Latent Heat Thermal Energy Storage Applications Research Articles

Super‐liquid‐repellent thin film materials for low temperature latent heat thermal energy storage: A comprehensive review of materials for dip‐coating

AbstractWhen discharging latent heat thermal energy storage (LHTES) systems, performance is influenced by the formation and adherence of a solid layer of phase change material (PCM) on heat eXchange (HX) surfaces. Super‐liquid‐repellent thin films (STFs) may be able to reduce solidifying PCM adhesion on HX surfaces during discharging, delay PCM solidification to lower temperatures, and by modifying nucleation sites potentially enable long‐term seasonal thermal storage. Techniques employed previously to fabricate sintered polymeric STF coatings include chemical vapour deposition, dip‐coating, spray‐coating, spin‐coating, layer‐by‐layer (LbL) assembly, sol‐gel, anodizing, electrodeposition, electrospinning, so on. Dip‐coating is considered attractive for fabricating thin films on simple and complex surface geometries due to process maturity, scalability, flexibility and cost‐effectiveness. To identify suitable materials for preparing STFs on metal HX surfaces using the dip‐coating process, more than 200 journal articles published in English during the period 2010 to 2022 were reviewed and the potential role of STFs in LHTES applications was assessed. The review identified key areas and applications stimulating STF material developments and formulations. The dip‐coating of potential STF materials was classified under three major themes driving current research and development (R&D) activities, that is, high performance thin films, eco‐friendly thin films and fundamental research formulations. This review provides a platform from which to develop coatings and HX systems to enable the cost‐effective implementation of STFs for improved heat transfer in future mobile/stationery LHTES systems.

Thermal performance of polymer gyroid heat exchangers combined with phase change materials as a latent heat thermal energy storage system: An experimental investigation

Latent heat thermal energy storage (LHTES) systems utilizing phase-change materials (PCMs) in conjunction with heat exchangers (HXs) have been widely investigated for efficient thermal energy utilization. This study experimentally evaluated the heat transfer performance and pressure loss of a PCM-based gyroid HX fabricated using a polymer 3D printer. Initially, the study compared the phase change time, heat storage and release characteristics, and pressure drop of the gyroid HX with those of a conventional shell-and-tube HX (S&T HX). The results demonstrate that the gyroid HX achieved up to 20 % shorter thermal charge and discharge times than the S&T HX, which is attributed to a higher heat transfer rate. Additionally, the measured pressure drop of the gyroid HX was up to 44 % lower than that of the S&T HX. Consequently, considering both the heat transfer rate and pressure drop, the gyroid HX showed an average improvement of 57 % and 31 % in the overall enhancement factor during charging and discharging, respectively, compared to the S&T HX. Further, metal gyroid HXs fabricated from steel and aluminum using metal 3D printing were experimentally compared with the polymer gyroid HX. Despite the polymer thermal conductivity being only 1/90 and 1/790 that of steel and aluminum, respectively, the heat transfer rate per unit mass of the polymer gyroid HX was 1.7 times that of the steel gyroid HX and approximately half that of the aluminum gyroid HX. This finding suggests that the polymer gyroid HX is suitable for LHTES applications where lightweight characteristics are crucial.

Development of novel phase change materials based on methyl laurate and fatty acids for low-temperature applications

ABSTRACT In response to the urgent need for latent heat thermal energy storage (LHTES) in the cryogenic field and the utilization of renewable energy sources, three novel eutectic phase change materials (PCMs) have been successfully developed. These materials, methyl laurate (ML)/lauric acid (LA), methyl laurate/myristic acid (MA), and methyl laurate/palmitic acid (PA), belong to the eutectic system of fatty acid methyl ester (FAME) and fatty acid. With a specific composition, these binary mixtures have desired melting temperatures, high melting enthalpy, and stable thermal performance. The phase diagrams of the eutectics were analyzed to obtain precise eutectic mass ratios. Theoretical predictions of the eutectic mass ratios and thermal properties were validated and determined through differential scanning calorimetry (DSC) and the hot-disk method. The ML-LA, ML-MA, and ML-PA mixtures had onset melting temperatures of 4.19°C, 5.45°C, and 5.69°C, respectively, with corresponding enthalpy of fusion values of 185.43, 190.47, and 194.39 J/g. The cycling stability test results showed that these mixtures had good thermal stability. The thermophysical properties and molecular structure of the mixtures were analyzed, indicating that these new mixtures of ML and fatty acids are suitable for low-temperature LHTES applications such as cold compresses and thermal-regulating textiles. This study provides insight into developing new PCMs that can meet the demand for LHTES in the cryogenic field and the utilization of renewable energy sources.

Epoxy⁻PCM Composites with Nanocarbons or Multidimensional Boron Nitride as Heat Flow Enhancers.

The need for affordable systems that are capable of regulating the temperature of living or storage spaces has increased the interest in exploring phase change materials (PCMs) for latent heat thermal energy storage (LHTES). This study investigates n-nonadecane (C19H40) and n-eicosane (C20H42) as alkane hydrocarbons/paraffins for LHTES applications. An epoxy resin is used as the support matrix medium to mitigate paraffin leakage, and a thickening agent is utilized to suppress phase separation during the curing process. In order to enhance the thermal conductivity of the epoxy–paraffin composite, conductive agents including carbon nanofibers (CNFs), carbon nanotubes (CNTs), boron nitride (BN) microparticles, or boron nitride nanotubes (BNNTs) are incorporated in different gravimetric ratios. Enhancements in latent heat, thermal conductivity, and heat transfer are realized with the addition of the thermal fillers. The sample composition with 10 wt.% BN shows excellent reversibility upon extended heating–cooling cycles and adequate viscosity for template casting as well as direct three-dimensional (3D) printing on fabrics, demonstrating the feasibility for facile integration onto liners/containers for thermal regulation purposes.

Ultra-High Temperature Interaction Between h-BN-Based Composite and Molten Silicon

Silicon has been recently proposed as a very promising phase change material for applications in latent heat thermal energy storage (LHTES) and conversion systems working at ultra-high temperatures. However, in order to successfully develop such kind of devices, suitable refractories showing low reactivity and non-wetting behavior upon the melting and storing of molten silicon at temperatures much higher than its melting point have to be selected. In our previous work, we have documented that the non-wetting behavior in Si/h-BN system is preserved at temperatures up to 1650 °C, with the absence of new reaction products formed at the interface. These findings make hexagonal boron nitride (h-BN) a reasonable first candidate for Si-based LHTES applications. Nevertheless, the rather poor mechanical strength of “pure” h-BN ought to be improved in order to enhance the reliability under thermocycling operational conditions and to increase the life period of the device. Therefore, in the present paper, we examine for the first time the interactions at ultra-high temperatures between a high strength commercial h-BN-based composite and molten Si. At temperatures up to 1750 °C, the wettability of the h-BN-based composite (h-BN + SiC + ZrO2) with molten Si is much lower if compared to the pure h-BN counterpart. Additionally, the role of reinforcements (SiC + ZrO2) and occured microstructural evolution is discussed based on the results obtained by SEM and XRD analyses.

Thermal enhancement of paraffin/hydrophobic expanded perlite granular phase change composite using graphene nanoplatelets

Thermal performance of latent heat thermal energy storage (LHTES) systems is often limited by low thermal conductivity of phase change materials (PCMs), which reduces the heat transfer rate and energy storage efficiency. This study investigates the development of a thermally enhanced paraffin/hydrophobic expanded perlite (EPOP) form-stable PCM seeded with graphene nanoplatelets (GNP) as a heat transfer promoter. Experimental research was carried out on fabrication, characterization and heat transfer performance analysis of EPOP–GNP composite. It was shown that the GNP particles were partially immersed into the paraffin occupied in the pores of EPO, which remarkably improved the thermal properties and heat transfer performance of composite PCM. In comparison with EPOP, the addition of 0.5 wt% GNP increased the thermal conductivity by up to 49%. Heat transfer performance test also showed that the EPOP–GNP composite reduced the heat storage/release duration by up to 20%, compared to EPOP. Moreover, prototype test room experiment conducted on cement mortars containing EPOP–GNP revealed that the introduction GNP into form-stable PCM significantly enhanced the thermal energy storage performance of cement mortars. This is particularly demonstrated by the reduction in peak inner surface temperature of 0.8 °C and the increase in inner surface convective heat gain energy by 78%, compared to cement mortars containing EPOP only. It can be said, therefore, the integration of GNP into form-stable PCMs is a promising way to achieve high energy storage efficiency for numerous LHTES applications such as solar energy storage and energy conversation in buildings.

Preparation, Characterization and Thermal Energy Storage Properties of Micro/Nano Encapsulated Phase Change Material with Acrylic-Based Polymer

The eutectic mixture of octacosane (C28)–heptadecane (C17) as core material was successfully encapsulated with an acrylic-based polymer (polymethylmethacrylate; PMMA) as shell material through emulsion polymerization. The polymeric reaction occurred around the core material was characterized by FTIR spectroscopy analysis. The polarized optical microscopy, scanning electron microscopy and particle size distribution investigations showed that the most of the prepared capsules had almost spherical shape with non-unimodal size distribution in micro-nano range. The differential scanning calorimetry analysis results exhibited that the capsules including highest amount of the eutectic PCM had a melting temperature of about 21°C and a latent heat capacity of about 98 J/g. The high thermal durability of the prepared capsules was confirmed by thermogravimetric analysis. The thermal cycling test designated that the synthesized capsules had good long-term usage latent heat thermal energy storage (LHTES) performance and chemical stability. Furthermore; the fabricated capsules with (1: 2) shell/core ratio had a reasonable thermal conductivity. It can be drawn a conclusion from all results that the prepared capsules especially PMMA/(C28–C17) (1: 2) product is a hopeful PCM that can be evaluated for low-temperature LHTES applications.

Preparation and characterization of PVC-based form-stable phase change materials

Several different form-stable phase change materials (FSPCMs), which comprise microencapsulated phase change materials (MEPCMs) as latent heat storage medium and poly(vinyl chloride)/wood flour compound as supporting material, were prepared by blending and compression molding method for the application of potential latent heat thermal energy storage (LHTES). SEM images reveal that prepared FSPCMs have homogeneous constitution and most MEPCM particles in them are undamaged. Both the shell of MEPCM and the matrix prevent the molten paraffin from leakage. DSC results show that melting and freezing temperatures as well as latent heats of the prepared FSPCMs are suitable for potential LHTES applications. Results of thermal performance tests show that the surface temperature fluctuation of the FSPCMs is obviously less than that of plate without MEPCM. Results of mechanical property tests indicate that bending strength, and bending modulus, as well as tensile and impact strength of the FSPCMs with 10wt% MEPCM are 26.7MPa, 3.48GPa, 9.8MPa and 10kJm−2 respectively. The mechanical properties of FSPCMs with poly(vinyl chloride)/wood flour compound as supporting material are superior to those of HDPE-based FSPCMs.

The Improvement of Thermal Stability and Conductivity via Incorporation of Carbon Nanofibers into Electrospun Ultrafine Composite Fibers of Lauric Acid/Polyamide 6 Phase Change Materials for Thermal Energy Storage

The ultrafine composite fibers consisting of lauric acid (LA) and polyamide 6 (PA6) were prepared via the technique of electrospinning as form-stable phase change materials. The influences of carbon nanofibers (CNFs) on structural morphology, as well as the properties of thermal energy storage, thermal stability, and thermal conductivity, of electrospun LA/PA6 composite fibers were studied. FE-SEM images revealed that the morphologies of electrospun LA/PA6/CNFs composite fibers changed from cylindrical shape with smooth surface (neat PA6 nanofibers) to non-uniform and coarse structure, and the CNFs were uniformly/randomly dispersed in the composite fibers. DSC measurements indicated that the heat enthalpies of the composite fibers were lower that that of neat LA powder, and the amount of CNFs in the fibers had slightly influence on the crystallization of LA (i.e., heat enthalpies of the composite fibers); while it had no appreciable effect on the phase change temperatures. TGA results suggested that the incorporation of the CNFs increased the maximum weight loss temperature and charred residue at 700ºC of the composite fibers, indicating the improved thermal stability for composite fibers. The increased thermal conductivity was also confirmed by comparison of the melting/freezing times of neat LA powder with those of composite fibers with and/or without CNFs. It was envisioned that the electrospun LA/PA6 ultrafine composite fibers would be utilized for latent heat thermal energy-storage applications because of its desired structural morphologies and thermal 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.

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.

Preparation and thermal properties of capric acid/palmitic acid eutectic mixture as a phase change energy storage material

This study focuses on the preparation, thermal properties and thermal reliability of capric acid (CA)/palmitic acid (PA) mixture as phase change material (PCM) for low temperature latent heat thermal energy storage (LHTES). The differential scanning calorimetry (DSC) results indicated that the CA/PA mixture with eutectic composition (76.5/23.5 wt.%) was suitable PCM for low temperature LHTES applications in terms of melting and freezing temperatures (Tm=21.85 °C; Tf=22.15 °C) and latent heats of melting and freezing (ΔHm=171.22 J/g; ΔHf=173.16 J/g). The thermal properties make it potential PCM for LHTES systems used in heating, ventilation, and air conditioning applications. Accelerated thermal cycling tests showed that the eutectic mixture as a PCM has good long-term thermal reliability. The probable reasons of the changes occurred in thermal properties of the PCM during accelerated thermal cycling were also investigated using Fourier Transform Infrared (FT-IR) spectroscopy method.

Preparation, characterization and thermal properties of styrene maleic anhydride copolymer (SMA)/fatty acid composites as form stable phase change materials

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 major drawback of them, limiting their utility area in thermal energy storage. The use of fatty acids as form stable PCMs will increase their feasibilities in practical applications due to the reduced cost of the LHTES system. In this regard, a series of styrene maleic anhydride copolymer (SMA)/fatty acid composites, SMA/SA, SMA/PA, SMA/MA, and SMA/LA, were prepared as form stable PCMs by encapsulation of fatty acids into the SMA, which acts as a supporting material. The encapsulation ratio of fatty acids was as much as 85 wt.% and no leakage of fatty acid was observed even when the temperature of the form stable PCM was over the melting point of the fatty acid in the composite. The prepared form stable composite PCMs were characterized using optic microscopy (OM), viscosimetry and Fourier transform infrared (FT-IR) spectroscopy methods, and the results showed that the SMA was physically and chemically compatible with the fatty acids. In addition, the thermal characteristics such as melting and freezing temperatures and latent heats of the form stable composite PCMs were measured by using the differential scanning calorimetry (DSC) technique, which indicated they had good thermal properties. On the basis of all the results, it was concluded that form stable SMA/fatty acid composite PCMs had important potential for practical LHTES applications such as under floor space heating of buildings and passive solar space heating of buildings by using wallboard, plasterboard or floors impregnated with a form stable PCM due to their satisfying thermal properties, easy preparation in desired dimensions, direct usability without needing additional encapsulation thereby eliminating the thermal resistance caused by the shell and, thus, reducing the cost of the LHTES system.

Poly(vinyl alcohol)/Fatty Acid Blends for Thermal Energy Storage

This article is aimed to prepare the blends of poly(vinyl alcohol) (PVA) with fatty acids (lauric, myristic, palmitic, and stearic acids) as shape-stabilized phase change material (PCM), to prove the miscibility of fatty acids with the PVA by microscopic investigation and infrared (IR) spectroscopy, and to measure their melting temperature and the latent heat of fusion by differential scanning calorimetry (DSC) analysis methods. In the blends, the fatty acids, which are dispersed in the solid network of the polymer, act as latent heat thermal energy storage (LHTES) material during its solid-liquid phase change when the polymer (PVA) has function of supporting material because of its structural strength. Therefore, the shape-stabilized fatty acids can keep the same shape in a solid shape without leakage of liquid fatty acids by aid of PVA in solid state. The maximum mixture ratio for all fatty acids in the shape-stabilized form was found as 50 wt%. By using DSC analysis method, the melting temperatures and latent heats of the shape-stabilized lauric, myristic, palmitic and stearic acids were determined as 39.8, 50.2, 56.2, and 67.4°C and 96.4, 105.3, 121.6, and 132.6 J/g, respectively. The results indicate that the PVA/fatty acids blends as shape-stabilized PCM have great potential for passive solar LHTES applications in terms of their satisfactory thermal properties and utility advantage of without encapsulation.

Thermal conductivity and latent heat thermal energy storage characteristics of paraffin/expanded graphite composite as phase change material

This study aimed determination of proper amount of paraffin ( n-docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat capacity using differential scanning calorimetry (DSC) technique. The paraffin/EG composites with the mass fraction of 2%, 4%, 7%, and 10% EG were prepared by absorbing liquid paraffin into the EG. The composite PCM with mass fraction of 10% EG was considered as form-stable allowing no leakage of melted paraffin during the solid–liquid phase change due to capillary and surface tension forces of EG. Thermal conductivity of the pure paraffin and the composite PCMs including 2, 4, 7 and 10 wt% EG were measured as 0.22, 0.40, 0.52, 0.68 and 0.82 W/m K, respectively. Melting time test showed that the increasing thermal conductivity of paraffin noticeably decreased its melting time. Furthermore, DSC analysis indicated that changes in the melting temperatures of the composite PCMs were not considerable, and their latent heat capacities were approximately equivalent to the values calculated based on the mass ratios of the paraffin in the composites. It was concluded that the composite PCM with the mass fraction of 10% EG was the most promising one for LHTES applications due to its form-stable property, direct usability without a need of extra storage container, high thermal conductivity, good melting temperature and satisfying latent heat storage capacity.

Poly(ethylene glycol)/acrylic polymer blends for latent heat thermal energy storage

AbstractIn the present study, polyethylene glycol (PEG) were blended with acrylic polymers like polymethyl methacrylate (PMMA), Eudragit S (Eud S), and Eudragit E (Eud E) as novel form stable phase change materials (PCMs) and characterized by optical microscopy, spectroscopy and viscosity techniques. Latent heat thermal energy storage (LHTES) properties of the blends were evaluated by using the differential scanning calorimetry (DSC) technique. In the form‐stable blends, PEG acted like phase change‐LHTES material when the acrylic polymers served as supporting material because of their adhesion property. The maximum percentage of PEG was found 80% w/w for any of the blend in which no leakage of PEG occurred for 100 heating/cooling cycles. The optical microscopy investigations revealed that the phase behavior of the blends was observed as self organized PEG distributed in the matrix of acrylic polymers rather than chain‐like structures. The interactions between the blend components (PEG and one of the acrylic polymers) were analyzed by Fourier transform infrared (FT‐IR) spectroscopy and the viscosimetry technique. The key LHTES properties (melting and freezing temperatures, and latent heats of melting and freezing of the blends) were evaluated by DSC. The DSC results indicated that PEG/PMMA, PEG/Eud S, and PEG/Eud E blends as form‐stable PCMs were convenient materials for LHTES applications in terms of their satisfying thermal properties. Therefore, these form‐stable PCMs could be incorporated into an LHTES system with the advantage of direct utility in order to store daytime solar energy for space heating. © 2006 American Institute of Chemical Engineers AIChE J, 2006