Thermal Properties Of Composite Phase Change Materials Research Articles

Preparation and Performance of Inorganic Hydrated Salt-Based Composite Materials for Temperature and Humidity Regulation

In this work, it was first proposed to combine hydrated salt phase change materials (PCMs) with humidity control materials to prepare the temperature and humidity control material. The composite PCM was prepared by absorbing Na2HPO4·12H2O with colloidal silicon dioxide, and diatomite was selected as the humidity control material. The humidity performance tests found that diatomite had good moisture absorption/desorption capacity and excellent moisture buffering capacity. The supercooling degree tests showed that Na2SiO3·9H2O as nucleating agent effectively reduced the supercooling degree, and the addition of deionized water improved the water loss problem of composite PCMs. The DSC tests showed that the enthalpy and melting temperature of composite PCMs were 153.1 J/g and 28.9°C, respectively. By placing the temperature and humidity control material in different humidity, it was found that the moisture content of diatomite affected the thermal properties of composite PCMs. Diatomite could not only transfer moisture to hydrated salts but also absorb moisture from hydrated salt. The application performance tests of the temperature and humidity control material in the room model showed that it could simultaneously regulate indoor temperature and humidity. Overall, this temperature and humidity control material was more suitable for environments with high relative humidity such as greenhouses.

Measurement of thermophysical properties with nanomaterials on the Melting/Freezing characteristics of phase change material

In the present work, four formulations of the composite phase change materials (PCMs) were produced by adding 0.5 wt% of nanoparticles (NPs), and each formulation comprised one of the types of nanoparticles. Myristic acid was considered as the base material; 0.5 wt% of Al2O3, SiO2, CuO, and Ag were reckoned as the supporting materials. Al2O3, SiO2, CuO, and Ag NPs were synthesized and they were studied by different characterization techniques. The melting and freezing temperatures of myristic acid were determined in the range from 55.54 °C to 55.94 °C and from 48.42 °C to 48.71 °C, respectively. Likewise, the latent heats for melting and freezing were found to be 192.31 kJ/kg and 192.53 kJ/kg, respectively. The thermal properties of composite PCMs were evaluated with respect to weight fractions of NPs and thermal cycles. With nanomaterial dispersion, the laser flash analyzer (LFA) confirmed the thermal conductivity enhancement of myristic acid. The composite PCMs have faster melting and freezing times than pure PCMs, as stated in the results of this study.

Preparation and characterization of binary and ternary composite PCMs with two phase transition temperatures for solar water heating system

This paper presented a novel binary or ternary composite phase change material (CPCM) composed of two or three single phase change materials (PCMs), which can be used for solar water heating system (SWHS) to accomplish the demand for seasonal thermal energy storage. Five single PCMs, capric acid (CA), lauric acid (LA), stearic acid (SA), 62# paraffin (62#) and octodecyl alcohol (OA), are selected to make CPCMs. Samples with different combination of single PCMs and different mass ratios are properly prepared and investigated. The thermal properties of CPCMs are analyzed via Schrader equation and series experiments, such as step cooling curve, differential scanning calorimetry (DSC), thermal cycling and Fourier-transform infrared (FTIR) spectroscopy tests. Investigation shows that the proposed CPCMs with 2 phase transition temperatures (PTTs) have stable properties, higher latent heat and lower price compared with their components. Especially the proposed ternary CPCM with a eutectic mixture as its low temperature component can demonstrate more excellent thermal characteristics. For example, compared with LA-62# (1:1), LA-OA-62# (3:1:4), with the same mass ratio of high and low temperature components as LA-62#, can increase its latent heat of the low temperature phase transition process and the whole phase transition process, maximum by 17.6%. The proposed CPCMs are suitable for seasonal thermal energy storage.

Preparation and thermal properties of palmitic acid @ZnO/Expanded graphite composite phase change material for heat storage

A novel palmitic acid @ZnO/Expanded graphite composite phase change material (PCM) was prepared. Palmitic acid (PA) was selected as phase change material and ZnO/Expanded Graphite as supporting material. Expanded graphite (EG), which was used to improve the thermal conductivity of PCM, was chemically modified using ZnO derived from ZIF-8. ZnO derived from ZIF-8 has abundant pore structure and large specific surface area. The structure of ZnO/EG additive was characterized by SEM analyzing method. The prepared ZnO/EG has a three-dimensional coupled network and hierarchical porous structure. Meanwhile, EG can effectively prevent the structural collapse and aggregation of Metal-Organic Framework (MOF) derivatives. The morphology and thermal properties of composite PCMs were analyzed with SEM, XRD, FTIR, DSC, TG, and DTG. The melting/solidifying temperatures and corresponding latent heats of composite PCM PA@ZnO/EG-6% are 60.38 °C and 58.46 °C, and 203.35 kJ/kg and 207.87 kJ/kg. Thermal conductivity of the composite PCM PA@ZnO/EG-6% increases by 137.5% than that of PA. The DTG results indicated the composite PCM has superior thermal stability. All test results suggested that this composite is a good PCM and has excellent potential in heat storage due to its excellent thermal properties, good thermal stability, and reliability.

Molecular dynamics simulation on thermal enhancement for carbon nano tubes (CNTs) based phase change materials (PCMs)

In the study, CNTs based nanocomposite phase change materials (NPCMs) is considered for breaking through the constraint of the low thermal conductivity of conventional PCMs for thermal energy storage. A molecular dynamics simulation method is newly established to predict the structural, diffusive and thermal properties of composite PCMs based on CNTs. It is found that the PCMs is preferentially distributed as either one or two ring-shaped layers that discretely separated from the CNTs wall with a distance of 3.8 Å and 8.0 Å, respectively. The mean square displacement (MSD) and the self diffusion coefficient are characterized for featuring the molecule mobility and predicting the melting temperature of the composite PCMs. Interestingly, the dense phase existing between the CNTs wall and the PCMs is proven to be the dominant factor that negates the phase change enthalpy of the composite system. In realistic experiments using the CNTs with a radius of 10∼15 Å, the thermal conductivity is highly potential to be improved to 5∼15 W/m·K, indicating an augmentation of the thermal conductivity by approximate 32∼100 times compared to pure PCMs. The formation of efficient heat conduction paths explains for the intrinsic mechanism of the tremendous improvement in the CNTs based NPCMs, which could be achieved in the premise of strong binding effect of materials and reduced contact thermal resistance among CNTs in macroscopic PCM modules.

Effect of composite orders of graphene oxide on thermal properties of Na2HPO4•12H2O/expanded vermiculite composite phase change materials

The leakage of Na2HPO4•12H2O phase-change materials (PCMs) in the liquid state can be prevented by encapsulating them into porous expanded vermiculite (EV) to prepare composite PCMs. The main issues of EV-based composite PCMs are the low thermal conductivity and the crystal water loss of inorganic hydrated salt. Graphene oxide (GO) can help enhance the thermal conductivity of composite PCMs and firmly adsorb water molecules through oxygen groups. The composite orders of GO play an important role in adjusting the thermal properties of composite PCMs because the suitable positions of GO in the stratified structure of EVs would positively influence the PCMs. The Na2HPO4•12H2O/EV composite with GO was prepared in three different orders. Compared with the common method that involves compositing GO in Na2HPO4•12H2O, compositing GO on the hole wall of the EV exhibited a higher thermal conductivity of 0.54 W/m•K and compositing GO out of Na2HPO4•12H2O/EV exhibited better thermal stability, which incurred a weight loss of 4.14% at a high temperature. A thermal energy storage behaviour analysis indicated that GO-modified PCMs show a large heat storage capacity (melting process: 98–126 J/g; solidification process: 56–91 J/g). Two new composite orders positively affected the heat storage of the composite PCMs.

Preparation of energy storage materials working at 20–25 °C as a cold source for long-term stable operation

As an inorganic phase change material (PCM), CaCl2·6H2O is an effective energy storage material because its energy can be transformed around 30 °C through the melting and crystallization. The different compositions of PCM were prepared in order to decrease the phase transition temperature to 20–25 °C and to improve its capability of heat storage and release. MgCl2·6H2O was added as a nucleating agent and the composite PCMs (CPCMs) of CaCl2·6H2O/MgCl2·6H2O binary salt system was prepared. At the same time, SrCl2·6H2O was added to reduce the supercooling degree of inorganic PCM. As a thickener, hydroxyethyl cellulose (HEC) was also included to improve the recycling ability. With the application of thermogravimetric analysis and differential scanning calorimeter, the phase transition temperature, thermal properties of CPCMs, supercooling degree and thermal cycle performance were studied by changing the content of each component in the CPCMs. The results demonstrated that the phase transition temperature of PCM with 35% MgCl2·6H2O, 5% SrCl2·6H2O, 0.5% HEC balanced by CaCl2·6H2O was reached to 23 °C. The phase change latent heat of PCM was kept at 130 J/g. The degree of supercooling was kept within 0.7 °C and the recyclability was greatly improved after 100 cycles.

Phase change materials stabilized by porous metal supramolecular gels: Gelation effect on loading capacity and thermal performance

Shape-stability, PCM loading capacity, and energy storage performance of organic phase change materials (PCMs) are crucial in broad applications of thermal energy storage and management. In this study, a facile strategy was followed to design 3D-porous metal supramolecular gels as supporting materials. The phase change composites were prepared by solution impregnation of polyethylene glycol. The porous supporting material exhibited large specific surface area, high total pore volume, and micro/mesopore characteristics. In addition, the influence of gel concentration on PCM encapsulation and thermal properties of composite materials were investigated in which increasing the concentration result in a decrease in energy storage capacity and loading ratio. The as-prepared phase change composites revealed a high PCM loading capacity up to 90 wt% and energy storage capability reaches 100%. Factors such as pore characteristics and gel concentration played a central role in the thermal properties of composite PCMs. Further, the phase change composites showed high durability after 100 heating/cooling cycles without a significant shift in latent heat and phase transition temperatures. This investigation provides an insight into making a facile synthesis of gel-based composite PCMs and possible thermal energy management systems.

Preparation and characterization of encapsulated phase change materials in presence of gamma alumina for thermal energy storage applications

Modified gamma alumina/fatty acids composite phase change materials (PCMs) were prepared via encapsulation with poly(St-co-DVB) shell by phase inversion emulsification method. The gamma alumina (γ-Al2O3) nanoparticles were modified by cetyl trimethylammonium bromide (CTAB). The modified gamma alumina (M-γ-Al2O3) was added into fatty acid mixture, which composed of oleic acid (OA) and capric acid (CA) besides to n-hexadecane. Thus, the effect of alumina addition on the morphological and thermal properties of composite PCMs was investigated. The attachment of CTAB onto gamma alumina nanoparticles was verified by thermogravimetric analysis (TGA) method. The morphological and chemical characterization of empty shell material (PS-DVB shell), microencapsulated PCM and composite PCMs was investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy, respectively. Furthermore, the thermal properties of the PCMs were examined by differential scanning calorimetry (DSC), thermogravimetric analyses and heat storage rate measurement.

Thermal characteristic investigation of eutectic composite fatty acid as heat storage material for solar heating and cooling application

A composite phase change material (CPCM) of myristic acid/palmitic acid/sodium myristate (MA/PA/SM) and of myristic acid/palmitic acid/sodium laurate (MA/PA/SL) were impregnated with purified damar gum as called Shorea Javanica (SJ) to improve the thermal conductivity of CPCM. The thermal properties, thermal conductivity, and thermal stability of both CPCM have investigated by using a Differential Scanning Calorimetry (DSC) thermal analysis, hot disc thermal conductivity analyzer, and Simultaneous Thermal Analyzer (STA), simultaneously. However, a chemical compatibility between both fatty acid eutectic mixtures and SJ in composite mixtures measured by Fourier Transform Infra-Red (FT-IR) spectrophotometer. The results were obtained that the thermal conductivity of MA/PA/SM/SJ and MA/PA/SL/SJ eutectic composite phase change material (CPCM) were improved by addition 3 wt.% and 2 wt.% of Shorea javanica (SJ), respectively, without occur a significant change on thermal properties of CPCM. Moreover, the absorbance spectrum of FT-IR shows the good compatibility of SJ with both MA/PA/SM and MA/PA/SL eutectic mixtures, the composite PCM also present good thermal performance and good thermal stability. Therefore, it can be noted that the purified Shorea Javanica proposed, the as high conductive material in this study was able to improve the thermal conductivity of eutectic PCM without any significant reduction on its thermo-physical and chemical properties and can be recommended as novelty composite phase change material for thermal energy storage application.

Synthesis and characterization of beeswax-tetradecanol-carbon fiber/expanded perlite form-stable composite phase change material for solar energy storage

In this study, beeswax-tetradecanol/expanded perlite composited with carbon fiber (BW-TD-CF/EP) composite phase change materials (CPCMs) have been prepared via vacuum impregnation method for solar energy utilization. The chemical compatibility, microstructure and thermal properties of CPCMs are characterized and measured, which proves that it is no chemical interaction among the raw materials but physical combination and BW-TD-CF is sufficiently absorbed into the EP porous structure with no leakage even in the molten state. According to differential scanning calorimeter (DSC) results, BW-TD-CF/EP composite melts at 34 °C with high enthalpy value of 178.7 kJ/kg, while thermal cycling measurements show that the form-stable composite PCM has adequate stability after being subjected to 200 melting/freezing cycles. Morever, thermal conductivity of BW-TD/EP composite is enhanced from 0.443 Wm−1 K−1 to 1.245 Wm−1 K−1 by adding CF. In result, the form-stable composite PCMs have more appropriate thermal properties and better thermal stability in building for solar energy utilization.

Preparation of nitrogen-doped graphene/palmitic acid shape stabilized composite phase change material with remarkable thermal properties for thermal energy storage

Palmitic acid (PA) is one of the main phase change materials (PCMs) for medium temperature thermal energy storage systems. In order to stabilize the shape and enhance the thermal conductivity of PA, the effects of adding nitrogen-doped graphene (NDG) as a carbon nanofiller were examined experimentally. NDG was dispersed in liquid PA at various mass fractions (1–5wt%) using high power ultrasonication. The dropping point test shows that there was clearly no liquid leakage through the phase change process at the operating temperature range of the composite PCMs. The thermal stability and thermal properties of composite PCM were investigated with a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC), respectively. The thermal conductivity of the PA/NDG composite was determined by the laser flash method. The thermal conductivity at 35°C increased by more than 500% for the highest loading of NDG (5wt%). The electrical conductivity of composite PCMs was increased significantly by using NDG. The thermal cycling test proved that the PA/NDG composites PCMs had good thermal reliability and chemical durability after 1000 cycles of melting and freezing. The thermal effusivity of the PA/NDG composite PCMs was larger than that of pure PA, which is advantageous for latent heat thermal energy storage (LHTES).

Effect of carbon nanospheres on shape stabilization and thermal behavior of phase change materials for thermal energy storage

Stearic acid (SA) is one of the main phase change materials (PCMs) for medium temperature thermal energy storage systems. In order to stabilize the shape and enhance the thermal conductivity of SA, the effects of adding carbon nanospheres (CNSs) as a carbon nanofiller were examined experimentally. The maximum mass fraction of SA retained in CNSs was found as 80wt% without the leakage of SA in a melted state, even when it was heated over the melting point of SA. The dropping point test shows that there was clearly no liquid leakage through the phase change process at the operating temperature range of the composite PCMs. The thermal stability and thermal properties of composite PCMs were investigated with a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC), respectively. The thermal conductivity of the SA/CNS composite was determined by the laser flash method. The thermal conductivity at 35°C increased about 105% for the highest loading of CNS (50wt%). The thermal cycling test proved that form-stable composite PCMs had good thermal reliability and chemical durability after 1000 cycles of melting and freezing, which is advantageous for latent heat thermal energy storage (LHTES).