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1.
Phase change materials (PCM) have an increasingly more important role as a thermal energy storage (TES) media. However, leakage problem of PCM causes limitation during their integration in TES systems. Therefore, the encapsulation of PCMs is attracting research interest to extend usage of PCMs in real TES applications in recent years. In this study, hydroxystearic acid (HSA) was encapsulated with polymethyl methacrylate (PMMA) and different PMMA comonomer shells via emulsion polymerization method for the first time in literature. HSA with high melting temperature range (74–78°C) can widen the scope of using PCMs, and the encapsulated form can make it more versatile. The chemical structures, morphologies, and thermophysical properties of capsules were determined by FT‐IR, SEM, DSC, TGA, and thermal infrared camera. Among the produced HSA capsule candidates, PMMA‐HEMA is the most promising with latent heat of 48.5 J/g with melting range of 47 to 85°C. SEM analysis indicated that the capsules have spherical shape with compact surface at nano‐micro (100–440 nm) size range; however, some capsules exhibited agglomeration.  相似文献   

2.
With advancement in technology—nanotechnology, various thermal energy storage (TES) materials have been invented and modified with promising thermal transport properties. Solid‐liquid phase change materials (PCMs) have been extensively used as TES materials for various energy applications due to their highly favourable thermal properties. The class of PCMs, organic phase change materials (OPCMs), has more potential and advantages over inorganic phase change materials (IPCMs), having high phase change enthalpy. However, OPCMs possess low thermal conductivity as well as density and suffer leakage during the melting phase. The encapsulation technologies (ie, micro and nano) of PCMs, with organic and inorganic materials, have a tendency to enhance the thermal conductivity, effective heat transfer, and leakage issues as TES materials. The encapsulation of PCMs involves several technologies to develop at both micro and nano levels, called micro‐encapsulated PCMs (micro‐PCM) and nano‐encapsulated PCMs (nano‐PCM), respectively. This study covers a wide range of preparation methods, thermal and morphological characteristics, stability, applications, and future perspective of micro‐/nano‐PCMs as TES materials. The potential applications, such as solar‐to‐thermal and electrical‐to‐thermal conversions, thermal management, building, textile, foam, medical industry of micro‐ and nano‐PCMs, are reviewed critically. Finally, this review paper highlights the emerging future research paths of micro‐/nano‐PCMs for thermal energy storage.  相似文献   

3.
The discovery of new eutectic phase change materials (PCMs) will overcome the current PCM challenges such as nonbiodegradability, super‐cooling, and limited thermal stability. This paper reports on the development of new bio‐based PCMs composed of binary mixtures of fatty acid esters and fatty alcohols at their eutectic compositions, which provide potential solid‐liquid PCMs for building applications. Six binary systems, namely 1‐dodecanol (DD) + methyl stearate (MES), DD + methyl palmitate (MEP), DD + methyl laurate (MEL), 1‐tetradecanol (TD) + MES, TD + MEP, and TD + MEL were prepared and their thermal behaviours were deliberated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), long‐term thermal stability test, and mass loss analysis. Amongst the studied systems, phase change transition temperature and latent heat of fusion of the eutectic mixtures of DD‐MES, DD‐MEP, TD‐MES, and TD‐MEP were found to be suitable for the building application with values of 22.46°C/201.91 J/g, 20.34°C/224.45 J/g, 32.05°C/209.38 J/g, and 26.72°C/210.15 J/g, respectively. The average degree of super‐cooling for all PCMs was below 2°C, and no significant changes in thermophysical properties of the developed PCMs were observed after 1000 thermal cycles.  相似文献   

4.
In this study, a numerical analysis is performed to investigate the freezing process of phase change materials (PCM) in a predesigned thermal energy storage (TES) device. This TES device is integrated with a milk storage cooling cycle operating under predefined practical conditions. Using this cooling unit, 100 litres of milk is kept cool at 4°C for 48 hours before it is collected. A 2-D model of the TES device is developed in COMSOL Multiphysics to analyze the phase change performance of water-based PCMs. The variations of thermal properties with temperature during the phase change are considered in the analysis. The model is used for exploring the solidification process of PCMs inside the TES device. Temperature variations with time, ice formation, and the impacts of boundary conditions are investigated in detail. Water PCM shows better characteristics in the solidification process in comparison to eutectic PCMs, which is mainly due to the differences between phase change temperatures of the PCMs.  相似文献   

5.
Phase change materials (PCMs) with suitable melting ranges for thermal energy storage applications are alkanes, paraffins, fatty acids, eutectic mixtures, and inorganic PCMs. Paraffinic hydrocarbons and fatty acids with low solubility in water are usually the preferred candidates. Pentadecane, which is an alkane hydrocarbon with the chemical formula C15H32, was used as PCM in this study. The pentadecane was microencapsulated with a poly(melamine‐urea‐formaldehyde (MUF)) shell for thermal energy storage. Pentadecane/poly(MUF) microcapsules were prepared by in situ polymerization method. The morphological analysis of pentadecane microcapsules was analyzed with scanning electron microscopy (SEM). Thermal properties of microcapsulated pentadecane were determined by differential scanning calorimetry (DSC). The results demonstrated that pentadecane/PUF microcapsules were prepared successfully, and they offer proper phase transition temperature range (8.7°C and 8.1°C) and heat enthalpy values (84.5 and ?88.2 kJ/kg) for thermal energy storage applications. According to the results, it was determined that pentadecane/poly(MUF) microcapsules have good potential for thermal energy storage applications.  相似文献   

6.
Organic and inorganic phase change materials(PCMs) are considered potential materials for thermal energy storage(TES) with different phase change characteristics. In this study, a novel organic-inorganic composite phase change material(PCM) called disodium hydrogen phosphate dodecahydrate-lauric-palmitic acid(D-LA-PACM) was prepared. Expanded graphite(EG) was selected as the support material, and the novel organic-inorganic form-stable PCM called D-LA-PAPCM/EG was prepared using the vacuum adsorption method. Differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, leakage testing, melting and solidification cycle testing, thermal conductivity testing, scanning electron microscopy observation of the micromorphology, and other characterization methods were used to study the microstructure and morphology, thermal physical parameters, thermal conductivity, stability of the PCMs, and the comprehensive material properties of D-LA-PAPCM under the composite action of EG. Results indicated that the melting and freezing temperatures and latent heats of D-LA-PAPCM/EG were measured to be 31.6℃ and 34.3℃ and 142.9 and 142.8 J/g, respectively. Although some of the lauric-palmitic acid(LA-PA) and disodium hydrogen phosphate dodecahydrate(DHPD) separated in the multiple porous structures of EG after 1000 cycles, they could still absorb and release latent heats independently, with D-LA-PAPCM/EG still exhibiting good thermal stability. The thermal conductivity of D-LA-PAPCM/EG was 1.361 W/(m·K). Therefore, the material and thermal properties of the prepared D-LA-PAPCM/EG indicate that it could be well used as a feasible material for energy-saving phase change floor units in indoor TES systems.  相似文献   

7.
Fatty acids are bio-based materials that can be used as phase change materials (PCMs). Microencapsulation of low carbon number fatty acids for mainly building applications have been realized in previous studies. In this study, behenic acid (BA), a fatty acid with medium melting range (65°C-85°C), has been microencapsulated for the first time. PMMA and its three copolymers were used as shell material of these novel encapsulated PCMs prepared by emulsion polymerization technique. The influences of using different comonomers in shell materials on the thermal, morphological, and chemical properties were investigated. Melting phase change temperature ranges were found as 65°C to 85°C for all capsule candidates. Capsules had uniform spherical geometry with size ranges under 500 nm. The capsules are suggested as novel PCM candidates in this temperature range that has potential applications in industrial waste heat, electronics, solar residential heating, lithium-ion batteries, and automotive application.  相似文献   

8.
Global warming is one of the most important consequences of excess energy consumption. Phase change materials (PCMs) have prominent advantages in thermal energy storage owing to their high latent heat capacities and small temperature variations during the phase change process. However, leakage is a major problem that limits the use of PCMs. Leakage may occur in encapsulated PCMs or in composites where the PCM is attached to the surface of a supporting material or within the pores of that material. In this study, pentadecane/diatomite and pentadecane/sepiolite nanocomposites were fabricated by using unmodified and microwave‐irradiated diatomite and sepiolite samples and by using different compounding processes, such as direct impregnation, vacuum impregnation, and ultrasonic‐assisted impregnation methods. The microstructures and the chemical and thermal properties of the composites were characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and differential scanning calorimetry. Subsequently, the thermal reliability and stability and the thermal conductivity of the PCM composites were also investigated. A melting temperature of 9.25°C and a latent heat capacity of 58.73 J/g were determined for the pentadecane/diatomite composite that was prepared with the direct impregnation method using a microwave‐treated diatomite sample. The pentadecane/sepiolite composite prepared in the melting temperature range 7.98°C to 8.53°C and latent heat capacity range 41.05 to 46.02 J/g. The results of the thermal analysis indicate that fabricated diatomite‐based or sepiolite‐based PCM composites have good potential as thermal energy storage materials.  相似文献   

9.
《Solar Energy Materials》1989,18(3-4):201-216
An analysis of thermal properties of fatty acids and their binary mixtures has shown that they are attractive candidates for latent heat thermal storage in space heating applications. In this study, the method of differential scanning calorimetry was used to determine the transition temperatures and latent heat of transition of the fatty acids and their binary mixtures. These properties are of prime importance in the design of a latent heat thermal storage system.The melting range of the fatty acids (capric, lauric, palmitic and stearic) was observed to be approximately from 30°C to 65°C. Their heat of transition was observed to have a range from approximately 153 to 182 J/g. The eutectic points were determined for the binary mixtures of the fatty acids. The melting points of the eutectics for the binary systems of capric-lauric, lauric-palmitic, lauric-stearic and palmitic-stearic acids were found to be 18°C, 32.7°C, 34°C and 51°C respectively. The corresponding heats of melting were 120, 145, 150 and 160 J/g, respectively. The fatty acids and their eutectic mixtures were examined with an infrared spectrophotometer to ascertain the polymorphic forms and material purities.  相似文献   

10.
Expanded graphite (EG) has shown excellent performances in compression resilience, thermal conductivity, and adsorption ability. EG can adsorb liquid phase change materials (PCMs) mainly because of capillary action; however, EG is hydrophobic, which makes it less compatible with hydrated salts. Herein, hydrophilic EG (HEG) was prepared with Triton X‐100 (TX‐100) as surface modifier. The HEG–magnesium nitrate hexahydrate (HEG‐MNH) composite as a PCM was investigated for thermal energy storage (TES) to understand the effect of hydrophilic modification on thermophysical properties. The powder‐state HEG is added into MNH to prepare HEG‐MNH composite PCM, which contains 1.71 wt% of TX‐100, 7.29 wt% of EG, and 91.00 wt% of MNH by control variable method. The melting point and latent heat of HEG‐MNH composite PCM were 89.05°C and 137.28 J/g, respectively. The endothermic enthalpy change of HEG‐MNH composite PCM only decreased by 0.90%, along with the exothermic values of HEG‐MNH composite that increased by 3.80% after 100 cycles. The thermal conductivity is higher 5.17 times than that of the pure MNH. Our work suggests that the HEG‐MNH composite PCM has a great potential to be used as a PCM for TES.  相似文献   

11.
A one‐dimensional (1D) physical model is developed for latent heat thermal energy storage (TES) systems using composite phase change materials (PCMs) with different phase change temperature (PCT) distributions. By theoretical investigation under the assumption of neglecting the sensible heat, the optimum linear PCT distributions which are corresponding to minimum phase change time are derived. To verify the theoretical results of the optimum linear PCT distributions, the finite difference method is adopted to simulate the cyclical freezing and melting processes of composite PCMs. The numerical results in which the sensible heat is taken into account show that: (1) the optimum linear PCT distributions obtained from the theoretical analyses seem to be the optimum ones of composite PCMs in practical latent heat TES systems; (2) the phase change time of composite PCMs with the optimum linear PCT distributions used in practical latent heat TES systems can be decreased by as much as 25–40% by properly selecting the segmented numbers of composite PCMs as compared with that of PCMs of a single PCT. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

12.
Sugar alcohols are promising solid‐liquid phase change materials (PCMs). However, problems such as possible leakage of liquid PCMs, high and unstable supercooling, and low thermal conductivity need to be solved. In this work, a novel form‐stable PCM in which m‐erythritol (ME), polyaniline (PANI), and silver nanowires (Ag NWs) were applied as solid‐liquid PCM, supporting material, and thermal conductive filler, respectively, was successfully prepared in anhydrous ethanol by surface polymerization of aniline. Form‐stable PCM with good form stability could be obtained when the ratio of ME/(aniline + ME) was no more than 78.7 wt%. The melting enthalpy (ΔHm) of the ME/PANI form‐stable PCMs could attain 234.8 J/g while that of the ME/PANI/Ag NWs form‐stable PCMs was about 220 J/g. In addition, the thermal conductivity of the form‐stable PCM was increased by 61.6% when 7.5 wt% Ag NW was added. Moreover, the supercooling of ME was effectively suppressed from 100°C for pure ME to 60°C, corresponding to an improvement of 40%, for the form‐stable PCM containing 7.5 wt% Ag NWs. The supercooling suppression could be ascribed to that PANI provided great amounts of nucleating centers and improved the nucleation kinetics, and Ag NWs improved the thermal diffusivity and thus increased the crystallization rate.  相似文献   

13.
High-chain fatty acid esters have not been investigated for their thermal properties as phase change materials (PCMs) in thermal energy storage. A series of high-chain fatty acid esters of myristyl alcohol (1-tetradecanol) were synthesized via esterification of lauric, myristic, palmitic, stearic and arachidic acids under vacuum and in the absence of any catalyst. The esterification reactions were studied by FT-IR spectroscopy. A differential scanning calorimeter (DSC) and a thermo-gravimetric analyzer (TGA) were intensively used to determine the thermal properties of the introduced thermal storage materials. The thermal properties were given in terms of phase change temperature, enthalpy, specific heat (Cp) and thermal decomposition temperature with related statistical data. The thermal reliability of the novel organic PCMs was investigated by thermal cycling with 1000 thermal cycles with respect to the thermal properties of the original synthesized PCMs. In addition to the synthesized esters, one commercial product was also investigated. The DSC analyses indicated that the melting points of the novel organic PCMs were between 38 and 53 °C with phase change enthalpy above 200 kJ/kg. The effect of chemical structure of the materials on thermal properties was also discussed. The results showed that these materials were favorable for low temperature heat transfer applications with superior thermal properties and reliability.  相似文献   

14.
Ethylene dilauroyl, dimyristoyl, and dipalmitoyl amides were synthesized as novel solid-liquid phase change materials (PCMs) via condensation of ethylene diamine with the respective carboxyl chlorides (lauroyl chloride, myristoyl chloride, and palmytoyl chloride). The synthesized ethylene dilauroyl amide (EDLA), ethylene dimyristoyl amide (EDMA), and ethylene dipalmytoyl amide (EDPA) were characterized structurally by FT-IR and 1H NMR spectroscopy techniques. Latent heats of melting and freezing determined using DSC technique were found to be 127.83 and −118.30 J/g for EDLA, 129.95 and −132.40 J/g for EDMA, and 150.66 and −145.22 J/g for EDPA, respectively. Phase change temperatures of these PCMs were ranged between 38.5 and 52.5 °C. The synthesized PCMs were tested for durability by accelerated thermal cyclings including 1000 melting/freezing cycles. Besides the thermal endurance of the PCMs were determined by TG analysis. Based on the results it was concluded that EDLA, EDMA, and EDPA compounds synthesized as novel solid-liquid PCMs have considerable amount of thermal energy storage potential in terms of suitable phase change temperatures, high latent heats, thermal reliability, and thermal stability. Moreover, the other advantages of the synthesized PCMs over the fatty acids used are better odor, low corrosivity, and low sublimation rates.  相似文献   

15.
Micro‐phase change materials (micro‐PCMs) are proposed to increase the thermal conductivity and the thermal energy storage capacity of a heat transfer fluid (HTF). In this work, we have selected dimethyl terephthalate (DMT) to be used as a PCM for performance enhancement of a synthetic oil in the temperature range of approximately 100 to 170 °C. Silicon dioxide (SiO2) was used as the microencapsulant, because of its desirable properties as containment material, including thermal stability. The SiO2‐coated DMT micro‐PCM was characterized to determine relevant properties and its suitability for HTF performance enhancement. The SiO2‐coated DMT was found to completely disperse in the synthetic oil, Therminol SP, silicone oil, at and above 100 °C. FTIR, thermal diffusivity and differential scanning calorimetry measurements were carried out on the materials, and these tests demonstrated that the coated particles can be used for HTF enhancement in the temperature range of 100–170 °C and potentially higher temperatures if pressurized pipes/vessels are utilized. Using the measured thermal diffusivity and known data for density and specific heat capacity, the thermal conductivity of the micro‐PCM was calculated. Our calculations indicate that both the thermal conductivity and the thermal energy storage heat capacity of the HTF would be enhanced by the addition of this micro‐PCM. It is expected that the thermal conductivity increase will enhance the heat transfer of the fluid when in use at temperatures above and below the melting temperature of the PCM. At the melting point, the latent heat of the PCM will increase the thermal energy storage capacity of the fluid. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

16.
In the present work, six new kinds of building composite PCMs (BCPCMs), PS/octadecane, BC/octadecane, PS/CA–MA, BC/CA–MA, PS/PEG1000, and BC/PEG1000 composites, were prepared by using vacuum impregnation method. The maximum percent of PCM in the composites was assigned to be 12, 13, 18, 23, 30, and 42 wt%, respectively. The form‐stable BCPCMs were characterized using SEM, FT‐IR, DSC, and TG analysis techniques. The characterization results showed the existence of homogenous dispersion of the PCM into the PBM matrixes. The DSC measurements indicated that the melting temperatures of the form‐stable BCPCMs are in the range of 20–33°C while they have latent heats of melting in the range of about 28–55 J/g. These results make them promising BCPCMs for low temperature‐passive TES applications in buildings. Thermal cycling test indicated that the prepared BCPCMs have good thermal reliability and chemical stability. TG analysis proved that the prepared BCPCMs have good thermal durability. In addition, the thermal conductivity of BCPCMs was enhanced considerably by addition of expanded graphite (EG). The improvement in thermal conductivity of the BCPCMs caused appreciably reduction in their melting times. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Abstract

This article focuses on the preparation and thermo-physical properties of paraffin/high density polyethylene (HDPE) composites as form-stable solid-liquid phase change material (PCM) for thermal energy storage. In the paraffin/HDPE blend, the paraffin (P) dispersed into the HDPE serves as a latent heat storage material when the HDPE, as a supporting material, prevents the melted paraffin leakage thanks to its structural strength. Therefore, this type composite is form-stable and can be used as a PCM without encapsulation for thermal energy storage. In this study, two paraffins with melting temperatures of 48°C–50°C and 63°C–65°C were used. The mass percentages of paraffins in the composites could go high as 76% without any seepage of the paraffin in melted state. The dispersion of the paraffin into the network of the solid HDPE was investigated using scanning electronic microscope (SEM). The melting temperatures and latent heats of the form-stable P1/HDPE and P2/HDPE composite PCMs were determined as 44.32°C and 61.66°C, and 179.63 and 198.14 Jg?1, by the technique of differential scanning calorimetry (DSC), respectively. Furthermore, the thermal conductivity of the composite PCMs were improved as about 33.3% for the P1/HDPE and 52.3% for the P2/HDPE by introducing the expanded and exfoliated graphite to the samples in the ratio of 3 wt%. The results reveal that the prepared form-stable composite PCMs have great potential for thermal energy storage applications in terms of their satisfactory thermal properties, improved thermal conductivity and cost-efficiency because of no encapsulation for enhancing heat transfer in paraffin.  相似文献   

18.
Latent heat thermal energy storage refers to the storage and recovery of the latent heat during the melting/solidification process of a phase change material (PCM). Among various PCMs, medium‐ and high‐temperature candidates are attractive due to their high energy storage densities and the potentials in achieving high round trip efficiency. Although a few review studies on high‐temperature PCMs have emerged in the past few years, the quantity, completeness, and accuracy of the presented data are relatively poor. Also, an efficient indexing methodology for retrieving useful PCM data is missing in the open literature. In this article, we created an up‐to‐date PCM database following a holistic review of the PCMs in medium‐ and high‐temperature applications over a temperature range of 100°C to 1680°C. Such effort then allows us to develop an accurate indexing tool for the fast selection of suitable PCM candidates and extraction of the related property data. More specifically, the created PCM database covers 496 entries of PCM materials, which are extracted from the scattered research works published during the year 1956 to 2017. The collected information includes both the basic thermo‐physical properties of PCMs (eg, melting temperature, heat of fusion, and thermal conductivity) and crucial design factors during construction and engineering phases (eg, energy storage density, volume expansion, liquid/solid densities, and cost). The reviewed PCMs comprise a wide variety of materials, including fluorides, chlorides, hydrates, nitrates, carbonates, metals and alloys, and other uncommon compounds and salts. In addition, the current work presents a brief review on high‐temperature latent heat thermal energy storage systems categorized into metallic and non‐metallic systems. The corrosivity and stability of PCMs, which are commonly ignored in previous studies, are also examined.  相似文献   

19.

Thermal energy storage performance of fatty acids and a eutectic mixture as phase change materials (PCMs) has been investigated experimentally. The selected PCMs for this study were palmitic acid, myristic acid, stearic acid, and a mixture of stearic and myristic acids in eutectic combination ratio of 65.7 wt% myristic acid and 34.3 wt% stearic acid. The PCMs have a melting temperature range of 50.0°C to 61.20°C and a latent heat range of 162.0 J/g to 204.5 J/g. The inlet temperature and the mass flow rate of heat transfer fluid (HTF) were selected as experimental parameters to test the thermal energy storage performance of the PCMs. The transition times, temperature range, propagation of the solid-liquid interface, as well as heat flow rate characteristics of the employed cylindrical tube storage system were studied at varied experimental parameters. The experimental results show that the melting front moves to inward in the radial directions as well as in the axial directions from the top toward to the bottom of the PCM tube. It was observed that the convection heat transfer in the liquid phase plays an important role in the melting process. The changes in the studied HTF parameters have more effect on the melting processes than the solidification processes of the PCMs. The average heat storage efficiency calculated from data for all the PCMs is 51.5%, meaning that 48.5% of the heat actually was lost somewhere.  相似文献   

20.
Screening alternatives for producing paraffinic phase change materials (PCMs) from natural gas‐based products was investigated. Based on the quality and cost of these PCMs, two sources were identified: (i) hydrogenated gas‐to‐liquid (GTL) products such as heavy detergent feedstocks; and (ii) linear alpha olefins. Fractionation of a typical hydrogenated GTL mixture, containing C14 – C18 alkene and alkane hydrocarbons, has been experimentally conducted to produce five paraffinic PCMs with melting points between 3 and 28 °C. ChemCAD simulation has been proved to be a valid tool for predicting the behaviour of the GTL fractionation, including optimum experimental conditions and compositions of products. Also, hydrogenation of technical 1‐octadecene was experimentally carried out in order to evaluate the quality of PCM produced from one of the available technical alpha‐olefins. All PCMs produced in this work were analysed by gas chromatography equipped with flame ionization detector to determine their compositions and by differential scanning calorimetry to determine their latent heats. The results showed that the PCM with a melting temperature in the range 22 to 25 °C can be technically produced through hydrogenation of commercial 1‐octadecene showing a higher latent heat compared to the PCM produced from fractionation of hydrogenated GTL mixture. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

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