Thermal Energy Storage Concept Research Articles

Heat transfer and fluid flow analysis of PCM-based thermal energy storage concept for double pass solar air heater

Solar air heaters (SAHs) are flat plate collectors used for drying applications without causing any negative impact to the environment. However, SAH suffers from two drawbacks: first is the low convective heat transfer due to formation of boundary layer along the absorber plate, and second is the low thermal efficiency resulting from the lack of solar energy available after sunshine hours. The present study aims to examine the heat transfer and friction factor characteristics of double-pass SAH using two composite roughness geometries: perforated baffles and semicylindrical PCM tubes. The study is conducted at design parameters: blockage ratio (eb/Hd) of 0.4 to 0.8 and tube radius ratios (rt/Hd) of 0.2 to 0.5 under different Reynolds numbers (Re) from 3000 to 13,000. The maximum Nusselt number (Nu) and friction factor (f) are determined to be 200 at Re of 13,000 and 0.629 at Re of 3000, respectively, for the constant value of rt/Hd as 0.3 and eb/Hd as 0.8. In the range of parameters analyzed, maximum increase in Nu and f is determined to be 5.08 times and 65.80 times, respectively, over the smooth duct. Furthermore, correlations are derived for Nu and f with mean absolute error of 4.7% and 3.8%, respectively.

Working Fluid Selection and Thermodynamic Optimization of the Novel Renewable Energy-Based RESTORE Seasonal Storage Technology

Abstract Seasonal-based energy storage is expected to be one of the main options for the decarbonization of the space heating sector by increasing the renewables dispatchability. Technologies available today are mainly based on hot water and can only partially fulfill the efficiency, energy density and affordability requirements. This work analyzes a novel system based on pumped thermal energy storage (PTES) concept to maximize renewables and waste heat exploitation during summer and make them available during winter. Organic fluid-based cycles are adopted for the heat upgrade during hot season (heat pump (HP)) and to produce electricity and hot water during cold season (power unit (PU)). Upgraded thermal energy drives an endothermic reaction producing dehydrated solid salts, which can be stored for months using inexpensive and high energy density solutions. This paper focuses on thermodynamic cycles design, comparing the performance attainable with several working fluids. Two different configurations are investigated: coupled systems, sharing the fluid and heat exchangers in both operating modes, and decoupled systems. A preliminary economic assessment completes the study, including a sensitivity analysis on electricity and heat prices. Cyclopentane is identified as a promising working fluid for coupled systems, reaching competitive round trip efficiencies (RTEs), maximizing the ratio between performance and HX surfaces, without excessive turbomachinery volume ratios and volumetric flows. Economic analysis shows that solutions with lower efficiency, but also lower capital cost, can achieve competitive payback times (PBT). On the contrary, decoupled systems are less attractive, as they reach slightly higher thermodynamic performance, but require higher capital costs, possibly being of interest only in specific applications.

Power availability of PV plus thermal batteries in real-world electric power grids

As variable renewable energy sources comprise a growing share of total electricity generation, energy storage technologies are becoming increasingly critical for balancing energy generation and demand.In this study, a real-world electricity system was modeled rather than modeling hypothetical future electric power systems where the existing electricity infrastructure are neglected. In addition, instead of modeling the general requirements of storage in terms of cost and performance, an existing thermal energy storage concept with estimated capital cost that are sufficiently low to enable large-scale deployment in the electric power system were modeled. The storage unit is coupled with a photovoltaic (PV) system and were modeled with different storage capacities, whereas each storage unit had various discharge capacities.The modeling was performed under a baseline case with no emission constraints and under hypothetical scenarios in which CO2 emissions were reduced. The results show that power availability increases with increasing storage size and vastly increases in the hypothetical CO2 reduction scenarios, as the storage unit is utilized differently. When CO2 emissions are reduced, the power system must be less dependent on fossil fuel technologies that currently serve the grid, and thus rely more on the power that is served from the PV + storage unit.The proposed approach can provide increased knowledge to power system planners regarding how adding PV + storage systems to existing grids can contribute to the efficient stepwise decarbonization of electric power systems.

Computational investigation of the influencing parameters on the melting of phase change material in a square enclosure with built in fin and Al2O3 nanoparticles

Recent advances in renewable energy resources set the interesting research development in the thermal energy storage concepts. The thermal energy storage system (TES) stores the thermal energy in the form of sensible or latent heat or by chemical exothermic and endothermic reactions. In this work, a numerical analysis is implemented to study the effect of Grashof number (Gr), simultaneous incorporation of longitudinal fin, and nanoparticles addition on the transfer of heat and rate of melting of phase change material (PCM). The variation in the position of the fin (0.25H, 0.5H, and 0.75H), length of the fin (0.25L, 0.5L, and 0.75L) relative to the height and length of the container respectively, and different concentrations of Al2O3 nanoparticles (0%, 1%, 3%, and 5%) were studied. The high temperature heat source is given to the left side of the wall, and the low temperature sink condition is applied to the right side. The analysis is carried out for three Gr (5000, 13000, and 20000). It is noted that the time of melting is reduced with longer lengths of the fin and Gr. Also, the melt fraction increases with the position and volume fraction of the nanoparticles up to a certain limit after it reduces. The fin’s optimum length and position were selected as 0.5H and 0.75L with 4.99% and 2.03% more liquid fraction than the other positions. Also the favourable nanoparticles concentration is adopted as 3% Al2O3 with an increase of 5.04%, 4% and 2.56% of melt fraction more than the pure PCM, PCM + (1% Al2O3) / (5% Al2O3) respectively.

Polypyrrole‐boosted photothermal energy storage in MOF‐based phase change materials

AbstractInfiltrating phase change materials (PCMs) into nanoporous metal–organic frameworks (MOFs) is accepted as a cutting‐edge thermal energy storage concept. However, weak photon capture capability of pristine MOF‐based composite PCMs is a stumbling block in solar energy utilization. Towards this goal, we prepared advanced high‐performance pristine MOF‐based photothermal composite PCMs by simultaneously integrating photon absorber guest (polypyrrole [PPy]) and thermal storage guest (1‐octadecanol [ODA]) into an MOF host (Cr‐MIL‐101‐NH2). The coated PPy layer on the surface of ODA@MOF not only serves as a photon harvester, but also serves as a phonon enhancer. Resultantly, ODA@MOF/PPy composite PCMs exhibit intense and broadband light absorption characteristic in the ultraviolet–visible–near‐infrared region, and higher heat transfer ability than ODA@MOF. Importantly, the photothermal conversion and storage efficiency of ODA@MOF/PPy‐6% is up to 88.3%. Additionally, our developed MOF‐based photothermal composite PCMs also exhibit long‐standing antileakage stability, energy storage stability, and photothermal conversion stability. The proposed coating strategy and in‐depth understanding mechanism are expected to facilitate the development of high‐efficiency MOF‐based photothermal composite PCMs in solar energy utilization.

Horizontal thermal energy storage system for Moroccan steel and iron industry waste heat recovery: Numerical and economic study

Implementing thermal energy storage for the recovery of massive and intermittent waste heat represents crucial milestone for energy-intensive sectors such as iron and steel industry. However, the constraints related to current available sensible heat storage systems remain a barrier for their deployment. This work aims at examining high temperature horizontal thermal energy storage concept filled with channels of byproduct issued from the same industry as filler material and air as heat transfer fluid. The storage tank design is investigated as promising cost-efficient configuration from numerical, technical, and economic viewpoints. The focus is to assess the thermal behavior as well as the economic savings of this emergent concept addressed for the recovery of waste heat in Moroccan iron and steel industry. Numerical findings demonstrate that thermal performances, i.e., discharge and cycle efficiencies as well as charging and discharging times remain stable after six cycles of charge/discharge but the challenge is related to discharge efficiency (approximately 30%). Consequently, more efforts are required to upgrade thermal performance for such configuration. However, outcomes also proved the profitability of this emergent concept for energy, electricity, fuel, and gas emission savings. The economic results show that implementing horizontal thermal energy storage tank has a lot of promise, with cost savings of up to 900000 dollars per year and a payback period of less than one year.

Aerogels Meet Phase Change Materials: Fundamentals, Advances, and Beyond.

Benefiting from the inherent properties of ultralight weight, ultrahigh porosity, ultrahigh specific surface area, adjustable thermal/electrical conductivities, and mechanical flexibility, aerogels are considered ideal supporting alternatives to efficiently encapsulate phase change materials (PCMs) and rationalize phase transformation behaviors. The marriage of versatile aerogels and PCMs is a milestone in pioneering advanced multifunctional composite PCMs. Emerging aerogel-based composite PCMs with high energy storage density are accepted as a cutting-edge thermal energy storage (TES) concept, enabling advanced functionality of PCMs. Considering the lack of a timely and comprehensive review on aerogel-based composite PCMs, herein, we systematically retrospect the state-of-the-art advances of versatile aerogels for high-performance and multifunctional composite PCMs, with particular emphasis on advanced multiple functions, such as acoustic-thermal and solar-thermal-electricity energy conversion strategies, mechanical flexibility, flame retardancy, shape memory, intelligent grippers, and thermal infrared stealth. Emphasis is also given to the versatile roles of different aerogels in composite PCMs and the relationships between their architectures and thermophysical properties. This review also showcases the discovery of an interdisciplinary research field combining aerogels and 3D printing technology, which will contribute to pioneering cutting-edge PCMs. This review aims to arouse wider research interests among interdisciplinary fields and provide insightful guidance for the rational design of advanced multifunctional aerogel-based composite PCMs, thus facilitating the significant breakthroughs in both fundamental research and commercial applications.

Simulation of a circulating fluidized bed power plant integrated with a thermal energy storage system during transient operation

In the current work, a transient/dynamic 1-dimensional model has been developed in the commercial software APROS for the 300 MWth circulating fluidized bed power plant of Sumitomo SHI FW. The operation of the plant is simulated under steady-state at two boiler loads: 100% and 60%, and the results for the distribution of temperature, pressure, mass and heat flow of the water/steam as well as for the flue gas composition and its thermodynamic properties are compared against performance data provided by the company, showing good agreement. Following this, the validated model is utilized to investigate the effectiveness of a thermal energy storage concept, which utilizes a bubbling fluidized bed to store particles during ramp down operation and return them to the fluidized bed during ramp up. Three dynamic scenarios are simulated for the load transition 100%-60%-100%: (a) a case without the use of thermal energy storage, (b) a case with thermal energy storage removing 20% of the solid inventory of the fluidized bed, and (c) a case with thermal energy storage removing 40% of the solid mass of the bed. The results of the three simulations are compared between them and the achieved ramp down/up rates (calculated based on the 90% method) are equal to: (a) 5.09/5.06%/min, (b) 5.64/5.73%/min and (c) 6.19/6.12%/min, respectively. These rates are higher than the current state-of-the-art rates of circulating fluidized bed power plants. The highest rates were achieved with the 3rd simulation scenario, in which, however, the live steam pressure fluctuations exceeded the technical limits of ±10 bar.

Numerical study of a high-temperature thermal energy storage system with metal and inorganic salts as phase change materials

This study proposes a novel thermal energy storage (TES) concept using two phase change materials (PCMs) (inorganic salt and metal alloy) as the storage media. The metal alloy PCM is encapsulated in a tube which is inserted in the inorganic salt PCM. Thus, the metal alloy PCM serves as the heat storage material as well as the heat transfer enhanced fin for the inorganic salt PCM. After validation, a numerical model is developed to simulate the charging and discharging processes of the presented TES unit. Furthermore, the influence of the storage material selection, the phase change temperature difference between those two PCMs, and the location of heat transfer surface on the thermal behavior of the charging and discharging process are discussed. The results show that, compared with the unit filled with only salt PCM, the proposed unit can significantly reduce the charging and discharging time by 33.2% and at least 50.3%, respectively. When selecting metal PCM, it is not recommended to use the metal PCM with higher melting temperature than the selected salt PCM. With 75 K melting temperature difference, the melting and solidification time of the unit was prolonged by 47.1% and 6.1%. In addition, if the unit has bottom heat transfer surface, the melting and solidification time of the unit are 356 and 1989 min, corresponding to 4.5 charging power and 0.8 kW discharging power.

Investigation of White Vaseline as an alternative phase change material for thermal regulation of physiological birth rooms

This research work encompassed the results of experimentation of an innovative composite (Plaster/white Vaseline) for indoor thermal regulation of physiological birth rooms using the Latent Heat Thermal Energy Storage (LHTES) concept. The indoor temperatures of these specific sanitary rooms need to be continually stabilized approximately at 35 °C. Accordingly, white Vaseline (petroleum jelly) was recovered from health facilities and then tested as an alternative PCM for a LHTES application at constant temperatures. The white petroleum jelly used in this work is mainly composed of microcrystalline wax and liquid paraffin; its phase change temperatures were found to be respectively at 36.56 °C and 35.53 °C for melting and solidification cycles with an enthalpy value of 95.38 J/g (±1.23). In addition to these suitable thermal properties, the substance is safe and available at low-cost. A mineral matrix prepared essentially from plaster was experimented to trap the PCM into its microstructure in order to prevent any risk of leakage during the phase change process. Finally, the innovative composite (Plaster/white Vaseline) underwent thermal and physico-chemical characterization tests that identified its properties and revealed a potential efficiency of the novel material for passive thermal regulation of physiological birth room's indoor environments.

A novel trigeneration system based on solid oxide fuel cell-gas turbine integrated with compressed air and thermal energy storage concepts: Energy, exergy, and life cycle approaches

Energy storage technologies are considered as an available solution to improve the reliability of conventional energy systems as well as responding to the peak load. This paper offers a novel integrated system with remarkable potential to provide users’ electricity, heating, and cooling demand for small-scale distributed generation applications. The main objective of this research is improving thermodynamic efficiency as well as mitigating emissions of the conventional solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system with the option of peak-shaving. A compressed air energy storage and thermal energy storage are employed to store the surplus power and recover the waste heat of the prime mover, respectively. The proposed system operates with a round-trip efficiency of 76.8 % and exergy efficiency of 46 % under the design condition: 8 h of off-peak period with 97.5 kW power demand and 8 h of peak period with 305.6 kW power demand; 113.4 kW cooling capacity; 37.4 m3 hot water production. Furthermore, the evaluation of environmental impacts indicates that GHG emissions are low at 0.27 kgCO2e/kWh. Also, the life cycle assessment shows that well-to-production GHG emissions of the proposed integrated system during a round-trip of operation are 1890 kgCO2e which is 6.6 % lower than the conventional SOFC-GT.

A modular cement-based subsurface heat storage: Performance test, model development and thermal impacts

This study investigates the performance of a recently developed modular cement based underground thermal energy storage concept and its thermal impacts on the geological subsurface by experimental work and numerical modeling. A field-scale pilot plant of the storage system was constructed in the shallow subsurface in northern Germany, consisting of 25 coupled 1.5 m3 storage units containing a tubular helical heat exchanger. A charging and passive cooling experiment was performed and monitored over a period of 82 days. For the numerical model of the storage and the surrounding ground a geometrical grid simplification procedure was developed, which substantially reduces the computational effort for 3D-simulations of multi-unit storage arrays. The model was validated by comparison of experimental and simulation data and used to corroborate the interpretation of the field test. Results show heat transfer rates of 15.2–2.8 kW during the first ten days, storing about 1280 kWh of thermal energy. During passive cooling the average heat loss rate amounts to 28kWh/day. The results demonstrate the technical feasibility of the storage concept at low thermal impact on the subsurface environment but also the necessity for an improved insulation in order to increase the storage efficiency. The numerical modelling approach can be applied for layout and operational optimization as well as thermal impact assessment for specific applications of the modular storage system, but is useful also for grid size reduction in models of related geothermal subsurface structures employing tubular heat exchangers like thermally activated pile foundations or borehole heat exchangers.

Analysis of a horizontal flow closed loop thermal energy storage system in pilot scale for high temperature applications – Part I: Experimental investigation of the plant

A unique large scale pilot plant of the CellFlux thermal energy storage concept is experimentally investigated. This storage concept consists of a regenerator type thermal energy storage volume, which is coupled to a finned tube heat exchanger by a circulating intermediate working fluid. The system investigated in this work operates at a temperature of 390 °C and uses air as intermediate working fluid which is conveyed by a centrifugal fan. The storage volume has a bed length of over ten meters and is of a novel design, where the air flows in horizontal direction. Since this approach could cause a flow maldistribution, a thorough analysis is of major interest for the accuracy of subsequent numerical simulations. The experiments reveal that the mass flow along the centerline can be up to 20% higher than the mean bulk flow. A significant maldistribution between top and bottom area, however, is not observed. As an alternative to the typically used rock filling, the storage volume is equipped with standard hollow bricks. These bricks are cost effective but do not have a well-defined shape. Thus, the predictability of the pressure drop by correlations found in the literature is unclear. It turns out that the measured pressure drop is evenly distributed in axial flow direction but generally higher than expected from the assumption of pure channel flow. Further experiments are conducted to validate the heat capacity of the bricks and to derive a correlation for the inner heat transfer between bricks and storage walls. Eventually, the aim of the experimental investigation is a general proof of concept as basis for the numerical investigation. Thus, all specifications of the plant and the storage material are provided. The plant is analyzed towards plausibility of heat losses, showing that heat losses can be predicted well within the given uncertainties.

Thermal performance analysis of thermocline combined sensible-latent heat storage system using cascaded-layered PCM designs for medium temperature applications

One tank type thermocline thermal energy storage (TES) concept is considered as a possible cost optimized solution for the medium temperature industrial applications, e.g., chemical processing, beverages industry etc. However, one of the drawbacks of this TES configuration is higher thermocline degradation at the end of discharging cycles and overall decrease in performance. In current work a new type of combined sensible-latent heat configuration is introduced to counter these issues. The concept of the proposed thermal storage configuration is to use structured sensible heat cheap material with the space between them occupied by encapsulated phase change material (PCM) capsules, forming cascaded layered packed bed along the tank height and the heat transfer fluid flows between them. A comprehensive unsteady numerical model is formulated based on two-phase Schumann model equations to evaluate performance of the each proposed prototypes. The numerical simulations are performed to investigate the effect of combined sensible rod structure and multi-layered PCMs designs on thermocline temperature profiles, exergy outputs, total thermal energy storage, efficiency in the use of total storage capacity, utilization ratio and the proportion of PCM effectively changing phase. The comparative analysis is performed for four different configurations, i.e., single layered sensible rod with PCM (SLSPCM) arrangement and the three cascaded layered sensible rod with PCM (CLSPCM) arrangements. The overall results show that the TES with a volume fraction arrangement of (40%-20%–40%) is performance wise the best configuration followed by (25%-50%–25%) and (10%-80%–10%), respectively. And SLSPCM is the lowest in the row. The analysis presented in the current study shows that the use of multistage PCMs having suitable combination of layer thickness and fusion temperature together with the inclusion of cheaper structured filler material, offer an efficient and cost effective TES alternative.

Transient thermal analysis of multilayer pipeline with phase change material

Based on thermal energy storage concept, multilayer composite pipeline with phase change material (PCM) has been proposed recently as an effective method to meet flow assurance challenges in deep water environment by releasing latent heat and extending cool-down time under shut-in condition. This work presents a mathematical model for the start-up and cool-down processes in a multilayer pipeline with an inner steel pipe, an intermediate PCM layer, and an external thermal insulation layer. With enthalpy formulation adopted for the PCM layer, the governing equations for heat conduction in the composite pipe walls and for energy transport in the produced fluid are solved numerically by explicit finite difference methods. The effects of the PCM thickness ratio, the phase change temperature, and the thermal conductivity ratio between the thermal insulation layer and phase change material are investigated. The effect of PCM hysteresis on the transient heat transfer process is also evaluated. It is found that there is an optimal PCM thickness ratio for a given combination of PCM and thermal insulation materials that maximizes the overall cool-down time. The cool-down time and the optimum PCM thickness ratio increase when the phase change temperature decreases. For a given PCM, the optimum PCM thickness ratio decreases for increasing thermal conductivity ratio. There is an interval of thermal conductivity ratio between 0.2 and 0.8 within which the PCM layer with optimum thickness ratio provides a significant increase in the cool-down time.

Spray-type packed bed concept for thermal energy storage: Liquid holdup and energy storage characteristics

The performance of a thermal energy storage system strongly influences the overall efficiency of a central solar power plant. Therefore, low-cost and high-efficiency thermal energy storage technologies have attracted considerable attention in recent years. A thermal energy storage concept using a spray-type packed bed is proposed in the present study. In addition, a small-scale semi-transparent spray-type packed bed thermal storage system was set up, using thermal oil as a transfer fluid and spherical particles as the storage media inside the packed bed. An experimental study on the liquid holdup and heat storage characteristics of the proposed spray-type packed bed system was conducted. The results indicate that the total liquid holdup increases as the volume flow rate increases, and the static liquid holdup inside the packed bed shows no relationship with the flow rate or height of the packed bed. Herein, a comparison of the unit cost for different thermal energy storage technologies is presented.

Pumped thermal energy storage (PTES) as smart sector-coupling technology for heat and electricity

Thermal energy storage combined with thermal cycles is an alternative option for storage in electrical power grids. Intermediate storage of electric energy as heat offers advantages such as free choice of site, small environmental footprint, life expectancies of 20–30 years and optional low-cost backup capacity. The key element in pumped thermal energy storage (PTES) concepts is the application of a left running thermal cycle to transform low temperature heat into high temperature heat, which is stored in the thermal storage during charging. PTES allows higher storage efficiencies than a direct electric heating of the thermal storage unit. The optional combination of electricity and heat during charging and discharging makes PTES a promising tool for the management of various types of energy in systems with high shares of renewable energy.CHEST (Compressed Heat Energy STorage) is a specific PTES variant based on Rankine cycles using either water or organic media as the working fluid in combination with latent heat storage units. This paper focuses on the application of CHEST for the management of heat and electricity. Different options for the implementation of CHEST will be presented, for these variants, characteristic values such as operating parameters and power ratio are given and the required components described. The focus is on the technological possibility of using pumped thermal energy storage as a sector-coupling technology for heat and electricity through low temperature heat integration. In addition, new findings of an in-depth numerical simulation of a fully heat-integrated, subcritical PTES using butene as the working fluid are presented.

A comprehensive analysis of a thermal energy storage concept based on low-rank coal pre-drying for reducing the minimum load of coal-fired power plants

In the context of renewables penetration, coal-fired power plants are required to operate at the minimum load in low-demand periods of the grid. However, combustion in the boiler will become unstable in low load conditions, which constrains the load reduction of coal-fired power plants, especially the plants fueled by low-rank coal (LRC). This work proposed a thermal energy storage (TES) concept based on LRC-drying (LD-TES) to reduce the minimum load of LRC-fired power plants (LCPPs). A simple experiment was employed to verify the feasibility of energy storage through LRC drying. The advantage of LD-TES compared with traditional low-temperature TES was revealed based on the thermodynamic analysis. Moreover, an LCPP system integrated with LD-TES was proposed, and the minimum load reduction attributed by LD-TES and the energy/environmental performance of the integrated system is determined quantitatively. To achieve this goal, a thermodynamic model is employed for system simulation and evaluation, and the TES scheme based on hot water tank (HWT-TES) using the same heat source as LD-TES is chosen for comparison. The results show that, pre-drying and storage of LRC is feasible for hourly thermal energy storage, and LD-TES can equivalently store electric power in megawatt magnitude (11.1–25.0 MW) with high round-trip efficiency (92.8%). Besides, LD-TES can also significantly reduce the CO2 emission of LCPP systems.

Opportunities and challenges of PCM-to-air heat exchangers (PAHXs) for building free cooling applications—A comprehensive review

Abstract With high energy consumption trend in buildings, the adoption of thermal energy storage systems toward reducing cooling load has been increased in recent years. Subsequently, utilizing the concept of latent heat thermal energy storage (LHTES) through phase change materials (PCMs) have been widely discussed in the literature. This paper is a comprehensive review of the utilization of PCM-to-Air Heat Exchangers (PAHXs) for building free cooling applications. The potential and limitations of using PAHXs in free cooling applications are discussed in detail, focusing on hot desert climate. Significant system influencing factors such as inlet temperature, phase change temperature, and airflow rates are analyzed and their impact on the thermal performance of PAHXs free cooling applications are addressed. Previous studies claimed that continuously maintaining outlet air temperature (of PAHX) within the preferred indoor thermal comfort is a system limitation, especially in extreme climates with exceptionally high cooling demand. However, they have assured the increased cooling potential by adopting multi-PCM approach and integration with other passive technologies in free cooling systems to increase system storage abilities and satisfy workability under high inlet temperatures. For magnifying the free cooling system’s cooling abilities in hot desert climate, this paper recommends considering the potential of nighttime sky radiation during the PCM charging process. The discussions made in the paper will be helpful in understanding the influencing parameters of PAHXs system for free cooling application, especially in hot desert climate.

Application of the thermal energy storage concept to novel epoxy–short carbon fiber composites

ABSTRACTFor the first time, multifunctional epoxy–short carbon fiber reinforced composites suitable for thermal energy storage technology were developed. Paraffin microcapsules (MC) and short carbon fibers (CFs) were added at different relative amounts to an epoxy matrix, and the microstructural and thermomechanical properties of the resulting materials were investigated. Scanning electron microscopy images of the composites showed a uniform distribution of the capsules within the matrix, with a rather good interfacial adhesion, while the increase in the polymer viscosity at elevated CF and MC amounts caused an increase in the void content. Differential scanning calorimetry tests revealed that melting enthalpy values (up to 60 J/g) can be obtained at high MC concentrations. The mixing and thermal curing of the composites did not lead to breakage of the capsules and to the consequent leakage of the paraffin out of the epoxy matrix. The thermal stability of the prepared composites is not negatively affected by the MC addition, and the temperatures at which the thermal degradation process begins were far above the curing or service temperature of the composites. Flexural and impact tests highlighted that the presence of MC reduces the mechanical properties of the samples, while CF positively contributes to retaining the original stiffness and mechanical resistance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47434.