Paraffin-based Phase Change Materials Research Articles

Thermal performance evaluation of a passive building wall with CO2-filled transparent thermal insulation and paraffin-based PCM

Novel thermal insulation materials and wall configurations have the potential to play a major role in reducing energy demand and carbon emissions from the building sector. In this study, a passive heating wall system composed by a CO2-filled transparent thermal insulation (TTI) and an organic phase change material (PCM), and a passive cooling system composed by a Tromble Wall with nano-film and a CO2-filled TTI are proposed and evaluated. The aim is to present a detailed analytical model for rapidly calculating thermal performance of the proposed wall configurations. As case study, a 108 m2 south façade of a building located in Mexico has been used. Outputs suggest that as a passive heating measure, the system has the potential to supply heat in the order of 118 W, 126 W, 134 W, and 157 W, during the months of December, January, February, and March respectively. Additionally, thermal performance and air velocity simulations suggest that for the heating case, considering an outdoor and indoor temperature conditions of 0 °C and 21 °C respectively, the internal layer surface reaches a temperature of 9.2 °C; while for the cooling case, considering outdoor and indoor temperature conditions of 25 °C and 21 °C respectively, it reaches 22.5 °C with a maximum indoor air velocity of 0.5 m/s. Compared to other gases, CO2 could hold a greater potential due to its low thermal conductivity and capital costs. Large-scale implementation of such systems could make the building sector an interesting option as an artificial sink for carbon storage.

Preparation of castable phase change materials beads based on millimeter-sized nanocarbon aerogels for thermal energy storage

Nanocarbon-based porous materials such as graphene foams and aerogels can improve the thermal conductivity and shape stability of phase change materials (PCMs) obviously and simultaneously. However, it is still inconvenient to use these nanocarbon-based composite PCMs in practical applications and engineering, and rare research attention has been paid to this problem. Here we report that making PCMs and nanocarbon aerogels into millimeter-sized PCM beads can be a promising solution of this problem. The nanocarbon aerogels were prepared from carbon nanotubes and graphene oxide, and had a thermal conductivity of 93 mW/mK. PCM beads had improved thermal conductivity and shape stability. The phase transition enthalpy of paraffin-based PCM beads reached 187–188 J·g−1. PCMs beads could be casted with a variety of matrix materials to create large-sized composites with designed size and shape. This castability makes PCM beads compatible with many current techniques and materials, such as concrete pouring techniques and decoration materials, that have already been used in practical applications and engineering. The heat conduction in PCM beads/paraffin casted composites was found to be 25 times faster than that in neat paraffin. PCM beads/concrete casted composites had the potential to be used in building temperature regulation. Overall, our work has demonstrated a new kind of nanocarbon-based composite PCMs with an integration of high properties and high convenience for practical applications and engineering.

Thermo-physical analysis of natural shellac wax as novel bio-phase change material for thermal energy storage applications

Abstract The high energy density of latent heat storage makes it more competent than other types of thermal energy storage (TES) systems. Studying thermophysical and rheological properties of phase change material (PCM) is required for effective storage design, simulation, and applications. Bio-based PCM (BPCM) is a renewable and eco-friendly option for commercial paraffin-based PCMs. This study intends to characterize the shellac wax using the conventional and non-conventional approach as novel BPCM. Analysis of Fourier transforms infrared spectrophotometer (FTIR) indicates that shellac wax has aliphatic hydrocarbons, carboxylic acid, alcohol, and esters functional group. Thermogravimetric analysis (TGA) shows shellac wax has no mass change for operating temperature range (50–85 °C). Differential scanning calorimetry (DSC) analysis reported enthalpy of melting and crystallization as 148 kJ/kg and 161 kJ/kg, respectively. The crystallization enthalpy measured in the T-history method (THM) is 210.5 kJ/kg. However, DSC analysis of sample undergone 0,100,200 and 300 thermal cycle shows no significant change in thermal properties. Other properties like thermal conductivity, density, specific heat and viscosity are comparable to the present PCM used in storage applications. The overall study outcome that shellac wax is thermally stable and is potential BPCM for the TES application like solar desalination, district heating, waste heat recovery and solar cooking.

A Comparative Study on the Thermal Energy Storage Performance of Bio-Based and Paraffin-Based PCMs Using DSC Procedures.

Thermal-Energy Storage (TES) properties of organic phase change materials have been experimentally investigated and reported in this paper. Three paraffin-based Phase Change Materials (PCMs) and one bio-based PCM are considered with melting temperatures of 24 °C, 25 °C and 26 °C. Sensible heat storage capacities, melting characteristics and latent heat enthalpies of the studied PCMs are investigated through Differential Scanning Calorimetry (DSC) measurements. Two alternative methods, namely the classical dynamic DSC and a stepwise approach, are performed and compared with the aim to eliminate and/or overcome possible measurement errors. In particular, for DSC measurements this could be related to the size of the samples and its representativity, heating rate effects and low thermal conductivity of the PCMs, which may affect the results and possibly cause a loss of objectivity of the measurements. Based on results achieved from this study, clear information can be figured out on how to conduct and characterize paraffin and bio-based PCMs, and how to apply them in TES calculations for building applications and/or simulations. It is observed that both paraffinic and bio-based PCMs possess a comparable TES capacity within the selected phase transition temperature, being representative for the human thermal comfort zone. The phase change of bio-based PCMs occurred over a much narrower temperature range when compared to the wider windows characterizing the paraffin-based materials. Bio-based PCMs turned out to be very suitable for building applications and can be an environmentally friendly substitute for petroleum-based PCMs.

Технология кристаллизационного фракционирования для получения парафиновых теплоаккумулирующих материалов

Технология кристаллизационного фракционирования для получения парафиновых теплоаккумулирующих материалов

Microstructural design and thermal characterization of composite diatomite-vermiculite paraffin-based form-stable PCM for cementitious mortars

The thermal performance of cementitious mortars can be improved with the use of form-stable phase change materials (PCMs) consisting of a solid-liquid paraffin mix impregnating diatomite in a diatomite-vermiculite mineral system. The present study includes designing, developing, and characterizing a novel PCM based on a combination of diatomite and calcined, expanded vermiculite, and an optimized paraffin system consisting of a mixture of solid paraffin and naphthenic oil. The diatomite is expected to store the paraffin and wrap the vermiculite particles, increasing the amount of stagnant air. X-ray fluorescence is used to assess the chemical composition of the diatomite and vermiculite. Differential scanning calorimetry (DSC) and Fourier transform infraredspectroscopy (FT-IR) measurements are used to characterize the paraffin mixes aimed at optimum performance for residential and commercial buildings. PCM samples made from paraffin and diatomite (PCM1), vermiculite (PCM2), and a mix of diatomite and vermiculite (PCM(1 + 2)) are characterized by scanning electron microscopy and FT-IR. Cement mortars are prepared in the volume ratios of 1:4 cement:sand (reference mortar), 1:4:1 cement:sand:diatomite, 1:4:1 cement:sand:vermiculite, and 1:4:1 cement:sand:PCM. The thermal properties of these materials are evaluated. The DSC results of the paraffin mixtures indicate that 20% naphthenic oil is the ideal concentration in the paraffin mixture to optimize the solid-liquid temperature (57.45 °C) and latent heat for building applications (159.42 J/g). All PCMs have reduced thermal conductivities compared to the reference mortar (1.47 W/m·K), with the lowest being associated with the PCM(1 + 2) sample (0.82 W/m·K). The PCM(1 + 2) sample also presents an improved combination of diffusivity, volumetric heat capacity, and thermal resistivity. The simultaneous addition of vermiculite and diatomite to the PCM composition improves the thermal properties, while maintaining the basic characteristics such as chemical and structural stability.

Improving the performance of TEM embedded with paraffin-based phase change materials with different thermal conductivity

In this work, the effect of thermal conductivity of phase change materials (PCMs) on the performance of thermoelectric module (TEM) was studied. Paraffin wax composites with different mass fractions (0%, 0.5%, and 1.5%) of carbon nanotubes (CNTs) were used for heat storage in the experiments. The experimental results show that PCM with high thermal conductivity have remarkable effects on improving the power generation of the TEM. Compared to the TEM without PCM, through increasing the thermal conductivity of PCM, the maximum electrical energy generated by TEM increased by 34.9%. Besides, through increasing the height and diameter of the embedded PCM, the effective length of the TEM was optimized and the heat storage of the PCM was increased. As a result, the output voltages of the TEM with PCM were increased 0.3–0.5 mV compared to those of the TEM without PCM. Specifically, the TEM (marked as “1.5%CNT-d30h8”) embedded with PCM with the highest thermal conductivity and the largest geometric dimension can generate a maximum of electrical energy and reach 372.1 mJ.

Surface modification of MWCNT and its influence on properties of paraffin/MWCNT nanocomposites as phase change material

ABSTRACTMultiwalled carbon nanotubes (MWCNTs) were modified by an organo‐silane in order to improve their dispersion state and stability in paraffin wax. A family of paraffin‐based phase change material (PCM) composites filled with MWCNTs was prepared with different loadings (0, 0.1, 0.5, and 1 wt%) of pristine MWCNTs and organo‐silane modified MWCNTs (Si‐MWCNT). Structural analyses were performed by means of Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and rheological studies using temperature sweeps. Moreover, phase change transition temperatures and heat of fusion as well as thermal and electrical conductivities of the developed PCM nanocomposites were determined. The SEM micrographs and FTIR absorption bands appearing at approximately 1038 and 1112 cm−1 confirmed the silane modification. Differential scanning calorimetery (DSC) results indicate that the presence of Si‐MWCNTs leads to slightly favorable enhancement in the energy storage capacity at the maximum loading. It was also shown that the thermal conductivity of the PCM nanocomposites, in both solid and liquid phases, increased with increasing the MWCNT content independent of the kind of MWCNTs by up to about 30% at the maximum loading of MWCNTs. In addition, the modification of MWCNTs made the samples completely electrically nonconductive, and the electrical surface resistivity of the PCMs containing pristine MWCNTs decreased with increasing MWCNTs loading. Furthermore, the rheological assessment under consecutive cyclic phase change demonstrated that the samples containing modified MWCNTs are more stable compared to the PCM containing pristine MWCNTs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48428.

Design and analysis of phase change material based floor heating system for thermal energy storage

Pleasant interior space is essential for modern people who spend considerably more time in the buildings than they did in the past. To achieve this, one aspect includes an ambient temperature that maintains the thermal equilibrium of the human body. The construction of wood framed buildings is becoming increasingly popular worldwide, and there have been recent trends toward constructing high-rise wooden houses. In this respect, heating methods appropriate for use in wooden buildings are being studied. Dry floor heating systems are predominantly used in wooden houses, but they provide a poor heat storage performance, which is not conducive to saving energy. In this study, the effects of thermal comfort and energy savings were analyzed after applying a phase change material (PCM) to floor heating, which can be used to reduce the peak temperature and contribute to energy savings. To enable shape stabilization, this study used Macro-Packed PCM (MPPCM), as shape stabilization is necessary when applying PCM. The heat storage performance was improved by applying MPPCM to a dry floor heating system. Paraffin-based PCMs, such as n-octadecane, n-eicosane, and n-docosane, were used to obtain a comfortable floor temperature range. Experimental temperatures ranged from 28 °C to 35 °C, with an entire temperature range of 7 °C. Experimental results showed that the heat storage performance of MPPCM reduced the amount of energy used for heating by 43%, and n-eicosane was the most effective PCM for use in floor heating with respect to obtaining a comfortable floor temperature.

Experimental performance of latent thermal energy storage for sustainable cooling of buildings in hot-arid regions

The use of phase change material (PCM) as energy storage of cooling during the night-time to be retrieved during the daytime is one of the sustainable strategies for cooling buildings. Application of this strategy in hot climates is scarce, and the majority of published work has been conducted in moderate and continental climates. Therefore, in the present work, a modular PCM-air heat exchanger appropriate for buildings application in hot-arid regions has been investigated, utilising commercial paraffin-based RT28HC PCM modules. The thermal performance of the proposed system has been investigated under various operating conditions for different PCM modules arrangements. The results confirmed that a compact TES unit with narrow air flow channels has a better thermal performance, resulting in 10–14% reduction in the charging time, whilst this has a negligible impact on the comfort time during the discharging period. The results have shown that the proposed system is capable of operating satisfactorily under hot-arid climate conditions, and substantial energy savings are achievable.

Zeolitic imidazolate framework-67 for shape stabilization and enhanced thermal stability of paraffin-based phase change materials.

Zeolitic imidazolate framework-67 (ZIF-67), a new kind of metal–organic framework, has large surface area as well as outstanding thermal and chemical stability. In this paper, micro-sized ZIF-67 crystals were prepared and further employed as the reinforcing material to design novel paraffin-based composite phase change materials (PCMs) with a polymethyl methacrylate (PMMA) shell. The composite PCMs were fabricated by using a ZIF-67 crystal-stabilized oil-in-water (O/W) Pickering emulsion as a template. Morphologies and thermal properties of the prepared composite PCMs with different contents of ZIF-67 crystals were determined by SEM, DSC and TGA. Results showed that the ZIF-67 concentration in the emulsion system has a significant effect on the microstructure, phase change behavior and thermal stability of the resultant composite PCMs. When adding 1.5 g of ZIF-67 crystals, the resultant composite PCMs achieved a stable sphere-like structure and had about 106.06 J g−1 of latent heat. The prepared composite PCMs also exhibited a good thermal stability. Compared with pure paraffin, the thermostability of the shape-stabilized paraffin was significantly enhanced at a low content of ZIF-67 crystals.

Evaluating a prototype compact thermal energy storage tank using paraffin-based phase change material for domestic hot water production

A full-scale thermal energy storage system using phase change materials (PCM) is experimentally investigated for solar and geothermal applications. The system consists of a rectangular tank filled with PCM and a staggered fin tube heat exchanger (HE). The system is designed for the production of Domestic Hot Water (DHW) based on the EU Commission Regulation No 814/2013 [1] requirements. The characteristics that are studied are the stored energy density of the system, the heat transfer rate through the HE during the charging and discharging processes, the adequacy of produced hot water amount and the storage efficiency of the tank. The results of the experiments confirmed the potential of the system to meet several prerequisites of a DHW installation and in addition to make the operation of the coupled solar collector or ground heat pump efficient.

Experimental investigations on the thermal behavior of phase change material (PCM) in ventilated slabs

Experiments were conducted using a small wind tunnel to identify the thermal behavior during energy charging processes of phase change material (PCM) in rectangular slabs. A commercially available paraffin-based PCM with a nominal melting temperature range of 26–28 °C was encapsulated in high-density polyethylene (HDPE) slabs for thermal storage applications in buildings. The influence of air temperature and velocity as well as the slab inclination angle was evaluated using melting time and energy charging speed. The melting time was 18.8–50.8% shorter at top zone than it at bottom zone of the slabs because of the natural convection. The average energy charging speed increased from 36.3 W to 109.4 W by 201.7% when the inlet air temperature increased from 35 °C to 55 °C. However, it was slightly enhanced by 8.7% when the air velocity increased from 4 m/s to 5 m/s. The aspect ratio should be considered when studying the impact of inclination angle on energy charging process. The maximum energy storage capacity was 97.2 W·h with a fraction of 20.2% sensible heat with an energy charging speed of 109.4 W when the inlet air temperature was 55 °C, the air velocity was 3 m/s, and the inclination angle was 90°.

Sinusoidal response measurement procedure for the thermal performance assessment of PCM by means of dynamic heat flow meter apparatus

The implementation, in Building Performance Simulations (BPS) tools, of robust models capable of simulating the thermophysical behaviour of a Phase Change Material (PCM) represents a fundamental step for an appropriate thermal evaluation of buildings that adopt PCM-enhanced envelope components.Reliable and robust measuring procedures are essential, at a material and component level, to provide experimental data for the empirical validation of software tools. The traditional laboratory tests that are generally used for the validation of models present some limitations, because PCMs are usually subjected to conditions that may be very different from the real boundary conditions of the building components in which PCMs are applied. Furthermore, in many experimental full-scale mockups, the relatively small quantity of installed PCM and the combination of several thermal phenomena do not allow software tools to be tested in a reliable way.In this paper, an experimental procedure, based on a modified Heat Flow Meter Apparatus, has been developed to test the behaviour of PCM-enhanced components; the procedure, which is based on the measurement of the sinusoidal response, has been set up to provide data for the comparison and testing of numerical models and of BPS tools. Moreover, general indications and guidelines are provided to solve some issues related to building specimens that contain bulk PCM in order to obtain a more accurate measurement of their performance.The experimental results presented in this paper were obtained from two different bulk PCMs (organic and inorganic). It was found that it is important to evaluate different PCM typologies and different thermophysical boundary conditions, including partial and full phase transitions, to test simulation codes that implement PCM modelling functions. In fact, some phenomena, such as hysteresis and subcooling effects are more evident when partial phase transition takes place. The results related to the characterization of the thermal conductivity of a paraffin-based PCM have shown a significant increase (up to 42%) of the equivalent thermal conductivity from a solid to a liquid state, with an upward heat flux, thus highlighting that further investigations and improvements are needed to measure the equivalent thermal conductivity in the different PCM phases.

Polysaccharide assisted microencapsulation for volatile phase change materials with a fluorescent retention indicator

Low freeze point paraffin-based phase change materials (PCMs) for thermal energy storage often have very high vapor pressure, rendering it extremely challenging to encapsulate. This work reports our success in fabricating amino resin microcapsules with low freeze point PCMs cargos. Our findings challenge the emulsifier selection criteria proposed a decade ago, and enable better understanding of the role of emulsifiers in the one-step encapsulation process without precondensate synthesis. A facile, low cost, efficient and efficacious screening method utilizing a fluorophore is reported here for fast examination of core retention without resorting to more complex or unnecessary quantification techniques. This method is transferable to other encapsulation methods or materials as a qualitative analysis tool. We report two new emulsifiers, i.e. xanthan gum and methylcellulose, which contribute to successful encapsulation of volatile cargos via the one-step in situ polymerization route. The concentration of xanthan gum affects not only the capsule size, but also shell thickness and surface roughness. Most importantly, we have demonstrated with methylcellulose that carboxyl or anhydride moieties in emulsifiers are not essential for the one-step process, contrary to the literature. Capsules produced with methylcellulose also demonstrate superior thermal cycling fatigue resistance.

Preparation and Characterization of Expanded Clay-Paraffin Wax-Geo-Polymer Composite Material.

Paraffin-based phase change material (PCM) is impregnated into the pores of lightweight expanded clay aggregate (LECA) through vacuum impregnation to develop PCM containing macro-capsules of LECA. Three different grades of LECA varying in size and morphology are investigated to host the PCM to determine the impregnation effectiveness, viability for coating, and its stability. The produced LECA-PCM is coated with geopolymer paste (GP) to provide leak proofing during the phase change. The PCM is thermophysically characterized by employing differential scanning calorimetry (DSC) and the temperature history method (THM) to determine the phase transition and the latent heat. The stability of the macro-capsules is determined by weight loss through rapid thermal cycling (RTC) at elevated temperatures. Leakage of the PCM is tested using the diffusion-oozing circle test (DOCT). The results show that the GP coated LECA-PCM macro-capsules achieved 87 wt % impregnation efficiencies and no noticeable loss of PCM, which indicates leak proofing of the developed capsules up to 1000 RTC.

Thermal conductivity enhancement of phase change materials with 3D porous diamond foam for thermal energy storage

For thermal energy storage applications using phase change materials (PCMs), the power capacity is often limited by the low thermal conductivity (λPCM). Here, a three-dimensional (3D) diamond foam (DF) is proposed by template-directed chemical vapor deposition (CVD) on Cr-modified Cu foam as highly conductive filler for paraffin-based PCM. Results showed the foam substrate was completely covered by continuous diamond films with high quality. And it showed a faster thermal response than that of Cu foam (CF) and Cu disc, while only a little slower than that of free-standing diamond disc with the same thickness. The incorporation of interconnected diamond foam with the diamond volume fraction of only 1.3% in the composite phase change material represented a great thermal conductivity enhancement over the pure paraffin, CF/paraffin and diamond particles reinforced paraffin by a factor of 25.8, 1.62 and 13.88, respectively. The great enhancement of the thermal conductive property was mainly attributed to interconnected diamond networks with high thermal conductivity, which effectively reduced the phonon-phonon and phonon-boundary scatterings. Besides, the DF/paraffin composite PCM exhibited an improved shape stability and a fast heat charging rate with the latent heat of 124.7 J/g. The marriage of the excellent properties of diamond and the inherent advantages of the 3D interconnected structure makes the diamond foams potential components or act as reinforcements in the field of high-efficiency heat dissipation and thermal energy storage.

Experimental investigations on the heat transfer of melting phase change material (PCM)

Experiments were conducted to figure out the heat transfer mechanisms during the melting process of phase change materials (PCMs) in high-density polyethylene (HDPE) rectangular panels. A commercially available paraffin-based PCM with a nominal melting temperature range of 26-28 °C was adopted. Phase change time was monitored with an air velocity of 1-5 m/s and an air temperatures of 35–55 °C, respectively. HDPE panels were fixed at various inclination angles ranging from 30° to 90°. Because of the presence of natural convection, a melting time reduction ranging from 18.8% to 50.8% was observed for different conditions. With proceeding melting, the heat transfer mechanisms were thermal conduction, a combination of conduction and convection, and thermal conduction.

Experimental Analysis of the Impact of Nanoinclusions and Surfactants on the Viscosity of Paraffin-Based Energy Storage Materials

Phase change materials (PCMs) are commonly used in many applications, including the transient thermal management of electronics. For many systems, paraffin-based PCMs are used with suspended nanoinclusions to increase their effective thermal conductivity. The addition of these materials can have a positive impact on thermal conductivity, but can also increase the viscosity in the liquid phase. In this paper, the impact of different nanoinclusions and surfactants on the dynamic viscosity of a common paraffin wax PCM is quantified in order to determine their suitability for thermal energy storage applications. The effect of the nanoparticles on the viscosity is found to be a function of the nanoparticle type with multiwalled carbon nanotubes (MWCNT) yielding the greatest increase in viscosity. The addition of both nanoparticle and surfactant to the base PCM is found to affect the viscosity even when the loading levels of the nanoparticles or surfactant alone are not enough to affect the viscosity, thus the combination must be carefully considered in any heat transfer application.

Potential applications of phase change materials to mitigate freeze-thaw deteriorations in concrete pavement

A study was performed to evaluate the feasibility of using phase change materials (PCMs) to mitigate freeze-thaw deteriorations in concrete pavements. The approach taken in this paper was to reduce the expected number of freeze-thaw cycles by harnessing the latent heat of fusion of a paraffin-based organic PCM with a phase transition temperature of 4.5 °C (N-Tetradecane). To ensure stable and proper functioning of PCM in mortar, the PCM was coated with tiny melamine-formaldehyde resin shells using a microencapsulation technique. A preliminary study verified successful thermal storage/release functions of the PCM microencapsulated with a melamine-formaldehyde resin. Thermal response tests showed that the low-transition temperature PCM has a promising potential to extend the service life of concrete pavements against freeze-thaw deteriorations even though its effect became minimal with prolonged exposure to ambient temperature far below the transition temperature. A microencapsulated PCM (mPCM) inclusion was found to negatively affect the compressive and flexural strengths or mortar, whereas the volume stability at early ages was rather enhanced in the presence of mPCM.