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In this study, paraffin was selected as the phase change materials (PCMs) and rude-Palygorskite (Pal), rinsed-Pal, H + -Pal and organic-Pal were selected as porous materials. A series of paraffin/Pals composite PCMs were prepared by direct impregnation method without vacuuming. In the composite PCMs, up to 150 wt% of paraffin could be loaded in H + -Pal. The Differential Scanning Calorimetry (DSC) tests revealed that paraffin/ H + -Pal composite PCM had a melting temperature of 54–56 °C and latent heat of 132.18 J g −1 . In addition, the composite PCMs were characterized by Scanning Electron Microscope (SEM), Brunauer, Emmett, and Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR). Good thermal stability was observed for composite PCMs by cycling test; we found that paraffin/H + -Pal composite PCM maintained ~95% of the initial latent heat after the cycling test. In conclusion, the impregnation of Pals with paraffin was a promising method for preparation of excellent PCM composites. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are able to melt and solidify at a certain temperature with a high heat of fusion. These promising functional materials for acting as energy as latent heat storage units have one major problem, leakage of the PCMs when molten. Polymer/phase change material (PCM) blends were investigated as a possible solution of PCM leakage. In this research, paraffin was used as the PCM and three types polyethylene (PE) were used as the structural matrix. To investigate the morphology of PE/ paraffin blends and evaluate the influence on blend behavior, paraffin was blended with either high density polyethylene (HDPE), low density polyethylene (LDPE), or linear low density polyethylene (LLDPE) using a parallel co-rotating twin screw extruder. Chloroform extraction was utilized to estimate the maximum amount of paraffin able to be released by the PE network at equilibrium. Scanning electron microscope (SEM) images of chloroform-extracted samples were collected to investigate the blend structure. Thermal transition temperatures and crystallinity of components in the blends were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) was used to investigate crystal perfection changes of the polyethylenes before and after blending with paraffin. Paraffin leakage of the blends was investigated by accelerated degradation test in an oven at 60 °C. The leakage behavior was analyzed by Korsmeyer–Peppas equation to determine the underlying mechanisms. Chloroform extraction indicated that almost all the paraffin would leak out from the blends in the long run. A co-continuous structure of the blends was evident from the chloroform extraction and subsequent SEM images. While this co-continuous structure controlled leakage behavior, it had little influence on paraffin thermal transition temperatures and crystallinity based on DSC study. In contrast, PE crystal perfection decreased with paraffin level as evident in POM images. This structure resulted in leakage of paraffin in all formulations. [ABSTRACT FROM AUTHOR]

This paper deals with the preparation, characterization, thermal properties and thermal reliability of form-stable composite phase change materials (PCMs), composed of n-octadecane, expanded vermiculite, and perlite for thermal energy storage. The composite PCMs were prepared by incorporation of liquid n-octadecane within the expanded vermiculite (eVMT) and expanded perlite (ePLT), using a vacuum impregnation method. The microstructures of n-octadecane/expanded vermiculite and pearlite were characterized by scanning electron microscopy (SEM). Analysis of Fourier transform infrared spectroscopy (FT-IR) of the prepared composite PCMs showed good compatibility between n-octadecane and the expanded vermiculite and pearlite. The thermal conductivities of composites were reduced, based on the TCi results. Differential scanning calorimetry (DSC) analysis indicated that the n-octadecane/eVMT and n-odtadecane/ePLT composites maintained their large latent heat capacity and original phase change temperatures, due to large surface area and good dispersion of the eVMT and ePLT. TGA analysis revealed that the prepared composite PCMs had good thermal durability in the working temperature ranges. Therefore, n-octadecane based composite PCMs can be considered as suitable candidates for latent heat thermal energy storage, with high thermal performance. [ABSTRACT FROM AUTHOR]

Paraffin is a common organic phase change material (PCM) that finds many applications in thermal energy storage (TES) systems. One common characteristic of organic PCMs is their low thermal conductivities. This – in turn – causes a slow thermal response when paraffin is used in high power applications. In this study, paraffin–nanomagnetite (Fe 3 O 4 ) composites (PNMC) were prepared by a dispersion technique to enhance their thermal properties. Nano magnetite prepared using the cost-effective sol–gel method was mixed into paraffin at two different mass fractions: 10% and 20%. Scanning electron microscope (SEM) was used to observe the morphologies of nanomagnetite and PNMCs during different stages of the composite production process. SEM analysis results showed that nanomagnetite particles of 40–75 nm in size were homogeneously distributed in the paraffin structure. The latent heat storage capacity of PNMC, measured by differential scanning calorimetry (DSC) at 1 °C/min, was found to be 8% higher than paraffin alone. Thermal conductivities and diffusivities of paraffin and PNMCs were determined by the “DICO” method. For 10% and 20% by weight PNMCs, the thermal conductivities were increased by 48% and 60%, respectively. These results clearly indicate that the addition of Fe 3 O 4 nanoparticles is an efficient and cost effective method to enhance the heat transfer properties of paraffin, when they are incorporated into latent heat storage systems. [ABSTRACT FROM AUTHOR]

Abstract: Mesophase pitch based graphite foams (GFs) with different thermal properties and pore-size were used to increase the thermal diffusivity of phase change material (PCM), paraffin wax, for latent heat thermal energy storage application. To predict the performance of the Paraffin-GFs as a thermal energy storage system, their structure, thermal diffusivity and latent heat were characterized. Results indicated that thermal diffusivity of the Paraffin-GF can be enhanced 190, 270, 500, and 570 times as compared with that of pure paraffin wax. Latent heat of Paraffin-GF systems increased with the increasing of the mass ratio of the paraffin wax in the composite. Moreover, pore-size and thickness of ligaments of the foam played a key role in improving the thermal diffusivity and the storage capacity of the Paraffin-GF system: small pore-size (less paraffin wax were filled) and thicker ligament in GF resulted in a higher thermal diffusivity; large pore-size (less paraffin wax were filled) and thinner ligament in GF resulted in a larger latent heat. [Copyright &y& Elsevier]

Abstract: The shape-stabilized phase change material (PCM) based on paraffin and high-density polyethylene (HDPE) is used as a storage media in thermal energy storage. This storage media can retain the shape even when paraffin is in the liquid state, and no paraffin is observed, but it has a low thermal conductivity and is easily flammable, which limits the utility area in thermal energy storage. The motivation of this study was to improve thermal conductivity and flame retardant property of shape-stabilized PCM. A flame retardant shape-stabilized PCM made of paraffin, HDPE, expanded graphite (EG) and intumescent flame retardant (IFR) was presented. To characterize the resulting product, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), hot disk thermal constants analyzer, attenuated total reflectance fourier transform infrared (ATR-FTIR) and cone calorimeter measurements were employed to investigate their microcosmic shapes, crystalline behaviors and thermal properties. The SEM results indicated that paraffin and EG were well dispersed in the network formed by HDPE. The thermal conductivity and the flame retardant efficiency of IFR could be improved by adding EG. The possible flame retardant mechanism for paraffin/HDPE/IFR/EG as a shape-stabilized PCM was proposed. [Copyright &y& Elsevier]

Abstract: Using exfoliated graphite nanoplatelets (xGnP), paraffin/xGnP composite phase change materials (PCMs) were prepared by the stirring of xGnP in liquid paraffin for high electric conductivity, thermal conductivity and latent heat storage. xGnP of 1, 2, 3, 5 and 7wt% was added to pure paraffin at 75°C. Scanning electron microscopy (SEM) morphology showed uniform dispersion of xGnP in the paraffin wax. Good dispersion of xGnP in paraffin/xGnP composite PCMs led to high electric conductivity. The percolation threshold of paraffin/xGnP composite PCMs was between 1 and 2wt% in resistivity measurement. The thermal conductivity of paraffin/xGnP composite PCMs was increased as xGnP loading contents. Also, reproducibility of paraffin/xGnP composite PCMs as continuous PCMs was manifested in results of electric and thermal conductivity. Paraffin/xGnP composite PCMs showed two peaks in the heating curve by differential scanning calorimeter (DSC) measurement. The first phase change peak at around 35°C is lower and corresponds to the solid–solid phase transition of the paraffin, and the second peak is high at around 55°C, corresponding to the solid–liquid phase change. The latent heat of paraffin/xGnP composite PCMs did not decrease as loading xGnP contents to paraffin. xGnP can be considered as an effective heat-diffusion promoter to improve thermal conductivity of PCMs without reducing its latent heat storage capacity in paraffin wax. [Copyright &y& Elsevier]

When solar radiation reaches its peak value during the midday, buildings' external walls absorb the highest amount of heats and result in dramatic spikes in cooling load and energy consumption. To flatten the energy peak, promote energy efficiency, and preserve thermal comfort, this study developed a novel foamed thermal insulation cement block with extraordinary heat storage capacity. To prepare the proposed foamed cement block, a paraffin/expanded graphite composite phase change heat storage material with a phase transition temperature of 41.9 °C and an enthalpy value of 207.8 J/g was used to load paraffin into expanded graphite in a water bath at 44 °C. After mixing the paraffin/expanded graphite composite phase change material (PCM) with cement, foams were added, stirred and poured into the mold to make a novel foaming cement thermal insulation block. Due to its porous structure, the foamed cement has lightweight as well as high heat preservation capacity. To investigate the characteristics of the proposed material, this investigated its physical structure, thermal conductivity, and heat energy storage performance when the material mass fractions of PCM are 10%, 15%, 20%, 25% and 30%, and regular (pure) cement blocks. The experimental results show that there is no chemical reaction during material preparation. In addition, composite materials' PCM mass fraction and their thermal storage capacity increase simultaneously. The comprehensive analysis shows that foamed cement blocks with 30% PCM contents have the best thermal energy storage performance and can maintain the lowest average indoor temperature. Therefore, the proposed foamed cement blocks can be applied to building outer surfaces and sandwiched middle enclosures to develop energy efficiency insulation walls. [ABSTRACT FROM AUTHOR]