Latent Heat Capacity Research Articles

Preparation and properties of composite phase change material based on solar heat storage system

Solar phase change hot water storage tank is a kind of storage / exothermic system with solar energy as heat source and phase change heat storage material. It can store heat during the day, continue to operate at night with stored heat without consuming other energy. Because of the poor thermal conductivity of solid-liquid phase heat storage materials, carbon fiber is added to enhance the thermal conductivity of phase change materials. Stearic acid is used as phase change material, carbon fiber as heat transfer material and ethyl cellulose as auxiliary material to prepare carbon fiber / stearic acid composite phase change material. Carbon fiber / stearic acid in the mass ratio of 7.5:92.5 is the optimal material and the chemical compatibility, phase change temperature, phase change latent heat, thermal conductivity and thermal stability of carbon fiber / stearic acid are measured by using SEM, XRD and DSC. From the DSC test, the latent heat capacity was determined as 192.6 J/g and the phase change temperature as 67.7°C. Thermal conductivity was measured as 0.4011 W/m⋅K. The storage / exothermic experimental system of carbon fiber / stearic acid composite phase change material is built. The melting process and solidification process of the composite phase change material are tested, and the storage / exothermic characteristics are analyzed. SEM and DSC analysis results revealed that the PCM had high thermal stability. XRD revealed that the binary eutectic mixture had good chemical stability. Thus, the new PCM possessed high latent heat with good thermal and chemical stabilities making it a potential phase change material for solar heat storage applications.

Nanoflaky nickel-hydroxide-decorated phase-change microcapsules as smart electrode materials with thermal self-regulation function for supercapacitor application

A nanoflaky nickel-hydroxide-decorated phase-change microcapsule system [designated as Ni(OH)2-SiO2-MEPCM] was designed as a smart electrode material for supercapacitor application. This system was constructed through microencapsulating n-docosane core into a silica shell via emulsion-templated interfacial polycondensation, followed by fabricating a nanoflaky Ni(OH)2 layer on the surface of silica shell through structure-directed interfacial precipitation. Such a combination of phase-change microcapsules and electrochemically active material makes the Ni(OH)2-SiO2-MEPCM synchronously implement thermal self-regulation and electrochemical energy storage. The Ni(OH)2-SiO2-MEPCM shows a perfect core-shell structured morphology and well-defined nanoflaky surface microstructure. The Ni(OH)2-SiO2-MEPCM not only possesses a good temperature regulation capability with a latent-heat capacity of around 140 J/g but also exhibits an excellent thermal cycle stability and good high-temperature shape stability. Most importantly, compared to traditional electrode materials, the Ni(OH)2-SiO2-MEPCM can perform effective thermal self-regulation to regulate the micro-ambient temperature by its n-docosane core when used as an electrode material for supercapacitors, leading to improved electrochemical performance and good long-term cycle stability with capacitance retention of 86.2% after 3000 charge-discharge cycles at a high ambient temperature of 50 °C. All of these features indicate that the Ni(OH)2-SiO2-MEPCM developed by this work has great potential as a smart electrode material for electrochemical energy-storage applications.

Effects of Phase Change Materials on heat flows through double skin facades

The potential of exemplary organic and inorganic Phase Change Materials (PCMs) as facade integratedstorage is tested. The impact of two PCMs on heat flows is assessed in comparison with water andconcrete. The simulation-study employs a transient Modelica simulation model of a test cell featuringthe Solar Energy Balanced Facade (SEBF). It is shown that, when compared to water, PCMs of identicalvolume change the seasonal energy balance in winter and summer by only ± 4%. Other than water,the PCMs maintain this effect even if the storage volume decreases. Due to spatial constraints, thiscan support the integration of thermal storage in facade design considerably. Preliminary resultsindicate that designing thermal storage in facades with PCMs must not only consider the latent heatstorage capacity, but also take into account the combined effects of latent heat capacity, meltingpoint, conductivity, and dead load. The application of PCMs promises to foster the integration of thetechnology of SEBF into facades, but the necessary deliberate selection of, and design with, PCMsrequires further research.

Performance Assessment of Nano-enhanced Phase Change Material for Thermal Storage

The use of nano phase change material in thermal energy storage applications appears promising, but the often-poor performance and the lack of understanding of the heat transfer mechanisms interconnectedness remains a challenge and hinders their widespread integration. The existing numerical work has unveiled numerous impediments in predicting the actual melting behaviour. They rarely combine the effects of conduction enhancement, convection degradation, and latent heat reduction, due to inaccurate characterization of the thermophysical properties and the limitations of their model assumptions. In the present study, an enhanced numerical approach was developed to investigate the melting performance of xGnP-octadecane filled in a vertical cylindrical enclosure at different weight concentrations. The model results for the pure phase change material were compared and validated against the experimental data. The progression of the melting front, temperature probes, energy storage capacity and heat transfer rate of the nano phase change material were thoroughly evaluated. The current numerical observations demonstrate that the addition of nanoparticles improves, up to a critical concentration of 0.5wt%, the melting rate. The results showed that by adding 0.5wt% of xGnP in the base phase change material (octadecane), the melting rate decreases by 9.7% and the heat storage rate increases by 12.6%. However, at higher loadings, the heat transfer rate is deteriorated due to worsening of other thermophysical properties provoking the prevalence of viscous forces over natural convection and latent capacity. The system overall efficacy was found to be dependent on the net effects of relative changes of all thermophysical properties with nanoparticle concentration and temperature in the solid, so called mushy, and liquid zones. Finally, when characterizing nano phase change material, the thermal conductivity cannot be considered alone as a criterion for nano phase change material selection. A high thermal conductivity is needed for maximum heat absorption in thermal transport applications. Nevertheless, low viscosity, high latent heat and specific heat capacities are also essential to ensure a better thermal energy storage efficiency in terms of capacity and heat extraction/release rate.

Development of poly(ethylene glycol)/silica phase-change microcapsules with well-defined core-shell structure for reliable and durable heat energy storage

Microencapsulation of poly(ethylene glycol) (PEG) with a silica material to form a phase-change microcapsule system is universally acknowledged as a tough job due to its hydrophilic nature. This paper reported a feasible approach for the fabrication of core-shell structured PEG/silica phase-change microcapsules (PEG@SiO2-MEPCM) through reverse emulsion-templated in-situ polycondensation. The investigation of synthetic technique indicates that the proportion of surfactant and cosurfactant plays a key role in optimizing the morphology and microstructure of the resultant microcapsules, leading to optimal heat energy-storage performance. With the determination of an optimal mass ratio of surfactant to cosurfactant as 5/6, the synthesized PEG@SiO2-MEPCM exhibits a well-defined core-shell structure with regularly spherical morphology and uniform size distribution. It also achieves a high encapsulation ratio of over 80% with a satisfactory latent heat capacity of about 130 J/g thanks to the formation of a perfect microstructure and morphology. Moreover, the PEG@SiO2-MEPCM not only exhibits a good heat energy-storage capability together with high thermal stability and good shape/form stability, but also presents reliable and durable phase-change performance in practical use. This study is notable for its synthetic technique of the core-shell structured PEG/silica phase-change microcapsules with a reliable and durable heat energy-storage capability.

Application of Machine Learning (ML) for Enhancing the Transient Performance of Thermal Energy Storage (TES) Platforms Using Radial Basis Function (RBF)

Thermal energy storage (TES) can be utilized as supplemental platforms for improving operational reliability and systemic efficiency in variety of industries, such as for reducing water usage in power production (food-energy-water/ FEW nexus), chemical and agro-process industries and for improving sustainability (e.g., desalination), etc. Phase change materials (PCMs) can be used in TES due to their high latent heat storage capacity during phase transformation. Inorganic PCMs typically have the highest latent heat capacity and are attractive for their ability to store the larger quantities of thermal energy in small form factors while conferring respectable power ratings (however, they suffer from compromised reliability issues, that often arise from the need for subcooling). Subcooling (also known as supercooling) is a phenomenon where the temperature needs to be reduced substantially below the melting point to initiate solidification. A technique for obviating subcooling issues is to allow a small portion of the PCM to remain un-melted. This allows the PCM to initiate nucleation from the un-melted portion of PCM (this is termed as the “cold finger” technique). Thus, reliability is enhanced at the expense of substantial reduction in storage capacity. A fundamental challenge for using this technique is the inability to reliably predict and control the amount of melt fraction in the total volume of the PCM (such that a target amount of the PCM remains solidified or un-melted at the end of each melt-cycle during repeated melting and solidification of the total mass of PCM). However, using Machine Learning (ML) techniques, this deficiency can be addressed by reliably predicting and thus controlling the amount of melt fraction in the total volume of the PCM with a higher accuracy than conventional techniques (such as using multi-physics-based models or numerical solvers). Conventional techniques for predicting transient characteristics in real time control schemes typically leverage multi-physics-based models that are often effective only for a narrow range of operating conditions with concomitant disadvantages: they are highly sensitive to small variations in the measurement uncertainties and are therefore susceptible to large levels of error in the real time predictions (and are unreliable for implementation in diverse range of operating conditions). In this pioneering study, nearest neighbor search processes (such as radial basis functions) were utilized along with machine learning (ML) algorithm using a training data set to predict the PCM melt fraction and to demonstrate the feasibility (and efficacy) of this approach. This technique is simple to implement and is device independent as well as robust (i.e., it can be deployed successfully even under conditions where the sensors malfunction, such as thermocouples that are off-calibration). This technique was demonstrated successfully for predicting the melt fraction of a PCM with high accuracy and robustness. With this method, the melt fraction of a PCM can be accurately determined, which allows the maximum thermal capacity of a PCM to be utilized while mitigating reliability issues (such as subcooling) and enhancing the thermodynamic efficiencies of the TES platforms. Melting experiments were performed using a digital camera (for video recording) and a graduated cylinder containing PCM for monitoring the transient values of the melt fraction based on the height of the liquid phase of the PCM in the cylinder. An array of 3 thermocouples was mounted at specific heights within the body of the PCM to monitor the temperature transients at these specific location during the propagation of the melt front within the PCM. In the final stages of the melting process, the predictions from the ML algorithm was found to be more accurate (90~95% accuracy) than that of the conventional techniques based on physics-based solvers (~60% accuracy). The accuracy of the ML algorithm was low at smaller melt fractions (~30%) and improved substantially at higher melt fractions (~95%). Furthermore, the accomplishments of this study display the feasibility of a RBF ML method which can be implemented for the accurate prediction and control of a real world stochastic system which can exhibit nonlinear and chaotic dynamics which change over time.

Mitigation of thermal curling of concrete slab using phase change material: A feasibility study

In this study, the effects of phase change material (PCM) on the thermo-mechanical behaviors of concrete pavement slabs are investigated so as to test the feasibility of utilizing PCM for mitigation of thermal curling of pavement. The PCM is elaborately stabilized in porous lightweight aggregate then loaded into concrete, without compromising strength associated with PCM incorporation. Thermal analysis indicates that the PCM introduces a latent heat capacity of about 21 J/g to the pavement slab. Two emerging fiber-optic monitoring techniques, i.e., truly distributed strain/temperature sensors and a high-resolution inclinometer, are employed to continuously monitor distributions of the temperature, strain, and tilting angle of the slabs subjected to heating and cooling, respectively. Validated by the obtained experimental results, a finite element simulation framework is established to further investigate the temperature gradient distributions, slab deformations/curvatures, and thermal strain and stress inside the slabs. The results suggest that the PCM-incorporated slab has a higher top surface temperature, a larger top-vs-bottom surface temperature difference, and thereof a larger curvature. However, the temeprature gradient reveals that heat accumulates at the upper layer before PCM melts completely, thus accounting for most of the temerpature difference. Moreover, regardless of the larger top-vs-bottom strain difference and stress nonlinearity, the linear strain of the PCM slab is smaller due to its lower coefficient of thermal expansion, and the later stage stress at the middle of the PCM slab center is smaller. Based on the findings, strategies of using PCM to control thermal curling of pavement slabs are proposed.

The heat capacity of low-temperature phase change materials (PCM) applied in thermal energy storage systems

Due to dependence of energy generation from renewable sources on weather conditions, such systems require cooperation with energy storage facilities. Thermal energy storage with phase change materials (PCM) is often used in systems working with solar collectors, photovoltaic panels, heat pumps, air conditioning systems, waste heat recovery systems and other. However, the appropriate application of PCMs requires a good knowledge of the thermo-physical properties of the materials and practical knowledge of the actual stored energy which depends on the PCM heating/cooling rate. The paper presents measurements of the latent heat for PCMs that are used in low-temperature thermal energy storage. The measurement method used was differential scanning calorimetry (DSC). In the experiments, two commercially available materials – RT15 and RT22 HC – were investigated. The tests were performed at different heating/cooling rates ranging from 0.5 to 10 K/min for samples of a mass 6–11 mg. On the basis of the test results and the proposed calculation method, the total values of energy stored during the phase transition, the temperature of phase change and the heat capacity distributions were determined as a function of temperature. Attention has been paid to the effect of temperature change rate on the measured latent heat capacity that is an important issue in practical applications of PCM. The heat capacity (energy stored) versus temperature distributions for RT15 and RT22 HC materials resulting from the tests can be used in design of latent heat thermal energy storage (LHTES) systems co-working with renewable energy systems. The presented methodology can also be used for investigation of other PCMs.

Form-stabled phase change material loaded with Ag NPs onto encapsulated n-tertracosane@SiO2, and thermal energy storage behavior

n-tetracosane (C24H50), a phase change material (PCM) that undergoes a phase transition at 50.6°C, was successfully encapsulated by silica (SiO2) as shell material in order to prevent it from leakage in this study (n-tetracosane@SiO2). Additionally, silver nanoparticles (Ag NPs) with various sizes (20, 40, and 80nm) having excellent thermal conductivity were loaded on the capsules to improve its thermal conductivity (n-tetracosane@SiO2@Ag NPs). It has been found that the encapsulation capacity, the thermal conductivity of the capsule, and the degree of n-tetracosane leakage affect the thermal energy storage capacity of the encapsulated n-tetracosane@SiO2@Ag NPs. As the size of Ag NPs loaded on the encapsulated n-tetracosane@SiO2 increased the thermal conductivity of capsules increased, especially when the Ag NPs of 80nm was loaded the thermal conductivity was enhanced more than three and two times compared to pure n-tetracosane and n-tetracosane@SiO2 capsule, respectively. The maximum melting and crystallization points in n-tetracosane@SiO2@Ag NPs (80nm) were 51.05 and 43.27°C, respectively, temperatures higher than those of pure n-tetracosane. The encapsulated n-tetracosane@SiO2@Ag NPs (80nm) exhibited a fusing and freezing latent heat capacities of 170.51 and 169.07J/g, respectively, an energy-storage efficiency of 63.41%, and a thermal storage capacity of 100%. Moreover, even with repeated fusing and freezing over 100 cycles, there was no significant change in the thermal energy storage capacity, and the shape of the capsules was maintained as it was. These results indicate that the encapsulated n-tetracosane@SiO2@Ag NPs have good thermal stability, which could be used as form–stabilized phase change materials for thermal energy storage.

Performance Assessment of Composite Phase Change Materials for Thermal Energy Storage-Characterization and Simulation Studies

Background: The present study mainly focuses on the development of new Thermal Storage Materials (TSM) and compare the performance for thermal energy storage capacity. Linear Low- Density Polyethylene (LLDPE) based Composite Phase Change Materials (CPCMs) is prepared, and its properties are analyzed using characterization, analytical calculations, and numerical simulation methods. The composites are prepared by blending the functionalized graphene nanoparticles (1, 3 & 5%) with three different concentrations into LLDPE. All three CPCMs show enhanced thermal performance compared to the base material, but it is noticed that higher concentrations of nanoparticles increase the dynamic viscosity and produce an adverse effect on thermal performance. Thermal characterization shows improved latent heat capacity with nanoparticle concentration, analytical and numerical results also compared, which shown a difference of 10 to 25%. Objective: The purpose of this study is the development and evaluation of the thermal storage capacity of different thermal storage materials and enlighten the techniques used for characterizing the storage materials. Methods: Composite material preparation is carried out by using twin-screw extruders, characterization of developed material is done through FTIR, SEM, and DSC analysis. For complete analysis characterization, analytical calculations and numerical simulation methods are used. Results: Linear low-density polyethylene-based composite materials can be successfully developed using a twin-screw extruder. This extrusion provided proper dispersion of nanoparticles into the base material, and it is validated by SEM analysis. DSC analysis confirmed the enhancement in the thermophysical properties of composite materials. Conclusion: The latent heat capacity increased around 20% during the heating cycle and reduced approximately 23% during the cooling cycle for base material and 5% addition of nanoparticle, respectively. The comprehensive study accomplishes that the optimum concentration of nanoparticle provides better thermal performance for thermal energy storage applications.

Elaboration of a composite material based on plaster reinforced with phase change material/Oakum Fiber: physical, thermal and mechanical properties.

Clay mineral is an important material available in nature. Montmorillonite (MMT) is widely used in a variety of materials because of its natural sources, physical and chemical properties, chemical structure, and functional utilization. In this paper a novel stable composite phase change material (PCMs) is prepared by the encapsulation of Capric Acid (CA) and Lauric Acid (LA) in alginate sodium biopolymer and their integration with oakum fiber in a plaster matrix. The SEM and FTIR analyses showed the existence of homogenous confinement of PCMs with the additive materials and good compatibility among its constituents. After a thermal cycling, DSC test of composite material exhibits a good thermal and chemical stability with suitable phase change temperature of 16.54°C and latent heat capacity of 35.18 J/gThe TGA analysis demonstrates the thermal stability of the capsules, all capsules show good stability up to 210°C. The bending tests show that beads addition enhances the composites ductility.Due to the high latent heat, low cost and its melting temperature, the composite material can be considered as potential for energy storage in the building sector.

Thermal and mechanical properties of gypsum sandwich-panels with phase change material

Energy deficiency and environmental pollution are always the most significant issues that researchers confront. One of the solutions for economising on energy consumption in structures is to use phase change materials (PCMs) in elements such as wallboards, roofs and floors. PCMs have good thermal characteristics such as high fusion heat, large latent heat capacity, solid–liquid phase change and they are also eco-friendly. In this research, PEG600 was used as a PCM in gypsum sandwich-panels with thicknesses of 7 and 10 cm and a PCM ratio of 10 and 15%wt. Gypsum/PEG600 sandwich-panels were constructed in three types – standard, hollow-core and macro-encapsulated. They were tested using apparatus under the thermal conditions of two different cities, to measure the maximum reduction of the specimens’ inner side temperature, the time delay to reach the maximum daily temperature and the amount of reduction in temperature, comparing different ratios of integrating PEG600 into gypsum panels. Macro-encapsulated sandwich-panels performed better. These reduced the maximum daily temperature by up to 5.7°C; this amount was 5.6°C and 3.4°C for standard and hollow-core specimens, respectively. The compressive and flexural strengths of gypsum/PEG600 panels reduced with an increasing PEG600 ratio.

Sodium acetate trihydrate-based composite phase change material with enhanced thermal performance for energy storage

Sodium acetate trihydrate (CH3COONa·3H2O, SAT), as the medium-low temperature phase change material (PCM), has been broadly utilized in thermal energy storage system. The specific objective of this study was to develop a new SAT-based composite PCM (CPCM) in order to restrain the supercooling and phase segregation of pure SAT. In this dissertation, SAT-CN/Nano-Cu was synthesized by adding carboxymethyl cellulose (CMC), sodium chloride (NaCl) and Nano-copper (Nano-Cu). The experimental results manifest that CMC is resultful to constrain phase separation of pure SAT. Supercooling degree of pure SAT is reduced from 30°C to less than 5°C by the addition of varying NaCl content. The Nano-Cu was furnished to further prevent the supercooling phenomenon of CPCM as well as intensify the heat transfer characteristics of pure SAT. Thermal properties containing thermal conductivity, latent heat and specific heat capacity were systematically analyzed using DSC and thermal properties analyzer. The analysis results demonstrate that a satisfactory thermal conductivity, high latent heat and inclusive of an appropriate specific heat capacity are achieved by the SAT-CN/Nano-Cu. In short, this work reported optimum CPCM consisted of SAT, 3 wt% CMC, 4 wt% NaCl and 0.8 wt% Nano-Cu that possesses superior phase change performance. Additionally, admirable thermal stability is retained by the CPCM.

Mechanical and thermal properties of artificial stone finishing materials mixed with PCM impregnated lightweight aggregate and carbon material

In this study, lightweight aggregates and carbon materials were impregnated with a phase change material (PCM) to improve the thermal performance of artificial stone used as an interior finishing material. The PCM used was n-octadecane; the carbon materials used in the mixture were exfoliated graphite nanoplatelets, activated carbon, and biochar. The compressive strength was slightly lower in the specimens with PCM; it was found that PCM can affect the adhesion of the cement paste and aggregate. When carbon materials are used in the mixtures, the thermal conductivity is improved. Depending on the type and amount of carbon material added, the thermal conductivity can be improved and the peak temperature adjusted. The combination of PCM and carbon materials allows for high latent heat capacity, efficient use of thermal energy through efficient storage and release, sustainable thermal stability and durability, and peak temperature control.

Silica fume/capric acid-stearic acid PCM included-cementitious composite for thermal controlling of buildings: Thermal energy storage and mechanical properties

In this paper, we produced new kind cement mortars with thermal energy storing/releasing properties, containing silica fume (SF)/capric acid-stearic acid eutectic mixture (CA-SA) as form-stable composite phase change material (FSC-PCM). The physicochemical compatibility between CA-SA eutectic PCM and SF was studied by fourier-transform infrared (FTIR), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) techniques. The differential scanning calorimetry (DSC) results indicated that the FSC-PCM including 37 wt% CA-SA eutectic PCM has a phase change temperature and latent heat capacity of 23.28 °C and 65.6 J/g, respectively. Thermogravimetric (TG) measurements and thermal cycling examination demonstrated that FSC-PCM has great stability in terms of its chemical structure, thermal degradation and cycling reliability in LHTES properties. To achieve novel type cementations composite mortar, the FSC-PCM was replaced with ordinary cement mortar (OCM) in weight fraction of 10%, 15% and 20%. Thermoregulation performance test showed that the maximum indoor temperatures differences between the OCM and latent heat storage-cement mortar (LHS-CM) based rooms were found as 2.48 °C during the heating stage and 1.71 °C during the cooling stage. Mechanical test findings of the LHS-CMs showed acceptable mechanical properties and have suitable properties for regulation of indoor temperatures and reducing energy consumption in buildings.

Numerical simulation of flashing using a pressure-based compressible multiphase approach and a thermodynamic cavitation model

A recently published pressure-based compressible multiphase flow model Labois and Narayanan (2017) is validated for applications relevant to safety of pressurized systems, such as flashing of high-pressure water through valves and nozzles. The pressure-based compressible multiphase flow solver is based on non-conservative discretization of the mixture continuity equation and has the advantage of being applicable to interface tracking and n-phase mixture formulations. For simulation of flashing, two well-known cavitation models Singhal et al.(2002), Yuan et al.(2001) have been implemented along with thermodynamic effects such as latent heat of phase change, variable saturation pressure, and heat capacities. The limitations of the well-established cavitation models in terms of their applicability to compressible flows have been clarified. The model was applied to the Super Moby Dick experiment Rousseau (1987). Good flow rates, and pressure and void fraction variations were obtained for three chosen conditions by tuning the cavitation model under incompressible conditions. It was found that the void fraction stops increasing beyond the throat due to thermodynamic effects where the latent heat and heat capacity are functions of pressure and temperature. The reduction of latent heat and rapid changes in liquid and vapour heat capacities close to the saturation line at high pressures was shown to be important. The accuracy, robustness, and efficiency of the pressure-based method has been proven for flashing under strong depressurization conditions. The cavitation model predictions are strongly sensitive to model parameters such as the nucleate density making the models not general enough to be applied to different problems without calibration. It was shown that there is significant room for development of improved cavitation models especially focussing on the constant number density constraint due to the strong sensitivity of the current models to this input parameter. The assumption of incompressibility and homogeneity of the phasic velocities is also identified as serious limitations requiring further study.

Cryogenic conditioning of microencapsulated phase change material for thermal energy storage

Microencapsulation is a viable technique to protect and retain the properties of phase change materials (PCMs) that are used in thermal energy storage (TES) applications. In this study, an organic ester as a phase change material was microencapsulated using melamine–formaldehyde as the shell material. This microencapsulated PCM (MPCM) was examined with cyclic cryogenic treatment and combined cyclic cryogenic heat treatment processes. The surface morphology studies showed that the shell surfaces had no distortions or roughness after cryogenic treatment. The cryogenically conditioned microcapsules exhibited diffraction peak intensity shifts and crystal structure changes. The onset of melting for the nonconditioned and conditioned microcapsules were measured to be 8.56–9.56 °C, respectively. Furthermore, after undergoing the cryogenic and heat treatment processes, the PCM microcapsules had appreciable latent heat capacities of 39.8 kJ/kg and 60.7 kJ/kg, respectively. Additionally, the microcapsules were found to have good chemical stability after the cryogenic treatment. In addition, the cryogenically conditioned microcapsules were found to be thermally stable up to 128.9 °C, whereas the nonconditioned microcapsules were stable up to 101.9 °C. Based on the test results, it is obvious that the cryogenically conditioned microcapsules exhibited good thermal properties and are very desirable for cool thermal energy storage applications.

Parametric study of a sustainable cooling system integrating phase change material energy storage for buildings

Free cooling of buildings uses the nocturnal outdoor air as a heat sink via a ventilation process. This could be performed by storing the night coolness for use during the daytime as appropriate. Due to the latent heat capacity, phase change material (PCM) could play anessential role in the effective operation of the free cooling systems by shifting the daytime peak load to the night. However, there is a scarceness on the technology application in hot climates. This paper presents results of a parametric investigation into the application of PCMs as thermal energy storage (TES) to provide sustainable cooling to buildings in hot arid climate by making use of the night-time free cooling. The proposed TES medium comprises an arrangement of metallic modules filled with RT28HC PCM. Numerous geometrical configurations and operational parameters have been assessed. A transient CFD simulation has been employed using ANSYS Fluent software. Validation of the numerical results with experimental data has shown a good agreement. The results have demonstrated that the temperature difference between the PCM and the air, at appropriate air flow rate would have a significant impact on the performance of the system. A free cooling system based on the proposed arrangement has the potential to meet around 42% of a typical building cooling load and has the ability to save up to 67% of building cooling energy load in summer season compared to conventional air-conditioning systems in hot arid climates.

Experimental study on a functional microencapsulated phase change material for thermal management

Phase change materials play a vital role in the field of thermal management field, in particular for the microencapsulated protocols owing to its large specific area, enhanced thermal stability and controlled volume variation. However, its sophisticated preparation process associated with complex chemical or physical events still heavily hinders the advance application. Herein, microencapsulation of phase change materials through an facile in-situ copolymerization of N-(tert-butyl)acrylamide, divinylbenzene and para-quaternary ammonium functionalized styrene has been studied. The ratio of core/shell, oil/water ratio and the different monomers were investigated towards the encapsulation efficiency and morphology of the as prepared microcapsules. Chemical composition, morphology of the microcapsules were analyzed by Fourier-transform infrared spectroscopy, X-ray diffraction instrument, thermal gravimetric analysis, scanning electron microscopy and transmission electron microscopy. Thermo-physical characteristics, such as leakage-proof performance, latent heat capacity and phase change temperature were also studied. This study, for the first time, using a quaternary ammonium functionalized styrene based amphipathic monomer, which was designed to be able to stay at the interface of oil and water, as one of the shell materials with the purpose of attaining a high encapsulation rate. As a result, the encapsulation efficiency of our protocol can achieve to 84.50% without observation of any PCMs leakage. Additionally, it was noteworthy that this study offers a facile way to construct PCMs microcapsule, which only needs a simple and rough mixing and filtration, thanks to the self-assembly characteristic of this amphipathic monomer.

Thermally-enhanced nanoencapsulated phase change materials for latent functionally thermal fluid

Phase-change materials (PCMs) have attracted numerous attentions in thermal energy storage area due to their high latent heat capacity. However, their inherently low thermal conductivity and potential leakage risk severely decrease the thermal storage efficiency. In this study, thermally-enhanced nanoencapsulated phase change materials (NEPCMs) were proposed to overcome those limitations. Through a miniemulsion polymerization approach, the n-Octadecane is encapsulated by SiO2/BN shell, which not only enhances the thermal conductivity, but also avoids the leakage problem during the phase change process. Compared with pristine PCMs, the thermal conductivity of the prepared NEPCMs was reinforced by 527% to 0.912 W m−1 K−1, which is the highest record among all the encapsulated PCMs with encapsulation ratio above 50%. The latent heat of the NEPCMs reaches 136.8 J/g with an encapsulation ratio as high as 60.4%. The thermal gravity analysis (TGA) and thermal cycling tests reveal that the nanocapsules possess excellent thermal stability and reliability. Furthermore, the NEPCMs were applied in latent functionally thermal fluid (LFTF) to enhance its thermal storage capacity. A microchannel cooling setup, with the NEPCMs/water LFTF as the coolant, was developed to evaluate the LFTF cooling performance. Compared with the pristine water, LFTF with 20 wt% NEPCMs reduced the heat source temperature by 12.1 °C at 80 W, showing their potential for the thermal management applications in electronic devices.