Capric-myristic acid/vermiculite composite as form-stable phase change material for thermal energy storage

Phase change materials (PCMs) can be incorporated with building materials to obtain novel form-stable composite PCM which has effective energy storage performance in latent heat thermal energy storage (LHTES) systems. In this study, capric acid (CA)-myristic acid (MA) eutectic mixture/vermiculite (VMT) composite was prepared as a novel form-stable PCM using vacuum impregnation method. The composite PCM was characterized using scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis technique. Thermal properties and thermal reliability of the composite PCM were determined by differential scanning calorimetry (DSC) analysis. The CA-MA eutectic mixture could be retained by 20 wt% into pores of the VMT without melted PCM seepage from the composite and therefore, this mixture was described as form-stable composite PCM. Thermal cycling test showed that the form-stable composite PCM has good thermal reliability and chemical stability although it was subjected to 3000 melting/freezing cycling. Thermal conductivity of the form-stable CA-MA/VMT composite PCM was increased by about 85% by introducing 2 wt% expanded graphite (EG) into the composite. The increase in thermal conductivity was confirmed by comparison of the melting and freezing times of the CA-MA/VMT composite with that of CA-MA/VMT/EG composite. The form-stable PCM including EG can be used as energy absorbing building material such as lightweight aggregate for plaster, concrete compounds, fire stop mortar, and component of interior fill for wallboards or hollow bricks because of its good thermal properties, thermal and chemical reliability and thermal conductivity.     

Synthesis and thermal energy storage properties of ethylene dilauroyl, dimyristoyl, and dipalmitoyl amides as novel solid-liquid phase change materials

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.     

Preparation of capric acid/halloysite nanotube composite as form-stable phase change material for thermal energy storage

A novel form-stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing capric acid (CA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can contain capric acid as high as 60 wt% and maintain its original shape perfectly without any CA leakage after subjected to 50 melt-freeze cycles. The melting temperature and latent heat of composite (CA/HNT: 60/40 wt%) were determined as 29.34 °C and 75.52 J/g by DSC. Graphite (G) was added into the composite to improve thermal storage performance and the thermal storage and release rates were increased by 1.8 times and 1.7 times compared with the composite without graphite, respectively. Due to its high adsorption capacity of CA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical applications such as solar energy storage, building energy conservation and agricultural greenhouse in the near future.     

Development of a ventilation system utilizing thermal energy storage for granules containing phase change material

We have developed an experimental ventilation system that features direct heat exchange between ventilation air and granules containing a phase change material (PCM). Measurement of outlet air temperature when the inlet air temperature was periodically varied to simulate changes of outdoor ambient air temperature showed that the outlet air temperature was stabilized and remained within the phase change temperature range. This effect is expected to be useful in practical ventilation systems. The potential of such systems for reducing ventilation load was examined through computer simulation for eight representative cities of Japan. This revealed how different temperature conditions would affect required heat storage capacity.     

Preparation, thermal properties and thermal reliability of palmitic acid/expanded graphite composite as form-stable PCM for thermal energy storage

This study is focused on the preparation and characterization of thermal properties and thermal reliability of palmitic acid (PA)/expanded graphite (EG) composite as form-stable phase change material (PCM). The maximum mass fraction of PA retained in EG was found as 80 wt% without the leakage of PA in melted state even when it is heated over the melting point of PA. Therefore, the PA/EG (80/20 w/w%) composite was characterized as form-stable PCM. From differential scanning calorimetry (DSC) analysis, the melting and freezing temperatures and latent heats of the form-stable PCM were measured as 60.88 and 60.81 °C and 148.36 and 149.66 J/g, respectively. Thermal cycling test showed that the composite PCM has good thermal reliability although it was subjected to 3000 melting/freezing cycles. Fourier transformation infrared (FT-IR) spectroscopic investigation indicated that it has good chemical stability after thermal cycling. Thermal conductivities of PA/EG composites including different mass fractions of EG (5%, 10%, 15% and 20%) were also measured. Thermal conductivity of form-stable PA/EG (80/20 w/w%) composite (0.60 W/mK) was found to be 2.5 times higher than that of pure PA (0.17 W/mK). Moreover, the increase in thermal conductivity of PA was confirmed by comparison of the melting and freezing times of pure PA with that of form-stable composite. Based on all results, it was concluded that the form-stable PA/EG (80/20 w/w%) has considerable latent heat energy storage potential because of its good thermal properties, thermal and chemical reliability and thermal conductivity.     

Galactitol hexa stearate and galactitol hexa palmitate as novel solid-liquid phase change materials for thermal energy storage

Galactitol has a melting point of 187.41 °C and a fusion enthalpy of 401.76 J g⁻¹. Its melting temperature is not suitable for many thermal energy storage applications although it has good latent heat storage capacity compared to the several traditional phase change materials (PCMs). The galactitol also has high supercooling degree as about 72 °C. These unfavorable properties limit the usage potential of galactitol in thermal energy storage applications. However, the phase change temperature and supercooling degree of galactitol can be reduced to a reasonable value and therefore its feasibility for energy storage systems can be increased. For this aim, in this study, galactitol hexa stearate (GHS) and galactitol hexa palmitate (GHP) were prepared as novel solid-liquid PCM by means of esterification reaction of the galactitol with palmitic acid and stearic acid. The GHP and GHS esters were characterized chemically using FT-IR and ¹H NMR techniques. By using DSC analysis method, the melting temperature and latent heat value of the PCMs were determined as 31.78 °C and 201.66 J g⁻¹ for GHP ester and 47.79 °C and 251.05 J g⁻¹ for GHS ester. Thermal cycling test showed that the prepared PCMs had good thermal reliability after thermal 1000 melting-freezing cycles. Thermogravimetric analysis (TGA) results revealed that the PCMs have good thermal stability over their working temperatures. In addition, thermal conductivity of the prepared PCMs was increased as about 26.3% for GHP and 53.3% for GHS by addition of 5 wt.% expanded graphite. Based on all results it can be concluded that the prepared GHP and GHS esters can be considered as promising solid-liquid PCMs for many energy storage applications such as solar energy storage, indoor temperature controlling in buildings, production of smart textile and insulation clothing due to their good energy storage properties.     

Micro-encapsulated paraffin/high-density polyethylene/wood flour composite as form-stable phase change material for thermal energy storage

Six novel polymer-based form-stable composite phase change materials (PCMs), which comprise micro-encapsulated paraffin (MEP) as latent heat storage medium and high-density polyethylene (HDPE)/wood flour compound as supporting material, were prepared by blending and compression molding method for potential latent heat thermal energy storage (LHTES) applications. Micro-mist graphite (MMG) was added to improve thermal conductivities. The scanning electron microscope (SEM) images revealed that the form-stable PCMs have homogeneous constitution and most of MEP particles in them were undamaged. Both the shell of MEP and the matrix prevent molten paraffin from leakage. Therefore, the composite PCMs are described as form-stable PCMs. The differential scanning calorimeter (DSC) results showed that the melting and freezing temperatures as well as latent heats of the prepared form-stable PCMs are suitable for potential LHTES applications. Thermal cycling test indicated the form-stable PCMs have good thermal stability although it was subjected to 100 melt–freeze cycles. The thermal conductivity of the form-stable PCM was increased by 17.7% by adding 8.8 wt% MMG. The results of mechanical property test indicated that the addition of MMG has no negative influence on the mechanical properties of form-stable composite PCMs. Taking one with another, these novel form-stable PCMs have the potential for LHTES applications in terms of their proper phase change temperatures, improved thermal conductivities, outstanding leak tightness of molten paraffin and good mechanical properties.     

Morphology and thermal properties of electrospun fatty acids/polyethylene terephthalate composite fibers as novel form-stable phase change materials

The ultrafine fibers based on the composites of polyethylene terephthalate (PET) and a series of fatty acids, lauric acid (LA), myristic acid (MA), palmitic acid (PA), and stearic acid (SA), were prepared successfully via electrospinning as form-stable phase change materials (PCMs). The morphology and thermal properties of the composite fibers were studied by field emission scanning electron microscopy (FE-SEM) and differential scanning calorimetry (DSC), respectively. It was found that the average fiber diameter increased generally with the content of fatty acid (LA) in the LA/PET composite fibers. The fibers with the low mass ratio maintained cylindrical shape with smooth surface while the quality became worse when the mass ratio is too high (more than 100/100). Moreover, the latent heat of the composite fibers increased with the increase of LA content and the phase transition temperature of the fibers have no obvious variations compared with LA. In contrast, both the latent heat and phase transition temperature of the fatty acid/PET composite fibers varied with the type of the fatty acids, and could be well maintained after 100 heating-cooling thermal cycles, which demonstrated that the composite fibers had good thermal stability and reliability.     

Fatty acid eutectic/polymethyl methacrylate composite as form-stable phase change material for thermal energy storage

This work is focused on the preparation and characterization of fatty acid eutectic/polymethyl methacrylate (PMMA) form-stable phase change material (PCM). Capric acid (CA), lauric acid (LA), myristic acid (MA) and stearic acid (SA) were selected to prepare binary fatty acid eutectic for the sake of decreasing the phase change temperature. Using the method of self-polymerization, CA–LA, CA–MA, CA–SA and LA–MA eutectics acting as the heat-absorbing materials and PMMA serving as the supporting material were compounded in the ratio of 50/50 wt.%. The relations between mass fraction of LA–MA eutectic and latent heat and compressive strength of LA–MA/PMMA composite were discussed, and the feasible maximum mass fraction of LA–MA eutectic was determined to be 70%. CA–LA/PMMA, CA–MA/PMMA, CA–SA/PMMA and LA–MA/PMMA composites were examined to investigate their potential application in building energy conservation. Scanning electron microscope and polarizing optical microscope observations showed that fatty acid eutectic was coated by PMMA thus the composite remained solid when the sample was heated above the melted point of the fatty acid. Fourier-transform infrared results indicated that fatty acid and PMMA had no chemical reaction and exhibited good compatibility with each other. According to the differential scanning calorimetry results, phase change temperatures of CA–LA/PMMA, CA–MA/PMMA, CA–SA/PMMA and LA–MA/PMMA composites were 21.11 °C, 25.16 °C, 26.38 °C and 34.81 °C and their latent heat values were determined to be 76.3 kJ/kg, 69.32 kJ/kg, 59.29 kJ/kg and 80.75 kJ/kg, respectively. Moreover, thermal stability and expansibility of the form-stable PCMs were characterized by thermogravimetric analysis and volume expansion coefficient respectively, and the results indicated that the composites were available for building energy conservation.     

PolyHIPE composite based-form stable phase change material for thermal energy storage

A novel shape-stabilized n-hexadecane/polyHIPE composite phase change material (PCM) was designed and thermal energy storage properties were determined. Porous carbon-based frameworks were produced by polymerization of styrene-based high internal phase emulsions (HIPEs) in existence of the surface modified montmorillonite nanoclay. The morphological and mechanical properties of the obtained polyHIPEs were investigated by scanning electron microscopy analysis and the compression test, respectively. The polyHIPE composite with the best pore morphology and the highest compression modulus was determined as a framework to prepare the form stable n-hexadecane/polyHIPE composite phase change material using the one-step impregnation method. The chemical structure and morphologic property of composite PCM was investigated by FT-IR and polarized optical microscopy analysis. Thermal stability of the form-stable PCM (FSPCM) was examined by TG analysis. The n-hexadecane fraction engaged into the carbon foam skeleton was found of as 55 wt% from TG curve. differential scanning calorimetry analysis was used for determining melting temperature and latent heat storage capacity of FSPCM and these values were determined as (26.36°C) and (143.41 J/g), respectively. The results indicated that the obtained composite material (FSPCM) has a considerable potential for low temperature (18°C-30°C) thermal energy storage applications with its thermal energy storage capacity, appropriate phase change temperatures and high thermal stability.     

Thermal energy storage properties of polyethylene glycol grafted styrenic copolymer as novel solid-solid phase change materials

Polymeric solid-solid phase change materials (S-SPCMs) are functional materials with phase transition-heat storing/releasing ability. With this respect, a series of polyethylene glycol (PEG) grafted styrenic copolymer were produced as novel S-SPCMs. PEGs with three different molecular weights were used for synthesis of isocyanate-terminated polymers (ITPs). To achieve cross-linking S-SPCMs, the ITPs were grafted with styrene-co-ally alcohol) (PSAA) at three different PSAA:PEG mole ratios. The produced polymers were characterized using Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (¹H NMR), and X-ray diffraction (XRD) technique. The crystalline-amorphous phase transitions of the polymers were examined using polarized optical microscopy (POM). The FT-IR, NMR, and XRD results confirmed the expected chemical structures and crystallization performances of the polymers. Thermal energy storage (TES) properties of the S-SPCMs were determined by differential scanning calorimetry (DSC). The DSC results revealed that the polymers with grafting ratio of PSAA:PEG(1:1) had phase transition enthalpies between about 74 and 142 J/g and phase transition temperatures between about 26°C and 57°C. Thermogravimetric analysis (TGA) measurements demonstrated that the S-SPCMs were resistant to thermal decomposition until about 300°C. Thermal conductivities of the produced S-SPCMs were measured in a range of about 0.18 to 0.19 W/mK. Furthermore, TES properties of the S-SPCMs were slightly changed as their chemical structures were remained after 5000 thermal cycles. By overall evaluation of the findings, it can be foreseen that particularly PSAA-g-PEG(1:1) polymers can be considered as promising S-SPCMs for some TES practices such as air conditioning of buildings, thermoregulation of food packages, automobile components, electronic devices, and solar photovoltaic panels.     

Microencapsulation of phase change material with poly(ethylacrylate) shell for thermal energy storage

Microcapsules containing caprylic acid and polyethylacrylate shells were prepared using an emulsion polymerization technique for thermal energy storage applications. Ethylene glycol dimethacrylate was used as a crosslinking agent. The influence of the crosslinking agent concentration on the phase change properties of microcapsules was examined. The caprylic acid microcapsules (MicroPCMs) were analyzed by Fourier transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, and differential scanning calorimetry. The results showed that microcapsules were synthesized successfully and that the best shell material:crosslinking agent concentration ratio was 1:0.2. The melting and freezing temperatures were measured through differential scanning calorimetry analysis and found to be 13.3 and 7.1°C, respectively. The melting and crystallization heats were determined to be 77.3 and ?77.0 kJ/kg, and the mean particle diameter was 0.64 μm. The thermal cycling tests of the microcapsules were performed for 400 heating/cooling cycles, and the results indicate that the synthesized microcapsules have good thermal reliabilities. Air stability test proved that the thermal properties and physical form of microcapsules were not affected by air. We recommend the prepared thermal, air, and chemically stable caprylic acid microcapsules for thermal energy storage applications as novel microPCM with latent heat storage capacities and properties. Copyright © 2014 John Wiley & Sons, Ltd.     

Microencapsulation of coco fatty acid mixture for thermal energy storage with phase change material

Thermal energy storage systems provide several alternatives for efficient energy use and energy conservation. Microcapsules of natural coco fatty acid mixture were prepared to be used as phase change materials for thermal energy storage. The coacervation technique was used for the microencapsulation process. Several alternatives for the capsule wall material were tried. The microcapsules were characterized according to their geometric profiles, phase transition temperatures, mean particle sizes, chemical stabilities, and their thermal cycling. The diameters of microcapsules prepared in this study were about 1 mm. Coco fatty acid mixtures have kept their geometrical profiles even after 50 thermal cycles for melting and freezing operations in temperature range from 22 to 34°C. It was found that gelatin+gum Arabic mixture was the best wall material for microencapsulating coco fatty acid mixtures. Copyright © 2005 John Wiley & Sons, Ltd.     

Preparation and properties of caprylic‐nonanoic acid mixture/expanded graphite composite as phase change material for thermal energy storage

To satisfy the application demands for latent heat storage in the temperature range from 5°C to 15°C, an original composite phase change material (PCM), CA‐NA/EG (caprylic‐nonanoic acid/expanded graphite), was prepared and characterized. For CA‐NA/EG, the mass ratio of CA and NA was 8:2, and the mass percentage of the CA‐NA in CA‐NA/EG composite PCM was determined as 90% by leakage test. The melting and freezing points of the CA‐NA/EG were 6.84°C and 9.34°C, and corresponding latent heats were 108.75 kJ/kg and 107.67 kJ/kg. In addition, its thermal conductivity, thermal stability and reliability were investigated by thermal conductivity apparatus (TCA), thermal gravimetric analyzer (TGA), and accelerated thermal cycle test for 100 melt/freeze cycles, respectively. The results showed that the CA‐NA/EG had a good thermal stability and an excellent thermal reliability. Moreover, the thermal conductivity of CA‐NA/EG had an improvement of 25% than that of the CA‐NA. On the other hand, the accelerated thermal cycle test also indicated that the CA‐NA/EG had no supercooling during all melt/freeze cycles. Therefore, the prepared composite PCM, CA‐NA/EG, can be applied for low‐temperature thermal energy storage owing to its proper melting temperature, acceptable latent heat and thermal conductivity, excellent thermal stability and reliability.     

Microencapsulated n-octacosane as phase change material for thermal energy storage

This study deals with preparation and characterization of polymethylmetracrylate (PMMA) microcapsules containing n-octacosane as phase change material for thermal energy storage. The surface morphology, particle size and particle size distribution (PSD) were studied by scanning electron microscopy (SEM). The chemical characterization of PMMA/octacosane microcapsules was made by FT-IR spectroscopy method. Thermal properties and thermal stability of microencapsulated octacosane were determined using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The melting and freezing temperatures and the latent heats of the microencapsulated octacosane as PCM were measured as 50.6 and 53.2 °C, 86.4 and −88.5 J/g, respectively, by DSC analysis. TGA analysis indicated that the microencapsulated octacosane degrade in two steps and had good chemical stability. Thermal cycling test shows that the microcapsules have good thermal reliability with respect to the accelerated thermal cycling. Based on the results, it can be considered that the microencapsulated octacosane have good energy storage potential.     

Recent progress in diatomite based composite phase change materials for thermal energy storage

硅藻土是一种含量丰富的非金属矿,具有较高的孔隙率,良好的表面结构和热物理性能,因而可作为复合储热材料的载体.本文综述了复合储热材料的种类和制备工艺,并介绍了硅藻土的结构,性能和以硅藻土为载体的复合相变储热材料的研究及应用现状.     

Fatty acid/poly(methyl methacrylate) (PMMA) blends as form-stable phase change materials for latent heat thermal energy storage

Fatty acids such as stearic acid (SA), palmitic acid (PA), myristic acid (MA), and lauric acid (LA) are promising phase change materials (PCMs) for latent heat thermal energy storage (LHTES) applications, but high cost is the most drawback which limits the utility area of them in thermal energy storage. The use of fatty acids as form-stable PCM will increase their feasibilities in practical LHTES applications due to reduced cost of the energy storage system. In this regard, a series of fatty acid/poly(methyl methacrylate) (PMMA) blends, SA/PMMA, PA/PMMA, MA/PMMA, and LA/PMMA were prepared as new kinds of form-stable PCMs by encapsulation of fatty acids into PMMA which acts as supporting material. The blends were prepared at different mass fractions of fatty acids (50, 60, 70, 80, and 90% w/w) to reach maximum encapsulation ratio. All blends were subjected to leakage test by heating the blends over the melting temperature of the PCM. The blends that do not allow leakage of melted PCM were identified as form-stable PCMs. The form-stable fatty acid/PMMA (80/20 wt.%) blends were characterized using optic microscopy (OM), viscosimetry, and Fourier transform infrared (FT-IR) spectroscopy methods, and the results showed that the PMMA was compatible with the fatty acids. In addition, thermal characteristics such as melting and freezing temperatures and latent heats of the form-stable PCMs were measured by using differential scanning calorimetry (DSC) technique and indicated that they had good thermal properties. On the basis of all results, it was concluded that form-stable fatty acid/PMMA blends had important potential for some practical LHTES applications such as under floor space heating of buildings and passive solar space heating of buildings by using wallboard, plasterboard or floor impregnated with a form-stable PCM due to their satisfying thermal properties, easily preparing in desired dimensions, direct usability without needing an add encapsulation and eliminating the thermal resistance caused by shell and thus reducing cost of LHTES system.     

Energy and exergy analysis of a latent heat storage system with phase change material for a solar collector

Analysis of energy and exergy has been performed for a latent heat storage system with phase change material (PCM) for a flat-plate solar collector. CaCl₂·6H₂O was used as PCM in thermal energy storage (TES) system. The designed collector combines in single unit solar energy collection and storage. PCMs are stored in a storage tank, which is located under the collector. A special heat transfer fluid was used to transfer heat from collector to PCM. Exergy analysis, which is based on the second law of thermodynamics, and energy analysis, which is based on the first law, were applied for evaluation of the system efficiency for charging period. The analyses were performed on 3 days in October. It was observed that the average net energy and exergy efficiencies are 45% and 2.2%, respectively.     

Performance comparison of a group of thermal conductivity enhancement methodology in phase change material for thermal storage application

Phase change materials (PCM) are able to store thermal energy when becoming liquids and to release it when freezing. Recently the use of PCM materials for thermal energy storage (TES) at high temperature for Concentrated Solar Power (CSP) technology has been widely studied. One of the main investigated problems is the improvement of their low thermal conductivity. This paper looks at the current state of research in the particular field of thermal conductivity enhancement (TCE) mechanisms of PCM to be used as TES. This work considers a numerical approach to evaluate the performance of a group of TCE solutions composed by particular configurations of two of the principal TCE systems found on the literature: finned pipes and conductive foams. The cases are compared against a single PCM case, used as reference. Three different grades of graphite foams have been studied, presenting a charge time 100 times lower than the reference case for the same capacity. For fins two materials are analyzed: carbon steel and aluminum. The charge times of fin cases are from 3 to 15 times faster, depending on the amount and type of material employed. The internal mechanisms are analyzed to understand the results and locate possible improvement.     

Design of three-dimensional interconnected porous hydroxyapatite ceramic-based composite phase change materials for thermal energy storage

In this article, three-dimensional connected porous hydroxyapatite ceramics (PHCs) were prepared by using the Pickering emulsion template, which possessing controlled pore structure simply by adjusting the solid content from 35 to 55 wt%. The polyethylene glycol (PEG) and PHCs were compounded by vacuum impregnation to acquire composite phase change materials (CPCMs) with admirable shape stability. The SEM and EDS images showed that PEG was successfully adsorbed in the pore, and the results of FT-IR, XRD, TGA, and thermal cycles test, demonstrated the CPCMs possessed satisfactory chemical stability, favorable thermal stability, and wonderful thermal reliability. The maximum package ratio obtained was 66 wt%, which was supported by the PHC sample prepared with a solid content of 40 wt%. Moreover, the phase transition temperature and latent heat during melting and solidification were 53.41°C and 117.5 J/g, 36.49°C and 111.1 J/g, respectively. Therefore, the prepared PCM composites had a controlled pore structure, stable chemical properties, high latent heat, and excellent thermal reliability, making it a reliable application of thermal energy storage.