floor heating system. This system incorporates two layers of phase change materials (PCMs) with distinct phase change temperatures as the thermal energy storage medium. A coupled heat transfer numerical model is developed to analyze the heat charging and release processes within the floor heating system. The evolutions of liquid fraction of PCMs, flow field and floor surface temperature are investigated during the heat charging and release processes. The findings demonstrate that the cascade PCM energy storage floor heating system avoids overheating and saves >19 % of energy consumption during the heat charging process, elevates the floor surface temperature by about 2 K during the late stage of heat release and thus reduces floor surface temperature fluctuation in comparison with the single-stage PCM system. These improvements are conducive to enhancing the energy utilization rate. Due to better synergistic solidification of the two PCM layers, the system with a PCM proportion of 1:1 exhibits superior overall heat release performance when compared to systems with PCM proportions of 1:2 or 2:1. The research outcomes provide a theoretical foundation and technical guidance for the practical implementation of cascade PCM energy storage technology in the field of building energy conservation.

Flexible and photo-responsive composite phase change materials for thermal therapy

The medical dressings with appropriate temperature can relieve body pain by promoting blood circulation. In order to endow the thermal compress dressings with multifunction and facilitate their application in different scenarios, the flexible films employing paraffin (PF) as thermal energy storage medium, styrene-ethylene/butylene-styrene (SEBS) triblock copolymer as matrix and graphene as photo-thermal conversion agents were fabricated. The film containing 77 wt% of PF has high latent heat of 157.26 J·g−1 and exhibits smooth and dense morphology. The film also exhibits tensile strain of 2576.75 %, photothermal conversion efficiency of 70.52 % and enviable self-healing properties, which makes it possible to meet the needs of different body parts and reuse in practical applications. In addition, under natural sunlight, the thickness of 3 mm thermal film can maintain the temperature ranging from 40 °C to 50 °C for more than 25 min; under the action of an electrically heated film, the film can maintain at 40 °C to 50 °C for about 22 min. The extraordinarily long thermal therapy time and suitable thermal therapy temperature are remarkable. In summary, the excellent thermal storage properties, mechanical properties, self-healing properties and photothermal conversion properties make it a good application prospect for thermal therapy.

Thermal stability and durability of solar salt-based nanofluids in concentrated solar power thermal energy storage: An approach from the effect of diverse metal alloys corrosion

Concentrated Solar Power (CSP) technology has witnessed substantial growth, with forecasts predicting an increase of 3.4 GW between 2019 and 2024. This expansion necessitates the installation of energy storage systems to meet the growing demand. Solar molten salts, specifically a mixture of 60 % NaNO3 and 40 % KNO3, have emerged as the primary thermal energy storage (TES) medium in commercial CSP plants. However, a significant challenge lies in the corrosive nature of molten salt at high temperatures, which poses limitations in TES applications. The literature has explored a promising solution: reducing corrosion rates by incorporating nanoparticles into molten salts, creating nanofluids. To assess the viability of nanofluids for CSP, it is essential to understand how they perform under working conditions, especially regarding their thermal stability and durability. This study presents further evidence of nanofluid interactions with component materials under static working conditions. Specifically, focus on the impact of corrosion products precipitated during corrosion tests on the physical and thermal properties of Solar Salt-based silica dioxide nanofluids. In this research, nanofluids in contact with stainless steel, nickel‑chromium alloy, and carbon steel were examined before and after subjecting them to a 90-day thermal exposure at 500 °C. These findings provide valuable data on key thermo-physical properties during service, contributing to the design of more precise TES systems and enhancing their overall efficiency and effectiveness.

Phase Change Materials Meet Microfluidic Encapsulation.

Improving the utilization of thermal energy is crucial in the world nowadays due to the high levels of energy consumption. One way to achieve this is to use phase change materials (PCMs) as thermal energy storage media, which can be used to regulate temperature or provide heating/cooling in various applications. However, PCMs have limitations like low thermal conductivity, leakage, and corrosion. To overcome these challenges, PCMs are encapsulated into microencapsulated phase change materials (MEPCMs) capsules/fibers. This encapsulation prevents PCMs from leakage and corrosion issues, and the microcapsules/fibers act as conduits for heat transfer, enabling efficient exchange between the PCM and its surroundings. Microfluidics-based MEPCMs have attracted intensive attention over the past decade due to the exquisite control over flow conditions and size of microcapsules. This review paper aims to provide an overview of the state-of-art progress in microfluidics-based encapsulation of PCMs. The principle and method of preparing MEPCM capsules/fibers using microfluidic technology are elaborated, followed by the analysis of their thermal and microstructure characteristics. Meanwhile, the applications of MEPCM in the fields of building energy conservation, textiles, military aviation, solar energy utilization, and bioengineering are summarized. Finally, the perspectives on MEPCM capsules/fibers are discussed.

Electrodeposited nickel coatings for exceptional corrosion mitigation in industrial grade molten chloride salts for concentrating solar power

Molten chloride salt eutectics are attractive candidates for use as thermal energy storage media and heat transfer fluids in generation-three concentrating solar thermal power (Gen3 CSP) plants. However, corrosion of alloys in molten chloride salts, especially at high temperatures, is an extremely challenging problem that studies focus on lower temperatures, shorter durations, or analytical grade, and high-purity, salts. To date, there has been no study on corrosion or corrosion mitigation in an industrial-grade salt at a high temperature such as 750 °C. To alleviate this knowledge gap, the study presents new multiscale fractal-textured Ni coatings on various alloy surfaces for effective corrosion mitigation at 750 °C in molten chloride salts. Using the electrodeposition method, durable double-layer textured coatings were formed on stainless steel alloys (SS316, SS310, and SS347) and In800H. The corrosion performance of the coatings is investigated in both analytical-grade purity and, for the first time, practically relevant industrial-grade chloride salts. Ni-coated ferrous alloys showed an exceptionally reduced corrosion rate in the range of 350–480 μm/y in analytical-grade salts, and between 450 and 490 μm/y in purified industrial-grade salts at 750 °C. Ni coatings on ferrous alloys reduced corrosion rates by as much as 70% compared to uncoated surfaces and were comparable to the expensive Ha230 alloy with a high Ni content. By the use of innovative fractal corrosion mitigation coatings, for the first time, low-cost structural alloys are rendered viable for use with industrial-grade chloride salts, which is profoundly beneficial in practical systems.

Corrosion behavior of Fe based container alloys in molten Na2CO3-K2CO3 as thermal energy storage medium for reversible solid oxide cells

In this work corrosion behavior of SUS 441, Crofer 22 APU and Canthal APM in molten Na2CO3-K2CO3 at 800 °C is studied. The 441 and APU corrode heavily as the element Cr in the steel is oxidized to NaCrO2. Cr diffuses along grain boundary preferentially and the molten salt penetrates through the corrosion layer. Several porous corrosion layers rich in Cr, O, Na or rich in Fe are formed alternatively on the APU surface. On the contrary, the APM alloy shows excellent corrosion resistance (0.02 mm/y) due to formation of a protective Al2O3 layer.

Comparative study on pentagonal pyramid (PPy) and tubular (Tub) solar stills with thermal energy storage (TES)

The solar stills are known for their application in desalting of saline water to produce potable water output. However, they have been characterized with their low production rate due to the limited availability of the solar insolation. In this work, the real-time examination was carried-out with two types of solar stills with different structural arrangement by using latent heat based thermal energy storage medium (LHTES). The first still was a pentagonal pyramid (PPy) still and the other one was a tubular (Tub) still. Both the stills were examined with and without the use of LHTES in actual ambient conditions in south India under a fixed water depth of 30 cm. In total, four configurations of stills were examined, namely, PPy without LHTES (PPy), Tub without LHTES (Tub), PPy with LHTES (PPy-LHTES), and Tub with LHTES (Tub-LHTES) for their potable water output. The results proved that the arrangements with LHTES had displayed the better water yield and Tub with LHTES yielded the best output among all the four arrangements.

Encapsulation of paraffin-magnetite, paraffin, and polyethylene glycol in concretes as thermal energy storage

These investigations analyze the encapsulation of phase change materials (PCMs): paraffin-magnetite composite, paraffin, and polyethylene glycol (PEG) in concretes. The research aimed to analyze PCMs as a thermal energy storage medium. The concretes were fabricated using the composition of lightweight aggregate, cement, sand, and water. Copper tubes (diameter of 12.7 mm and length of 50 mm) with various formations were installed in the concretes (50 × 50 × 50 mm). The arrangements of the copper tube consist of four-square, four-cross, and six-rectangular tubes. The concretes were then cured for 28 days at an ambient temperature. The copper tubes were filled with the melting paraffin-magnetite composite, paraffin, and PEG. The PCMs analyses include morphology, melting point, latent heat, thermal conductivity, and melting phase transition. The temperature distributions on the concretes filled with the PCMs were monitored using thermocouples and a data logger. The DSC test suggested the highest melting point of 61.65 °C and latent heat of 161.53 J/g obtained in the PEG sample. Adding magnetite particles in paraffin could improve the thermal conductivity to 0.53 W/m·°C compared to paraffin only (0.32 W/m·°C) and PEG (0.28 W/m·°C). The melting phase behavior on the PCMs was affected by the melting point, latent heat, and thermal conductivity. The highest thermal resistance occurred on the concrete where the copper tube only contributes to the low thermal resistance.

Experimental and numerical study on heat transfer and flow characteristics of molten salt nanofluids in spiral-wound tube heat exchanger

Molten salt is one of the most promising heat transfer and thermal energy storage medium for the third-generation solar thermal power generation, and the spiral-wound tube heat exchanger can improve the heat transfer performance of molten salt. In this paper, the flow and heat transfer characteristics of molten salt nanofluids in spiral-wound tubes are experimentally and numerically studied. Molten salt nanofluids and synthetic oil as the heat transfer fluids, the heat transfer performance of them in the spiral-wound tube heat exchanger were studied. The Wilson separation method was used to process the experimental data, and the heat transfer correlation of molten salt nanofluids is obtained through experiments. The heat transfer correlation can be in good agreement with the experimental data, the heat transfer correlation on the molten salt nanofluids side is Nu=0.3897Re0.4370Pr1/3, Re = 4296–8348, Pr = 13–23, and the maximum error is 17.9%. A three-dimensional model of the spiral-wound tube heat exchanger is used to explore the distribution of the pressure, temperature and velocity fields of the molten salt nanofluids. The friction factor correlation on the molten salt nanofluids side is f=4.6729Re−0.4855, Re = 3536–17684, Pr = 13–23 and the maximum error is 12.65%. The heat transfer correlation and resistance correlation of molten salt nanofluids obtained in this paper can contribute to the design of heat exchanger for the third-generation solar thermal power.

Experimental investigation of an indirect solar dryer with PCM-integrated solar collector as a thermal energy storage medium.

An indirect-type forced convection solar dryer implementing a phase-changing material (PCM) as the energy-storing medium was designed, fabricated, and investigated in this study. The effects of changing the mass flow rate on the valuable energy and thermal efficiencies were studied. The experimental results showed that the instantaneous and daily efficiencies of the indirect solar dryer (ISD) increased with the initial increase in mass flow rate, beyond which the change is not prominent both with and without using the PCM. The system consisted of a solar energy accumulator (solar air collector with a PCM cavity), a drying compartment, and a blower. The charging and discharging characteristics of the thermal energy storage unit were evaluated experimentally. It was found that after using PCM, drying air temperature was higher than ambient air temperature by 9-12 ℃ after sunset for 4h. Using PCM accelerated the process by which Cymbopogon citratus was effectively dried between 42 and 59°C of drying air. Energy and exergy analysis of the drying process was performed. The daily energy efficiency of the solar energy accumulator reached 35.8%, while the daily exergy efficiency reached 13.84%. The exergy efficiency of the drying chamber was in the range of 47-97%. A free energy source, a large reduction in drying time, a higher drying capacity, a decrease in mass losses, and improved product quality all contributed to the proposed solar dryer's high potential.

Experimental Investigation on Solar Water Heater Integrated with Thermal Battery Using Phase Change Material and Porous Media

Evacuated tube heat pipe solar collector as a passive solar water heating system is a simple, reliable, and cost-effective way to capture the sun’s thermal energy to supply hot water to homes. In the proposed system, the manifold is reshaped to a tank and filled with phase change materials (PCM) and porous media, which the PCM acts as a latent heat thermal energy storage medium. In order to increase the heat flux from the heat pipe to the PCM and overcome the low thermal conductivity of the PCM, porous media is used. The porous media is connected to the heat pipe condenser to collect the heat and distribute it uniformly throughout the PCM filling the pores. This design of the manifold acts as a heat storage tank or thermal battery. Another pipe in the tank transfers heat from the PCM to the water. Experiments were conducted in 2 modes: charging/discharging and periodic draw-off. The results demonstrated that this thermal battery design could provide homes with the hot water they require on sunny days, while it needs an auxiliary heater or larger solar collector to provide enough hot water on rainy/cloudy days. Considering the solar radiation fluctuation, the efficiency of the thermal battery is 50% ± 9.3%. The thermal battery can warm up the cold water higher than the operating temperature on a sunny day (more than 120 L per day at 38 °C). Using porous media provides better heat distribution in the PCM.

Shape-stable erythritol composite phase change materials with controlled latent heat release for spatiotemporally thermal energy utilization

Phase change materials (PCMs) have been extensively concerned recently as suitable medium for thermal energy storage due to their absorbing or releasing a large amount of latent heat in the phase change process. However, traditional PCMs usually crystallize spontaneously to release their latent heat in the cooling process, which greatly limits their practical application in thermal energy long-term storage and controllable release. Herein, we designed and synthesized a shape-stable erythritol (ERY)-based composite PCM with attractive performance of latent heat controlled storage and release using a facile aqueous fabrication route. In this composite, calcium ions cross-linked with sodium alginate is introduced to construct strong hydrogen bonding with ERY to increase the activation energy barrier for stabilizing supercooling, thus realizing long-term latent heat stored in supercooling state. The supercooled ERY composite can be maintained at room temperature for 50 days and subsequently controllably releases latent heat by thermal or mechanical trigger method. Meanwhile, the ERY composite exhibits excellent shape stability without any leakage over the phase change temperature. In addition, the crystallization enthalpy can reach 181.2 J/g, which can be maintained even after 80 thermal cycles, showing superior thermal energy storage capacity and repeatability. The crystallization kinetics study reveals that the crystallization mode of the ERY composite is three-dimensional growth spherical diffusion. This work provides an important strategy for the design and synthesis of shape-stable PCMs with controllable latent heat storage and release performance, which is of great prospect for the development of spatiotemporally thermal energy storage technology.

An Overview of the Molten Salt Nanofluids as Thermal Energy Storage Media

The research in the field of the nanofluids has experienced noticeable advances since its discovery two decades ago. These thermal fluids having minimal quantities of nano-scaled solid particles in suspension have great potential for thermal management purposes because of their superior thermophysical properties. The conventional water-based nanofluids have been extensively investigated so far with emphasis in their improved thermal conductivity. A novel class of nanofluids based on inorganic salts has been developed in the last few years with the goal of storing and transferring thermal energy under high temperatures. These molten salt-based nanofluids can in general be recognized by an enhanced specific heat due to the inclusion of the nanoparticles. However, it should be emphasized that this does not always happen since this thermophysical property depends on so many factors, including the nature of the molten salts, different preparation methods, and formation of the compressed layer and secondary nanostructures, among others, which will be thoroughly discussed in this work. This peculiar performance has caused a widespread open debate within the research community, which is currently trying to deal with the inconsistent and controversial findings, as well as attempting to overcome the lack of accurate theories and prediction models for the nanofluids in general. This review intends to present an extensive survey of the published scientific articles on the molten salt nanofluids. Other important realities concerning the development and thermal behavior of the molten salt nanofluids, such as the stability over time of the nanoparticles dispersed in the molten salts, latent heat, viscosity, and thermal conductivity, will be reviewed in the current work. Additionally, special focus will be given to concentrated solar power technology applications. Finally, the limitations and prospects of the molten salts nanofluids will be addressed and the main concluding remarks will be listed.