Thermal Properties Of Phase Change Materials Research Articles

Recent advancements in latent heat phase change materials and their applications for thermal energy storage and buildings: A state of the art review

Phase change materials (PCMs) have received substantial interest for their ability to store and release latent heat for energy conservation and thermal control purposes. PCMs are available in a variety of latent heat and melting points but their performance is low due to low value of thermal conductivity which limits its usage. The addition of highly thermal conductivity nanoparticles, porous metal foams and encapsulation methods have been used to address this issue and try to fix the low thermal conductivity of PCMs which is broadly discussed in this manuscript. The ability of PCM to store and release the thermal energy prompted the researchers to use it in potential applications. The energy retained and emitted by PCMs may be used for a variety of purposes, such as in photovoltaic (PV) panels, thermoelectric generators, building air-conditioning, air and water heating systems, heat exchangers, desalination solar stills, textiles, thermal management of electronic equipment and batteries and food packaging. Therefore, in this review, first the advancements in thermal properties of PCMs are thoroughly discussed in terms of enhancement in melting and solidification rates. After that, the use of PCMs in various applications is then explored, and conclusions are drawn accordingly. Based on analysis of recent literature, it was discovered that the phase transition temperature, phase transition enthalpy and thermal conductivity are three important parameters for the selection of an appropriate PCM for use in various applications. The current status of these advanced energy storage materials is also presented in this review. Lastly, some challenges and future recommendation are also proposed for future researchers which will bring a revolution in thermal management field.

One-dimensional numerical analysis for the porosity impact of open-cell metal foam on the effective thermal properties of PCMs

Metal foam has found its way in many engineering industries due to its ability to improve the heat transfer rate in thermal applications. Thermal energy storage based on phase change materials (PCMs) have significant importance as a part of renewable energy sources, and thermal management applications, However, low thermal conductivity is the essential drawback associated with the PCMs, especially the organic type of it, such as paraffin. Various experimental and numerical studies performed to test the effect of using metal foam with PCMs, in order to improve PCMs thermal conductivity. Many models suggested for evaluating the effective thermal conductivity of high porosity open cells metal foam, which immersed in base fluids of low thermal conductivity such as air, water, and PCMs. This work achieved numerically by using different models for calculating the effective thermal properties of metal foam with various range of porosities impregnate in paraffin. The study discussed the temperature distribution, which control the heat transfer rate, the behavior of temperatures versus time, and improvements in the melting front phase of the paraffin, under the effect of copper metal foam of various porosities and by applying different models, for estimating the effective thermal conductivity. The results exhibit an augmentation in the effective thermal conductivity with porosity decreasing. The outputs showed paradoxical results using the presented models and the differences between them have been discussed.

Thermal storage effect of radiant floor cooling system using phase change materials in the hot and humid climate of Indonesia

We proposed a novel radiant floor cooling system using phase change materials (PCMs) with night ventilation in the hot and humid climate of Indonesia. This study aims to clarify the measures to ensure the thermal storage effect of the proposed cooling system during daytime for a naturally ventilated room within a relatively narrow diurnal temperature range, focusing mainly on the thermal properties of PCMs. We analyzed the relationship between the indoor vertical air temperature distributions and heat flows of the proposed system using an experimental building in Tangerang, Indonesia. The results confirmed that the thermal mass of PCMs and the cooling strategy for the floor structure at night strongly contributed to maintaining a low floor surface temperature during the subsequent daytime. Calm wind conditions and warm nocturnal ambient temperature, which was 0.7–3.2 °C lower than the set-point solidifying temperature and is common in the tropics, prevented PCMs from solidifying in case of natural ventilation for the underfloor space. In contrast, forced ventilation for the underfloor space attaching PCMs was effective in ensuring sufficient solidification. Furthermore, 95% of the thermal storage capacity of PCMs might be utilized when the ambient temperature was 2–3 °C higher than the set-point melting temperature during the daytime. The phase change temperature for PCMs can be determined based on the average ambient temperature, whereas a relatively wide diurnal ambient temperature range, at least 4.7 °C, was required to ensure the latent heat thermal storage effect caused by the supercooling.

A Review of Thermal Property Enhancements of Low-Temperature Nano-Enhanced Phase Change Materials.

Phase change materials (PCMs) are of increasing interest due to their ability to absorb and store large amounts of thermal energy, with minimal temperature variations. In the phase-change process, these large amounts of thermal energy can be stored with a minimal change in temperature during both the solid/liquid and liquid/vapor phase transitions. As a result, these PCMs are experiencing increased use in applications such as solar energy heating or storage, building insulation, electronic cooling, food storage, and waste heat recovery. Low temperature, nano-enhanced phase change materials (NEPCM) are of particular interest, due to the recent increase in applications related to the shipment of cellular based materials and vaccines, both of which require precise temperature control for sustained periods of time. Information such as PCM and nanoparticle type, the effective goals, and manipulation of PCM thermal properties are assembled from the literature, evaluated, and discussed in detail, to provide an overview of NEPCMs and provide guidance for additional study. Current studies of NEPCMs are limited in scope, with the primary focus of a majority of recent investigations directed at increasing the thermal conductivity and reducing the charging and discharging times. Only a limited number of investigations have examined the issues related to increasing the latent heat to improve the thermal capacity or enhancing the stability to prevent sedimentation of the nanoparticles. In addition, this review examines several other important thermophysical parameters, including the thermal conductivity, phase transition temperature, rheological affects, and the chemical stability of NEPCMs. This is accomplished largely through comparing of the thermophysical properties of the base PCMs and their nano-enhanced counter parts and then evaluating the relative effectiveness of the various types of NEPCMs. Although there are exceptions, for a majority of conventional heat transfer fluids the thermal conductivity of the base PCM generally increases, and the latent heat decreases as the mass fraction of the nanoparticles increases, whereas trends in phase change temperature are often dependent upon the properties of the individual components. A number of recommendations for further study are made, including a better understanding of the stability of NEPCMs such that sedimentation is limited and thus capable of withstanding long-term thermal cycles without significant degradation of thermal properties, along with the identification of those factors that have the greatest overall impact and which PCM combinations might result in the most significant increases in latent heat.

Experimental and numerical analysis of the thermal performance of polyurethane foams panels incorporating phase change material

The potential thermal regulation effect of rigid polyurethane (RPU) foams can be enhanced by the incorporation of phase change materials (PCM). The main goal of the present work is to evaluate the thermal characteristics of RPU panels using two different types of PCM (a commercial one and another based on paraffin and calcium carbonate) and to quantify their potential as thermal regulators of indoor spaces.The experimental results obtained revealed that the RPU panels incorporating PCM can lead to a thermal amplitude reduction of about 3.5–1 °C (peak maximum temperature – peak minimum temperature). Furthermore, it was demonstrated that the performance of the RPU panel with PCM was enhanced when the external and internal mean temperature were closer to the melting peak temperature of the PCM. Additionally, it was also verified that the thermal amplitude reduction due to the PCM is more significant for the RPU panel incorporating PCM.In brief, the results showed that the efficiency of the RPU panels incorporating PCM is not exclusively dependent on the presence and quantity of PCM (equivalent in wt% in all cases) but it is also affected by the imposed temperature profile and the PCM thermal properties.

Calibration of differential scanning calorimeter (DSC) for thermal properties analysis of phase change material

Phase change material (PCM) selection for particular applications mainly depends on its phase change temperature and latent heat, which were commonly measured by the differential scanning calorimetry (DSC). However, the DSC instruments are not absolute measuring devices and calibration is extremely important to ensure the accuracy of determined data. Meanwhile, the PCM with melting temperature between 0 and 65 °C is the most common interest for energy saving in buildings. This study, therefore, calibrated the DSC produce (NanoTechnology Inc.) by the high-purity metals with various regression methods for low melting temperature PCM thermal properties analysis. In the end, the paraffin n-eicosane was introduced to evaluate the accuracy of the temperature and latent heat measurements of the DSC. The experimental results showed that the accuracy of calibration could be improved by higher-order and more reference materials in a broad temperature range. However, the measurement results of n-eicosane proved that the 0-order regression method could offer good accuracy with only one suitable calibrant in a particular temperature range. Therefore, this research suggests the selection of reference materials for DSC calibration should consider the target of measurement temperature range as well as the thermal stabilities of calibrants.

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.

Influence of single and multiple coupling factors on the stability of paraffin-based nanofluids

Nanofluids have been introduced to improve the thermal properties of phase-change materials. However, stability problems caused by agglomeration and deposition have greatly restricted the use of nanofluids. In this work, paraffin-based nanofluids were prepared under the dual coordination of magnetic stirring and ultrasonic oscillation, the influence of ultrasonic power and time, base fluid volume, particle concentration and type on fluid stability was studied by single factor method, and the influence degree of the above four factors on fluid stability was studied by fractional factor design method. The following conclusions were drawn from the experiment: (1) With the increase of ultrasonic power, the relative absorbance increases within the allowable range of the experimental instrument, and the maximum improvement is 3.06%.(2) The optimal ultrasonic time for nanofluids preparation is 2 h. (3) The sample volume under the optimal state is 45 ml. (4) With the increase in concentration, the absorbance per concentration decreases, and the reduction range becomes slow. (5) The stability of the nanofluid is also related to the characteristics of the particle surface. (6) The coupling effect of ultrasonic power - concentration (PC) has the most significant effect on the overall absorbance change. This study provides a clear improvement direction and basis for the preparation of highly stable nanofluids.

The impact of thermal properties on performance of phase change based energy storage systems

Phase change materials (PCMs) are used commonly for thermal energy storage and thermal management. Typically, a PCM utilizes its large latent heat to absorb and store energy from a source. The rate of energy stored (W) and energy storage density (J/m3) over a certain time period are both important performance parameters of a phase change based energy storage system. While significant experimental research has been carried out to improve thermal conductivity of PCMs, there is a lack of theoretical understanding of how thermal conductivity and other thermophysical properties affect these performance parameters. This paper presents a theoretical heat transfer model to predict the rate of energy storage and energy storage density as functions of PCM thermal properties. Using perturbation method based techniques, expressions for these parameters are derived for two geometries, first for a simplified assumption of constant temperature at the source-PCM interface, and then for a more realistic scenario of time-dependent interface temperature. Results indicate that while increasing thermal conductivity results in improvement in rate of energy stored, the energy storage density does not change for a Cartesian system and actually decreases for cylindrical system. This shows that using a high thermal conductivity PCM may not be ideal when energy must be stored compactly because while this increases the total energy absorbed, it also results in greater rate of melting, which reduces the energy storage density. Results also provide guidelines for material selection for phase change based energy storage systems. For example, a trade-off in the choice between materials of disparate thermal properties is identified in terms of whether the rate of energy stored or energy storage density is paramount. Differences in the performance of Cartesian and cylindrical systems is investigated. Theoretical results presented in this work highlight various performance trade-offs related to the thermal properties of the PCM and help understand the impact of thermal conductivity enhancement on phase change energy storage performance.

Impact of Phase Change Material's Thermal Properties on the Thermal Performance of Phase Change Material Hollow Block Wall

ABSTRACTComposite phase change material (PCM) hollow block wall (CPCMHBW) can be established by introducing PCM into the holes of generally used hollow block wall, and good thermal insulation performance will probably produce together with the energy storage function from PCM simultaneously. In this article, the impact of PCM's thermal properties on the thermal performance of CPCMHBW has been analyzed, using two-dimensional enthalpy model. The conclusions include: complete melting and freezing processes and a bit amount of remaining PCM which has not melted or solidified, are fundamental and necessary for high performance; furthermore, that the average surrounding temperature equals to PCM's central phase change temperature determines whether the PCM's function can be used; besides, the PCM's total latent heat controls wall's thermal storage level; in addition, relatively low block material's thermal conductivity and Fourier number (better smaller than 1.0 W·m−1·K−1 and 59.83) and medium PCM's corresponding values (lies in the ranges 0.2–0.7 W·m−1·K−1 and 0.80–2.80) generate optimum thermal performance. Finally, the thermal factors are ranked with the functions in descending order.

Understanding the thermal properties of amorphous solids using machine-learning-based interatomic potentials

Understanding the thermal properties of disordered systems is of fundamental importance for condensed matter physics - and for practical applications as well. While quantities such as the thermal conductivity are usually well characterised experimentally, their microscopic origin is often largely unknown - hence the pressing need for molecular simulations. However, the time and length scales involved with thermal transport phenomena are typically well beyond the reach of ab initio calculations. On the other hand, many amorphous materials are characterised by a complex structure, which prevents the construction of classical interatomic potentials. One way to get past this deadlock is to harness machine-learning (ML) algorithms to build interatomic potentials: these can be nearly as computationally efficient as classical force fields while retaining much of the accuracy of first-principles calculations. Here, we discuss neural network potentials (NNPs) and Gaussian approximation potentials (GAPs), two popular ML frameworks. We review the work that has been devoted to investigate, via NNPs, the thermal properties of phase-change materials, systems widely used in non-volatile memories. In addition, we present recent results on the vibrational properties of amorphous carbon, studied via GAPs. In light of these results, we argue that ML-based potentials are among the best options available to further our understanding of the vibrational and thermal properties of complex amorphous solids.

Improvement of shape stability and thermal properties of PCM using polyethylene glycol (PEG)/sisal fiber cellulose (SFC)/graphene oxide (GO)

This study prepared a polyethylene glycol (PEG)/sisal fiber cellulose (SFC)/graphene oxide (GO) composite using a novel dynamic impregnating method to obtain a high-performance shape-stabilized phase change materials (PCMs). In this material, the ternary system PEG served as the latent heat storage material and SFC and GO served as the supporting materials. The structure, morphology, thermal conductivity, phase change temperature, and latent heat of the composite PCMs were characterized by fourier transform infrared spectroscopy, wide-angle X-ray diffraction, polarizing microscope, digital camera, scanning electron microscopy, differential scanning calorimetry, and thermal conductivity analysis. Results show that the composite PCMs exhibit a fine impregnation morphology and excellent shape-stabilized feature during the phase change process, the shape of the PEG/SFC/GO composite PCMs are unchanged even after being placed on a 85 °C hot plate. Thermal behavior tests indicate that the composite PCM (PEG weight percentage of 80 wt.%) shows a high latent heat storage capacity of approximate 140 J/g after more than 100 thermal cycling, and exhibits good heat-conducting performance.

Numerical analysis for the optimal location of a thin PCM layer in frame walls

The thermal performance of building walls can be improved using phase change materials (PCMs). The objective of this study was to estimate the optimal location of a “thin” PCM layer to be incorporated into frame walls, parallel to the frame and insulation, for the purpose of increasing thermal mass and reducing peak heat fluxes through the wall. Based on a mathematical model built in this paper, it was found that an optimal location of this “thin” PCM layer can be estimated, and it was affected by the thermal properties of PCM and the environmental conditions. The optimal locations for the PCM layer were found to be closer to the exterior surface of the wall when the thickness of PCM layer, the heat of fusion of PCM, and the PCM melting temperature were increased, while the optimal location was closer to the interior surface of the wall when the interior surface temperature of the wall was increased.

Estimation of the Thermal Properties of PCMs through Inverse Modelling

Even though the use of Phase Change Materials (PCMs) is promising to improve the energy efficiency of buildings, their application in the building sector is still very limited. One of the obstacles to the diffusion of PCMs is the lack of information regarding their thermo-physical properties. A method for estimating the specific heat-temperature curve of a PCM through inverse modelling is herewith presented. This method combined experimental data with a numerical tool able to simulate multilayer walls with the inclusion of PCM materials. Results were validated against tests on different samples and discussed in comparison with a low-speed DSC measurement.

A new validated TRNSYS module for simulating latent heat storage walls

Lightweight structures have suffered long from low thermal inertia making them more vulnerable to climatic conditions. The adoption of phase change material (PCM) can potentially reduce this climatic deficiency. In order to evaluate its thermal potential, computational modeling has shown to be promising design tools. In this paper, a new TRNSYS type is developed and validated for simulating PCM-enhanced walls. Using the validated module, it is found that the best PCM's configuration is when placed in direct contact with the indoor controlled environment. Additionally, a wide range of PCM's thermal properties were simulated under typical U.S. climates to evaluate the thermal performance and identify the optimal thermal properties. The results show that a maximum saving of 0.8–15.8% is achieved on annual cooling load depending on the climate. For heating dominated climates, the savings on annual heating load is insignificant being less than 4%. The saving in peak loads was found to show more potential than annual loads for some climates. The maximum savings in peak cooling load range from 6.8 to 13.3% while savings in peak heating load range from 7 to 10.5%. For maximum savings in zonal loads, the optimal thermal properties of PCM are found to hover around the operational thermostat setpoints.

Improvement of thermal conductivity of paraffin by adding expanded graphite

This paper investigated the use of graphite with different configuration designs to improve the thermal energy storage of phase change material systems. Two types of graphite have been combined with paraffin in order to improve thermal conductivity of phase change material: synthetic graphite (Timrex SFG75) and graphite waste obtained from damaged tubular graphite heat exchangers. Paraffin/graphite phase change material composites have been prepared by the cold uniaxial compression technique. Their morphologies have been observed and analyzed by scanning electron microscope, and their thermophysical properties have been estimated using new experimental tools. Results show that the thermal conductivity and thermal diffusivity can be accurately measured by these new experimental tools. Moreover, results highlight the fact that the phase change material thermal properties are greatly influenced by the graphite addition.

A new experimental device and inverse method to characterize thermal properties of composite phase change materials

A new experimental device has been developed in order to characterize the phase change material (PCM) thermal properties (thermal conductivity k, sensible and latent heat thermal energy storage, cp and Lf) in the solid phase, during the solid–liquid transition and in the liquid phase. It allows to measure cylindrical samples of maximum 60mm radius and 10mm thick. A typical measurement consists in imposing a vertical temperature gradient through the PCM sample driven by a heat source, monitoring during the experiment time all the boundary conditions (temperatures and heat fluxes) and measuring temperature evolution in three locations within the PCM sample. In this work, we will focus only on the solid thermal conductivity characterization. These experiment data are used to solve the inverse heat conduction problem by applying the conjugate gradient method and finally, to determine the PCM thermal properties. Two types of composite PCM have been thermally characterized: paraffin mixed with synthetic graphite (Timrex SFG75) and paraffin mixed with graphite waste.

Preparation and thermal properties characterization of carbonate salt/carbon nanomaterial composite phase change material

To enhance the performance of high temperature salt phase change material, four kinds of carbon nanomaterials with different microstructures were mixed into binary carbonate eutectic salts to prepare carbonate salt/nanomaterial composite phase change material. The microstructures of the nanomaterial and composite phase change material were characterized by scanning electron microscope. The thermal properties such as melting point, melting enthalpy, specific heat, thermal conductivity and total thermal energy storage capacity were characterized. The results show that the nanomaterial microstructure has great effects on composite phase change material thermal properties. The sheet structure Graphene is the best additive to enhance specific heat, which could be enhanced up to 18.57%. The single walled carbon nanotube with columnar structure is the best additive to enhance thermal conductivity, which could be enhanced up to 56.98%. Melting point increases but melting enthalpy decreases with nanomaterial specific surface area increase. Although the additives decrease the melting enthalpy of composite phase change material, they also enhance the specific heat. As a combined result, the additives have little effects on thermal energy storage capacity. So, for phase change material performance enhancement, more emphasis should be placed on thermal conductivity enhancement and single walled carbon nanotube is the optimal nanomaterial additive.

Thermal properties of phase-change materials based on high-density polyethylene filled with micro-encapsulated paraffin wax for thermal energy storage

Microcapsules consisting of paraffin wax cores with a melting point of approximately 42°C and a melamine-formaldehyde resin shell were synthesized using in situ polymerization. These microcapsules have a uniform distribution with a spherical shape and an average diameter of approximately 15μm. The thickness of the shell was approximately 1.5μm. Shape-stabilized phase change materials (PCM) based on high-density polyethylene (HDPE) mixed with micro-encapsulated paraffin wax were prepared and investigated for application in thermal energy storage. The distribution of the capsules within the HDPE matrix was uniform without any tendency toward agglomeration. The microencapsulated paraffin wax acts as a high-latent-heat material, whereas the HDPE matrix ensures the compact shape, structural compactness and mechanical strength of the final PCM. The periodic temperature method was used to determine the thermal conductivity and thermal diffusivity of the phase change materials. A guarded hot plate unit was used to determine the latent heats of these phase-change materials. The thermal conductivity and diffusivity of the investigated PCMs decreased as the microcapsule content increased. In contrast, the latent, sensible and total heat of the PCMs increased with the paraffin content.

Performance analysis and optimization of direct contact condensation in a PCM fixed bed regenerator

Aim of this work is to model, optimize and characterize the design of a direct contact condenser utilizing spherical phase change material (PCM) elements as a packing medium in a solar driven humidification–dehumidification (HDH) desalination plant. Assuming local thermal non-equilibrium and departing from the continuous solid phase model, a simplified one-dimensional heat and mass transfer model has been developed and solved using interpenetration continua approach with volume averaging technique. The model has been validated against experimental data and was then used for further parametric analysis. Comparison with measurements showed good agreement with less than 3% of the fresh water production rate. The thermal behavior of the new condenser equipment is discussed and analyzed. Fundamental variables and critical parameters affecting the system performance such as the effect of condenser geometrical aspect ratio, packing size, air to water mass flow rate ratio, PCM thermal properties, and the effect of different types of packing media were studied. A system parameters analysis and characteristic guidelines for the optimum parameters and operation conditions have been obtained and will be presented thoroughly. Comparative performance of the system is clearly documented using PCM and Non-PCM packing elements.