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Developing phase change materials for thermal energy storage using polyols with cold crystallization property
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Phase change heat storage has gained a lot of interest lately due to its high energy storage density. However, during the phase shift process, Phase Change Materials (PCMs) experience issues such as low thermal conductivity , stability, leaking, and low energy-storing capacity. Materials that mimic or derive from nature can effectively offset the shortcomings attributed. This work presents a methodical overview of the synthesis, thermo-physical properties, comparison and Thermal Energy Storage (TES) applications of bio-derived and biomimetic composite PCMs (BD/BM-CPCMs). Several studies have observed increase in thermal conductivity up to 950-1250 % for BD/BM-CPCMs, as well as great thermal stability with no matrix leakage at an average temperature of 150-250 • C. These types of composites have a relative enthalpy efficiency of up to 98.1 % and can endure 200-1000 heating-cooling cycles on average. Additionally, enviro-economic aspects, numerical approaches to heat transfer during phase change and multivariate and multi-objective optimizations from a technical, financial and environmental standpoint using machine learning techniques with underlying scopes of BD/BM-CPCM are presented. It is necessary to fabricate adaptable BD/BM-CPCM for multifunctional energy harvesting and storage in future. With regard to the advancement in substance functionalism, it is necessary to show and research the use of bio-derived composite with innovative effects like versatility, light to thermal conversion, electro-thermal conversion, and anti-bacterial qualities in real-world systems.
Phase change materials (PCMs) possess remarkable properties that make them highly attractive for thermal energy storage and regulation purposes. Their ability to store energy in the form of latent heat while maintaining a nearly constant temperature has led to growing interest in their practical applications. However, a significant challenge in utilizing PCMs lies in their susceptibility to leakage and fluidity in the melt state. Therefore, it becomes imperative to develop effective methods to create leakage-free form-stabilized PCMs, enabling their widespread use in various industries. In this review, we comprehensively evaluate the advantages and disadvantages of different stabilization methods by summarizing the key research advancements in this field. We delve into the effectiveness of the various techniques in mitigating leakage issues and enhancing the overall performance of form-stabilized PCMs. Furthermore, we present the multifunctionalities that form-stabilized PCMs can offer, including self-healing, self-cleaning, fire-retardancy, and electrical and thermal conductivities. Moreover, we explore the diverse application areas of form-stabilized PCMs, including solar energy storage, buildings, textiles, biomedical, and electronics. These explorations promise advancements in energy efficiency, thermal comfort, and sustainable design. This review aims to shed light on the potential of form-stabilized PCMs in revolutionizing various sectors and contributing to a greener and more energy-conscious future.
A new sustainable material for storing heat and releasing it on demand has been demonstrated for long-term latent heat storage (LLHS). The material consists of a high-latent-heat sugar alcohol phase change material (PCM) dispersed within ionic cross-linked matrices of polyvinyl alcohol (PVA). This material´s unique property is the inhibition of undesired crystallization of the PCM during cooling due to the strong intermolecular interactions of the polymeric matrices, which leads to vitrification instead of crystallization. The release of latent heat can be controlled due to the PCM’s stability below its cold-crystallization, which is triggered by reheating, demonstrated by differential scanning calorimetry (DSC), optical microscopy (OM) and in situ X-ray diffraction (XRD). The addition of an ionic citrate cross-linker further tunes the vitrification and cold-crystallization properties of the PCM. Homogeneity and the presence of hydrogen bonding of the cold-crystalizing PCM (CC-PCM) were showed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Fourier transform infrared spectroscopy (FTIR) and XRD. Thermal stability was confirmed by thermogravimetric analysis (TGA) and 100 consecutive DSC heating-cooling cycles. The CC-PCM demonstrated high latent heat of fusion, up to 266 J/g, depending on the composition. As a super-adsorbent, PVA was able to swell and hold the liquid PCM resulting in form-stability and leakage-preventive properties above the melting temperature. Taken together, these results confirm that PVA matrices are promising for thermal and structural stabilization of sugar alcohol PCMs, overcoming unexpected heat release and phase separation, and withstanding repeated melting-cooling cycles for LLHS.
Renewable energy usage would benefit from efficient and high-capacity long-term heat storage material. However, these types of material solutions still lack reliable and durable operation on bulk level. Previously, we showed that cold-crystallizing material (CCM), which consists of erythritol in cross-linked polymer matrix, stored heat for a long-term period in a milligram scale by supercooling stably and preventing undesired crystallization during storage. Crystallization of CCM can be triggered efficiently by re-heating the material (i.e. cold-crystallization). Supercooling and cold-crystallization are stochastic phenomena which manifest in a way that the properties in bulk scale often deviate from the microscale. In this work, we scale up CCM to a bulk size of 160 g, and analyze its supercooling and crystallization characteristics for long-term heat storage. In order to identify the impact of the scale-up on the tested compositions and to discover optimal storage conditions, CCM samples are maintained in storage mode at constant temperature between 0 and 10 °C and up to 97 days. To this end, the thermal chamber measurement procedure estimates the heat release of CCM samples based on the measured temperature data and the one-dimensional transient heat conduction model. Results indicate that the heat release in cold-crystallization is over 70% of the melting heat. This heat can be stored without reduction for at least 97 days, demonstrating the reliable performance of long-term heat storage. Analysing the thermal properties of CCM compositions indicates a maximum volumetric storage capacity of 250 MJ/m³ and excellent properties for further heat storage applications.
Thermal energy storage technologies based on phase‐change materials (PCMs) have received tremendous attention in recent years. These materials are capable of reversibly storing large amounts of thermal energy during the isothermal phase transition and offer enormous potential in the development of state‐of‐the‐art renewable energy infrastructure. Thermal conductivity plays a vital role in regulating the thermal charging and discharging rate of PCMs and improving the heat‐utilization efficiency. The strategies for tuning the thermal conductivity of PCMs and their potential energy applications, such as thermal energy harvesting and storage, thermal management of batteries, thermal diodes, and other forms of energy utilization, are summarized systematically. Furthermore, a research perspective is given to highlight emerging research directions of engineering advanced functional PCMs for energy applications. A comprehensive review regarding the tuning of the thermal conductivity of phase change composites for thermal energy conversion, storage, and utilization is provided, which gives an insightful understanding for the thermal energy storage and conversion processes. The aim is to stimulate potential emerging applications of phase change materials.
A lack of efficient crystallization methods and the metastability of supercooled liquids have limited the use of supercooling phase change materials (PCMs) in long-term thermal energy storage (LTES). Here, we propose a new supercooling PCM-polymer mixture that is not prone to spontaneous crystallization during the storage period. The material releases the stored thermal energy by cold-crystallization on re-heating. The PCM-polymer mixture is composed of supercooling polyol (erythritol or D-mannitol) dispersed in a cross-linked sodium polyacrylate (PAANa) matrix. PAANa efficiently prevents the conventional cooling crystallization of the PCM. Instead of crystallization, the melt polyol supercools and eventually vitrifies as an amorphous solid. Deeply supercooled or vitrified polyol is stable against crystallization below its cold-crystallization temperature. The heat charged and discharged remained similar in 100 repeated melting-crystallization cycles. Its good long-term performance and the stability of the supercooled polyol-PAANa against crystallization at low temperatures make the new material extremely promising for LTES.
Phase change materials (PCMs) when amalgamated in a shell material to form microencapsulated-PCMs (MPCMs) usually exhibit high levels of supercooling due to the limited crystallization process. In the present study, various efforts were made to reduce this phenomenon, including increasing the MPCM size, employing nucleating agents, and embedding copper nanoparticles into the MPCM shells. It was observed that with an increase in the microcapsule size from 43 μm to 76 μm, the supercooling was reduced by a value of 10.2 °C from melting/freeing point peak temperature differences of 37.6 to 27.4 for the 1200 rpm and 800 rpm samples respectively. Comparatively, the implementation of octadecanol nucleating agent 30 wt. % resulted in a reduction of supercooling by 22.9 °C. The introduction of Cu nanoparticles with a decane core can also reduce the supercooling degree by 4.6 °C, while the thermal conductivity the MPCM samples with a hexadecane core increased from 0.173 to 0.182 W.m–1.K–1 before and after the addiction of the Cu nanoparticles, respectfully. Furthermore, di(propylene glycol) methyl ether was used as a carrier fluid for the MPCMs to study the viscosity changes with various MPCM compositions. It was observed that the MPCM suspension with 10-20 % MPCM mass concentration did not exhibit shear thinning, while the 30 % sample conveyed shear thinning properties. Furthermore, near the crystallization temperature of the PCM, the slurry viscosity sharply rose, attributed to the volume changes and non-cooperative motion of MPCM microcapsules.
Seasonal thermal energy storage within organic phase change materials (PCMs) offers a promising way to solve intermittency of renewable energy, but the charged PCMs tend to undergo spontaneous crystallization and lose the stored latent heat to cold environment during storage. Herein, we report introduction of alkali hydroxides into sugar alcohols to increase the activation energy barrier for liquid-to-solid phase transition and stabilize the supercooling state, thereby realizing long-term phase change thermal energy storage. Owing to increased intermolecular hydrogen bonding interaction, the charged composites can maintain the supercooled state and conserve latent heat (∼200 J/g) during storage at room temperature or extremely cold temperatures for months. Further compounding with polydopamine organic pigments, the composites demonstrate high solar absorptance (∼91.6%) and thus enable seasonable storage of solar-thermal energy as latent heat at room temperature. The stored heat can be readily released through adding seed crystals or applying mechanical deformation, which triggers cold crystallization of the supercooled composites and releases latent heat within a suitable temperature range of 40-60 oC. Such phase change composites not only eliminate complicated thermal insulation engineering required in conventional long-term thermal storage processes, but also unlock diverse application opportunities for thermal energy systems.
The increasing use of renewable energy sources has highlighted the importance of energy storages, and in particular of latent heat thermal energy storages (LHTESs). Among the phase change materials (PCMs) that can be used in such systems, sugar alcohols (SAs) are considered potential substances that may lead to interesting applications in the LHTES sector. In this work, a detailed literature review analysis of six SAs (xylitol, sorbitol, erythritol, mannitol, inositol, dulcitol), their thermophysical properties, their thermal stability and their main LHTES applications is presented for the first time. The thermophysical properties under discussion include melting and crystallization temperatures, latent heats of melting and crystallization, specific heat, thermal conductivity, density and dynamic viscosity. Thermal stability was evaluated by taking into account studies of thermal endurance, degradation temperature and cycling stability. Differential scanning calorimetry (DSC), T-history, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were considered as measurement techniques. Applications include the use of SAs in solar collectors and cookers, heat exchangers, porous materials, absorption cooling systems, mobilized thermal energy storages (M-TESs). New measurements of phase transition properties and degradation temperature for the studied SAs were also carried out by the authors of the present study. A good agreement between the proposed data and the literature values was found. The analysis reveals that some SAs may be considered suitable for low-to-medium temperature LHTES applications, provided that their drawbacks are adequately evaluated and addressed. To this purpose, the study also highlights the most critical aspects that should be considered when developing both fundamental research and engineering applications related to SAs.
Erythritol has many advantages such as high latent heat, good stability, non-toxicity and abundance, which are extremely potential in the field of medium-temperature thermal energy storage. However, the application of erythritol in thermal energy storage is greatly restricts by high supercooling. Herein, sodium carboxymethyl cellulose (CMCNa) and hexagonal boron nitride (h-BN) are introduced to regulate the supercooling and thermal properties of erythritol. The crystal growth and nucleation process of erythritol is promoted effectively by CMC-Na and h-BN, as a result, the supercooling degree and solidification stability degree of erythritol is suppressed observably. According the results, while retaining the high latent heat of erythritol, the defect of supercooling of erythritol is effectively improved. The supercooling degree and solidification stability degree of erythritol are suppressed by 93% and 84%, respectively. Furthermore, the high latent heat, good thermal conductivity and excellent cycling thermal stability of erythritol composite phase change materials (ECPCM) are also available. This conclusion is important for supercooling regulation and thermal property optimization of erythritol, and indeed, can promote the utilization of erythritol in medium-temperature thermal energy storage.
The supercooling effect is deemed to be a crucial issue for thermal energy storage using phase change materials (PCMs). The exploration of promising additives plays a decisive role in effective suppression efforts for suppressing the supercooling effect of a PCM. The present work proposed a potential additive, polyvinylpyrrolidone (PVP), to reduce the supercooling of erythritol, which is the most promising polyol PCM candidate for medium temperature range. PVP with various loadings was dispersed in erythritol to make composites for the proof-of-concept tests. It was shown that the degree of supercooling of erythritol can be reduced significantly from over 64 °C to about 21 °C in the presence of only 1.0 wt.% PVP. Along with the mitigated supercooling effect, the addition of PVP also leads to an increase of the retrievable latent heat during crystallization, from ∼187 J/g to ∼224 J/g at the same minute PVP loading of 1.0 wt.%, by increasing the crystallinity of erythritol. The PVP-loaded erythritol composites exhibit little sacrifice in latent heat of fusion, i.e., only ∼15% loss when the PVP loading reaches 6.0 wt.%. In addition, multiple tests confirmed that PVP can be dissolved in erythritol, thus desirable compatibility was obtained and the composites would have long-term reliability. This proposed additive enables an efficient and cost-effective way for improving the crystallization behaviors of erythritol (and other polyol PCMs) towards real-world applications.
The main aim of this paper is to enhance the thermal conductivity of erythritol as phase change material (PCM). The expanded graphite (EG, thermal conductivity: 151 W/(m•K)) is dispersed into erythritol (melting point: 118 °C, thermal conductivity: 0.844 W/(m•K)) as the high thermal conductivity additive, in which erythritol can be adsorbed effectively. The 2% EG/erythritol composite PCM has better cycle stability and its thermal conductivity enhances obviously. The 1% calcium pimelate (CaPi) is used as nucleating agent to inhibit the supercooling of the composite PCM further. The 2%EG/1%CaPi/erythritol composite PCM starts to solidify at 98.5 °C and the equilibrium temperature is about 115 °C during 100 cycles. The latent heat is 352.66 J/g and the thermal conductivity measured by the laser flash method is 1.287 W/(m•K), which is 52.5% higher than pure erythritol. Therefore, it is a new candidate to be used in waste heat recovery, solar energy medium temperature heat collection and other fields.
Phase change materials (PCMs) have been extensively explored for latent heat thermal energy storage in advanced energy-efficient systems. Flexible PCMs are an emerging class of materials that can withstand certain deformation and capable of making compact contact with objects, thus offer substantial potential in a wide range of smart applications. To realize the flexibility, the energy storage capacity of flexible PCMs is partially reduced by the presence of thermally inactive flexible supports. Considering this tradeoff, several versatile methodologies have been proposed to develop flexible PCMs with optimal energy storage capacity and device-level flexibility. In this article, we systematically reviewed these strategies including (1) confinement of rigid PCM into flexible porous scaffolds, (2) encapsulation of PCM into elastic shells, and (3) development of intrinsically flexible PCM based on molecularly engineered structures. Besides, the applications of flexible PCMs in diverse fields including thermal management of electronic devices, thermal therapy of the human body, and flexible sensors have been presented. Finally, the major problems associated with the development of flexible PCMs and their prospective solutions are provided in detail.
The mesophase pitch derived graphite foams with low bulk density (L-GF) and high bulk density (H-GF) were spontaneously infiltrated by erythritol to prepare graphite foam/erythritol (GF/erythritol) phase change materials (PCMs) with ultrahigh thermal conductivity for medium temperature thermal energy storage applications. Results of thermophysical properties indicated that thermal diffusivity of the GF/erythritol PCMs can be enhanced by 66 and 117 times as compared with that of pristine erythritol in solid (0.36 mm²/s). This enhancement resulting from three-dimensional ordered network of graphite foam can significantly reduce the charging and discharging time of the PCM storage system. Although H-GF as a matrix can obtain a higher thermal conductivity (68.71 W/(m·K)) than L-GF (40.52 W/(m·K)), the smaller porosity cannot allow more erythritol to be absorbed, and its melting enthalpy (178.4 J/g) is lower than L-GF (266.6 J/g). In addition, the enhancement of thermal conductivity and the increase of interfacial surface area caused by graphite foam structure strongly suppresses the supercooling of erythritol, which can be reduced from 86.0 °C to 53.2 °C. The obtained results demonstrated that the GF/erythritol PCM as a stable PCM is a promising material for medium temperature thermal energy storage applications.
Based on the non-isothermal phase change behaviors of twenty-one pure and mixture sugar alcohols presented in our previous study (Part Ⅰ), the isothermal melting and crystallization behaviors were further tested in this supplemental work for five selected pure sugar alcohols (xylitol, erythritol, d-mannitol, d-dulcitol and inositol) and their five binary eutectic mixtures to make an advanced screening of these candidates for low-to-medium temperature latent heat storage. The isothermal melting and crystallization behaviors of these ten candidates were tested at a constant degree of superheat (10 °C) and various degrees of subcooling up to 210 °C. The phase change temperatures, degrees of supercooling and durations of phase change were determined by the recorded temperature-history curves. It was found that the incrystallizable xylitol and its eutectic mixture of xylitol (75 mol%) + erythritol with low melting points under 100 °C are also unable to crystallize during isothermal cool-down at any degrees of subcooling (30–90 °C) due to the unavailability to nucleation. The rest eight crystallizable candidates all suffer from severe supercooling and are unable to crystallize at low degrees of subcooling (<20 °C). They undergo both one-phase supercooling due to poor nucleation performance and two-phase supercooling, which was unable to be obtained previously by non-isothermal cooling, due to slow crystallization kinetics. However, it seems difficult to find a correlation between the observed degrees of supercooling in both the liquid and solid phases and the prescribed degrees of subcooling by only three consecutive isothermal melting and crystallization cycles, as a result of the randomness of nucleation and large size of samples. The duration of crystallization was shown to decrease with increasing the degree of subcooling for both pure and mixture sugar alcohols due to the enhanced driving force for crystallization. The durations of crystallization of the mixture sugar alcohols appear to be longer than those of their pure compounds, due to the lower thermal conductivity and higher dynamic viscosity of the mixtures. Combining the present isothermal and the previous non-isothermal test results, it has been confirmed that the difficulty in crystallization and the severe supercooling are the primary issues for sugar alcohols, which must be addressed before they can be used in real-world latent heat storage systems.
Thermal energy harvesting technologies based on composite phase change materials (PCMs) are capable of harvesting tremendous amounts of thermal energy via isothermal phase transitions, thus showing enormous potential in the design of state-of-the-art renewable energy infrastructure. Great progress has been recently made in terms of enhancing the thermal energy storage capability, transfer rate, conversion efficiency and utilization of composite PCMs. Although there are some recent reviews on composite PCMs, they are mainly concentrated on the thermal transfer enhancement and conventional utilization of PCMs. There are few systematic reviews concerning optimization strategies of PCM for thermal energy conversion. In particular, advanced multifunctional utilization of PCMs is still in its infancy. Herein, we systematically summarize the optimization strategies and mechanisms of recently reported composite PCMs for thermal energy storage, thermal transfer, energy conversion (solar-to-thermal, electro-to-thermal and magnetic-to-thermal conversion) and advanced utilization (fluorescence emission, infrared stealth technologies, drug release systems, thermotherapy and thermal protection), including some novel supporting materials (BN nanosheets and metal organic frameworks (MOFs)). Simultaneously, we provide in-depth and constructive insights into the correlations between the structural optimization strategies and thermal performances of composite PCMs. Finally, future research trends, alternative strategies and prospects are also highlighted according to up-to-date optimization strategies.
This paper describes a high thermal conductive phase change composite (PCC) of erythritol and Al filler with percolating network. The PCCs with various Al amounts were prepared by both melt-dispersion method and hot-press (HP) method. The effective thermal conductivity of PCCs was measured, and the distribution status of the erythritol and Al filler was observed. The percolated filler network in the PCCs can be easily formed by HP method, which is important for enhancing the thermal conductivity of PCCs. The PCM particles with nonuniform particle size and high packing ratio is essential for the formation of filler percolating network. A high thermal conductivity of 30 W m ⁻¹ K ⁻¹ can be obtained at a filler fraction of 42.2 vol%.
Towards latent heat storage in the low-to-medium temperature range (70–250 °C), screening of sugar alcohols and their binary eutectic mixtures as potential phase change materials was carried out by focusing on the non-isothermal melting and crystallization behaviors. A preliminary screening shortened the long list of isomers from common four-carbon to six-carbon sugar alcohols to only six affordable candidates, i.e., xylitol, d-sorbitol, erythritol, d-mannitol, d-dulcitol and inositol (ordered with increasing the melting point). Based on the six pre-screened sugar alcohols, a total of 15 binary eutectic mixtures were prepared to manipulate the melting points for more flexible match with real applications. Non-isothermal tests were then performed on a differential scanning calorimeter at various ramping/cooling rates up to 10 °C/min. In addition to determination of the melting point and latent heat of fusion, a special attention was paid to the crystallization behaviors by undertaking consecutive melting-crystallization cyclic tests. It was found that the two candidates with the lowest melting points (both below 100 °C), i.e., xylitol and d-sorbitol, as well as the nine binary eutectic mixtures containing at least one of them, are unable to crystallize from the melt during cool-down at any cooling rates tested (down to 0.5 °C/min). Four other binary eutectic mixtures, i.e., erythritol (84 mol%) + d-mannitol, erythritol (95 mol%) + d-dulcitol, erythritol (96 mol%) + inositol and d-dulcitol (69 mol%) + inositol, were also shown to be unable to crystallize upon cooling, with the crystallization occurring during the reheating process instead, referred to as cold crystallization. The rest four pure sugar alcohols with relatively high melting points (110–230 °C), i.e., erythritol, d-mannitol, d-dulcitol, inositol, and two mixtures, i.e., d-mannitol (70 mol%) + d-dulcitol and d-mannitol (82 mol%) +inositol, were found to be able to crystallize upon cooling, although they all suffer from severe supercooling (e.g., up to over 100 °C for erythritol). The affordable pure and mixture sugar alcohols were deemed to have desirably high latent heat storage density, especially for those with higher melting points. However, they all face specific issues associated with crystallization, which must be addressed before they can really be utilized in real applications. In addition, it may not worth making eutectic mixtures, although this is deemed to be an effective way of manipulating the melting points of sugar alcohols.
Sugar alcohols (SA) are emerging as one of better energy storage materials for thermal energy storage (TES) application due to its phase change temperature ranges (−15 to 245 °C) and considerable phase change enthalpies of 100–430 kJ/kg. However, the main challenges include the low thermal response of the phase change materials (PCM) owing to its very low thermal conductivity values. In this study, d-Mannitol (DM)-copper oxide (CuO) nanocomposites (DM-CuON) were prepared using dispersion technique to form high thermal conductive nanocomposites. In this view, copper oxide (CuO) nanoparticles were mixed in DM in various mass fraction of 0.1, 0.2 and 0.5 wt.% using high-speed ball mill. Structural analysis was done by SEM and crystallography by XRD diffraction techniques. The XRD data reveal that the pure DM exhibited the polymorphic form of beta (β) phase. By varying the weight percentage from 0.1 to 0.5 wt.% the rate of relative crystallization increased as compared to pure DM. Thermal conductivity enhancement of 25.2% was observed for DM-CuON with 0.5 wt.%. It was observed that the interaction between CuO nanoparticles and DM were only physical in nature which confirmed its high chemical stability. After repeated heating/cooling cycles the heat of fusion decreased yet it showed high latent heat value of 256.20 kJ/kg, 252.48 kJ/kg, 246.85 kJ/kg and 240.78 kJ/kg after 50 cycles and 241.16 kJ/kg, 237.49 kJ/kg, 229.86 kJ/kg and 205.48 kJ/kg after 100 cycles for DM and DM-CuON. Mass changes observed were less than 3% after thermal cycling for a temperature range up to 250 °C. Overall CuO helps to achieve improved thermo-physical and heat storage characteristics for DM-CuON which suggest their potential candidate of usage in the medium temperature thermal energy storage system.
In recent years, sugar alcohols have attracted much attention due to their remarkable phase change properties for thermal energy storage applications. The thermodynamic properties especially the heat capacities would play a crucial role in theoretically and technically investigating the energy storage performance for sugar alcohols. However, as far as we known, the heat capacities of sugar alcohols have never been studied in a wide temperature region. In this study, we have measured the heat capacities of six sugar alcohols of D-mannitol, Myo-Inositol, xylitol, D-arabinitol, L-arabinitol and erythritol in the temperature range from T = (1.9 to 550) K for the first time using a combination of Physical Property Measurement System and differential scanning calorimeter. Based on the heat capacity curve fitting, the standard molar heat capacity, entropy and enthalpy at 298.15 K and 0.1 MPa, and melting temperature and transition enthalpy in the solid-liquid phase transition region were consequently obtained for these sugar alcohols. Moreover, the heat capacity and phase transition properties obtained in this work were also compared with previous results reported in literature.
The thermal properties of the short carbon fibers (SCFs) filled erythritol phase change composites (PCCs) were investigated experimentally. The samples were prepared with different mass loadings of two kinds of SCFs, 1%, 2%, 4%, 7% and 10%. The melting points and phase change enthalpies were measured by differential scanning calorimeter (DSC). The effects of SCFs on the melting points are relatively small but the enthalpies were reduced with the loadings of SCFs. The greatest loss of enthalpies is 11.3% for composites filled with 10% SCFs. The thermal conductivities increased with the loadings of SCFs but not linearly. The highest thermal conductivity is 3.92 W/(m⋅K) for the composites with 10% longer SCFs, which was enhanced by 407.8% compared to pure erythritol (0.77 W/(m⋅K)). Composites filled with longer SCFs possess higher thermal conductivity and the mechanisms were discussed. A simple setup was made to test the temperature-regulated property of these materials. These include pure erythritol and phase change composites with different loading of SCFs. The PCCs have shown good application potential and the longer SCFs can lead to the better performance of PCCs.
Storing low-temperature surplus thermal energy from industries, power plants, and the like, using phase change materials (PCM) is an effective alternative in alleviating the use of fossil based thermal energy provision. Polyols; of some also known as sugar alcohols, are an emerging PCM category for thermal energy storage (TES). A review on polyols as PCM for TES shows that polyols have phase change temperatures in the range of −15 to 245 °C, and considerable phase change enthalpies of 100–413 kJ/kg. However, the knowledge on the thermo-physical properties of polyols as desirable PCM for TES design is presently sparse and rather inconsistent. Moreover, the phase change and state change behaviors of polyols need to be better-understood in order to use these as PCM; e.g. the state change glass transition which many polyols at pure state are found to undergo. In this work preliminary material property characterization with the use of Temperature-History method of some selected polyols, Erythritol, Xylitol and Polyethylene glycol (PEG) 10,000 were done. Complex behaviors were observed for some of the polyols. These are: two different melting temperatures, 118.5–120 °C and 106–108 °C at different cycles and an average subcooling 18.5 °C of for Erythritol, probable glass-transition between 0 and 113 °C for Xylitol, as well as a thermally activated change that is likely an oxidation, after three to five heating/cooling cycles for Xylitol and Erythritol. PEG 10,000 had negligible subcooling, no glass-transition nor thermally activated oxidation. However a hysteresis of around 10 °C was observed for PEG 10,000. Therefore these materials require detailed studies to further evaluate their PCM-suitability. This study is expected to be an initiation of an upcoming extensive polyol-blends phase equilibrium evaluation.
Broad-band dielectric relaxation measurements were performed for the four pentitols isomers, xylitol, adonitol, L-arabitol and D-arabitol. The comparison of the dynamical properties of these compounds shows similarities between the secondary relaxation processes but also important differences for the temperature dependence of the primary process characterized by the steepness index. These differences enable us to distinguish two groups of compounds that correspond to two kinds of molecular conformation. We show that the formation of more or less extended networks of hydrogen bonds, which reflects the more or less non-Arrhenius variation of the primary relaxation, can be related to the differences of conformation of the studied isomers.