Shape-stabilized Phase Change Materials Research Articles

Enhanced Thermal Energy Storage of n-Octadecane-Impregnated Mesoporous Silica as a Novel Shape-Stabilized Phase Change Material.

A series of n-octadecane/mesoporous silica (C18/MS) shape-stabilized phase change materials (SSPCMs) with varying C18 content were prepared, and the effects of adsorbed C18 distributed within porous MS on the thermal properties were analyzed. As characterized, C18 was first infiltrated into the mesoporous space, resulting in a SSPCM with a maximum of ∼52 wt % C18. Additional adsorption of C18 occurred on the external surface of MS. Consequently, the optimum 70 wt % C18 SSPCM had no C18 leakage and exhibited a heat storage capacity of 135.6 J/g and crystallinity of 83.5%, which were much larger than those of 52 wt % C18 SSPCM (60.2 J/g and 68.2%, respectively). The prepared C18/MS SSPCMs showed excellent thermal stability and thermal reliability up to 1000 accelerated thermal cycle tests. Moreover, the C18/MS SSPCM incorporated in gypsum effectively reduced the temperature changes compared with the original gypsum, suggesting the promising application of the prepared C18/MS SSPCM for energy-saving building applications.

Thermal and morphological study of paraffin/SEBS/expanded graphite composite phase change material for thermal energy storage

ABSTRACT This work aims to develop a high thermal conducting and leakage-proof composite phase change material (CPCM) for thermal energy storage (TES) applications. A leakage-proof shape-stable phase change material (SPCM) has been prepared by impregnating paraffin into the network of polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene (SEBS) tri-block copolymer. In order to improve the thermal conductivity of paraffin/SEBS composite, expanded graphite (EG) has been directly incorporated into paraffin/SEBS (4:1) composite. Two different mass fractions of EG, i.e., 1 wt% and 5 wt%, have been chosen for the thermophysical study of leakage-proof SPCM named CPCM1 and CPCM2, respectively. Structural, morphological, and thermal studies of prepared composites have been carried out by XRD, FTIR, SEM, TGA, and DSC. The latent heats of prepared SPCM, CPCM1, and CPCM2 composites have been found as 167.91 J/g, 163.25 J/g, and 146.71 J/g, respectively. The thermal conductivities of composites have been measured by Laser Flash Apparatus (LFA). Results show that the thermal conductivity (TC) of CPCM1 and CPCM2 remarkably increases to 0.501 Wm−1K−1 and 1.301 Wm−1K−1, respectively, which is 2.8 and 7.35 times of paraffin/SEBS composite (0.177 Wm−1K−1). Therefore, findings suggest that the CPCM1 and CPCM2 samples have a great potential for TES application, specifically for solar water heating systems.

Shape-stabilized phase change material convective melting by considering porous configuration effects

Phase change material (PCM) encapsulation within a porous medium, known as the shape-stabilized PCM (SS-PCM), is a kind of novel technique for maintaining the PCM during the melting process and improving the conductive heat transfer. However, the performance of the SS-PCM in thermal energy storages and slurries is highly dependent on the thermophysical properties of PCM and the stabilizer’s structure. In this state-of-art study, the convective melting within a circular porous region, as a representative for an embedded PCM particle, is investigated. The main characteristic parameters of SS-PCM, including porosity, permeability, effective thermal conductivity and latent heat of fusion, have been under scrutiny by developing enthalpy-based Lattice-Boltzmann code. The results revealed that the Rayleigh-Benard convection can be shaped at powerful flow circulation that has a significant impact on the melting trend and time. Moreover, improving the thermal conductivity by using highly conductive porous material is reasonable up to a certain optimum point depending on the application. Meanwhile, the porosity of the stabilizer and latent heat capacity of the PCM have shown an inverse impact on the melting performance. They are the main factors in changing heat transfer mechanism, between conduction and convection, and heat storage model, between sensible and latent.

Experiment and numerical simulation of an adaptive building roof combining variable transparency shape-stabilized PCM

Adaptive building envelopes with advanced optical materials have received much attention as they can actively regulate solar heat gain. In present work, an adaptive building roof (ABR) combining variable transparency shape-stabilized PCM (VTSS-PCM) was proposed. A numerical model was developed firstly for dealing with time-space effect of radiation properties of VTSS-PCM and validated by experiments. The difference in performance between ABR and the common insulation roof was simulated. Then, a global sensitivity analysis based on the Monte-Carlo method was conducted to determine key parameters among 22 system parameters. Finally, the influences of key parameters on the performance of ABR were studied in detail. The results show that the ABR can reduce the heat gain by 35.25 % compared with the common insulation roof. The thickness of VTSS-PCM, the extinction coefficient of VTSS-PCM in the transparent state, and the albedo of reflective film are three key parameters. The thickness of the VTSS-PCM layer and the extinction coefficient of VTSS-PCM in the transparent state have positive correlations with the heat gain, whereas the albedo of the reflective film has a negative correlation with the heat gain. The time-space effect of radiation properties of VTSS-PCM during the phase change causes the solar absorptance of ABR to be unstable. This research guides the modeling of VTSS-PCM and facilitates the application of ABR.

Shape-stabilized phase change material with internal coolant channel coupled with phase change emulsion for power battery thermal management

With the rapid development of new energy vehicles, fast charging and fast discharging are gradually popularized, which puts forward higher requirements for power battery thermal management. In this paper, a novel power battery thermal management system with emulsion as coolant and shape-stabilized phase change material (SSPCM) as its channel is designed and heat transfer performance was experimentally studied. The cooling performance of water, emulsion and graphene oxide emulsion (GO emulsion) were compared. The results show that GO emulsion with high thermal conductivity not only shows better temperature uniformity than water, but also exhibits maximum temperature control ability than pure emulsion. Furthermore, to verify the heat storage effect of SSPCM, thermal performance of the novel system is compared with metal (aluminium) channel system. The SSPCM cooling system can greatly improve temperature uniformity compared with metal cooling system at high charge–discharge rate. Based on the above comparative analysis, the SSPCM cooling system with GO emulsion cooling presents optimal cooling performance of batteries. Finally, to reduce pump consumption, the cooling strategies of different start-up times for GO emulsion are studied. The results show that compared with continuous cooling, starting GO emulsion cooling when the maximum temperature of power battery reaches 42 ℃ can improve latent heat utilization of emulsion and reduce the power consumption with few temperature rise (0.2 ℃).

Flexible phase change materials: Preparation, properties and application

• Preparation methods of FPCMs are reviewed and compared. • Properties of FPCMs are summarized and analyzed. • Applications of FPCMs are introduced in detail. • Various issues and challenges of FPCMs are identified. Phase change materials (PCMs) have been widely used in various fields of thermal energy storage because of their large latent heat value and excellent temperature control performance. Based on the microstructure packaging strategy, PCMs are developed into shape-stabilized PCMs, which can solve the problem of leakage when phase change occurs. However, shape-stabilized PCMs usually have the disadvantage of poor mechanical properties, and the thermal resistance increases due to the poor fit with heat transfer elements. With the development of flexible electronic devices and wearable devices, flexible phase change materials (FPCMs) with excellent mechanical properties have become a hot spot. This paper introduces the preparation methods of FPCMs from both internal molecular support and external skeleton support. In addition, the flexibility mechanism and the properties of FPCM are summarized and analyzed. Furthermore, the potential applications of FPCMs in thermal management of electronic devices, wearable devices and others are presented in detail. Finally, the main problems, solutions and future directions are put forward and discussed.

Shape-Stabilized Phase Change Materials with Superior Thermal Conductivity for Thermal Energy Harvesting

This work presents the preparation of highly thermally conductive and shape-stabilized phase change composites (SSPCMs) at low filler loading. Polyethylene glycol (PEG) served as the phase change component. The high thermal conductivity is realized by the construction of dual thermally conductive networks based on boron nitride (BN) and expanded graphite (EG). The shape stabilization is obtained by the combined effects of the physical absorption of EG and the chemical crosslinking of epoxy. The prepared composite has a thermal conductivity of 3.907 W m–1 K–1 at a low filler loading when filled with 6.00% EG and 16.00% BN. Correspondingly, the melting enthalpy and crystallization enthalpy can maintain 79.93 and 75.39 J g–1, respectively. The result indicates that the prepared composite has excellent thermal stability and PEG is firmly stabilized in the composites, it would not leak from the matrix when exposed to high temperature and long heating periods. The experiment also confirms that the prepared composite has superior solar-thermal energy conversion and thermal management ability.

Improving the phase transition characteristic and latent heat storage efficiency by forming polymer-based shape-stabilized PCM for active latent storage system

In this work, form-stabilized PCM (SSPCM) is evaluated for an active latent heat storage (ALHS) system. High-density polyethylene (HDPE) and styrene-butadiene-styrene (SBS) are used as supporting materials. Four different composites are prepared based on weight ratio: pure paraffin (P), paraffin/HDPE (80/20), paraffin/SBS (80/20), and paraffin/HDPE/SBS (80/20 + 20). The variation in the thermal conductivity depends on the supporting material where HDPE is good at solid-phase and SBS in liquid-phase. According to the DSC results, the supercooling degree is decreased for the all-composite SSPCM with the lowest supercooling degree by 0.6 °C for paraffin/SBS. The thermogravimetric results for composite SSPCM show a higher temperature decomposition with multi-step degradation. The thermal performance of the sample is assessed by using a tube-in-shell heat exchanger. The isothermal phase transition is observed for all composite SSPCM with the lowest temperature gradient by 5 °C. The composite SSPCM has a higher storage efficiency ranging from 85.6 to 88.4% than pure paraffin, with a storage efficiency of 72.3%. With a stable phase transition and a better storage efficiency, the proposed SSPCM can improve paraffin-based ALHS.

Carbide slag based shape-stable phase change materials for waste recycling and thermal energy storage

Massive accumulation of industrial carbide slag tend to cause ecological environment pollution and greenhouse gas emission. This innovative work proposed to fabricate shape-stable phase change materials (SSPCMs) with carbide slag to utilise industrial solid waste and protect precious natural resources. Seven SSPCMs were fabricated with different mass ratios of industrial carbide slag to sodium nitrate by cold-compression hot-sintering method, and key performance was investigated on the SSPCMs. Results showed that the SSPCM (sample CC6) with the mass ratio of 5:5 of carbide slag to sodium nitrate presented the best performance: sample CC6 achieved a high thermal energy storage density of 447 J/g in the range of 100–400 °C and reached a mechanical strength of 73.6 MPa; sample CC6 demonstrated a good thermal stability and chemical compatibility between carbide slag and sodium nitrate during the heating/cooling cycles; the thermal conductivity of sample CC6 was 0.93 W/(m•K), and elements distributed uniformly in sample CC6.

Development of a shape-stabilized phase change material utilizing natural and industrial byproducts for thermal energy storage in buildings

A comprehensive study was conducted to develop and utilize a novel shape-stabilized phase change material utilizing two abundantly available and low-cost natural materials, namely scoria and expanded perlite and an industrial byproduct, heavy oil ash, in combination with polyethylene glycol. The thermal and energy storage characteristics of the composite materials were evaluated with the aim of using them to conserve energy in the domestic facilities. The results of differential scanning calorimetry showed that expanded perlite composite has the highest melting and solidification latent heat values, 150.7 J/g and 134.6 J/g, respectively, compared to scoria and oil ash composite. However, expanded perlite composite has lower thermal conductivity compared to other composites. Consequently, a novel system incorporating carbon nano tubes (0.5 wt.% and 1 wt.%) in the expanded perlite composite was developed to improve its thermal conductivity. The thermal conductivity (0.453 W/m.K) of the new system with 0.5% carbon nano tubes is remarkably more than that of commonly used phase change materials. Further, the developed PCM with 0.5% carbon nano tubes can transform sunlight into thermal energy with a solar-to-thermal energy conversion efficiency of 59.4% and it has a thermal conductivity that is 97% more than that of polyethylene glycol alone. Besides, the newly developed PCM also shows excellent energy storage and release performance. All these favorable characteristics indicate that the developed phase change material can be beneficially utilized in thermal storage systems.

Aluminum doping of mesoporous silica as a promising strategy for increasing the energy storage of shape stabilized phase change materials containing molten NaNO3: KNO3 eutectic mixture

Efficient thermal energy storage at high temperature is necessary for both industrial waste heat utilization and continuous solar power generation. Shape-stabilized phase change materials containing mesoporous aluminosilicates and eutectic NaNO3: KNO3 (1:1 mol) molten salt mixture were obtained at 90% wt. salt. The influence of aluminum doping was studied for the first time. All samples show thermal stability up to 550 °C and two distinct phase transitions corresponding to the melting/freezing of nanoconfined and interparticle salt phases. The radius and spherical shape of the nanoconfined phase were determined from the melting and freezing point depressions with respect to bulk. The enthalpy decrease was quantified in terms of surface tension and the contributions of a non-melting fraction of surface adsorbed ions. SBA-15 type aluminosilicates matrices yield composites with high latent heat storage of 76–77 Jg−1, of which 8 Jg−1 for the nanoconfined phase and good thermal reliability. Aluminum doping is a simple and promising strategy for obtaining high temperature, efficient thermal energy storage materials due to a lack of non-melting salt fraction. The resulting shape-stabilized PCMs have a higher operating temperature range and latent heat storage, offering a 36% increase in total heat capacity over the pristine salt.

Functional Unit Construction for Heat Storage by Using Biomass-Based Composite.

How to construct a functional unit for heat storage by using biomass materials is significant for the exploration of phase change materials (PCMs). In this work, we try to design and construct a functional unit for heat storage by employing a vacuum impregnation method to prepare sugarcane-based shape stabilized phase change materials (SSPCMs) for improving the thermal conductivity of phase change materials (PCMs) and preventing the liquid state leakage of PCMs. The morphologies of the prepared materials are characterized by Scanning electron microscope (SEM) as containing a unique channel structure which is viewed as the key factor for heat storage. X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to characterize the prepared materials. The results indicated that no chemical reaction occurred between PEG and sugarcane-based biomass during the preparation process and SSPCMs showed great thermal stability. Their thermal properties are measured by using the differential scanning calorimetry (DSC) characterization and show a high melting enthalpy of 140.04 J/g and 94.84% of the relative enthalpy efficiency, illustrating the excellent shape stabilized phase change behavior. Moreover, the highest thermal conductivity of SSPCMs is up to 0.297 W/(mK), which is 28.02% higher than that of the pristine PEG. The excellent capability for thermal energy storage is attributed to the directional thermal conduction skeletons and perfect open channels and the unique anisotropic three-dimensional structure of the SSPCMs. Hence, the unique structure with PEG is testified as the functional unit for heat storage. Comprehensively considering the excellent properties of sugarcane-based materials—providing cheap raw materials via green preparation—it is conceived that sugarcane-based materials could be applied in many energy-related devices with reasonable function unit design.

Influence of surfactants and organic polymers on monolithic shape-stabilized phase change materials synthesized via sol-gel route

Shape-stabilized phase change materials (ss-PCMs) can store up to five times more thermal energy than commercially available composite PCM boards based on core-shell PCMs, but have low mechanical stabilities. Therefore, we have recently synthesized ss-PCMs with high mechanical stability via a novel porogen-assisted sol-gel process. Here, we track the ss-PCM formation in situ and analyze the influence of the porogens sodium dodecyl sulfate (SDS) and poly(vinyl alcohol) (PVA) on ss-PCM properties. During gelation the silica scaffold is built around PCM droplets covered with SDS in an O/W emulsion. All ss-PCMs exhibit a high shape-stability (∼100%), a high long-term performance (> 2000 thermal cycles) and a high chemical stability, regardless of the amount of porogen used in the synthesis. Higher PVA amounts separate the emulsion in large hydrophilic and small hydrophobic regions and increase the silica macropore width in ss-PCMs from 1007 nm to 8801 nm due to silica fragmentation during drying. The silica fragmentation lowers the compressive strength (1.2 MPa) and thermal conductivity (0.37 W/mK) of the ss-PCMs by 50% and by 17% (10 °C), respectively. In contrast, low SDS amounts can not stabilize all PCM droplets in the emulsion from phase-separation, resulting in a partially fragmented silica phase. Too high SDS concentrations decrease the viscosity and hence, stability of the emulsion. Consequentially, the silica macropores collapse during drying, which lower the compressive strength (1.02 MPa) and thermal conductivity (0.37 W/mK) of ss-PCMs by 63% and 25% (10 °C), respectively.

Novel composite phase change material of high heat storage and photothermal conversion ability

Using porous matrix as the supports for phase change materials (PCMs) can effectively eliminate the leakage problem of PCMs during the phase change process. In heat storage utilization, the as-prepared shape-stabilized phase change materials are highly desired to have high latent heat density, rapid heat transfer ability and less supercooling. Although mesoporous silica with large pore volume and specific surface area might be a promising matrix for PCMs, it would be more beneficial if its thermal conductivity and photo-thermal conversion capacity were further improved, especially for the utilization of solar thermal energy. Herein, a composite PCM, namely SA/CNTs@MS, was fabricated successfully using mesoporous silica coated carbon nanotubes (CNTs@MS) as the shape-stabilized matrix for the PCM stearic acid (SA). The results of characterizations showed that CNTs@MS had a core-shell structure with mesoporous silica of a thickness of about 30 nm coated on the outer surface of carbon tubes (CNTs) homogeneously. The melting enthalpy of the obtained SA/CNTs@MS composite was 125.6 J/g. Its thermal conductivity increased 64.7%, and the supercooling degree decreased 3.2 ℃ while compared with those of pure SA. The melting and solidification enthalpies of SA/CNTs@MS decreased 1.1% and 1.3%, respectively after 200 thermal cycles. Besides, it is also confirmed that SA/CNTs@MS had good photo-thermal conversion performance. These imply that the synthesized SA/CNTs@MS composite would be an ideal heat storage material, especially for solar energy utilization.

Study on thermophysical properties of pentadecane and its composites with thermally expanded graphite as shape-stabilized phase change materials

Study on thermophysical properties of pentadecane and its composites with thermally expanded graphite as shape-stabilized phase change materials

Cement based-thermal energy storage mortar including blast furnace slag/capric acid shape-stabilized phase change material: Physical, mechanical, thermal properties and solar thermoregulation performance

Solar thermal energy efficiency of cementitious mortar is enhanced by introducing a phase change material (PCM) with thermal energy harvesting/releasing ability. Within this framework, a new type of cement based-thermal energy storage mortar (CBTESM) was developed by substituting blast furnace slag (BFS)/capric acid (CA) shape-stabilized PCM (SSPCM) with 15%, 30% and 45 wt% of sand. The results of XRD indicated that crystalline structure of CA was not affected with addition of BFS. The results of SEM/EDS confirmed successful impregnation of the melted CA into the BFS as carrying material thanks to the capillary forces. DSC analysis indicated that melting temperature and latent heat of fusion for SSPCM is 28.0˚C and 55.5 J/g while they are 28.52˚C and 13.8 J/g for CBTESM containing 45 wt% SSPCM. When 45 wt% SSPCM was added to mortar, bulk density (1.45 g/cm3), compressive strength (8.16 MPa) and thermal conductivity (0.601 W/m.K) decreased by 28.57%, 85.37% and 41.25%, respectively. The CBTESM sample including 15 wt% SSPCM additive (22.51 MPa) can meet the standard conditions in terms of compressive strength. Thermoregulation performance test under actual ambient conditions demonstrated that the developed CBTESM considerably reduced the indoor temperature. Theoretical calculations showed that a 13.5 kWh energy saving can be achieved by using 1 kg CBTESM in a wall having size of 3 × 4 × 0.2 m. Also 36.67, 35.73 and 5.87 kg-CO2 reduction in carbon emission would be reduced as per 1 kWh coal, natural gas and electricity consumptions, respectively.

Biomass-based shape-stable phase change materials supported by garlic peel-derived porous carbon for thermal energy storage

Phase change materials with low cost, good thermal stability, and excellent shape stability are urgent in energy storage. Herein, a novel shape-stable phase-change material (SSPCM) for thermal energy storage is developed based on activated garlic peel (AGP), derived from widespread and cheap garlic peels. The paraffin (PA)/AGP composite PCM is prepared via vacuum impregnation method. The scanning electron microscope results show that AGP has many grooves, and the pores of AGP are filled by paraffin wax. The specific surface area of AGP is up to 1309 m2/g. The phase change enthalpy in the melting and freezing process is 52.5 J/g and 51.9 J/g, respectively. Moreover, the prepared SSPCM exhibits satisfied shape stability, thermal stability, and waste heat storage ability. Also, the SSPCM has a low latent heat loss rate of about 1.5% after 200 thermal cycles. This work provides an economical and environmental method for synthesizing shape-stabilized phase-change materials based on biomass materials with potential applications in waste heat recovery and recycling.

Thermo-regulating performance of concrete slab loaded with shape stabilized phase change material in tropical climate

The building overheating problem is one of the most important problems facing all over the world. Various methods like using highly thermal resistive building materials, composite building materials were used to reduce the heat gain of the buildings. One of the method which can be used in place of traditional methods is using building elements with high thermal energy storage capacity. The significance of this study is to improve the thermal energy storage capacity of the building element for improving indoor thermal performance of the building. In this study latent heat energy storage capacity of the concrete slab is enhanced by incorporating Shape Stabilized Phase Change Material (SS-PCM) in it. SS-PCM was prepared by incorporating eutectic PCM (Paraffin Wax 70% and Coconut Oil 30%) in highly porous material called zeolite. The zeolite powder successfully incorporate 30 wt% PCM without showing any leakage at elevated temperature. Morphology of the SS-PCM was evaluated through Scanning Electron Microscopy (SEM) images. The SS-PCM at 0 wt%, 10 wt%, 20 wt%, and 30 wt% was used to prepare composite concrete slab by replacing fine aggregates. Composite concrete slabs were tested for indoor thermal behavior in real outdoor testing of 72 h. Indoor thermal performance was evaluated on the basis of peak temperature reduction, thermal amplitude, time delay, and decrement factor. The 30% SS-PCM has a high latent heat capacity, which significantly improves thermal energy storage in buildings. Various parameters like peak temperature reduction, time lag, thermal amplitude and decrement factor were evaluated. Concrete slab integrated with 30% SS-PCM shows maximum peak percentage temperature reduction of 10.04 % and percentage reduction in thermal amplitude of 23.71 % in comparison to conventional concrete. Additionally, infrared thermography of all the concrete slabs at different time of the day was done.

Evaluation of thermal/morphological performance of SSPCM based nanoclay: Influence of the interlayer microstructure of hydrophilic and hydrophobic

The COVID-19 pandemic has led to an increase in construction energy consumption and indoor occupancy; this, in turn, has increased the demand for energy efficiency. Thermal energy storage is an effective method for energy saving and improving efficiency. In this study, improved shape-stabilized phase change materials (SSPCMs) for enhancing the energy efficiency of buildings were manufactured and evaluated. These SSPCMs were prepared via the vacuum impregnation of n-octadecane into bentonite nanoclay. Bentonite exhibits a layered tetrahedral and octahedral crystal structure with Na + cations (which feature high cation exchange capacity) in the interlayer space. The Na + ion is a hydrophilic ion that affects the properties of the interlayer. However, paraffin-PCMs are hydrophobic and have poor compatibility with water. Therefore, hydrophobicity is induced in the organic nanoclay by using an organic modifier as the PCM container. Cloisite Na + , Cloisite 15, Cloisite 20, and Cloisite 93 were used to fabricate the SSPCMs. This study compares the amount of PCM impregnated depending on the compatibility of different PCMs between hydrophilic/hydrophobic nanoclays and also evaluates the thermal performance. The observed reduction in peak temperature and the time lag effect of the PCMs confirmed that the organically modified nanoclay and the PCM composites significantly improved the amount of PCM impregnated, thermal conductivity, and latent heat characteristics. The latent heat of the hydrophobic organic nanoclay was 209% higher than that of the SSPCM-based hydrophilic nanoclay. • Composites using paraffin PCM and nanoclay were fabricated and analyzed. • Hydrophobic nanoclay showed 124% higher PCM impregnation than hydrophilic nanoclay. • It was observed that PCM impregnation was affected by the microstructure. • SSPCMs showed up to 84% improved thermal conductivity than pure PCM. • The overall thermal performance in the SSPCM based hydrophobic nanoclay were high.

Shape-Stabilized Phase Change Material with Internal Coolant Channel Coupled with Phase Change Emulsion for Power Battery Thermal Management

Shape-Stabilized Phase Change Material with Internal Coolant Channel Coupled with Phase Change Emulsion for Power Battery Thermal Management