Suitable Phase Change Temperature Research Articles

SiO2 hydrophilic modification of expanded graphite to fabricate form-stable ternary nitrate composite room temperature phase change material for thermal energy storage

A form-stable ternary nitrate (LiNO3·3H2O-KNO3-NaNO3) composite phase change material (CPCM) with modified expanded graphite (MEG) as carrier was investigated. In order to improve the hydrophilicity of expanded graphite (EG) and its compatibility with ternary nitrate, the SiO2 particles prepared by sol–gel method was used as modifier to form a hydrophilic coating on EG to obtain MEG. The pore structure morphology as well as the adsorption capacity for ternary nitrate of EG and MEG were analyzed in detail. The shape-stability and thermal properties of the obtained CPCM were also evaluated. The results showed that the MEG with 15 wt% SiO2 exhibited optimal affinity to water and ternary nitrate PCM. With the addition of 20 wt% MEG, the configured CPCM owned a suitable phase change temperature (21.66 °C), high phase change enthalpy (158.7 J/g), low supercooling degree (1.56 °C) and outstanding thermal conductivity (4.565 W/m·K). Moreover, the thermal performance differences of the CPCM were relatively small after 200 thermal cycles, indicating that the prepared CPCM can be applied in the room temperature thermal energy storage technology.

Thermal transport and storage performances of NaCl–KCl–NaF eutectic salt for high temperatures latent heat

The NaCl–KCl–NaF eutectic salt was designed and developed by Pandat software and experiment. Thermal transport and storage performances were determined by experimental measurements. The melting point of the NaCl–KCl–NaF eutectic salt is 604.1 °C and the fusion enthalpy is up to 398.4 J/g. The thermal conductivity average value was 1.037 ± 0.074 W/m−1·°C−1. The weight loss of NaCl–KCl–NaF eutectic salt is still less than 6.0% even up to 900 °C and the eutectic salt have very excellent thermal stability. The NaCl–KCl–NaF eutectic salt with high latent and suitable temperature have good economy performance even with expensive individual salt of NaF. The NaCl–KCl–NaF eutectic salt with suitable phase change temperature, low cost, high latent heat, excellent stability and good economy performance can be a candidate phase change material for next generation concentrated solar power with supercritical CO2 cycles.

Developing NaAc∙3H2O-based composite phase change material using glycine as temperature regulator and expanded graphite as supporting material for use in floor radiant heating

Floor radiant heating embedded phase change materials (PCMs) are a prospective field owing to its highly efficient energy-saving effect and comfortable thermal environment. In this work, using a non-eutectic mixture comprised of NaAc∙3H2O (main PCM) and glycine (temperature regulator) as PCM, and expanded graphite (EG) as supporting material, a novel composite PCM with high thermal performance used in the heat exchanger for the floor radiant heating was developed. The composition of the composite PCM was optimized, and its properties were studied. The results showed that the mixture containing 12% glycine was favorable due to its suitable phase change temperature (48.62 °C) and high phase change enthalpy (258.5 kJ·kg−1). The addition of 12% EG into the mixture could enhance thermal conductivity and prevent leakage of the mixture simultaneously. The resulting composite PCM melted at 47.14 °C with phase change enthalpy of 214.7 kJ·kg−1, supercooling degree of 1.49 °C and thermal conductivity of 6.400 W m−1 K−1. The composite PCM also presented a good thermal reliability. Hence, the as-prepared composite PCM would be of great promise for use in the heat exchanger for the floor radiant heating. Besides, the present work is expected to provide a new pathway for exploring new types of PCMs.

Thermal properties of a new type of calcium chloride hexahydrate-magnesium chloride hexahydrate/expanded graphite composite phase change material and its application in photovoltaic heat dissipation

PV-PCM technology can not only achieve higher photoelectric conversion efficiency, but also has the advantages of energy saving, high efficiency, and economical applicability. In this paper, a new type of CaCl2·6H2O-MgCl2·6H2O composite PCM for PV-PCM was prepared by physical blending method using calcium chloride hexahydrate-magnesium chloride eutectic mixture as PCM and expanded graphite as carrier. The shape stability, thermal properties and thermal reliability of CaCl2·6H2O-MgCl2·6H2O eutectic materials under EG conditions were discussed. The change of temperature and output power of PV panel combined with PV-PCM was studied. The experimental results show that the CaCl2·6H2O-MgCl2·6H2O composite with 8 %EG has high phase change enthalpy (171.4 kJ/kg), suitable phase change temperature (27.1 °C), and negligible supercooling degree (0.11 °C) and excellent thermal conductivity (3.359 W/m·K). After 100 heating–cooling cycles, the modified composite phase change material still has excellent thermal reliability. Surface temperature of photovoltaic panels can be significantly reduced, and the average temperature of photovoltaic panels can be kept below 40 °C. The photovoltaic panel power can work for a long time (3.5–4 h) close to the rated power, keeping the photovoltaic panel power at a high and stable state, and producing 7.9% more power than using only photovoltaic panels to generate electricity.

Preparation and characterizations of a novel temperature-tuned phase change material based on sodium acetate trihydrate for improved performance of heat pump systems

Application of latent heat thermal energy storage unit is regarded as an effective method to improve the coefficient of performance of hot water heat pump systems (HWHPS). With consideration of energy efficiency and domestic hot water usage, phase change materials with a melting temperature range of 45–48 °C are suitable for practical applications. The most commonly used PCMs, paraffin-based materials, are costly and have low latent heat density, which restrains their applications. This study therefore aims to prepare a novel sodium acetate trihydrate based composite PCM with suitable phase change temperature and cost-effectiveness for HWHPs. A series of SAT-based composites with varying mass fraction of potassium chloride (KCl), urea, disodium phosphate dodecahydrate (DSP) and carboxyl methyl cellulose (CMC) were prepared. Their thermophysical properties and stability were investigated by freezing-melting cycling tests, differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). The experimental results indicated that the optimized SAT-based CPCM with 8 wt% KCl, 3 wt% urea, 6 wt% CMC and 1.5 wt% DSP displayed a favorable phase change temperature of 47.8 °C and a higher latent heat of 242.0 kJ/kg. Meanwhile, the results demonstrated that it has extraordinary thermal cycling performance, negligible vibration in phase change temperature and latent heat, and good stability in chemical properties.

Thermal behavior analysis of hollow bricks filled with phase-change material (PCM)

Light-weight materials are comprehensively used to reduce the building weight in high-rise or super high-rise buildings, but they will reduce building thermal inertia remarkably, which can increase the air-conditioning load fluctuation and reduce indoor thermal comfortable. According to this condition, phase-change material (PCM) is filled to hollow bricks to improve thermal behavior by latent thermal storage. A numerical model with the heat transfer process of melting-solidifying was built, and a full-scale experiment was done to verify this model. Due to the filled PCM, the thermal performance of hollow bricks was improved obviously from experimental and numerical results. Under suitable phase-change temperature, the filled PCM can reduce the attenuation rate from 13.07% to 0.92%–1.93% and increase the delay time from 3.83 h to 8.83h–9.83 h. Meanwhile, the filled PCM can reduce the peak heat flux from 45.26 W/m2 to 19.19 W/m2-21.4 W/m2, but cannot reduce the average value. In addition, inner cavities were the better choice for PCM and there was an extra phase-change extent of close to 90% in favor of the different outdoor thermal environment. Finally, influence rules of latent heat and thermal conductivity coefficient of PCM were analyzed on temperature and heat flux in inner surfaces.

Palmitic Acid-Stearic Acid/Expanded Graphite as Form-Stable Composite Phase-Change Material for Latent Heat Thermal Energy Storage

The aim of this study is to prepare a novel form-stable phase-change material (PCM), palmitic acid-stearic acid/expanded graphite (PA-SA/EG) PCM, for latent heat thermal energy. A eutectic mixture of palmitic acid and stearic acid is incorporated with expanded graphite (EG). The thermal properties and microstructure of the novel PCMs were studied. The optimal mass ratio of PA-SA in composite PCM is approximately 92.8%. DSC results showed that the novel PCMs had suitable phase-change temperature (Tm: 55.18°C, Tf: 54.91°C) and high latent heat (Hm: 176.2 J/g, Hf: 175.6 J/g), and good thermal performance was maintained after 1500 times thermal cycling. The PA-SA binary eutectic mixture was uniformly distributed in the porous structure of EG, and the PCM did not leak even in molten state. EG had little effect on the thermal properties of the PA-SA binary eutectic mixture and remarkably improved the thermal conductivity of the composite PCMs. TGA test indicated that the composite PCM had nice thermostability in the range of operating temperature. Based on all these results, the PA-SA/EG composite PCM is a promising material for low-temperature thermal energy storage applications.

Preparation and Numerical Simulation of Heat Transfer Performance for Methyl Palmitate /Expanded Graphite Phase Change Composite

Methyl palmitate (MP) is a promising phase change energy storage material. It features high latent heat, suitable phase change temperature, low degree of supercooling and so on. However, like other organic phase change materials, the common problem of lower thermal conductivity makes it unable to perform better in energy storage. Expanded graphite (EG) has been proven to be high-efficiency for enhancing the thermal conductivity of organic phase change materials. MP/EG phase change composite was prepared and characterized in this research, and the heat transfer performance was numerical simulated by finite element analysis software ABAQUS. Results show that MP can be absorbed into the layered pores of EG, and the stable absorption ratio is 77%. Numerical simulation results reveal that EG can significantly enhance the heat transfer performance of MP. Moreover, EG can decrease the system temperature gradient during phase change process that makes the heat transfer and temperature distribution more uniform.

A novel enhancement of shape/thermal stability and energy-storage capacity of phase change materials through the formation of composites with 3D porous (3,6)-connected metal–organic framework

Leakage at temperatures above the melting point and thermal-transport performance are prime factors for the effective application of phase change materials (PCMs). In this study, a shape-stabilized composite PCM based on a three-dimensional (3D) porous (3,6)-connected metal–organic framework (MOF) and polyethylene glycol (PEG) was designed. The (3,6)-connected Zn2+ MOF gel was used as a porous supporting material, whereas PEG was employed as an energy-storage material. The PCM, which was impregnated by a capillary force and anchored by a weak hydrogen-bonding interaction between hydroxyl and amine groups, was stabilized by the supporting material. The 3D and two-fold interpenetrated structure of the MOF provided continuous heat-transfer paths in the composite PCM. The resulting composite material exhibited a high transition enthalpy (159.8 kJ/kg) with an encapsulation efficiency and impregnation ratio of 93.4% and 92.2%, respectively. The large interior surface accessibility of the MOF played a vital role in enhancing the thermal properties of the as-synthesized composite PCM. Additionally, the composite PCM exhibited excellent thermal stability and reliability even after 100 thermal cycles. Therefore, the composite PCM is a promising candidate for thermal-energy management systems owing to its high latent heat, suitable phase-change temperature, good chemical compatibility, reduced extent of supercooling, and high thermal stability.

Preparation and Properties of Paraffin/PMMA Shape-stabilized Phase Change Material for Building Thermal Energy Storage

The composite phase change material (PCM) consisting of phase change paraffin (PCP) and polymethyl methacrylate (PMMA) was prepared as a novel type of shape-stabilized PCM for building energy conservation through the method of bulk polymerization. The chemical structure, morphology, phase change temperature and enthalpy, and mechanical properties of the composite PCM were studied to evaluate the encapsulation effect of PMMA on PCP and determine the optimal composition proportion. FTIR and SEM results revealed that PCP was physically immobilized in the PMMA so that its leakage from the composite was prevented. Based on the thermo-physical and mechanical properties investigations, the optimal mass fraction of PCP in the composite was determined as 70%. The phase change temperature of the composite was close to that of PCP, and its latent heat was equivalent to the calculated value according to the mass fraction of PCP in the composite. For estimating the usability in practical engineering, thermal stability, reliability and temperature regulation performance of the composite were also researched by TG analysis, thermal cycling treatments and heating-cooling test. The results indicated that PCP/PMMA composite PCM behaved good thermal stability depending on the PMMA protection and its latent heat degraded little after 500 thermal cycling. Temperature regulation performance of the composite before and after thermal cycling was both noticeable due to its latent heat absorption and release in the temperature variation processes. The PCP/PMMA phase change plate was fabricated and applied as thermal insulator in miniature concrete box to estimate its temperature regulation effect under the simulated environmental condition. It can be concluded that this kind of PCP/PMMA shape-stabilized PCM with the advantages of no leakage, suitable phase change temperature and enthalpy, good thermal stability and reliability, and effective temperature regulation performance have much potential for thermal energy storage in building energy conservation.

Shape-stabilized composite phase change film with good reversible thermochromic properties fabricated via phase inversion-assisted impregnation.

In this study, the regenerated porous cellulose film (LD) was properly prepared by dissolving cellulose in a LiCl/DMAc solvent though a simple phase inversion method. LD has a porous structure, good mechanical properties and great thermal stability. In order to form a shape-stabilized reversible thermochromic phase change film (DTLD), a reversible thermochromic compound (DTBC) was added into the LD by simple vacuum impregnation. The effect of the weight ratio of 1-dodecanol/tetradecanol complex solvent (3 : 7, 2 : 8, 1.5 : 8.5 and 1 : 9) on the phase change properties was investigated. DTLD (1.5 : 8.5) showed the highest latent heat storage of 174.00 J g−1 with the suitable phase change temperature at 37.5 °C. The low thermal conductivity of DTLD (1.5 : 8.5) at 10 °C (50 °C) was 0.396 ± 0.004 W m−1 K−1 (0.408 ± 0.002 W m−1 K−1). The color of DTLD (1.5 : 8.5) can change reversibly between colorless and blue as temperature changes. Melting–cooling tests after 100 cycles indicated that DTLD (1.5 : 8.5) has a high latent heat storage capacity of 169.65 J g−1. A shape-stable reversible thermochromic phase change composite assembled from a regenerated porous cellulose membrane as a support matrix is expected to be applied to the field of thermal energy storage.

Preparation of ammonium aluminum sulfate dodecahydrate/stearic acid composite material and its phase‐change heat‐transfer characteristics

Energy-storage technology using phase-change heat-storage materials (PCHMs) has become a research focus to address the mismatch between the supply and demand of solar energy photothermal utilization. Ammonium aluminum sulfate dodecahydrate (AASD) is a promising PCHM due to its suitable phase-change temperature and high latent heat of fusion. However, there are disadvantages of this material, such as undercooling and a short service life. In this study, AASD was mixed with stearic acid, CaF2, and deionized water to prepare a composite PCHM. The results showed that the degree of undercooling decreased by 10 K with the optimized weight composition ratio of 92.2:5:1.8:1 (AASD:stearic acid:CaF2:deionized water). After repeated melting and solidification, the attenuation ratio decreased from 44.3% to 17.6%. The microstructure and heat-transfer characteristics of the PCHM were simulated and analyzed using the double temperature and equivalent specific heat capacity methods. The heat-transfer characteristics of the PCHM were quantified. The differential equation for the three-dimensional, unsteady heat conduction of the PCHM at the solid-liquid interface during the phase-change process was obtained, and the numerical results were in good agreement with the experimental results. Highlights For the first time, the organic compound, stearic acid, was combined with the inorganic hydrated salt, AASD. A new ammonium aluminum sulfate dodecahydrate/stearic acid composite phase-change heat-storage material was prepared. Superior heat-transfer characteristics were obtained when the ratio of AASD, stearic acid, CaF2, and deionized water was 92.2:5:1.8:1, and the degree of undercooling decreased by approximately 10 K. With the addition of stearic acid, the latent heat of fusion of the PCHM could be well maintained after repeated melting and solidification. The attenuation ratio of PCHM after 200 cycles was significantly lower than that of AASD, and the service life doubled. The differential equation for the three-dimensional, unsteady heat conduction of the PCHM at the solid-liquid interface during the phase-change process was obtained.

Polyethylene glycol based self-luminous phase change materials for both thermal and light energy storage

Except for the improvement enthalpy value and thermal conductivity of conventional solid-solid phase change materials (SSPCMs), expansion of additional functions other than thermal energy storage function of that has been particularly attractive. In this work, a novel self-luminous SSPCMs based polyethylene glycol have been successfully synthesized via incorporation of long afterglow luminescence (LAL) particles into SSPCMs in the absence of any isocyanates and solvents. The prepared self-luminous SSPCMs have high melting latent heats with a maximum value at 120.2 J g−1, maximum encapsulation ratio of 80.6%, and a suitable phase change temperature around 28 °C. Importantly, the prepared self-luminous SSPCMs with different concentrations of LAL particles can absorb and store visible light sources in the daylight but can slowly release blue light in the dark over a long time. Furthermore, the prepared self-luminous SSPCMs after thermal cycling tests and storing-releasing light energy cycling tests have preeminent thermal reliability, luminescence repeatability and chemical structure reliability for a long time practical application.

Enhanced thermal conductivity of form-stable phase change materials using carbon nanofiber-expanded graphite hybrid structure

Inorganic hydrated salt phase change materials (PCM) play a vital role in field of thermal energy storage and temperature control because of their high latent heat. However, inherent low conductivity of hydrated salt PCMs limits greatly their efficien cy in practical application. In this study, a hydrated salt (disodium hydrogen phosphate dodecahydrate)/carbon nanofiber-expanded graphite hybrid form-stable composite PCM (DSP/CNF-EG) is prepared using a physical mixing and the impregnation method. The enhanced thermal conductivity is achieved by the fill of CNF into the low thermal conductivity regions of EG. The thermal conductivity of DSP/CNF-EG is increased by 3.69 times compared with that of pure DSP, which is as high as 2.486 W m−1·k−1. Differential scanning calorimetry (DSC) indicates the outstanding latent heat (208.9 J g−1) and the suitable phase change temperature (33.7 °C) of the DSP/CNF-EG composite. Scanning electron microscopy (SEM) demonstrates that the thermal conductive reinforcements are formed by the addition of CNF. Moreover, Raman spectra results suggest that the hydrated salt is packaged well within the CNF-EG hybrid structure. Furthermore, the prepared DSP/CNF-EG composite maintains a good thermal stability after 200 thermal cycles. The obtained results indicate the DSP/CNF-EG composite is an excellent candidate used for thermal energy storage in building.

Experimental investigation on improvement of latent heat and thermal conductivity of shape-stable phase-change materials using modified fly ash

Abstract Fly ash (FA) is the solid waste discharged from thermal power plants and has become one of the largest industrial solid wastes produced annually. Meanwhile, as energy shortages and environmental pollution caused by the excessive use of fossil energy becoming increasingly prominent, an improvement in energy efficiencies and the exploitation of clean renewable energies is urgently required. In this research, we proposed to modify FA by a simple alkali treatment. The modified fly ash (mFA) exhibited an optimized multistage three-dimensional hollow morphology with abundant granules and pores on the microsphere surface. The specific surface area of the FA was 2.68 m2/g, while it increased to 10.32 m2/g for mFA. Meanwhile, the Al2O3 content of mFA increased from 31.26 to 38.7 wt%, whereas the SiO2 content decreased from 57.43 to 44.89 wt%. After lauric acid (LA) impregnated into mFA, the shape-stable phase-change material (SSPCM) exhibited simultaneously enhanced latent heat and thermal conductivity. The latent heat and thermal conductivity of the obtained LA/mFA SSPCM was 65.7 J/g and 0.52 W/mK, which was 51.7% and 67.7% higher than that of LA/FA SSPCM, respectively. The latent heat enhancement was attributed to the larger specific surface area and the richer pore structure provided by the mFA. The significant thermal conductivity improvement was ascribed to the higher relative content of Al2O3 and the smaller thermal resistance of LA/mFA SSPCM. Moreover, the LA/mFA SSPCM exhibited robust thermal, chemical, and morphological stability with respect to 1000 times thermal cycling. Considering the suitable phase-change temperature, high energy storage density, enhanced thermal conductivity, robust thermal reliability, applicable thermoregulatory capacity, low cost and easy processing, and role of environmental governance, the mFA based SSPCM may have widespread application in solar-energy storage, building air-conditioning system and geothermal energy utilization.

Study on properties of phase change foam concrete block mixed with paraffin / fumed silica composite phase change material

On-site renewable energy generation systems are installed for buildings to compensate for their energy consumptions due to cooling and heating loads. Fluctuated energy load can significantly affect the decision on the selection of renewable energy systems. This study developed a new phase change foam concrete with low thermal conductivity and suitable phase change temperature to shave the temperature peak in summer and improve the economic feasibility of renewable energy systems. With the adsorption method, this study utilized the fumed silica to absorb paraffin for the composite phase change materials (PCM) formation. Through morphology and liquid leakage tests, this study found that the composite PCM with paraffin content of 45% (wt) had the best adsorption capacity and setting performance. According to the scanning electron microscopy (SEM), metallographic microscopy and X-ray powder diffraction (XRD) tests, the proposed composite PCM and phase change foam concrete blocks have stable morphological structures and physical properties. Also, the differential scanning calorimeter (DSC) showed the proposed composite PCM within the concrete have suitable phase change temperature (about 41 °C) and phase change latent heat (the endothermic process is 113.3 J/g and the exothermic process is −112 J/g) to avoid building overheating in summer. Finally, the thermal conductivity and heating experiments suggested the proposed phase change foam concrete blocks have low thermal conductivity and strong heat storage capacity.

Capric Acid Hybridizing Fly Ash and Carbon Nanotubes as a Novel Shape-Stabilized Phase Change Material for Thermal Energy Storage.

Capric acid (CA) is one of the most promising phase change materials to be used in reducing the energy consumption of buildings due to its suitable phase change temperature and high latent heat. In this paper, a novel shape-stabilized phase change material (SSPCM) is fabricated by “hazardous waste” fly ash (FA) via simple impregnation method along with CA and carbon nanotubes (CNTs). In this composite, raw FA without any modification serves as the carrier matrix to improve structural strength and overcome the drawback of the leakage of liquid CA. Simultaneously, CNTs act as an additive to increase the thermal conductivity of composites. The results of leakage tests indicate that CA was successfully confined as 20 wt % in the composite. Then, various characterization techniques were adopted to investigate the structure and properties of the prepared SSPCM of CA/FA/CNT. Scanning electron microscopy and Fourier transform infrared spectroscopy results showed that CA was well adsorbed into the microstructure of FA, and there was no chemical interaction between the components of the composites. Thermogravimetric analysis results demonstrated that the SSPCM presented good thermal stability. Differential scanning calorimetry results indicated that the melting temperature and freezing temperature of CA/FA/CNT were 31.08 and 27.88 °C, respectively, and the latent heats of CA/FA/CNT during the melting and freezing processes were 20.54 and 20.19 J g–1, respectively. Moreover, compared to the CA and CA/FA, the heat transfer efficiency of CA/FA/CNT was significantly improved by doping 1, 3, 5, and 7 wt % of CNT. All of the results suggest that CA/FA/CNT possessed comfortable melting and freezing temperatures, excellent thermal stability, high latent heat value, and favorable thermal conductivity, and therefore, it is a suitable thermal storage material for building applications. Simultaneously, CA/FA/CNT can improve the comprehensive utilization level of FA.

Preparation and Performance of Capric-Myristic Acid Binary Eutectic Mixtures for Latent Heat Thermal Energy Storages

The capric-myristic acid (CA-MA) binary eutectic mixture phase change material (PCM) was prepared for low-temperature latent heat thermal energy storage (LHTES). The thermal properties, thermal stability, and long-term cycling reliability of the PCMs were measured. Differential scanning calorimetry results showed that the CA-MA binary eutectic mixture at the mass ratio (72/28 wt%) indicated a high-performance PCM for its suitable phase change temperature (Tm: 18.21°C, Tf: 17.40°C) and high latent heat (Hm: 148.5 J/g, Hf: 134.0 J/g). Thermal gravimetric analysis results indicated that the CA-MA binary eutectic mixture had excellent thermal stability in its operating temperature range. The thermal cycling tests and Fourier transform infrared spectroscopy results revealed that the CA-MA binary eutectic mixture had good long-term cycling thermal chemical reliability. In summary, in terms of thermal property, thermal stability, and reliability, the prepared CA-MA PCM could be applied particularly for low-temperature LHTES systems and backfill materials of ground source heat pump systems.

A sodium acetate trihydrate-formamide/expanded perlite composite with high latent heat and suitable phase change temperatures for use in building roof

Introducing a phase change material (PCM) with large latent heat, low thermal conductivity, and appropriate phase change temperatures into building roof favors reducing indoor temperature fluctuation and increasing thermal comfort, thus helping to realize building energy conservation. Herein, a sodium acetate trihydrate (SAT)-formamide (FA) mixture was combined with expanded perlite (EP) to prepare a novel composite PCM. It is shown that adding tetrasodium pyrophosphate decahydrate at a loading of 3 wt% can reduce the supercooling degree of the mixture from 34.5 °C to 0.4 °C. The obtained mixture, composed of 77.6 wt% of sodium acetate trihydrate, 19.4 wt% of formamide and 3 wt% of tetrasodium pyrophosphate decahydrate, can be absorbed into EP to prepare a form-stable composite PCM at a mass fraction of 55 wt%, which has a melting point of 40.5 °C and an enthalpy of as large as 148.3 J/g. This composite PCM possesses good thermal reliability and has a thermal conductivity of as low as 0.0978 W/(m·K). The thermal performance of the composite PCM when employed in the roof of a test room was investigated and compared with those of the previously reported CaCl2·6H2O/EP composite PCM and EP. It is found that, the test room with the SAT-FA/EP composite in the roof exhibits slower temperature rise and drop rates, a reduction in the highest temperature, and an increase in thermal comfort, compared with those containing the CaCl2·6H2O/EP composite PCM and EP. The better thermal performance of the SAT-FA/EP composite is attributed to its larger latent heat and more suitable phase change temperatures for use in roof, thereby showing great potential for practical applications.

Preparation and properties of polyacrylonitrile/polyethylene glycol composite fibers phase change materials by centrifugal spinning

Shape-stabilized phase change materials (ss-PCMs) have been extensively investigated by many researchers. However, poor form stability of organic PCMs, such as polyethylene glycol (PEG), is still severe. In this study, PAN/PEG composite fibers based on PEG as PCMs and polyacrylonitrile (PAN) as supporting material were successfully prepared by the centrifugal spinning technique. A combination of different parameters including concentrations of PAN, rotational speed and mass ratios of PAN/PEG are investigated to optimize the spinning technique of PAN/PEG composite fibers. The fibrous morphology of the obtained composite fibers was smooth and cylindrical as observed by scanning electron microscopy (SEM). X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) analyses were used to confirm that there was no chemical interaction occurred in the composite PCMs. Differential scanning calorimeter (DSC) results show that PAN/PEG composite fibers have suitable phase change temperature but low latent heat. Thermogravimetric analyses (TGA) results show that PAN/PEG composite fibers exhibited excellent thermal stability. Based on the above tests and analysis, it could be confirmed that the PAN/PEG composite fibers exhibited good thermal properties and may have application prospects in mass production.