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Fly ash is a kind of industrial solid waste that is considered "hazardous waste". In this study, a supporting matrix of modified fly ash (MFA) was employed to package lauric acid (LA) via a facile direct impregnation method involving less experimental error. A low-cost and eco-friendly form-stable phase change material (PCM) of LA/MFA/graphene (G) was fabricated, with G as the thermal conductivity enhancer. The preparation and leakage testing of an LA/MFA/G form-stable PCM (FSPCM) were investigated in detail. The leakage test results indicated that good package efficiency was obtained using MFA with a higher specific surface area and richer pore structure to pack the LA. Then, LA/MFA/G composites were characterized via scanning electronic microscope (SEM), Fourier transform infrared spectroscope (FTIR), differential scanning calorimeter (DSC), and thermal gravimetric analyzer (TGA). The results showed that excellent form stability was obtained by adding MFA as the supporting matrix. The SEM analysis indicated that LA could be well dispersed into the structure of MFA. The FTIR analysis demonstrated that the components of the FSPCM were quite compatible. The results of the DSC illustrated that LA/MFA/G (5 wt. %) had a melting point of 45.38 °C and a latent heat of 41.08 J/g. The TGA analysis revealed that the prepared FSPCM had better thermal stability compared with LA within its working temperature range. In addition, the effects of G on the heat transfer performance of the prepared FSPCM were examined. In short, using MFA with a higher specific surface area and richer pore structure to pack the LA via a simple preparation process with less experimental error can contribute to good performance. The research not only improved the comprehensive utilization of solid waste, but also promotes the application of FSPCM in the field of building energy conservation. [ABSTRACT FROM AUTHOR]

In this study, a novel ternary system form-stable phase change material (FSPCM) composed of lauric acid (LA)/raw fly ash (RFA)/carbon nanotubes (CNT) was prepared via low cost, easy and industrially applicable fabrication process for low-temperature heat storage. Particularly, the unmodified RFA was directly acted as supporting material to prevent the leakage of the melted LA almost at no cost. A series of leakage experiments were performed to evaluate the package efficiency. The maximum mass fraction of LA absorbed in RFA and CNT was found to be 25 wt% without the LA leakage. Hence, the LA/RFA/CNT (25/75/5 wt%) composite was characterized as FSPCM. The chemical structures, microstructure thermal properties and thermal stability of the FSPCM was investigated by Fourier transformation infrared spectroscope (FTIR), scanning electronic microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analyzer (TGA). The SEM and FTIR results indicated that LA was adsorbed on the RFA's surface porous or into the porous structure of CNT. And there was good chemical compatibility among LA, RFA and CNT. The DSC results demonstrated that the phase change temperatures and latent heats of LA/RFA/CNT FSPCM were 45.36 °C and 37.83 J/g for melting and 40.51 °C and 36.48 J/g for freezing, respectively. TGA analysis test revealed that the composite PCM had excellent thermal stability. Moreover, the heat transfer efficiency of LA/RFA/CNT FSPCM has been improved by the addition of RFA and CNT. In short, the LA/RFA/CNT FSPCM has a promising application prospect in low-temperature application due to feasible and in large scale industrial preparation, low-cost, simple and facile process. [ABSTRACT FROM AUTHOR]

Leakage issue and low thermal conductivity largely restrict feasibility of fatty acid in real application of thermal energy storage (TES). In this paper, a novel form-stable phase change material (FSPCM) capric acid/diatomite (CA/DT) for TES was prepared using direct impregnation method by using CA as PCM and diatomite as supporting material. The fabricated composites were investigated in detail via the leakage test to determine the optimization proportion, and the real mechanism of preventing leakage by diatomite was analyzed. The characterization techniques such as thermogravimetric analysis, differential scanning calorimetry, intelligent paperless recorder technology, Fourier transform infrared spectrometer and scanning electron microscopy were applied to systematically investigate the thermal properties, microstructure and thermal compatibility of the prepared composites. The results showed that the maximum mass ratio of CA adsorbed into DT without leakage is as high as 50 mass%, which is mainly ascribed to the porous structure of DT. The selected FSPCM has a melting point of 34.9 °C and latent heat of 89.2 J g−1. What is more, the CA/DT FSPCM exhibits a distinctly enhanced thermal stability by TG analyses. The heat transfer efficiency of the CA/DT FSPCM is higher than that of pristine CA. Due to the high adsorption capacity, high latent heat, good thermal stability as well as low cost, the CA/DT FSPCM can be considered as potential materials for thermal energy storage. [ABSTRACT FROM AUTHOR]

Abstract To improve the energy storage efficiency of phase change composites, porous mullite was used to encapsulate the PCM-palmitic acid and graphite powder was applied to enhance the overall thermal conductivity. During the experimental process, a series of palmitic acid/mullite/graphite (PA/mullite/GP) composites were prepared to obtain the PA/mullite/GP form stable phase change material (FSPCM) by facile direct impregnation method. Then their microstructure, chemical compatibility and thermophysical properties were studied by the method of SEM, FTIR, XRD, DSC, TGA and PR, systematically. The DSC results demonstrate that the PA, PA/mullite and PA/mullite/GP have the enthalpy of melting of 213.1 J/g, 54.7 J/g, and 52.3 J/g, while the enthalpy of freezing of 217.0 J/g, 53.6 J/g and 51.5 J/g, respectively. Compared with the pure PA, the thermal conductivity of the prepared PA/mullite/GP has been improved from 0.28 W m−1 K−1 to 0.52 W m−1 K−1 owing to the high thermal conductivity of GP (only 5 wt %). The reliability test shows that the PA/mullite/GP FSPCM maintains form-stable without any PA leakage even after 150 thermal cycles. In short, prepared PA/mullite/GP FSPCM exerts excellent chemical and thermal reliability and thus has a bright prospect in the field of solar energy storage and solar heating. Highlights • Palmitic acid/mullite/graphite powder FSPCMs were fabricated by facile direct impregnation method. • The PA, PA/mullite and PA/mullite/GP had the enthalpy of melting of 213.1 J/g, 54.7 J/g, and 52.3 J/g, respectively. • The thermal conductivity of PA/mullite/GP FSPCMs has been improved by 86%. • The mechanism of thermal conduction with the addition of mullite and GP has been analyzed. [ABSTRACT FROM AUTHOR]

• Palmitic acid/carbonized pepper straw phase change material (PCM) were developed. • Chemical compatibility and thermophysical properties of the novel PCM were analyzed. • The novel PCM had great thermal reliability even after 100 thermal cycles. In this paper, a novel form stable phase change material (FSPCM) of Palmitic acid (PA)/Carbonized pepper straw (CPS) was prepared by using the facile direct impregnation method. The chemical compatibility of PA/CPS FSPCM was investigated by using the Fourier Transform Infrared Spectroscopy. Differential scanning calorimetry and thermogravimetry analysis were applied to characterize the latent heat and thermal stability, the results of which show that the compatibility between PA and CPS is good. The phase change temperature and latent heat of PA/CPS FSPCM is 65.7 °C and 95.5 J/g for the melting process and 56.1 °C and 90.2 J/g for the solidification process. Moreover, the FSPCM had excellent thermal reliability even after 100 cycles. All the results indicate that the PA/CPS FSPCM has great potential for use in green building and indoor heat system. [ABSTRACT FROM AUTHOR]

• Phase change material-integrated interfacial solar vapor generator (SVG) is proposed. • Mass change of PCM-integrated SVG was 1.5 times that of the conventional evaporator. • COMSOL simulations indicate the performance of PCM-integrated SVG can be improved. • The study provides a novel strategy to improve all-day vapor generation yield. Owing to the intermittent nature of solar energy, the water generation yield of interfacial solar vapor generation during the nighttime is limited. Herein, we propose a phase change material (PCM)-integrated solar vapor generator to address this limitation. Specifically, three types of polyethylene glycol (PEG800, PEG1500, PEG2000)/expanded graphite (EG) form-stable PCMs (FSPCMs) with different thermophysical properties were fabricated. Upon comparing the performances of the three FSPCMs, PEG1500/EG was found to be the optimal specimen and the associated mechanism was discussed in detail. Further, a proof-of-concept evaporator was assembled to find that the all-day mass change of the FSPCM-integrated solar vapor generator was 1.5 times that of the conventional evaporator and 3.0 times that of pure water. Moreover, the mass change of the FSPCM-integrated solar vapor generator during the night was 3.6 times that of the conventional evaporator. Benefiting from the thermal energy storage capacity of the prepared FSPCMs, the FSPCM-integrated solar vapor generator can store the extra energy of the sun in the daytime and achieve continuous vapor generation in both daytime and nighttime. Furthermore, COMSOL simulations indicate that the overall performance of the FSPCM-integrated solar vapor generator can be further improved because the FSPCM module has good scalability. In a word, this study provides a novel strategy to effectively improve the all-day vapor generation yield of interfacial solar vapor generation and inspires further research aimed at the use of thermal storage technology to enable round-the-clock solar vapor generation. [ABSTRACT FROM AUTHOR]

The sodium acetate trihydrate (SAT)/expanded graphite (EG) composite phase change material (PCM) was firstly prepared by absorbing liquid SAT into a porous network of EG, in which SAT acted as the PCM. EG prepared at microwave irradiation power of 800 W for 30 s with maximum volumes has the largest sorption capacity for SAT. At the mass fraction of SAT <95 %, SAT uniformly disperse in the pores of EG without liquid leakage evidenced from scanning electron microscopy characterization. X-ray diffraction results further show that PCM is just a combination between SAT and EG without any chemical reaction. Differential scanning calorimeter measurements indicate that the melting temperature and latent heat of the composite PCM are 59.5 °C and 202 J g, respectively, close to those of pure SAT. The thermal conductivity of the composite PCM can be as high as 1.589 W m K.The form-stable SAT/EG composite with SAT mass fraction of 95 % has great potential in thermal energy storage due to its moderate melting point, significant latent heat storage capacity, form-stable property, direct usability without need for an extra storage container, and high thermal conductivity. [ABSTRACT FROM AUTHOR]

• Acid modification can improve the PCM loading of halloysite-based FSPCM. • Improvement of PCM loading via acid modification was systematically interpreted. • A novel halloysite-based FSPCM cement panel was developed. • Effect of cement thermal conductivity on its performance in building was identified. Phase change material (PCM) with large thermal storage capacity and constant phase change temperature is one of the most promising materials for building energy saving. However, its leakage problem and poor thermal conductivity have largely hindered its large-scale application. This study, therefore, utilizes acid-modified halloysite to encapsulate PCM for preparing form-stable PCM with enhanced thermal storage capacity and systematically investigates the thermal conductivity enhancement on the thermal performance of FSPCM cement panel by a lab-scale test chamber. The study results indicated that the maximum PCM loading for the acid-modified halloysite-based FSPCM was 55 wt%, 10 wt% higher than that of the original one and the associated mechanism of acid-modification was in-depth discussed. The as-prepared FSPCM had comparatively high thermal storage capacity and appropriate phase change temperature. Although the addition of FSPCM may decrease the mechanical properties of cement panels, the prepared sample can still meet the standard for building application. More importantly, the thermal conductivity enhancement of the FSPCM cement panel had a different impact on its thermal performance for various models and the reasons for this difference were systematically investigated. The study results can provide insights into the preparation and building application of FSPCM. [ABSTRACT FROM AUTHOR]

Owing to the high thermal capacity and nearly constant temperature during phase change, phase change material has been considered one of the most promising solar thermal energy storage materials. However, the development of high-performance shape-stabilized phase change material (SSPCM) based on a low-cost and eco-friendly supporting material remains a big challenge. Herein, a systematic experimental framework is proposed and used to respond to the challenge. By applying this framework, acid-modified fly ash (AMFA) was firstly used as the supporting material for lauric acid (LA) to prevent its leakage, while carbon nanotubes (CNTs) were utilized to improve its thermal conductivity. Specifically, the LA/AMFA/CNTs composites were synthesized via a facile and low-cost direct impregnation method. Subsequently, the as-prepared composites were systematically investigated by various characterization techniques. The results of leakage tests exhibited that the acid treatment could improve the PCM loading of fly ash and the relevant mechanism of acid-modified fly ash was identified. With the introduction of CNTs, the heat transfer efficiency of LA/AMFA/CNTs had been enhanced substantially. More importantly, compared with conventional supporting materials, the used fly ash in this work revealed much better environmental sustainability which we believe is of vital importance for the large-scale application of SSPCMs. Therefore, the study results not only facilitate the development of the desirable SSPCM based on cheap and eco-friendly supporting material and promote its practical application, but also serve to improve the comprehensive utilization level of fly ash solid waste. • Acid modification of fly ash was carried out to improve the latent heat of the SSPCM. • Mechanism of the latent heat enhancement was in-depth analyzed. • Heat transfer enhancement mechanism of the SSPCM was provided. • Sustainable assessment of the prepared SSPCM was performed. [ABSTRACT FROM AUTHOR]

In this study, a novel form-stable phase change material (FSPCM) consisting of calcination iron tailings (CIT), capric acid (CA), and carbon nanotubes (CNT) was prepared using a simple direct melt impregnation method, and a series of tests have been carried out to investigate its properties. The leakage tests showed that CA can be retained in CIT with a mass fraction of about 20 wt.% without liquid leakage during the phase change process. Moreover, the morphology, chemical structure, and thermal properties of the fabricated composite samples were investigated. Scanning electron microscope (SEM) micrographs confirmed that CIT had a certain porous structure to confine CA in composites. According to the Fourier transformation infrared spectroscope (FTIR) results, the CA/CIT/CNT FSPCM had good chemical compatibility. The melting temperature and latent heat of CA/CIT/CNT by differential scanning calorimeter (DSC) were determined as 29.70 °C and 22.69 J/g, respectively, in which the mass fraction of CIT and CNT was about 80 wt.% and 5 wt.%, respectively. The thermal gravity analysis (TGA) revealed that the CA/CIT/CNT FSPCM showed excellent thermal stability above its working temperature. Furthermore, the melting and freezing time of CA/CIT/CNT FSPCM doped with 5 wt.% CNT reduced by 42.86% and 54.55% than those of pure CA, and it showed better heat transfer efficiency. Therefore, based on the above analyses, the prepared CA/CIT/CNT FSPCM is not only a promising candidate material for the application of thermal energy storage in buildings, but it also provides a new approach for recycling utilization of iron tailings. [ABSTRACT FROM AUTHOR]

In this paper, mullite was adopted in order to absorb Palmitic Acid (PA) via a direct impregnation method. The prepared PA/mullite form-stable phase change materials (FSPCM) were systematically characterized by the Leakage Test (LT), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimeter (DSC), Thermogravimetry (TG) and Cooling Curve Method (CCM). The results indicated that, among these composites with different mass fractions of PA, the sample with the 32 wt % Palmitic Acid has the best properties without any leakage. The enthalpy of 32%PA/68%mullite FSPCM is 50.8 J/g for melting process, and 58.3 J/g for solidifying process. The phase change point of 32%PA/68%mullite FSPCM is 64.1 °C for melting and 58.7 °C for solidifying. The heat storage efficiency of the PA/mullite FSPCM was enhanced considerably by adding mullite. The leakage and thermal properties of PA/mullite FSPCM were discussed and the performance of the FSPCM has been apparently improved. [ABSTRACT FROM AUTHOR]

This study presents the fabrication of a novel shape-stabilized phase change material (SSPCM) characterized by high thermal capacity and heat transfer efficiency. The material was composed of lauric acid (LA) embedded in roasted iron tailings (RIT) and expanded graphite (EG), utilizing a straightforward, low-cost, and direct impregnation method. The as-prepared LA/RIT-EG SSPCM underwent a comprehensive analysis of leakage tests, surface morphology, chemical compatibility, phase change properties, thermal stability, and reliability. Furthermore, the heat transfer efficiency and thermal conductivity were measured through cooling tests and a laser thermal conductivity analyzer, respectively. The LA/RIT-EG formulation demonstrated an ability to absorb 61.57 wt% LA without leakage, maintaining excellent form-stability with a mass fraction proportion of 29:9.43 for RIT and EG. DSC results revealed phase temperatures and latent heats of 42.49–46.31 °C and 108.1–113.1 J/g, respectively. Compared to pure LA, LA/RIT-EG exhibited a 489.7 % increase in thermal conductivity. Additionally, heat storage and release rates were improved by 81.25 % and 88.24 %, respectively. The study elucidated the mechanism behind the enhancement in encapsulation capacity and thermal conductivity by RIT-EG, validated through specific surface area and wettability tests. Overall, the results suggest that LA/RIT-EG, characterized by high thermal capacity and heat transfer efficiency, holds promise as a potential candidate for thermal energy storage, particularly in the context of energy conservation in buildings. [Display omitted] • A novel SSPCM based on RIT-EG binary material with preferred EG content was prepared. • LA/RIT-EG revealed an ability to absorb 61.57 wt% LA without leakage by using RIT-EG. • The latent heat of the LA/RIT-EG SSPCM was 113.1 J/g for the melting process. • The enhancement mechanism was investigated by specific surface area and wettability. • LA/RIT-EG could be as a potential candidate for energy conservation in buildings. [ABSTRACT FROM AUTHOR]

Phase change material (PCM) based thermal storage technology can help mitigate the increasing energy problems caused by the rapid economic developments and population growth. However, the extremely low thermal conductivity of PCM has substantially impeded their wide applications in practice. Therefore, this study has developed a novel palmitic acid (PA)/halloysite nanotubes (Hal) form-stable PCM (FSPCM) with enhanced thermal conductivity utilizing the synergetic effect of carbon nanocoating and graphene addition. To enhance the thermal conductivity of the Hal, the C-Hal (CH) was firstly prepared through sucrose decomposition, and the effect of calcination temperature and sucrose concentration on the CH were systematically investigated for identifying the optimal carbonization condition. Then, the obtained CH was used to encapsulate PA by a low-cost and facile direct impregnation method, and the leakage test was implemented to identify the loading of the FSPCM. Meanwhile, graphene was added to further improve the thermal conductivity of the FSPCM. Finally, the critical thermal, microstructure, and chemical compatibility properties of as-prepared PA/CH/graphene FSPCM were systematically investigated. The study results indicated that the FSPCM exhibits melting temperature at 62.89 °C with a thermal energy storage density of 71.35 J/g and desirable thermal reliability. More importantly, the thermal conductivity of the prepared FSPCM has been substantially improved up to 1.51 W/mK, which is 3.60 times that of pristine PCM. The main reason is that the synergistic effects of carbon nanocoating and graphene addition have built a continuous highway for heat transfer. The study provides a practical means to greatly improve the thermal conductivity of the FSPCM, thereby promoting its practical applications. [Display omitted] • PCM low thermal conductivity largely impedes its wide applications. • Carbon coating and graphene were utilized to improve PCM thermal conductivity. • The PCM thermal conductivity can be improved by 260%. • The synergistic effect on thermal conductivity enhancement was elaborated. • Results provide a practical means to largely improve PCM thermal conductivity. [ABSTRACT FROM AUTHOR]

• A novel FSPCM based on hybrid MTSW supporting materials were prepared. • The optimized mass proportion was 3:2:2:3 for PA, BSW, IT and DT without PA leakage. • The values of freezing latent heat for PA/MTSW/CNT (4 wt%) were 55.36 J/g and 53.10 J/g. • This work creates an innovative approach for recycling utilization of solid wastes. In this study, palmitic acid (PA)/hybrid multivariate typical solid wastes (MTSW) phase change materials (PCMs) were fabricated by integrating PA into MTSW via a facile direct impregnation method to overcome the leakage of PA. The hybrid MTSW was composed of biomass solid wastes (BSW), iron tailings (IT) and diatomite (DT) at different mass ratios. Simultaneously, carbon nanotubes (CNT) was employed to enhance the thermal conductivity of the PCMs, and then the novel PA/MTSW/CNT composite was firstly prepared. The preparation, shape-stabilization level, morphologies, chemical compatibility, thermal properties and thermal conductivity of these composite PCMs were systematically characterized by tableting leakage tests, scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot dist and cooling test method. It was found that the MTSW could adsorb 30 wt% PA without any PA leakage and the composites can keep form-stable with mass fraction proportion of 3:2:2:3 for PA, BSW, IT and DT, respectively. The SEM images showed PA was well infiltrated into pore structure of MTSW which had good loading capacity to adsorb PA. FTIR analysis indicated that no chemical reaction had occurred among the components of composite PCMs. The DSC results suggested that the melting points were 63.65 °C and 63.08 °C for PA/MTSW and PA/MTSW/CNT (4 wt%) form-stable phase change materials (FSPCM), respectively. Correspondingly, the latent heats were 55.36 J/g and 53.10 J/g for PA/MTSW and PA/MTSW/CNT FSPCM, respectively. The TGA results showed that PA/MTSW/CNT FSPCM exhibited better thermal stability than pure PA. Compared with pure PA, the thermal conductivities of PA/MTSW/CNT were increased by 25.71%, 36.44% and 91.35% by CNT doping 2, 4 and 6 wt%, respectively. In addition, the heat storage and discharge time of PA/MTSW/CNT were reduced appreciably. In Conclusion, the as-prepared FSPCM has very good properties and a good application prospect in the field of energy-saving building. [ABSTRACT FROM AUTHOR]