Phase Change Materials For Thermal Storage Research Articles

Functional Soft Materials with Resistance to Liquid Leakage for Thermal Energy Storage

AbstractFunctional soft materials have great potential commercial applications in thermal energy storage, which are required to have a long life, good flexibility, and resistance to liquid leakage. Herein, a composite hydrogel with thermal storage properties is prepared through coupling molecular self‐assembly and in situ polymerization. Hydrophobic stearic acid (SA), as a thermal storage phase change material (PCM), is dispersed in polyacrylamide (PAM) hydrogel network in the form of oil–water emulsion (O/W). The PAM polymer network with good flexibility physically limits high‐frequency collision between SA PCM droplets. This unique design avoids demulsification in phase change emulsion so that the as‐prepared hydrogel composite can resist liquid leakage. The PAM hydrogel network plays the role of heterogeneous nucleation, resulting in the super‐cooling of SA emulsion at only 0.3 °C. On the other hand, SA PCM droplets in as‐prepared soft material do not directly contact with liquid water, so melting/crystallization process is independent of water. As a result, the soft material exhibits a thermal storage density of up to 99.3 J g−1. The present study is an important step toward designing soft energy storage materials.

Residential Micro-CHP system with integrated Phase change material thermal energy storage

This paper presents an analysis and experimental investigation of the effect of integrating Phase Change Material (PCM) within a heat exchanger within a Micro Combined Heat and Power (Micro-CHP) system intended for residential applications. A commonly used Micro-CHP layout is replicated in a test rig to characterise the performance of two alternative heat exchanger arrangements. The first is a conventional arrangement where the exhaust gas produced by the prime mover is directed to an air-to-water heat exchanger to heat water and store it in a tank. In the second arrangement, PCM material is encapsulated within specially designed compartments in a heat exchanger to store part of the exhaust thermal energy from the prime mover while heating the water in the storage tank. The time needed to heat the water and discharge heat is compared for both cases, as well as the amount of thermal energy stored during the same operating period. The study also explored the potential to improve the designed unit by using different PCM materials. The test results show that adding 4.7 Liters capacity paraffin compartments within the heat exchanger extended the discharge time of the hot water by over 400%, which reflects a marked improvement in the heat storage capacity of the system. This would result in a significant increase in the viable operating period of a CHP system. The one-dimensional analysis revealed that replacing the paraffin with ClimSel C58 PCM can reduce the charging time of the water tank by around 54% improve the heat storage capacity by factor of 2.35 comparing to Paraffin. The proposed heat exchanger with encapsulated PCM has a potential in other applications such as storage of excess renewable energy or integration with heat pumps to improve matching of supply and demand and thus flexibility of an energy system with integrated intermittent renewables.

Analysis of Solar Water Heater with Modification Absorber Plate Integrated Thermal Storage

In various countries worldwide, solar water heater systems (SWHs) are utilized as devices that harness solar energy as a primary energy source. This study investigates the performance of SWHs numerical simulation by integrating phase change material (PCM) paraffin wax onto an absorber plate collector at the bottom for thermal storage. This study presents the thermal performance of a SWHs that uses an absorber plate with PCM for thermal energy storage. In this test, four variations of the model tested, namely a) standard flat plate (SFP), b) standard flat plate with PCM storage thickness 10mm (SFP+PCM 10mm), c) standard flat plate with PCM storage thickness 7mm (SFP+PCM 7mm), and d) standard flat plate with PCM storage thickness 4mm (SFP+PCM 4mm), were investigated using numerical simulation. Initially, an analytical investigation was conducted to examine the material qualities of paraffin wax utilised for phase change material (PCM) storage. The SWH systems were subsequently imported and simulated under three different levels of continuous solar radiation: 400 W/m2 700 W/m2 and 1000 W/m2. The simulation incorporates the use of computational fluid dynamics (CFD) tools. The results of the study revealed that the collector of the SWH system, which utilised an absorber plate containing phase change material (PCM) storage, demonstrated exceptional performance. Models with a thickness of 7mm PCM or SFP+PCM 7mm have the highest efficiency compared to other models with an efficiency value of 64%. There is a 3-4% increase in efficiency with variations in models that use PCM thermal storage compared to models that do not use PCM thermal storage.

Hydrophilicity regulation of carbon nanotubes as phase-change materials for thermal energy storage

Solid-liquid phase-change materials (PCMs) offer exciting prospects for thermal energy conservation, whose performance is greatly affected by the carrier materials. Using expanded vermiculite (EV) as frameworks, carbon nanotube arrays (CNTs) were grown between EV layers by chemical vapor deposition (CVD). Then, the paraffin (PA) was loaded on the EV@CNTs composite by vacuum impregnation to prepare composite PCMs (PA/EV@CNTs), where the PA is organic carrier and the EV@CNTs acts as porous supports with high structural strength. The loading capacity of PA is further regulated by the hydrotropism of CNTs which effectively prevents the leakage of molten PA. The in-situ grown CNTs significantly improves the thermal conductivity of PCMs, improving the efficiency of energy conversion. With maximum PA loading capacity of 95 wt%, the thermal conductivity of PA/EV@CNTs-95% reaching 0.7176 W/mK, which was 1.73 and 2.96 times higher than that of pristine EV and PA. The phase change latent heat of PA/EV@CNTs-95% was measured to be 168.54 J/g, which is 1.48 times higher than that of PA/EV. After 100 cycles, the PA/EV@CNTs still maintains excellent thermal stability, and the enthalpy retention rate is 98.73%. The incorporation of high thermal conductivity amphipathicity CNTs in these PCMs makes them promising candidate for various applications such as energy-efficient buildings, thermal management in electronic devices, and self-cleaning materials.

Numerical investigation of an amalgamation of two phase change materials thermal energy storage system

In the last three decades, many researchers have published their findings on the storage of thermal energy using various phase transition materials (both organic and non-organic). One of their goals was to have a higher heat storage capacity with a shorter heat charging cycle for thermal energy storage. This study looked into a floating capsule thermal energy storage system (TESS). A number of spherical capsules filled with beeswax were placed in a paraffin-filled cylindrical shell. With heat transfer fluid flowing through three hexagonal tubes arranged at 120° inside the TESS core, the two phase change materials (beeswax with a thermal conductivity of 0.25 W/mK and paraffin with a thermal conductivity of 0.23 W/mK) were charged and discharged. For the proposed TESS, a mathematical model was created and utilised to forecast thermal energy storage capacity and charging/discharge times for various configurations. In TESS, a 70–30% mixture of the two PCMs results in a 21.5 percent increase in heat storage capacity when beeswax alone is used, and an 8.4 percent decrease in storage capacity when paraffin alone is used. For a heat storage capacity of 7300 kJ, the model estimates charging and discharging times of around 2.6 and 3.2 hours, respectively.

Experimental research of photovoltaic-valley power hybrid heating system with phase change material thermal storage

The widespread integration of high-ratio distributed photovoltaic (PV) systems in buildings calls for flexible load management to align with municipal power peaks and PV variability. To address the timing and demand mismatches between PV generation and building energy needs, energy storage systems are used to manage PV excess, aid in grid peak shaving, and support building heating. This research develops a Photovoltaic-Valley power complementary phase change energy storage heating system, designed to consume photovoltaic and valley power for the decentralized heating of individual rooms, thus optimizing distributed energy utilization. A CPCM of magnesium chloride hexahydrate, EG, and calcium hydroxide, designed for indoor heating, was created with a phase change temperature around 117.9 °C and an enthalpy of 106.2 kJ/kg. An experimental platform was established to test the system and its control strategy, showing that the PV-powered phase change energy storage heater effectively keeps indoor temperatures above the thermal comfort minimum of 18 °C. As the PV guarantee rate increases, the system improves indoor temperature regulation and significantly reduces fluctuations. Operating costs are over 30% lower than those of traditional heating networks and natural gas systems, underscoring substantial energy savings and emission reductions. This research provides an integrated approach for optimizing building PV consumption, managing grid peaks, and regulating indoor temperatures with phase change energy storage heating systems.

Study on thermal storage performance of a novel conical spiral tube heat storage system

Due to the structural advantage of the conical spiral tube, which is narrow at the top and wide at the bottom, it helps to improve the thermal response rate of the heat storage system. Therefore, this study proposes a novel conical spiral tube heat storage system. The software Fluent is used to conduct three-dimensional unsteady state calculations and investigate the effects of the conical ratio, taper, and length-to-diameter ratio on the phase change material (PCM) thermal storage performance. The results indicate that when the conical ratio is increased from 1.0 to 3.0, the PCM heat storage capacity is reduced by 1.05%, the melting time is shortened by 17.60%, the average heat storage rate is increased by 20.10%, and the heat storage efficiency is reduced by 0.10%. Continuing to increase the conical ratio, the optimization of the performance is not obvious. Subsequently, a conical ratio of 3.0 heat storage tank is used as the reference unit. When the tank taper is increased from 0 to 0.22 and the length-to-diameter ratio is increased from 1.44 to 1.85, the melting time is shortened by 7.59% and 32.62 %, the heat storage capacity is reduced by 3.45% and 9.24%, the average heat storage rate is increased by 4.47% and 34.69%, and the heat storage efficiency is reduced by 0.02% and increased by 7.99%, respectively. Continuing to increase the taper from 0.22 to 0.32 does not result in an effective improvement of the performance. This study is a good guide for the optimization of the thermal storage performance of spiral tube heat storage systems and the efficient use of solar energy.

Thermal Energy Storage Heat Exchanger Design: Overcoming Low Thermal Conductivity Limitations of Phase-Change Materials

Abstract Recently, there has been a renewed interest in solid-to-liquid phase-change materials (PCMs) for thermal energy storage (TES) solutions in response to ambitious decarbonization goals. While PCMs have very high thermal storage capacities, their typically low thermal conductivities impose limitations on energy charging and discharging rates. Extensive research efforts have focused on improving PCM thermal conductivity through the incorporation of additives. However, this approach presents challenges such as achieving uniform mixtures, maintaining high latent heat, and cost. Alternatively, it has been demonstrated that, in this study, reducing the length scale of the PCM-encasement thickness can eliminate the low thermal conductivity effect of PCMs. To illustrate this concept, a one-dimensional PCM slab was numerically simulated. The thickness of the slab was varied to represent dimensions found in flow passages of compact heat exchangers, and the heat transfer coefficient of the heating fluid was varied to represent lower and upper bounds while also including nominal values encountered in air-to-air heat exchangers. The thermal conductivity was parametrically varied from the natural value of the PCM to simulated enhanced values (potentially achieved through additives) of up to 400 times larger. Results show that reducing the PCM-encasement thickness yields substantially better performance than by improving the thermal conductivity, thereby demonstrating the potential for compact heat exchanger design to overcome the PCM thermal conductivity limitations.

Development and experimental investigation of full-scale phase change material thermal energy storage prototype for domestic hot water applications

The paper presents an experimental analysis of the full-scale phase change material (PCM) thermal energy storage (TES) prototype that is designed for use in domestic hot water preparation systems. The PCM-TES prototype is based on the external arrangement of organic PCM and a custom-made compact fin-and-tube type of heat exchanger. The prototype has been designed, constructed, and tested according to the Ecodesign Directive requirements for water heaters and hot water storage tanks. Several parameters have been analysed, including the heat transfer fluid (HTF) temperature and mass flow rate, heat transfer rate, accumulated and released energy, and quantity of domestic hot water (DHW) delivered. Additional attention was paid to the reliability and repeatability of the results. Experimental research allowed to determine the quantity and temperature of DHW at a constant mass flow rate of 0.1 kg/s. The prototype unit showed that it can deliver 99.1 l of hot water at 40 °C for up to 15 min and 39 s, while the use of lower temperature DHW (up to 37 °C) allows to increase the quantity of hot water delivered up to 156.2 l. Experimental results showed the viability of the prototype, areas for improvement and further possibilities for its optimization. Overall, the study results are relevant for developing latent heat thermal energy storage systems using fin-and-tube heat exchangers in tanks and the feasibility of integrating such systems into DHW systems.

Analysis of thermal characteristics and thermal storage performance of energy-saving phase change thermal storage materials in buildings

In order to explore the thermal characteristics and thermal storage performance analysis of energy-saving phase change heat storage materials in buildings, taking the common exterior wall insulation composite wall structure in southwestern China as an example, the influence of insulation board structure thickness design on the total cost of residential air conditioning energy consumption and insulation board cost is studied, thus clarifying the concept and calculation origin of economic insulation thickness. The experimental results show that by drawing mathematical functions of energy consumption cost, total cost, and insulation material cost in the same 2-D coordinate, it is intuitively demonstrated that the minimization of total cost can be ensured when the insulation thickness is in an economic state, and the specific economic thickness can be accurately calculated through example data. Therefore, specific measures for improving external wall insulation from refined insulation structure design are proposed. It has been proven that the design of the exterior wall insulation layer structure is an important way to improve the overall energy-saving benefits of building exterior wall insulation.

Application of performance dynamic equationin numerical simulation and optimization of waste heat utilization and storage system

In order to improve the current situation of double energy loss in waste heat recovery and utilization, according to the factors such as phase change temperature, thermal conductivity, phase change latent heat, economy, and safety of thermal storage materials, 70# phase change thermal storage balls produced by XX company were selected as phase change thermal storage materials, and differential scanning calorimetry was used to test and analyze them, and the melting point, freezing point and phase change latent heat value of PCM were obtained, provide data reference for simulation in the following text. The shell and tube heat exchanger is selected as the core component of the mobile heat storage system, and its heat storage and release processes are simulated using FLUENT software. The results show that when the heat transfer equipment is charged for 7 hours, almost all of the inner-heat exchangers have completed the heat supply, and only the phase change products at both sides and bottom of the heat supply have ?dead zone?, which is the major effect of heat storage. In order to improve the heat storage and release rate and break the ?bottleneck? of heat storage, the heat transfer was strengthened by changing the diameter size, arrangement, and adding fins of the heat exchange tube. The effects of straight fins, T-shaped fins, as well as the number, height, thickness, and width of fins on the heat storage performance were explored. The results indicate that, adding fins cannot only improve heat transfer efficiency, but also inhibit natural-convection. The heat storage and release time decreases to varying degrees with the increase of fin width, thickness, height, and the number of circumferential fins in a single heat exchange tube.

Efficient solar thermal storage of foamy bamboo charcoal-based composite phase change materials

Solid/liquid phase change materials (PCMs) with high phase change latent heat have been widely used in thermal energy storage in recent years, but their own disadvantages such as poor light-absorbing capacity, easy leakage, and low thermal conductivity seriously limit their practical use in solar thermal storage applications. In this study, a series of biomass-derived porous carbons (CB400, CB550, and CB700) were synthesized by combining the template method with the activation method through high-temperature carbonization using bamboo as raw material and Ca(OH)2 as precursor. 1-octadecanol (OC) is selected as the PCM, and four different composite photothermal phase change thermal storage materials (CB550-85, CB550-80, CB550-75 and CB550-70) were prepared by using CB550 as the photosensitizer and support material. The phase change enthalpy of CB550-85 with 85 wt% OC content was 299.8 J/g, the thermal conductivity of CB550-70 with 70 wt% OC content was 0.71 W·m−1·K−1, which is 184 % higher than that of 1-octadecanol. CB550-OC has good thermal and shape stability, excellent solar energy absorption capacity and photothermal conversion performance. This study provides a new technological pathway for the utilization of biomass. CB550-OC has a broad application prospect in the field of solar thermal utilization and thermal energy storage.

Simulation optimization and energy consumption evaluation on the wood solar drying kiln with heat storage and dehumidification system

The conventional wood drying process has high energy consumption and detrimental environmental impact. While solar energy has found widespread application in material drying, simulation software has been instrumental in optimizing drying processes and curbing energy consumption. Nevertheless, there remains a dearth of simulation and optimization studies specifically focusing on wood drying systems, particularly those incorporating phase-change heat storage devices.This study delves into the wood drying process in one year within a solar drying kiln equipped with a phase-change heat storage and dehumidification system. The investigation scrutinizes the impact of different operating parameters and heat storage devices on the temperature distribution across the entire system. Results indicate that through a new programming method, the simulation of the temperature change of the phase change thermal storage material is realized, and the visualization degree of the system is improved. The average relative error of simulated temperature and measured temperature is 2.29 %, which has a strong consistency. When dehumidifier air flow rate is 1500 m3/h, solar panel angle is 36°, the dehumidifier is turned off when the drying room temperature reaches 55 °C, and the dehumidifier is turned on when the drying room temperature drops below 55 °C, the highest energy efficiency can be achieved. Moreover, through simulation and optimization, the average indoor temperature increased by 24.05 %, and the system energy consumption reduced by about 56.23 %. This is equivalent to a reduction of 3,312.22 kg of CO2 emissions.In essence, this study provides a pathway for enterprises to realize tangible energy savings and emission reductions in the wood drying process, showcasing the potential of integrating solar energy, phase-change heat storage, and dehumidification for enhanced efficiency.

Advancements in Phase Change Materials: A Path to Sustainable Energy Solutions in China

With the rapid development of China, the country's demand for energy has significantly increased. According to the "World Energy Outlook 2020," China's annual average growth rate of primary energy consumption is 1.9%, and it is predicted that China's energy consumption will account for over 20% of global energy consumption by 2050. In the energy budget, 90% is allocated to thermal energy conversion, transmission, and storage. Facing an impending energy crisis, enhancing energy production while minimizing energy loss has become a matter of widespread concern. Phase Change Materials (PCMs), also called phase change energy storage materials, have garnered attention as a novel energy-efficient and environmentally friendly material. PCMs refer to substances that undergo a change in state and provide latent heat without changing their temperature. Phase change thermal storage materials utilize phase transitions during heat exchange processes to store energy by means of these phase changes. Compared to chemical energy storage materials, PCMs offer high thermal efficiency and energy storage density, maintain constant temperature, and are more easily controllable. They hold great potential as a promising material in the field of thermal energy storage and have been widely applied in areas such as solar energy, lithium batteries, building insulation, and medical applications. This article offers a comprehensive overview of the principles and classification of Phase Change Material (PCM), including organic PCM, inorganic PCM, and composite PCM. It discusses their applications in solar thermal energy storage, cooling of photovoltaic panels, building materials, and industrial waste heat recovery. The article also highlights China's research and development efforts in these areas, emphasizing the country's significant contributions to advancing PCM technology.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects.

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Adaptive machine learning based control of multi-temperature, multi-module latent thermal storage ensembles

Phase change material thermal energy storage systems can be used to alleviate disparities in renewable energy supply and demand. Performance of such systems can be enhanced using a cascade of multiple phase change materials but efficiency benefits currently rely on precise optimization of design parameters. Therefore, there is motivation to develop storage technologies which provide greater flexibility for applications with dynamic operating conditions. In this study, a novel system is proposed called a multi-temperature, multi-module ensemble which consists of multiple phase change materials combined in series and parallel configurations. The system is optimized and controlled by an artificial neural network trained using a multi-objective optimization scheme. The performance for the novel system is compared to two baseline systems: a single phase change material system and a cascaded system. Across a wide range of fixed operating conditions, the results show that the ensemble reduces the rate of exergy destruction by 60% compared to the single module system and achieves a 10 °C improvement in performance for matching target outlet temperature compared to the cascaded system. Over a dynamically changing load profile, the results show that the multi-temperature, multi-module ensemble with artificial neural network controller is the preferable design as it achieves the excellent exergy efficiency of a cascaded system while maintaining the flexibility needed to respond to dynamically changing operating conditions. Furthermore, this novel approach widens the potential applications of latent thermal energy storage by providing a means to standardize manufacturing to drive down system cost and allowing the system to adapt to unforeseen design parameters.

A novel method to improve the performance of PCM thermal energy storage units using a small oscillator plate-numerical analysis

Employing a small oscillator plate is proposed as a novel idea to improve the performance of phase change material (PCM) based thermal energy storage unit. This idea could make mixing heat flow toward the PCM solid-liquid interface to hasten the melting and heat transfer rates. Opposite to the vibration of the whole PCM heat sink suggested in the literature, it needs very slight mechanical energy for oscillation. The oscillator plate was installed at three positions for the horizontal and vertical PCM heat sink: i) the middle of the hot plate, ii) the bottom of the hot plate, and iii) the corner of the heat sink. A computational fluid dynamics model has been employed to model the PCM melting process and evaluate the induced mixing heat flow and its effect on natural convection. A new mechanical method using vibration energy accelerates heat flow to improve heat transfer and thermal energy absorption. The results reveal that in the best case with transversal oscillation at the corner of the heat sink, the melting rate and heat transfer rate (Nusselt number) increase by 39 % and 64.2 % compared to no vibration case, respectively. Also, the absorbed heat energy rate (AHR) within the PCM heat sink is elevated from 0.51 to 0.79 (54.9 %), while the oscillator just consumed as small as 438 mJ of mechanical energy, reflecting this mechanical approach's uniqueness.

Phase-Change Material Thermal Energy Storage for the Smart Retrofitting of Existing Buildings

This article presents the use of phase-change material (PCM) thermal storage within the Horizon 2020 HEART project (Holistic Energy and Architectural Retrofit Toolkit), aimed at decarbonising the European building sector through the retrofitting of existing structures into energy-efficient smart buildings. These buildings not only reduce energy consumption, but also incorporate advanced technologies for harnessing green energy, thereby promoting environmental sustainability. The HEART project employs state-of-the-art technologies for electricity production/dispatching and heat generation/storage, managed by a cloud-based platform for the real-time monitoring of parameters and optimising energy utilisation, enabling users to control their environmental comfort. The article provides a detailed examination of one of the project’s demonstration sites in Italy, focusing on various components such as heat pumps, photovoltaic systems (PV), controllers, and particularly emphasising the significance of storage tanks. The study involved the measurement and analysis of three heat storage tanks, each with a total volume of 3000 L. These tanks utilised PCM modules for latent heat storage, significantly enhancing overall heat accumulation. Water served as the heat transfer fluid within the tanks. Through meticulous calculations, the article quantifies the accumulated heat and presents a comparative evaluation between PCM-based storage tanks and conventional water tanks, showcasing the advantages of PCM technology in terms of increased heat retention and efficiency.

Design and preparation of carbon fiber, carbon particle doped C4H10O4 phase change thermal storage materials and performance

C4H10O4 is an environmentally friendly phase change material that can release high phase change enthalpy, but its high super-cooling degree and low thermal conductivity hinder its wide application. This paper adopted C4H10O4 as a phase change material, and the composite phase change material was prepared by melting and blending C4H10O4 with carbon fiber, carbon particles. The results indicate that the composite phase change material with 1.5% filler has better comprehensive properties. Compared with pure C4H10O4, 167% improvement in thermal conductivity, the under-cooling decreases by 42%, and 3% increase in enthalpy of phase change. FT-IR analysis shows that no new substances are produced, and TG analysis shows that the chemical stability is good. Heat storage/release analysis shows that the exothermic time reaches 4 hours, and the exothermic time is 5 °C higher.

N‐doped flexible triazine‐based porous polymer for thermal energy storage

AbstractNitrogen atoms has been widely adopted in preparation of porous organic polymers (POPs). In our study, flexible nitrogen porous organic polymers (FNPOPs) with high nitrogen content are synthesized by using acetic acid both as solvent and catalyst. The materials show moderate Brunauer–Emmett–Teller (BET) surface area and outstanding thermal stabilities (Td: 330°C). FNPOP‐2 is prepared into phase change material (PCM) composites by self‐adsorption method. From differential scanning calorimetry (DSC) analysis, the PCM composites show high encapsulation ratio (55.2 wt%) and latent heat (135.7 J g−1) due to flexible structure and high nitrogen atomic content. Furthermore, the thermal energy storage properties of all PCM composites remained after several thermal cycles. In general, FNPOPs have potential applications in phase change materials adsorption and thermal energy storage.