Potential Phase Change Materials Research Articles

Thermal Energy Storage Using Phase Change Materials in High-Temperature Industrial Applications: Multi-Criteria Selection of the Adequate Material.

Thermal energy storage (TES) plays an important role in industrial applications with intermittent generation of thermal energy. In particular, the implementation of latent heat thermal energy storage (LHTES) technology in industrial thermal processes has shown promising results, significantly reducing sensible heat losses. However, in order to implement this technology, a proper selection of materials is important. In this study, a new multi-criteria phase change material (PCM) selection methodology is presented, which considers relevant factors from an application and material handling point of view, such as hygroscopicity, metal compatibility (corrosion), level hazard, cost, and thermal and atmospheric stability. The methodology starts after setting up the system requirements where the PCM will be used, then a material screening is able to find all possible candidates that are listed with all available properties as listed before. Then, a color map is produced, with a qualitative assessment of material properties drawbacks, hazard level, melting enthalpy, and price. The experimentation starts with a preliminary set of tests on hygroscopicity and one-week corrosion test, which allows disregarding PCMs and selecting a short list of potential PCMs that would need further characterization before the final selection.

Indium-Mediated Acyloxyallylation-Based Synthesis of Galacto-Configured Higher-Carbon Sugar Alcohols as Potential Phase Change Materials.

Sugar alcohols fulfilling specific structural requirements are a substance class with great potential as organic phase change materials (PCMs). Within this work, we demonstrate the indium-mediated acyloxyallylation (IMA) as a useful strategy for the synthesis of higher-carbon sugar alcohols of the galacto-family featuring all hydroxyl groups in a 1,3-anti-relationship with three major synthetic achievements: first, the dihydroxylation of the IMA-derived allylic sugar derivates was systematically studied in terms of diastereoselectivity, revealing a high degree of substrate control toward anti-addition. Second, we demonstrated the use of a "double Mitsunobu" reaction, inverting the stereochemistry of terminal diols. Third, the IMA toolbox was expanded to accomplish the synthesis of derivatives with up to 10 carbon atoms from particularly unreactive aldoses. Thermal investigations of all synthesized sugar alcohols, including examples with exclusive 1,3-anti- and suboptimal 1,3-syn-relationships as well as even and odd numbers of carbon atoms, were performed. We observed clear trends in melting points and thermal storage densities and discovered limitations of organic substances in this class with melting points above 240 °C as PCMs in terms of thermal stability. With our study, we provide insights into the dependence of thermal properties on structural features, thus contributing to further understanding of organic PCMs for thermal energy storage applications.

Design and Construction of a Rapid Milk Chiller Using Cold Energy Storage System in the Context of Bangladesh

Milk is a highly sensitive product that must be collected and cooled within a few hours to reduce losses due to chemical spoilage and to preserve quality. As milk production is often remote from markets and processing facilities, milk chillers using thermal energy storage (TES) units provide the means for preserving quality through chilling during a power cut and hygienic storage before onward transportation to processing facilities and operation of the chiller at maximum thermal efficiency. This study gives an overview of thermal energy storage (TES) base rapid milk chiller. A review of TES for cold storage applications utilizing solid-liquid phase change materials has been done. Various perspectives were focused on the different stages of the work: phase change materials (PCMs), exemplification, improvement in exchange of heat, and the impact of the whole process on the quality of the milk Materials used as potential PCMs by specialists at low temperatures (less than 4 °C) are condensed and a portion of their thermo-physical properties are accounted for. The concept of planning and measuring procedures based on the determined load profile for structure day is introduced. In this design of a milk chilling unit using thermal energy storage, two cycles have been combined to get the desired cooling temperature. One is the vapor compression cycle, which can also be called the ice storage cycle. Another one is the milk chilling cycle. The main purpose of the milk chilling cycle is to keep the milk temperature between 2°C to 4°C. The comparison of using cold water with ethylene glycol (PCM) as a storage source of refrigeration for the milk cooling process based on the compressor capacity, ice storage box volume, and power consumed at the variable of cooling load is presented. Also, the effect of using cold storage to reduce the refrigeration capacity and energy saving is presented. The time duration of the milk chiller’s capacity to keep a specific amount (20 liters) of milk cool has been calculated to determine the variance and efficiency of the system compared to other milk chilling processes. Some suggestions concerning the planning of milk chiller hardware are given. Unique consideration was paid to the examination of explicit highlights of heat transfer phenomena in ice storage boxes including the appraisal of the length and the rate of ice arrangement and dissolution. The approach of estimating parts of the ice storage capacity framework incorporated into the milk chilling framework arranged in hot, wet, and dry atmospheres is exhibited. In light of the hourly cooling burden figuring that was completed utilizing Carrier’s Hourly Analysis Program, estimating the ice thermal capacity framework for various working procedures including full, chiller priority, and ice priority storage tasks for the design are displayed. At last, an examination of some operational qualities of the framework is broken down.

Investigation of the intermolecular origins of high and low heats of fusion in azolium salt phase change materials for thermal energy storage

Azolium salts are potential intermediate-temperature phase change materials. Crystallographic analysis shows that H-bonding along with other intermolecular interactions strongly influence the melting enthalpy of azolium salts.

The synthesis of higher-carbon sugar alcohols via indium-mediated acyloxyallylation as potential phase change materials

AbstractIn recent years, sugar alcohols have gained significant attention as organic phase change materials (PCMs) for thermal energy storage due to their comparably high thermal storage densities up to 350 J/g. In a computational study, outstandingly high values of up to ~ 450500 J/g have been postulated for specific higher-carbon sugar alcohols. These optimized structures feature an even number of carbon atoms in the backbone and a stereochemical configuration in which all hydroxyl groups are in an 1,3-anti-relationship, as found in the natural hexitol d-mannitol. However, these manno-configured higher-carbon sugar alcohols have not been experimentally investigated as PCMs yet and described synthetic routes are elaborate multiple steps syntheses. Therefore, we aimed to synthesize sugar alcohols of the manno-series with a concise synthetic protocol based on the indium-mediated acyloxyallylation (IMA) of aldoses. En route the C2-epimers were easily accessible, namely gluco-configured sugar alcohols, bearing one set of hydroxyl groups in a suboptimal 1,3-syn-realtionship. The synthesized compounds were found to possess thermal properties consistent with the predicted values, and the “perfect” higher-carbon sugar alcohol with eight carbon atoms was found to have indeed an outstanding high latent heat of fusion of ~ 380 J/g with a melting point of 260 °C. Graphical abstract

Ionenes as Potential Phase Change Materials with Self-Healing Behavior.

Ionenes are poly(ionic liquids) (PILs) comprising a polymer backbone with ionic groups along the structure. Ionenes as solid-solid phase change materials are a recent research field, and some studies have demonstrated their potential in thermal dissipation into electronic devices. Eight ionenes obtained through Menshutkin reactions were synthesized and characterized. The analysis of the thermal tests allowed understanding of how the thermal properties of the polymers depend on the aliphatic nature of the dihalogenated monomer and the carbon chain length. The TGA studies concluded that the ionenes were thermally stable with T10% above 420 °C. The DSC tests showed that the prepared ionenes presented solid-solid transitions, and no melting temperature was appreciated, which rules out the possibility of solid-liquid transitions. All ionenes were soluble in common polar aprotic solvents. The hydrophilicity of the synthesized ionenes was studied by the contact angle method, and their total surface energy was calculated. Self-healing behavior was preliminarily explored using a selected sample. Our studies show that the prepared ionenes exhibit properties that make them potential candidates for applications as solid-solid phase change materials.

Characterisation of erythritol as a potential phase change material

ABSTRACT Erythritol ((2 R,3S)-Butane-1,2,3,4-tetrol) is being considered as a phase change material (PCM) of interest owing to its potential applicability for solar thermal applications. But however, lack of inclusive material characterisation outcomes drives the need to bridge this research gap. In this study, erythritol was subjected to both chemical and thermal characterisation investigations. X-ray diffractometry (XRD) investigation estimated the degree of crystallinity to be 73.48% and the crystallite size to be 38.79 nm. The fourier transform infrared spectroscopy (FT-IR) investigation has identified -OH, -C-H and -CH2 to be the major functional groups. The scanning electron microscopy (SEM) investigation visualised the crystalline architecture of the PCM. The energy dispersive x-ray spectroscopy (EDAX) investigation quantified the composition of C and O in the eclectic constituency. The UV-visible spectrophotometry investigations confirmed that erythritol could be utilised for direct solar thermal applications. The thermal characterisation investigations rendered the latent heat of the PCM to be 333.48 kJ kg −1 and its peak melting temperature to be 118.18°C. The thermal stability investigations estimated the latent heat loss per cycle to be 1.1451 kJ kg −1.

Thermal analysis of phase change materials storage in solar concenter

Thermal analysis of high-temperature phase change materials (PCM) is conducted with the consideration of a 20% void and buoyancy-driven convection in a stainless-steel capsule. The effects of the thermal expansion and the volume expansion due to phase change on the energy storage and retrieval process are explored. The used water to fill the void between two different wax paraffin and stearic acid spheres is considered as a potential PCM for concentrated solar power. The charging/discharging process into and from the capsule wall is simulated under different boundary conditions for laminar and turbulent flows. Computational models are conducted by applying an enthalpy-porosity method and volume of fluid method to calculate the transport phenomena within the PCM capsule, including an internal air void. A simplified two-dimensional model of the PCM contained within the spheres is constructed and thermal analyses are performed for the transition from solid to liquid states. Simulated charging process modes are compared with the theory. According to experiments, the temperature distributions from 40-60 mm without and with 60 mm with copper fin have different behavior. The paraffin takes less time than stearic acid for total transformation at a rate of 0.5. The size of the sphere increases over the amount of time and the phase of the sphere to complete changes as stearic acid expands more than paraffin during the transition. Inserting a rectangular fin, that is made from copper into the ball reduces the cycle time and increases output.

Electrospun PEO/PEG fibers as potential flexible phase change materials for thermal energy regulation

AbstractPolyethylene glycol (PEG) is widely used as phase change materials (PCM) due to their versatile working temperature and high latent heat. However, the low molecular weight of PEG prevents from the formation of flexible microfibers, and the common leakage problem associated with solid–liquid PCM further hinders their applications in various fields. To address these challenges, polyethylene oxide (PEO) is incorporated as the supporting matrix for PEG, leading to a successful electrospinning of fibrous mats. Due to the similar chemical nature of both PEG and PEO, the blended composites show great compatibility and produce uniform electrospun fibers. The thermal properties of these fibers are characterized by DSC and TGA, and supercooling for the PEG(1050) component is effectively reduced by 75–85%. The morphology changes before and after leakage test are analyzed by SEM. Tensile and DMA tests show that the presence of PEG(1050) component contributes to plasticization effect, improving mechanical and thermomechanical strength. The ratio of PEO(600K):PEG(1050) at 7:3 affords the optimal performance with good chemical and form‐stability, least shrinkage, and uniformity. These fibrous mats have potential applications in areas of food packaging, flexible wearable devices, or textiles to aid in thermal regulation.

Beeswax as a potential replacement of paraffin wax as shape stabilized solar thermal energy storage material: An experimental study

Thermal Energy Storage (TES) using paraffin wax as Phase Change material (PCM) has been widely used for solar to thermal energy conversion and storage application. Being petroleum by-product, production of paraffin wax have embodied environmental impact and high carbon footprint. Beeswax can replace paraffin's as one of the clean, sustainable, eco-friendly and potential TES PCM. However, TES potential of Beeswax was not investigated thoroughly in previous literatures. Also, limited study has been found which evaluates solar to thermal conversion potential of Beeswax. This study presents a comprehensive analysis of TES performance of Beeswax supported by Bentonite clay and loaded with Graphite was evaluated. Bentonite clay was used as supporting material and Graphite powder is used as additive in varying percentage to form Shape Stabilized Composite Phase Change Material (SSCPCM). SSCPCM was initially investigated for anti-leakage behaviour and was found that Bentonite can hold maximum 40 wt% of Beeswax without leakage above phase transition temperature. Thermal energy storage parameters, thermal degradation, solar to thermal conversion performance, chemical stability, surface morphology, and thermal conductivity were evaluated. Bentonite and graphite has shown good morphology to form SSCPCM samples. Also, SSCPCM has proved to be chemically and physically stable thermal energy storage material. Melting enthalpy of 101.79, 100.66, 98.80, 100.43, 96.51, and 105.01 at melting point of 59.43, 58.88, 58.12, 57.98, 57.36, and 57.11 of SSCPCM-0, SSCPCM-1, SSCPCM-3, SSCPCM-5, SSCPCM-7, and SSCPCM-9 was obtained. Adding Graphite has reduced supercooling of SSCPCM samples maximum by 84.13 %. Increasing additives in PCM improves heating rate and thermal conductivity of the SSCPCM.

Short range order of glassy KSb5S8 by diffraction, EXAFS, vibrational spectroscopy and DFT calculations

We report on a detailed experimental and simulation study of the short- and medium-range order of a potential phase change material – glassy KSb5S8. On the experimental side, diffraction techniques and EXAFS have been employed to record accurate structural data. Structural models have been generated by fitting multiple datasets simultaneously with the reverse Monte Carlo simulation technique. In addition, density functional theory was employed to study the structure and vibrational modes of selected clusters, representative of the glass structure. Unconstrained RMC simulation runs revealed that the average Sb-S coordination number is 3.18 ± 0.2, thus Sb is mostly threefold coordinated in the glassy state. The fraction of edge and corner sharing SbSn polyhedra and distribution of bridging S atoms (Qn distribution) have also been obtained. Distribution of bridging S atoms around Sb is similar in the crystalline and glassy states. DFT calculations assisted in the identification of a Raman mode at ∼468 cm−1, assigned to hypervalent bonding (quasi-tetrahedral units) in the glass structure.

Solar Salt with Carbon Nanotubes as a Potential Phase Change Material for High-Temperature Applications: Investigations on Thermal Properties and Chemical Stability.

Nano-enhanced phase change materials are highly employed for an enhanced heat-transfer process. The current work reports that the thermal properties of solar salt-based phase change materials were enhanced with carbon nanotubes (CNTs). Solar salt (60:40 of NaNO3/KNO3) with a phase change temperature and enthalpy of 225.13 °C and 244.76 kJ/kg, respectively, is proposed as a high-temperature PCM, and CNT is added to improve its thermal conductivity. The ball-milling method was employed to mix CNTs with solar salt at various concentrations of 0.1, 0.3, and 0.5% by weight. SEM images display the even distribution of CNTs with solar salt, with the absence of cluster formations. The thermal conductivity, phase change properties, and thermal and chemical stabilities of the composites were studied before and after 300 thermal cycles. FTIR studies indicated only physical interaction between PCM and CNTs. The thermal conductivity was enhanced with an increase in CNT concentration. The thermal conductivity was enhanced by 127.19 and 125.09% before and after cycling, respectively, in the presence of 0.5% CNT. The phase change temperature decreased by around 1.64% after adding 0.5% CNT, with a decrease of 14.67% in the latent heat during melting. TGA thermograms indicated the weight loss was initiated at about 590 and 575 °C before and after thermal cycling, after which it was rapid with an increase in temperature. Thermal characterization of CNT-enhanced solar salt indicated that the composites could be used as phase change materials for enhanced heat-transfer applications.

A comprehensive evaluation on the cycling stability of sugar alcohols for medium-temperature latent heat storage

Sugar alcohols have been proposed as a class of potential phase change materials (PCMs) for medium-temperature latent heat storage. The present work investigated the cycling stability of four pure and three mixture sugar alcohols by a specially-designed test setup, followed by a comprehensive evaluation based on their phase change behaviors (reported in our previous publication) and stability. It was found that the latent heats of fusion/crystallization degrade upon consecutive melting-crystallization cycles, and a higher degree of superheat ΔTsh leads to a faster degradation. An extremely low level of only 10.5 % degradation was obtained for erythritol after 200 cycles at a relatively low ΔTsh of 20 °C. The corresponding degrees of supercooling ΔTsc become higher due to the remarkable reduction of crystallization temperatures. It was shown that introducing protective nitrogen gas could suppress oxidation and improve cycling stability. The cycles of half degradation on latent heat of fusion was ~3.6 times with nitrogen protection. A comprehensive evaluation identified that the crystallization-related issues and poor stability are the primary challenges for sugar alcohols. Nevertheless, other than common PCMs, some particular application scenarios like controllable latent heat retrieval and seasonal heat storage can be hopefully developed by virtue of the deep supercooling nature of sugar alcohols.

Enablers for Overcurrent Capability of Silicon-Carbide-Based Power Converters: An Overview

With the increase in penetration of power electronic converters in the power systems, a demand for overcurrent/ overloading capability has risen for the fault clearance duration. This article gives an overview of the limiting factors and the recent technologies for the overcurrent performance of SiC power modules in power electronics converters. It presents the limitations produced at the power module level by packaging materials, which include semiconductor chips, substrates, metallization, bonding techniques, die attach, and encapsulation materials. Specifically, technologies for overcurrent related temperatures in excess of 200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\,{}^{\circ }$</tex-math></inline-formula> C are discussed. This article also discusses potential technologies, which have been proven or may be potential candidates for improving the safe operating area. The discussed technologies are use of phase-change materials below the semiconductor chip, Peltier elements, new layouts of the power modules, control and modulation techniques for converters. Special attention has been given to an overview of various potential phase-change materials, which can be considered for high-temperature operations.

Thermophysical studies, corrosion analysis, and discharging characteristics of lauryl alcohol/lauric acid eutectic mixture as a potential phase change material for human comfort applications

AbstractClimate change has been identified as the greatest threat of the 21st century. Recently, many cities around the world recorded their highest ever temperatures as a result of heat waves, negatively impacting several communities and livelihoods. Due to this warmer environment around the world, there has been a tremendous increase in cooling energy requirements in the last decade, particularly for human thermal comfort. It is critical to accelerate studies based on latent heat storage systems for personal comfort applications such as cooling vests that can maintain the human body temperature at a comfortable level in hot climates, which will eventually reduce the dependency of fossil fuel based energy resources to a certain extent. The purpose of this study is to conduct a thorough examination of the thermophysical properties of a eutectic phase change material (PCM) developed, which is comprised of lauryl alcohol and lauric acid, as a viable contender for human cooling applications. The melting temperature and latent heat of fusion of the eutectic combination were discovered to be 13.13°C and 164.23 J g−1, respectively, via differential scanning calorimetry (DSC). Four important thermophysical properties: thermal cycling, thermogravimetric analysis, Fourier transform infrared spectroscopy, and thermal conductivity studies were conducted, and the results obtained ascertain the material's suitability for the intended application. Based on corrosion studies, stainless steel and aluminum are particularly suited for fabricating the metal containers for the developed PCM. The results of the discharging studies of the chosen PCM in the vapor absorption refrigeration chamber appear promising as well.

Preparation and thermal properties of novel inorganic-organic eutectic composite material with high latent heat and thermal conductivity based on aluminum sulfate salt

Potassium aluminum sulfate dodecahydrate (Alum) and ammonium aluminum sulfate dodecahydrate (AAS) are two potential inorganic phase change materials with high transformation enthalpy. To make them more flexible to match temperature requirements of various fields, the melting temperature needs to be manipulated but less effect on latent heat. In this work, two novel eutectic mixtures of Alum-E and AAS-E were obtained by adding erythritol (E) with high latent heat into aluminum sulfate salts. The results denoted that the melting temperatures of the two eutectic mixtures were 72.46 °C and 73.20 °C when containing 35 wt% and 37 wt% erythritol, respectively. It was worth noting that they still possessed high latent heat of 243.4 J/g and 257.4 J/g. Considering the stability of NH4+ at high temperature, Alum-E was chosen to fabricate Alum-E/EG (expanded graphite) composite material with high thermal conductivity via melt-blending method. EG not only increased the thermal conductivity from 0.61 W/(m·K) to 10.95 W/(m·K) as an excellent enhanced heat transfer carrier, but also prevented leakage of Alum-E/EG composite material effectively as a porous adsorption carrier when contained 15 wt% EG. Moreover, the thermal stability tests indicated that Alum-E possessed favorable thermal stability after 250 heat-cooling cycles. Above all, the obtained composite energy storage material is a promising candidate for afterheat recovery and medium and low-temperature energy storage areas else.

Thermal Energy Storage Characteristics of Paraffin in Solar Water Heating Systems with Flat Plate Collectors

Indonesia is a tropical country with a relatively stable intensity of solar radiation throughout the year, ranging from 10 to 12 hours a day, and averaging 4.8 kWh/m²/day. This great potential can be used for heating water for bathing. Water heating technology based on solar collectors is now widely available in the commercial market. Additionally, thermal energy storage from solar radiation is performed using sensible heat and requires a large volume. Assuming that the water is not used until the afternoon, then the heated water is stored in the tube. A phase change material (PCM) was used in several studies to maximize thermal energy storage (TES) from solar radiation. Also, PCM uses latent heat to absorb and release heat. This is adjusted to the water temperature produced from the solar collector, which attains 70°C. Hence, the potential PCM used is solid paraffin, which is widely available in the market with melting temperatures of 40° to50°C. The study was conducted on a solar water heating system using an 80 cm x 50 cm flat plate collector, and thermal energy storage using paraffin wax. Meanwhile, the heat exchanger used a tube with a diameter of 1 inch arranged in series with a pipe length of 50 cm and 36 rods. The mass of paraffin used was 15 kg or 17.7 liters. Furthermore, the test was performed with variations in the flow rate of water, namely: 2, 3, and 4 lpm, and solar radiation of: 997.5 W/m², 1183 W/m², and 1399.8 W/m². From the results, the thermal energy storage process in PCM paraffin with an amount of 15 kg, took 3.2 hours with a total stored energy of 3.6 MJ. Moreover, solar radiation of 1,399.8 W/m² was used as an energy source and water with a flow rate of 4 lpm as a medium heat transfer. Therefore, this radiation has a very significant effect on the heat transfer process to the PCM, while the flow rate with a value of 2 to 4 lpm does not have.

The Use of Fe-26Si-9B Alloy as Phase Change Material in Si3N4 Container

Fe-26Si-9B alloy was selected as a potential phase change material (PCM) to store energy at temperatures up to 1300 °C. A suitable refractory material is crucial to building a PCM container for Fe-26Si-9B alloy in thermal energy storage systems. The refractory material should have the ability to withstand corrosion from liquid Fe-26Si-9B alloy and should not pollute the alloy after long-term thermal cycles at high temperatures. In this work, Si3N4 was selected as a candidate refractory material. To investigate the interaction between Si3N4 and Fe-26Si-9B alloy, the wettability property of an Fe-26Si-9B/Si3N4 system was examined in a sessile drop furnace at temperatures up to 1350 °C. Moreover, Fe-26Si-9B alloy was subjected to 1–12 thermal cycles at temperatures between 1100 and 1300 °C, where the alloys were placed in Si3N4 crucibles in a resistance furnace under argon. According to the experiments, the equilibrium contact angle between the Fe-26Si-9B droplet and Si3N4 substrate was measured to be ~143°, which is non-wetting behavior. Microstructural analyses showed that FeSi, FeB, FeSiB3, and SiB6 were formed in the solidified Fe-26Si-9B alloy, in which FeSi + FeSiB3 constituted the eutectic structure. No nitride phases were introduced to the Fe-26Si-9B alloy, and no new interlayer was produced at the interface between the Fe-26Si-9B alloy and Si3N4 crucible after the thermal cycle experiments. In addition, the formed phases were stable with the increase in thermal cycles. All the results show that Si3N4 refractory material is suitable for Fe-26Si-9B alloy containers at high temperatures.

Capric-stearic acid mixture impregnated carbonized waste sugar beet pulp as leak-resistive composite phase change material with effective thermal conductivity and thermal energy storage performance

The present investigation aims to develop a potential composite phase change material (PCM) with leak-resistive and high thermal conductivity. Sugar beet pulp (CSBP) as an industrial waste was carbonized to produce a porous framework and used for solving leakage issue and boosting thermal conductivity of capric-stearic acid eutectic mixture (CSEM) used as PCM. FTIR and XRD results proved that the integration of CSEM and CSBP was carried out physically. The SEM analysis demonstrated that the CSEM was well uniformly impregnated within the pores of CSBP scaffold. DSC analysis revealed that the CSBP/CSEM (70 wt%) composite showed melting enthalpy and temperature as 117 J/g and 24 °C. The TGA measurements demonstrated that the produced composite was thermally stable. The incorporation of CSEM with CSBP leaded to a 79% increase in its thermal conductivity and this improvement was proved by comparing heating-cooling periods of CSEM and the composite PCM. The latent heat of the composite PCM was reduced less than 3% as its melting temperature was almost constant after 1000 thermal cycles. All findings of this work disclosed that the developed CSBP/CSEM as cost-effective and environmentally friendly composite PCM can be handled potential TES material for temperature controlling of buildings.

Experimental study on operating characteristics of nitrate salt-based latent heat thermal energy storage unit

Inorganic salts are potential phase-change materials for medium- and high-temperature thermal applications. It is essential to acquire knowledge of their behavior in latent heat thermal energy storage for the design of storage devices and the construction of an energy conversion and utilization system. In this study, a eutectic mixture of NaNO3 (mass ratio of 46%) and KNO3 was selected as phase change material, and a nitrate salt-based latent heat thermal energy storage unit was built to experimentally investigate its operating characteristics during charging and discharging. The thermophysical properties of the eutectic nitrate salt were measured and presented. The air outlet temperature remained almost unchanged during the melting of salt in the charging process, but it decreased gradually during the discharging process because the thermal resistance increased with the salt solidification. The melting time was shortened by 31.0% and 38.1% when the air inlet temperature was increased from 260 °C to 270 and 280 °C, respectively. The solidification time was shortened by 22.2% and 33.3% when the air inlet temperature was reduced from 210 °C to 200 and 190 °C, respectively. When the air mass flow rate was increased from 0.964 g/s to 1.446 and 1.962 g/s, the melting time was shortened by 32.4% and 57.4%, respectively, while the solidification was only shortened by 8% and 16%, respectively. The charging ratio or discharging ratio can be calculated through heat-loss evaluation to depict the thermal energy change in a charging or discharging process. The results indicated that charging ratio increased almost linearly with the melting of the salt. The air mass flow rate had a significant impact on this parameter. The influence of the air inlet temperature was gradually weakened with the increasing air inlet temperature. Owing to the coupling effect of heat loss and airflow, the influence of air parameters on the discharging ratio was weak. The effectiveness of storage indicates the extent to which the latent heat of salt can be utilized. It increased from 29.7% to 52.8% when the air inlet temperature was reduced from 210 to 190 °C. This study provides insights into the phase-change characteristics of the nitrate salt and the nitrate salt-based latent heat thermal energy storage unit.