Shape-stabilized Phase Change Materials Research Articles

Encapsulation of inorganic phase change thermal storage materials and its effect on thermophysical properties: A review

Latent heat energy storage has received lots of concern on account of its high energy storage density and almost constant operating temperature. Phase change materials (PCM) possess unavoidable defects, like flammability, low thermal conductivity, subcooling, phase separation, etc. Encapsulation techniques have been adopted to address these challenges. Many efforts have been devoted to this by researchers, but the bulk of the work is based on organic PCMs, and particularly, reviews on encapsulating organic PCMs are frequent. In contrast, there are only a handful of comprehensive reviews on encapsulating inorganic PCMs, which hardly deliver complete information. Therefore, this review aims to provide a comprehensive look at the recent research advances for encapsulated inorganic PCMs. Two broadly adopted encapsulation methods are observed: core-shell encapsulated PCM and shape-stabilized PCM. Three main preparation processes for core-shell encapsulation (in situ polymerization, solvent evaporation and sol-gel methods) are described. The two former techniques are mostly adopted for the microencapsulated hydrated salt PCMs and forming organic shells. The latter is suitable for inorganic shells. The porous skeleton materials widely adopted for shape-stabilized PCMs are presented. The advantages and disadvantages of porous carbon, porous clay minerals, porous silica, and other materials were evaluated. In addition, thermophysical properties, such as supercooling, phase separation, phase change temperature, tent heat, thermal conductivity and thermal cycling reliability are discussed. It was found that encapsulation technology can have positive effects on thermophysical properties. It is hoped that this work will assist readers in gaining a comprehensive insight into the development of inorganic PCMs.

Compact latent heat exchanger for the fast supply of hot water with serpentine tubes in shape-stabilized composite phase change material and auxiliary electric heating

• A composite phase change material-based heat exchanger is designed. • The composite phase change material owns a large enthalpy of 252 J/g. • An electric heating film is introduced to improve the heating efficiency. To realise a fast supply of hot water, this study proposes a compact latent heat exchanger. This heat exchanger consists of a certain number of heat-exchange plates. In each plate, serpentine tubes are wrapped with an inorganic composite phase change material (CPCM), Ba(OH) 2 ·8H 2 O/modified expanded graphite (MEG). An auxiliary electric heating film is attached to the face of the entire heat exchanger to improve the heating efficiency. The parameters of the plate, such as thickness, tube pass number, thermo-physical properties of the CPCM, flow rate, auxiliary heating power size, and position are numerically evaluated to achieve the best performance of this heat exchanger. The reliability of the simulation method is verified by comparing the simulated results with the experimental data in previous study. The simulation results indicate that a plate with a thickness of 15 mm, plate tube pass number of 10, and CPCM with a Ba(OH) 2 ·8H 2 O mass fraction of 85.8 wt% is the optimal choice. Based on the optimal conditions, 196.48 kg of hot water over 40 ℃ can be produced in 875 s and the average power reaches 23 kW. Furthermore, with the addition of a heating film (3600 W), the mass of heated water can be increased by nearly 50 kg.

The molecular dynamics study of atomic compound and functional groups effects on the atomic/thermal behavior of polyethylene glycol/graphite-based matrixes

In this study, Molecular Dynamics (MD) simulations were conducted for a thermophysical analysis of polyethylene glycol (PEG)/graphite (G), PEG/expanded graphite (EG), PEG/graphite oxide nanoparticle (GONP), and PEG/reduced GONP (rGONP) nanocomposites as shape stabilized phase change materials (SSPCMs). Specifically, thorough information regarding the PEG penetration in diverse graphite atomic structures and thermal conductivity (TC) under varied temperatures was investigated. The results of equilibrium MD simulations showed that PEG atoms penetration was increased at first and then remained constant with step time. Further, non-equilibrium MD simulations revealed that the thermal conduction could be improved by introducing graphite whit nanostructure and a low amount of oxygen-containing functional groups (relative to rGONP). So that the TC measured for PEG/rGONP is about 18% higher than that of PEG/GONP. We expect MD outcomes of this research could benefit the future development of SSPCMs with high TC.

Preparation of n-nonadecane based shape-stabilized composite phase change materials containing modified kaolinite clay-doped and determination of their properties

Faz değiştiren maddeler (FDM’ler) ısıl enerjiyi sabit sıcaklıkta faz değişim yoluyla gizli ısı olarak depolayabilen ve yüksek gizli ısı depolama kapasiteleri sayesinde birçok mühendislik alanında kullanılan fonksiyonel akıllı malzemelerdir. Bu çalışmada, ısıl enerji depolama sistemlerinde kullanılmak üzere modifiye edilmiş kaolinit kil içeren gözenekli polimerler emülsiyon şablonlama yöntemiyle sentezlenmiş ve elde edilen malzemeler n-nonadekan esaslı şekilce kararlı faz değiştiren maddelerin hazırlanması için destek malzemesi olarak kullanılmıştır. Hazırlanan kompozit malzemelerde, hiyerarşik gözenekli yapının elde edildiği, alüminyum silikat esaslı modifiye edilmiş kaolinit dolguların artmasıyla gözenek morfolojisinin düzeldiği, en yüksek ısıl kararlılık ve yüzey alanına %1 dolgu içeren gözenekli kompozitin sahip olduğu görülmüştür. Sentezlenen tüm gözenekli kompozit malzemelere tek adımda impregnasyon yöntemiyle, n-nonadekan faz değiştiren maddesi yüklenmiş ve şekilce kararlı kompozit FDM’ler üretilmiştir. Gerçekleştirilen analiz sonuçlarına göre üretilen PHPK1,00-ND kompozit FDM’nin pik erime sıcaklığı Tpik-erime=36,37ºC, ısıl enerji depolama kapasitesi ΔHerime=132,3 J/g olarak belirlenmiş ve n-nonadekan içeriği %52,5 olarak hesaplanmıştır. Destek malzemesi olarak gözenekli kompozitler kullanılarak üretilen n-nonadekan içeren şekilce kararlı tüm FDMlerin, yüksek ısıl enerji depolama kapasitesine sahip oldukları (92-142 J/g arasında değişen) ve termal enerji depolama uygulamaları için sızdırmazlık özelliği gösterdikleri tespit edilmiştir.

Shape-stabilized phase change materials: Performance of simple physical blending synthesis and the potential of coconut based materials

This research reports, for the first time, the combination of food-grade coconut oil and coconut shell-based activated carbon as precursors for the synthesis of bio-based shape-stabilized phase change materials (bioSSPCM). Despite its low melting enthalpy, simple physical blending by heating and mixing is found to be a very reliable preparation method for the completely coconut-based materials, producing a thermally stable bioSSPCM with anti-leakage. No difference between food grade and analytical grade coconut oil, in terms of its application for SSPCMs, was evident. Further, comparing the performance of coconut oil against octadecane, a conventional phase change material, it was found that with the same synthesis conditions, the coconut oil exhibited improved stability, with less leakage after phase change cycling.

Activated carbon nanotube/polyacrylic acid/stearyl alcohol nanocomposites as thermal energy storage effective shape-stabilized phase change materials

Stearyl alcohol (SA) as one of organic phase change materials (PCMs) has promising thermal energy storage prospective. However, the leakage issue during solid-liquid phase change period and low heat harvesting and releasing rate significantly attenuates its TES potential. Towards to overcome these drawbacks, the SA was shape-stabilized using the cross-linked poly acrylic acid (PAA) and activated single walled carbon nanotubes (a-SWCNTs) at three different weigh ratio of 1:1:2, 1:3:4 and 1:5:6 (a-SWCNTs:PAA:SA). The chemical/crystalline and morphologic structures of the produced shape stabilized-nano composite PCMs (SS-NCPCMs) were investigated by FT-IR, XRD and SEM analyses. The latent heat storage (LHS) features and thermal stability of the SS-NCPCMs were measured by DSC and TGA techniques. The thermal cycling effect on the LHS properties and chemical structures of the SS-NCPCMs was also estimated. The DSC findings indicated that the SS-NCPCMs had melting temperature of around 55–56 °C and latent heat capacity of about 135 J/g. TGA measurements disclosed that the thermal degradation temperatures of the nano composite PCMs were prolonged somewhat compared to the SA. A 500 heating-cooling cycling test revealed that the SS-NCPCMs had great chemical and LHS stability. The heat harvesting and releasing performance of the NCPCMs were considerably shortened compared to those of pure SA. The obtained results exposed that the synthesized SWCNTs/PAA/SA composites can be evaluated as promising LHS materials for thermal management of electronic systems, automobile modules, food carriers, solar PV panels etc.

Fabrication of shape-stabilized phase change materials based on waste plastics for energy storage

High value-added use of waste plastic has emerged an urgent research topic due to its heavy pollution to environment. Meanwhile, fluctuant characteristic of renewable energy leads to energy storage techniques to be always at the core of energy research. A protocol which could solve the pollution brought by waste plastics and making an energy storage material is highly meaningful. Herein, we found waste plastics could serve as a supporting material for the encapsulation of phase change material (PCMs), it would not only solve the leakage problem of PCMs in phase transition process, but also makes contribution to the problem of waste plastic pollution to the environment and ecology. Paraffin wax (PW) was used as a phase change material and encapsulated with porous carbon material which prepared from waste plastics through a vacuum absorption method. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) analysis and X-ray diffraction (XRD) analysis were carried out to study the chemical composition and microstructure on this PCMs waste plastics based thermal energy material. Thermal conductivity, phase change temperature and latent heat of PCMs were tested to understand thermophysical properties of the obtained materials. Moreover, heat storage platform was installed to further know the energy storage performance of this PCMs composite made from waste plastics.

Laboratory and numerical study on innovative grouting materials applicable to borehole heat exchangers (BHE) and borehole thermal energy storage (BTES) systems

In this study, a laboratory-scale prototype of a borehole field has been designed and built to assess various innovative grouting products in a fully controlled environment. Three novel grout formulations are developed and evaluated: enhanced grout, a mixture of enhanced grout and microencapsulated phase change material, and a mixture of enhanced grout and shape stabilized phase change material. The objective is to evaluate the enhancement in their thermal properties (i.e., thermal conductivity and thermal energy storage capacity) compared to those using a commercial reference grout. Besides, three-dimensional numerical modeling is performed to provide a better understanding of the heat transfer and phase transition inside and outside the grout columns and to study the capability of the developed grouts to be used in a borehole heat exchanger or as borehole thermal energy storage system. To the best of the authors' knowledge, there have been just a few numerical studies on using phase change materials inside borehole heat exchangers to assess thermal energy storage applications. The experimental and numerical results showed much higher efficiency of the grout developed with a high thermal conductivity than the reference grout in terms of heat transfer in both the grout column and the surrounding sand. Furthermore, the results indicated the noticeable influence of the microencapsulated phase change material's presence in the grout formulation in terms of heat absorption/storage during the phase transition (from solid to liquid). However, it is concluded that reengineering shape stabilized phase change material should be conducted to make it more appropriate for thermal energy storage applications.

3D network structural shape-stabilized composite PCMs for integrated enhancement of thermal conductivity and photothermal properties

Metal organic frameworks (MOFs) are rarely used in the field of phase change heat storage, because their low thermal conductivity affects the practical application of composite phase change materials (PCMs). Three dimensional porous materials with good thermal conductivity and adsorption properties can be synthesized by cleverly combining high adsorption MOF with high thermal conductivity expanded graphite (EG). In this paper, ZIF-8 of zeolites with imidazole structure with high adsorption was prepared by method of co-precipitation. ZnO was prepared by carbonizing ZIF-8 in a vacuum tube furnace at 700°C. EG/[email protected] was synthesized by compounding EG, the crosslinking agent polyvinylpyrrolidone (PVP) and photothermal materials (CuS). Finally, OC/EG/[email protected] was prepared by stirring impregnation process according to four different proportions of octadecanol (OC) and compounding with EG/[email protected] The microstructure and thermal properties of the samples were characterized. The result shows that the enthalpy of composite phase change materials OC/EG/[email protected] reaches 202.97 J/g, which greatly improves the adsorption performance of OC and improves the heat storage performance. The thermal conductivity test results show that the thermal conductivity of the composite PCMs with the ratio of ZnO to EG (1:8) is as high as about 11.77 W/(m·K). The results of photothermal experiments show that the composite PCM with CuS can improve its photothermal properties.

Shape-stabilized phase change material with high phase change enthalpy made of PEG compounded with lignin-based carbon

Lignin-based porous carbon (LTC), lignin-based hierarchical porous carbon (LTCA) and lignin-based ordered porous carbon (MC) with different pore structures were prepared by template method and chemical activation method using lignin as raw material. The lignin-based carbon composite phase change materials were prepared by vacuum impregnation with polyethylene glycol (PEG) and porous carbon material. The results showed that LTCA has the largest loading capacity of Phase change Materials, which could load 85% of PEG; MC has the largest phase transition enthalpy value (ΔHm), which is 89.7 J·g−1. When the loading amount is the same as 60%, the thermal conductivity of LTCA/PEG is the largest, which is 0.5167 W/mK, 53.8% higher than that of pure PEG. Under constant heating at 70 °C, the pure cotton fabric and the polyurethane coated fabric reached 60 °C in the 4th and 10th second, The cotton fabric coated with composite phase change material reached 60 °C only at 16 s, and a significant slowdown in the temperature rise rate occurred between 50–60 °C. It showed that the cotton fabric coated with composite phase change material had good phase change temperature regulation performance.

MIL-101(Cr)-NH2/reduced graphene oxide composite carrier enhanced thermal conductivity and stability of shape-stabilized phase change materials for thermal energy management

In order to address the leakage issue and enhance the thermal conductivity of phase change material (PCM), a composite carrier for shape-stabilized phase change material is developed for thermal energy management of battery. Metal organic framework (MOF): MIL-101-NH2, reduced graphene oxide (RGO), and paraffin wax (PW) were combined into a shape-stabilized CPCM to strengthen the heat transfer. MOF/RGO composite carrier was the heat transfer intensifier and the shape-stabilized container for PW. Here, the structural and thermal properties of CPCMs were evaluated by BET, SEM, XRD, FTIR, XPS, DSC, TGA and Hot Disk. The results show that MIL-101(Cr)-NH2/RGO/PW CPCMs were successfully prepared without any chemical reaction and the CPCM with mass fraction of PW of 60% has the best thermophysical properties. The melting enthalpy of the MOF(35%)/RGO(5%)/PW(60%) CPCM after 500 thermal cycles was calculated to be 80.55 J/g, which is close to its theoretical value. The thermal conductivity of the MOF(35%)/RGO(5%)/PW(60%) CPCM is increased by 472%, which is far higher than that of pure PW.

Novel shape-stabilized phase change materials: Insights into the thermal energy storage of 1-octadecanol/fumed silica composites

Here, novel C18OH/FS shape-stabilized phase change materials (SSPCMs) were simply prepared by incorporating 1-octadecanol (C18OH) into a porous fumed silica (FS). Given the high porosity (88%), FS provided sufficient inner space for the impregnation of a large C18OH amount up to 75% of the total mass. It was found that C18OH was effectively stabilized in the FS porous network, which could be due to physical interactions such as capillary force, surface tension, and hydrogen bonding at the interfacial region. C18OH PCM was infiltrated into FS porous network by initial adsorption onto particle surfaces and subsequent filling micropores, mesopores, and finally macropores of the support FS. The resultant C18OH/FS SSPCM (75 wt% of C18OH) showed an excellent leakage resistance, high crystallinity of 92.7% and latent heat storage capacity of 160.3 J/g. In addition, the C18OH/FS SSPCM provided excellent thermal reliability with a test of 500 accelerated thermal cycles. The solid 13C NMR, DSC, and XRD analyses successfully characterized the formation of non-freezable layer during the infiltration of C18OH into the pores by forming hydrogen bonding between C18OH and surface silanol groups. This non-freezable layer negatively affected the crystallinity of C18OH and lowered the heat storage capacity, which could be minimized at a large content of impregnated C18OH. Overall, these results suggest that the C18OH/FS SSPCMs have great latent heat storage capacity with good thermal reliability, simple fabrication, and cost-effectiveness that would be potential for large-scale applications in thermal energy storage.

Effect of Solid-Solid Phase Change Material’s Direct Interaction on Physical and Rheological Properties of Asphalt

Asphalt pavement is a temperature−sensitive structure that is prone to temperature-related diseases. Phase change material (PCM) is an excellent candidate for mitigating these diseases. This paper looked into the effects of indirect composite shape-stabilized PCM incorporation on the characteristics of asphalt. The compatibility, physical properties, and rheological properties of asphalt with various PCM content before and after aging were thoroughly investigated. No phase separation and no chemical reaction occurred between PCM and asphalt. The physical properties improved with the addition of PCM, and the high−temperature performance indexes improved while the low−temperature performance indexes decreased as the aging process progressed. The effects of PCM on the rheological properties of the matrix and SBS−modified asphalt was distinct. PCM was added to improve the high−temperature rheological characteristics of the matrix asphalt when the temperature was higher than 52 °C, while PCM reduced the high−temperature rheological properties of the SBS−modified asphalt. The aging process has an impact on the high−temperature rutting factor of asphalt with a high PCM content. The low−temperature creep behavior and PG grade of asphalt were both improved. The implication of PCM is that it cannot increase the thermoregulation of asphalt pavement without the cost of scarifying the performance of the asphalt or mixture.

Preparation of paraffin/silica–graphene shape-stabilized composite phase change materials for thermal energy storage

Preparation of paraffin/silica–graphene shape-stabilized composite phase change materials for thermal energy storage

Synthesis and Properties of Shape-Stabilized Phase Change Materials Based on Poly(triallyl isocyanurate-silicone)/n-Octadecane Composites.

Triallyl isocyanurate (TAIC) was modified by hydrogen silicone oil (SO) via hydrosilylation reaction, generating the original TAIC-SO (TS) intermediate. After the cross-linking polymerization of TS (PTS), the shape-stabilized phase change materials (PCMs) consisting of n-octadecane and silicone-modified supporting matrix were first synthesized by an in situ reaction. Remarkably, the novel three-dimensional PTS network effectively prevents the leakage of n-octadecane during its phase transition, solving the prominent problem of solid–liquid PCMs in practical applications. Moreover, n-octadecane is uniformly dispersed in the continuous and high-strength cross-linked network, contributing to excellent thermal reliability and structural stability of PTS/n-octadecane (TSO) composites. Differential scanning calorimetry analysis of the optimal TSO composite indicates that melting and freezing temperatures are 29.05 and 22.89 °C, and latent heats of melting and freezing are 130.35 and 129.81 J/g, respectively. After comprehensive characterizations, the shape-stabilized TSO composites turn out to be promising in thermal energy storage applications. Meanwhile, the strategy is practical and economical due to its advantages of easy operation, mild conditions, short reaction time, and low energy consumption.

Preparation and Characterization of Sodium Sulfate Decahydrate–Sodium Acetate Trihydrate Shape-Stabilized Phase Change Materials

Preparation and Characterization of Sodium Sulfate Decahydrate–Sodium Acetate Trihydrate Shape-Stabilized Phase Change Materials

Preparation and performance improvement of chlorides/MgO ceramics shape-stabilized phase change materials with expanded graphite for thermal energy storage system

Cold compression and mixed sintering methods have attracted attention for their applicability to industrial mass production. Due to the wettability of expanded graphite (EG) and salt chlorides, the decoupling of the encapsulation effect of EG and ceramics should be considered in the form-stable composite materials ratio of ternary chlorides (TC)/MgO ceramics/EG. In this study, 40 wt%-55 wt% MgO and 5 wt%-20 wt% EG are added to the composites, respectively. It is found that the composite system can be loaded with nearly 45 wt% molten salts. The 45 wt% TC-15 wt% EG-40 wt% MgO sample named 15EG-40MgO is considered a close to optimal formulation in terms of thermal conductivity enhancement and energy density reduction. This proportional composite has a thermal conductivity of 8.86 W∙m−1∙K−1, and in the temperature range of 300–600 °C, the thermal storage density reaches 439.53 J·g−1. With the increase of TC content, the density of the composites shows a decreasing trend. However, all samples have excellent mechanical strength due to the MgO ceramics as the supporting material. Moreover, these composites can be easily integrated into a solar thermal storage system, which proposes a new strategy for applying a high-temperature packed-bed containing salt-based composite phase change materials.

Mechanically strong hectorite aerogel encapsulated octadecane as shape-stabilized phase change materials for thermal energy storage and management

Phase change materials (PCMs) are considered one of the most advanced energy-saving materials owing to their high thermal energy storage density during the phase transition process. To solve the leakage problem and poor thermal properties in PCMs, a three-dimensional (3D) hectorite aerogel, with an abundant porous structure, was synthesized to encapsulate octadecane (ODE) for preparing hectorite/octadecane composite PCMs with shape stability, large latent heat capacity, and good mechanical strength. The mechanical and thermophysical properties of the composite PCMs were investigated in depth in this study. Due to the high porosity characteristic of hectorite aerogel, the composite PCMs exhibited a large latent capacity of 196.70 J/g with an ODE loading rate larger than 85 wt%. It was also found that the aerogel played an important role in maintaining shape stability, as no significant leakage was observed during the phase-change process. In addition, the composite PCMs exhibited a compressive strength of approximately 2.4 MPa, suggesting good mechanical strength. The thermal stability was found to be excellent, considering that the thermal decomposition temperature of the composite was far higher than the phase change temperature. The excellent shape stability and thermal stability contributed to the outstanding recycling performance of the composite PCMs. The thermal management performance of the composite, in a building house model, was also tested to verify its superior thermal regulation function. Thus, these mechanically strong composite PCMs, with stupendous energy storage capacities and good form stabilities, can be applied in the energy storage and thermal management fields, thereby showing great potential for a sustainable society.

Preparation of porous titanium dioxide foam impregnated with polyethylene glycol as shape-stable composite phase change materials

In this work, a novel shape-stabilized composite phase change material, was prepared by using high porosity and uniform, open, controllable, 3D interconnected porous titanium dioxide foam (PTF) as the package carrier material and polyethylene glycol (PEG) as phase change material. The heat storage performance and non-isothermal crystallization process of prepared composite phase change material were further studied and the effect of 3D fully interconnected pore structure of PTF on the phase change behavior and thermal conductivity of PEG were also further investigated. The DSC results indicated that the enthalpy of melting and solidification of the PEG-PTF were 145.9 and 142.9 J/g, respectively, and the corresponding actual impregnation ratio (φ) reached 70%. Because PTF porous matrix provides abundant crystallization sites during PEG solidification process, the inhibition effect of matrix on PEG phase transformation is significantly alleviated, which is demonstrated by the decrease in DH value. Non-isothermal crystallization results showed that the activation energy of PEG (−2.67 kJ/mol) was higher than that of PEG-PTF (−2.19 kJ/mol) but the half crystallization time of PEG was similar with that of PEG-PTF, which indicated that the 3D fully interconnected pore structure of PTF partially eliminated the inhibition effect of porous carrier on PEG phase transformation behavior. The results of XRD, FT-IR, thermal cycle and TGA tests showed that PEG-PTF composite phase change material had good chemical compatibility, thermal reliability, and thermal stability. This study showed that the PTF was a novel and promising support material for the preparation of PEG composite phase change materials.

A modified method to quantify the photo-thermal conversion efficiency of shape-stable phase change materials

Photo-thermal conversion phase change materials (PCMs), which can overcome the gap between the demand and supply of solar energy, have shown significant potential in solar energy utilization. The photo-thermal conversion efficiency is a critical factor in determining the photo-thermal conversion performance of PCMs. Most previous investigations only considered the latent heat stored by PCMs to determine the photo-thermal conversion efficiency. The sensible heat absorbed by PCMs before and after the phase transition process was neglected, which might overestimate the photo-thermal conversion performance of PCMs. As an improvement, a modified method, considering both sensible and latent heat absorption and the temperature difference within the PCMs, was proposed to determine the photo-thermal conversion efficiency of PCMs accurately. Shape-stable PCMs with polyethylene glycol (PEG), few-layers graphene (FLG), and melamine foam (MF) as the PCM, photo absorber, and supporting material, respectively, were prepared to test the reliability and effectiveness of the proposed method. Results showed that the actual efficiency of PCMs was less than 25%, which truly reflected the photo-thermal conversion performance of PCMs, demonstrating that more work should be conducted to enhance the photo-thermal conversion performance for efficient solar energy utilization.