Liquid Phase Change Material Research Articles

Performance enhancement of latent heat thermal energy storage systems via dynamic melting process of PCM under different control strategies

Latent heat thermal energy storage (LHTES) systems merging high energy densities with near isotherm operations have made a reliable solution to ease the intermittence difficulties of renewable energy and manage periodic energy demands to ensure supply–demand balances on electricity grids. This study experimentally and numerically explores the liquefaction characteristics of phase change material (PCM) in the LHTES tank with the dynamic melting technique, involving the liquid PCM recirculation in the liquefying process to enhance the melting outcomes. Experimental measurements are conducted to investigate the dynamic melting progression for revealing the system effectiveness in terms of the complete melt time and mean power with different control strategies modifying the formations and inlet velocities of recirculating PCM flows. The computational fluid dynamics (CFD) simulations are also conducted to resolve the liquid fraction, vorticity and temperature distributions for offering the insights of the transfiguration of heat transfer and liquefaction behaviors. The photos of ice-water interfaces and measured temperature data in the LHTES tank are thus acquired to verify the computational model generating the CFD predictions. The performance assessments signpost the optimization of dynamic melting arrangements adopting the top to bottom layout with a PCM inlet velocity of 0.22 m/s, achieving the reduction of full melting time by 48.1 % and the enhancement of estimated mean power by 132.6 %, respectively.

A Novel Liquid–Solid Fluidized Bed of Large-Scale Phase-Changing Sphere for Thermal Energy Storage

The storage of thermal energy has been hindered by the low heat-transfer rate of the solid phase of the phase-changing materiel. With water being the heat-transfer fluid as well as the liquid phase in the liquid–solid two-phase system, a novel type of fluidized bed is designed in this study. Numerous hollow spheres are fabricated with phase-changing materiel encapsulated. Adding the solid–liquid phase-change material capsules to the flowing fluid, the capsules are dispersed suspended in the carrier. The large spheres, 25 mm in present experiment, possess the merits of guaranteeing energy-storage density and tolerating internal interface chaotic motion. Both the fluidization status and phase-changing process are recorded by photography combined with image-processing technology. It is found that the large spheres, with density less than water, can be fluidized by the downward flowing fluid. As the flow rate increases, the expansion ratio of the solid phase increases and the regimes of incipient fluidization and bubbling fluidization can be observed. In comparison to the fixed bed, the oscillation of pressure drop across a fluidized bed is more severe, but the averaged value is less than the fixed bed. The melting and solidifying can be accelerated by 22.6% and 50%, respectively, thus proving the superiority of the fluidized bed in improving the heat-transfer rate while charging/discharging the thermal energy. Three types of basic movement of the spheres are shown to contribute to the enhanced phase-changing rate, which are shifting, colliding and rotating.

Experimental study on an improved direct-contact thermal energy storage container

Direct-contact thermal energy storage (TES) systems characterized by high heat density and rapid heat transfer rates have been exploited for the collection of industrial waste or surplus heat for subsequent utilization. In order to address blockage issue at the initial stage of charging process, an improved direct-contact TES container was developed by incorporating a double-pipe structure at both the inlet and outlet. Within the container, a U-shaped tube serving as the inner tube was concentrically positioned from the inlet to the outlet. Erythritol was selected as the phase change material (PCM), while heat transfer oil (HTO) functioned as the heat transfer medium during experimentation. During the charging process, hot HTO initially flowed through the U-shaped tube, establishing an indirect contact with the PCM. The high thermal conductivity of the U-shaped tube wall expedited the formation of a flow channel within the solid PCM. The duration of forming flow channel was 6 to 13 min. In the discharging phase, the liquid PCM was segregated into convection and conduction zones. The indirect-contact TES experiments were also conducted in the same container. Comparison between indirect-contact and direct-contact TES were analysed from the aspects of phase change behavior, charging and discharging time with the identical container structure and theoretical heat capacity. Results indicated that the direct-contact TES container exhibited superior heat storage and release rates, with the direct-contact discharging time being approximately a quarter of the indirect-contact duration. The phase change behavior of the PCM was notably influenced by the movement of HTO within the direct-contact storage container.

Preparation and performance study of modified diatomite based PCM for construction

Phase change energy storage technology provides a good solution to the spatial and temporal mismatch of energy use in buildings, but organic solid–liquid phase change materials suitable for the building sector limit their application due to leakage problems. To mitigate the effects of the above problems, diatomite (DME) is designed as the carrier for encapsulation in this experiment. Adsorption performance of DME is improved through double effects of 600°C high-temperature calcination and hydrochloric acid modification. The binary low eutectic mixture was prepared by co-melting of lauric acid (LA) and octadecyl alcohol (OD) with mass ratio of 70:30. Shape-stabilized composite phase change material (SSCPCM) was prepared by vacuum adsorption method with LA-OD and DME with a mass ratio of 35:65 and the melting temperature and latent heat of SSCPCM are 39.10°C and 54.02 J/g. It was experimentally evaluated that the surface impurities of modified DME under microscopic conditions were removed and LA-OD was uniformly embedded in the micropores of DME, and the prepared SSCPCM was able to maintain a thermal inertia of 39°C with good thermal properties and thermal stability, thus SSCPCM could be used as a building energy-saving material to reduce building energy consumption, in addition to expanding the utilization of inorganic mineral materials.

Bio-based eutectic composite phase change materials with enhanced thermal conductivity and excellent shape stabilization for battery thermal management

Organic phase change materials (PCMs) are commonly used for battery thermal management. Organic petroleum-based PCMs such as paraffin have an adverse effect on environment. Fatty acids as environmentally friendly bio-based PCMs, have enormous potential in sustainable development strategies. Nevertheless, the application of fatty acids in battery thermal management (BTMS) is restricted by the leakage of liquid PCM, poor thermal performance and the improper phase change temperature. We proposed a novel bio-based eutectic composite phase change materials (CPCM) with enhanced thermal conductivity and excellent shape-stabilization, composed of ethylene-vinyl acetate (EVA), Aluminum nitride (AlN), and the eutectic PCM of Lauric acid (LA) and Stearic acid (SA). Significantly, the screened eutectic PCM of LA-SA possesses a suitable phase change temperature(37.03 °C) corresponding to the battery operating temperature, and long-term thermal cycling stability of up to 100 cycles. And the cross-linked structure of EVA effectively encapsulated the eutectic PCM, whose mass only lost below 4% after being heated at 80 °C for 24 h. Simultaneously, the introduction of AlN can greatly improve their heat transfer ability and mechanical properties. LA-SA/EVA/AlN composites with 5 wt% AlN has adequate latent heat of 107.94 J.g−1 and high thermal conductivity of 0.726 W.(m·K)−1 as well as with low flexural strength of 1.72 MPa. Additionally, the proposed CPCM with 5 wt% AlN achieved the maximum temperature of battery below 45 °C during 4C discharging test. It suggested that the CPCM incorporated with AlN is capable effective cooling battery and dissipate energy inside PCM rapidly.

Alkali alkanoate ionic liquids for thermal energy storage at mid-to-high temperature: Synthesis and thermal–physical characterization

Thermal energy storage is gaining much attention and experiencing a renascence in last years. In this sense, storing thermal energy in form of latent heat is of special interest due higher energy density, lower energy losses and higher energy efficiency. To store thermal energy as latent heat the presence of a phase change material (PCM) is needed and its performance the key for its implementation in a thermal energy storage (TES) system and the temperature at which the phase change takes place, low (<150 °C) or high (>150 °C) temperature, will condition the application of a given PCM. In this context, the development of PCM materials to store latent heat at mid-to-high temperature in between 150 °C and 350 °C is of special interest e.g., in the field of concentrated solar power or heat recovery. There are already some solid–liquid phase change materials working in this range of temperature e.g., sugar alcohols, aromatic organic compound, inorganic salts, or blend of inorganic salts but all of them present different drawbacks, such as vapor pressure, degradation, low thermal conductivity, corrosion, etc. In consequence, there is a need to explore new PCM materials in this range of temperature applications. In this context, ionic liquids could play a key role in the development of novel PCMs due to their intrinsic properties. Indeed, ILs are gaining increased attention in the field of thermal energy storage in the last years but mainly in the low temperature range (<150 °C) remaining their application in the mid-to-high temperature range in between 150 °C and 350 °C underestimated. In this work, we prepared six different alkali alkanoate ionic liquids, namely [Na][MeOC2], [K][MeOC2], [Na][MeOC3], [K][MeOC3], [Na][MeOC4] and, [K][MeOC4] by direct reaction between the desired methyl methoxycarboxylate ester with NaOH or KOH. The prepared ionic liquids were structurally characterized, and their thermal–physical properties evaluated. Five of them but [K][MeOC3] showed good enthalpy values ranging from 119 J/g to 197 J/g and four of them [Na][MeOC2], [K][MeOC2], [Na][MeOC4] and, [K][MeOC4] have showed excellent thermal stability above 380 °C. In addition, these four ionic liquids have successfully passed the cyclability test showing no significant enthalpy losses (between 0 % minimum and 7 % maximum) after 50 heating/cooling cycles compiling with the cycling category F of the RAL-GZ 896 (Quality Association PCM). All in all, these prepared ionic liquids surpass sugar alcohols in terms of cyclability and thermal stability and are comparable with the inorganic salts e.g. NaNO3 employed in the studied range of mid-to-high temperature (150–350 °C).

Investigation on Cooling Performance of Composite PCM and Graphite Fin for Battery Thermal Management System of Electric Vehicles

ABSTRACTModern electric vehicle (EV) batteries need phase change materials (PCM) that are capable of efficient battery cooling. In this work, a composite PCM is prepared by mixing Fe3O4 nanoparticles (1 wt.%) in paraffin, and the effects of these nanoparticles on the enthalpy and melting point of PCM are studied. It is found that the Fe3O4 nanoparticle additives reduce the onset of melting from 61.46°C to 57.03°C. The composite PCM is used for the cooling of a battery module of 6 substitute‐18 650 batteries, and the cooling performance is experimentally and numerically investigated. The hybrid battery thermal management system (BTMS) utilizing composite paraffin demonstrates a significant reduction of 11.2°C in lithium‐ion battery (LIB) temperature compared with natural convection cooling at a heat generation rate of 2W. The numerical results in this study are in good agreement with the experimental temperature values, with a modest mean absolute error of 1.35°C detected between experimentally obtained and simulated battery temperature values. In order to deal with the low thermal conductivity of liquid PCM after PCM melting, a numerical investigation is conducted to study the effect of a graphite fin on the battery temperature. The use of a fin in hybrid BTMS considerably reduces the temperature of LIBs and temperature difference in the module. The numerical simulations capture the behavior of the phase change phenomenon, showing the evolution of liquid PCM under constant heating. This work presents the dynamic melting patterns of PCM along the length of LIB with and without a fin, which is useful for the effective design of BTMS.

Nano-enhanced phase change materials for temperature regulation of a LiFePO4 lithium-ion pouch cell using CFD simulation

The temperature control of Lithium-ion (Li-ion) cells plays a crucial role in enabling high current discharge performance. To address this, the present study explores the use of RT35 phase change material (PCM) and single-walled carbon nanotubes (SWCNT) as an additive approach to regulate the temperature of LiFePO4 Li-ion cells. By employing computational fluid dynamics (CFD), incorporating buoyancy force and a turbulent approach, an unsteady problem was simulated to investigate the effects of key parameters such as SWCNT concentration and PCM thickness. Notably, SWCNT addition exhibits a double effect, reducing liquid PCM volume and modifying temperature profiles. The average melting fraction at SOC = 100 % decreased from 100 % to 88 % with increasing PCM thickness from 9δ to 17δ, while it reduced the battery temperature by 3394 K to 331 K. Additionally, the impact of SWCNT volume fraction is most pronounced at 0.02, with similar effects observed at 0.04 and 0.06.

Tube cross-section flatness optimization to enhance the cooling performance of nanofluid-based photovoltaic thermal systems combined with nano-enhanced phase change material

Photovoltaic (PV) systems have emerged as a crucial technology in transitioning to sustainable energy. Despite their growing prominence, PV panels face challenges related to temperature-induced that can lead to reduced energy output. By considering this, the utilization of cooling systems is useful. In the quest to design the active cooling system for PV panels, a key challenge remains in optimizing tube cross-section configurations. In this study, a validated CFD simulation investigates the impact of the tube cross-section flatness (tube flattening) on the cooling performance of the nanofluid-based photovoltaic thermal system combined with nano-enhanced Phase Change Material (PCM). Evaluation parameters for cooling performance are PV surface temperature (T_s), PCM liquid Fraction (LF), tube pressure drop (ΔP), and the PV temperature uniformity (ΔT). Aluminum Oxide (Al2O3) and Silver (Ag) nanoparticles are used in different concentrations (0 %, 1 %, 5 %, 10 %). Also, using the Response Surface Method (RSM), a multi-objective optimization determines the optimal tube flattening percentage for achieving the best cooling performance. The ideal state entails minimizing T_s, maximizing LF, minimizing ΔP, and minimizing ΔT. The findings indicate that increasing tube flattening leads to a decrease in T_s, a decrease in LF, an increase in ΔP, and a reduction in ΔT. Reducing the T_s and ΔT is a favorable effect but increasing the ΔP and reducing the LF is unfavorable to the system's cooling performance. After evaluating different parameters in the optimized scenarios, the most optimal mode is determined when the system uses Ag nanofluid in 10 % concentration, PCM without nanoparticles, and tube with 44 % flattening. In this scenario T_s, LF, ΔP, and ΔT are respectively 54.04 °C, 37.7 %, 117.67 Pa, and 34.74 °C.

Numerical investigations on thermal performance of PCM-based lithium-ion battery thermal management system equipped with advanced honeycomb structures

Electric vehicles (EVs) have a key role in reducing the greenhouse gas emissions contributed by the transportation sector. Lithium-ion (Li-ion) battery which is composed of different cells is the major component in EV, that serves as the power source due to its superior performance. Battery thermal management systems (BTMS) are essential to improve the life and performance and to reduce the risk of fire hazards. In the present study, a single Li-ion cell with Phase Change Material (PCM) and fins is numerically modeled. The finite volume-based simulation is used to predict the heat transfer and flow characteristics of the systems at various operating conditions. Three different unconventional honeycomb-shaped finned PCM systems including baseline model are simulated and compared against the case of PCM without fins and simple honeycomb fin. Cell maximum temperature, temperature difference, and PCM liquid fraction are selected as the parameters for the performance comparison among the different finned configurations. A reduction of 2.77% in maximum cell temperature is obtained in a simple honeycomb structure compared to no fin design at 5C discharge conditions. It is also concluded that the three advanced honeycomb structure shows similar thermal performance but shows better performance than simple honeycomb structure. It is found that 1-Tetradecanol and n-Eicosane PCMs reduce the maximum cell temperature by 13.36 K and 11.81 K, respectively, compared to RT-35 PCM at 5C discharge. The results show that the proposed BTMS exhibits maximum performance at 309.15 K ambient temperature with copper fins and 1-Tetradecanol as PCM.

Enhancement of Thermo-Physical Properties of Form-Stable Nano-Enhanced Phase Change Materials: Advancing Maritime Sustainability

This paper explores the application of novel, form-stable eutectic mixtures in thermal energy storage systems for maritime environments. These advanced materials present a significant leap forward, addressing critical challenges faced by conventional phase change materials (PCMs) in marine environments. The stability, eliminating leakage and fluidity issues encountered with liquid PCMs are ensured by incorporating 2-hydroxypropyl ether cellulose (HPEC) as a gelling agent. Additionally, the thermal properties and heat transfer capacities were significantly enhanced, and eventually, overall system efficiency improved by including nano-graphene platelets (NGPs). Notably, NGPs effectively suppress supercooling, minimizing energy losses and guaranteeing consistent performance at elevated temperatures. Further, the eutectic mixture demonstrates exceptional durability through an accelerated thermal reliability test, guaranteeing optimal performance over a projected seventy-year lifespan. This enhanced thermal performance, and enduring stability combination establishes the form-stable eutectic mixture with NGPs as an up-and-coming solution for diverse maritime applications requiring efficient and reliable thermal energy storage. This research provides a compelling case for implementing form-stable eutectic mixtures with NGPs in maritime thermal energy storage systems. Its superior performance and sustainability offer significant advantages for diverse shipboard and offshore applications, contributing to improved energy efficiency, environmental sustainability, and operational resilience within the maritime sector.

Study on phase change materials integration in concrete: Form-stable PCM and direct addition

As the economy continues to develop, building energy consumption rises, necessitating sustainable solutions. Concrete, a pivotal building material, assumes a vital role in this context. To address the challenge of escalating energy consumption and environmental impact, this study studied the integration of phase change materials (PCMs) into concrete by two methods. Recycled aggregates serve as form-stable mediums for PCM absorption, while direct addition methods incorporate 7.5 % and 15 % free liquid PCM by volume of river sand. Six concrete mixtures underwent comprehensive evaluation encompassing workability, density, water absorption by immersion, compressive strength, flexural strength, chloride ion penetration, freeze-thaw cycling tests, and carbonation. The results reveal a decrease in concrete density and mechanical properties with increasing PCM content. Nevertheless, notable enhancements in chloride ion penetration resistance, reaching up to 18.5 % with free PCM incorporation, and zero carbonation depth were observed. These results underscore the potential of PCM-concrete composites in harmonizing energy efficiency and structural integrity, offering a sustainable alternative to fossil fuel-based air conditioning systems and with great potential from the point of view of the durability of the structures.

Self-healing, adaptive and shape memory polymer-based thermal interface phase change materials via boron ester cross-linking

Addressing the thermal resistance between rough interfaces without applying pressure to the interfacial sandwich has been a challenge. Herein, a thermal interface phase change material (TIPCM) is designed to realize a 3D support skeleton with a dynamic crosslinking network by introducing a boron ester crosslinking backbone into paraffin wax (PW) and ethylene-octene copolymer (EOC), thus enabling the TIPCM to ensure mechanical integrity without leakage even above the melting temperature of EOC. The chemical cross-linking between the organic solid–liquid phase change material (PCM) and the polymer realizes thermally triggered self-healing and adaptive shape memory properties. The phase transition of PW leads to a decrease in the modulus of TIPCM and activates the ester exchange of the dynamic covalent bonding of boron esters, which allows TIPCM to self-heal and self-adapt to a variety of object surfaces. These enabled the TIPCM to fill the interface gaps through small stress deformations, forming an interlocking structure that reduces contact thermal resistance and promotes heat transfer. The obtained TIPCM achieves excellent chip thermal management performance, cooling the analog CPU temperature by 67 °C at 5 V. In conclusion, this study provides a potential strategy for redesigning TIPCMs with high latent heat and special physical properties for thermal management.

Bis(dialkylammonium)-based hybrid organic–inorganic ionic materials as solid–solid phase change materials

The application of phase change materials (PCMs) in thermal energy storage (TES) systems is often restricted by challenges such as volume expansion, phase segregation, stability issues and potential leakage, particularly prominent in conventional solid–liquid PCMs. In response to these limitations, solid–solid PCMs have emerged as a promising alternative, garnering increasing attention. While both organic and inorganic solid–solid PCMs have been extensively studied, hybrid organic/inorganic materials represent a distinct class of solid–solid PCMs that have recently garnered significant interest due to their inherent properties such as high thermal stability, non-flammability or long cycle life. Organic-inorganic layered perovskites are emerging as potential good solid–solid PCMs as they present energetic solid–solid transitions and high thermal stability. In this work we propose the synthesis and thorough thermal characterization and cyclability of a series of new hybrid organic–inorganic ionic materials based on n-dialkylamines of different lengths (C8, C10, C12 and C18) with general formula of the type 2[(CnH2n+1)2NH2][MX4], using three different tetrachlorometalates anions ([FeCl4]2-, [MnCl4]2- and [CuCl4]2-). Among the new ionic materials prepared six of them have shown solid–solid transition enthalpies higher than 100 J/g. In particular, the 3 bearing the secondary n-dioctadecylamines as cations have shown unprecedent solid–solid transitions enthalpies ca. 90 °C, for this kind of ionic materials of 167.5 J/g, 157.7 J/g and 146.9 J/g for [DODA]2[MnCl4], [DODA]2[CuCl4] and [DODA]2[FeCl4] respectively. In addition, the latter ionic materials have undergone reliability tests showing excellent performance up to 500 heating/cooling cycles.

Performance assessment of single-sided operation in a high-temperature latent heat storage system under fault conditions during charging and discharging

As the high-temperature latent heat storage (LHS) market continues to expand, ensuring its safe and stable operation is paramount for facilitating its rapid development. In specific operational scenarios and instances of failures, large-scale integrated LHS systems may operate with either single or partial sets of heat exchange tubes. However, a notable research gap exists in the comprehensive exploration of the impact of partial operational conditions on the thermal performance of LHS systems. Consequently, this study conducted experiments involving both- and single-sided charging and discharging using a cylindrical high-temperature LHS system equipped with two sets of heat exchange tubes. To comprehend the ramifications of single-sided operation on temperature distribution across both active and inactive sides, as well as its influence on charging/discharging power and accumulated stored/released energy on the active side. The analysis of phase change material (PCM) temperature distribution revealed that single-sided charging significantly influenced the inactive side, while single-sided discharging exhibited a comparatively minor impact on the inactive side. As PCM melted during charging, temperature disparities diminished due to natural convection, while non-uniform temperature persisted in unmelted PCM. Examination of the PCM liquidus indicated that the metal heat exchange tube enhanced heat transfer on the inactive side, resulting in substantial PCM melting during charging. However, the heat transfer effect of metal heat exchange tubes during discharging was insignificant, leading to a considerable amount of liquid PCM on the inactive side after discharging. The total heat storage for both-sided charging was 1002.71 MJ, whereas, for single-sided charging using two tubes, it was 1074.42 MJ and 1000.60 MJ, respectively. Correspondingly, during discharging, the average powers were 682.74 MJ, 543.62 MJ, and 538.11 MJ, respectively. The cycle efficiency for the both-sided operation was 68.09 %, while those for single-sided operations of two tubes were 50.6 % and 53.78 %, respectively. The reduced cycle efficiencies of single-sided operations were attributed to prolonged charging and discharging durations and the presence of more liquid PCM on the inactive side after discharging.

Multi-Faceted Analysis of Phase-Change Composite Intended for Autonomous Buildings.

This paper presents the long-term, holistic results of research into an innovative heat accumulator based on an organic phase-change material in the form of a mixture of aliphatic alkanes, molecular silica sieves, carbon recyclate and epoxy and cement matrices. The research included chemical testing of vacuum soaking of molecular silica sieves with a liquid phase-change material. The results proved an improvement in the heat storage efficiency of the heat accumulators due to the addition of carbon recyclate by 28%, while increasing the heat storage time by 134 min, and a reduction in PCM leakage due to the use of molecular silica sieves. In addition to its cognitive scientific value, another research objective of the work achieved was to obtain response functions in the form of approximating polynomials. They provide a useful, validated and verified tool to predict the physical and chemical characteristics of heat accumulators with different contents of individual components. As part of the ongoing research, technical problems related to leak-proofing assurance and matrix selection for organic phase-change materials were also solved. The solution presented is in line with the issues of efficient use of renewable energy, low-carbon and energy-efficient circular economy.

Boosting thermal energy transport across the interface between phase change materials and metals via self-assembled monolayers

Thermal energy storage using phase change materials (PCMs) has great potential to reduce the weather dependency of sustainable energy sources. However, the low thermal conductivity of most PCMs is a long-standing bottleneck for large-scale practical applications. In modifications to increase the thermal conductivity of PCMs, the interfacial thermal resistance (ITR) between PCMs and discrete additives or porous networks reduces the effective thermal energy transport. In this work, we investigated the ITR between a metal (gold) and a polyol solid–liquid PCM (erythritol) at various temperatures including temperatures below the melting point (300 and 350 K), near the melting point (390, 400, 410 K, etc) and above the melting point (450 and 500 K) adopting non-equilibrium molecular dynamics. Since the gold-erythritol interfacial thermal conductance (ITC) is low regardless of whether erythritol is melted or not (<40 MW m−2 K−1), self-assembled monolayers (SAMs) were used to boost the interfacial thermal energy transport. The SAM with carboxyl groups was found to increase the ITC most (by a factor of 7–9). As the temperature increases, the ITC significantly increases (by ∼50 MW m−2 K−1) below the melting point but decreases little above the melting point. Further analysis revealed that the most obvious influencing factor is the interfacial binding energy. This work could build on existing composite PCM solutions to further improve heat transfer efficiency of energy storage applications in both liquid and solid states.

A self‐regulated phototheranostic nanosystem with single wavelength‐triggered energy switching and oxygen supply for multimodal synergistic therapy of bacterial biofilm infections

AbstractThe exploration of antibiotic‐independent phototherapy strategies for the treatment of bacterial biofilm infections has gained significant attention. However, efficient eradication of bacterial biofilms remains a challenge. Herein, a self‐regulated phototheranostic nanosystem with single wavelength‐triggered photothermal therapy (PTT)/photodynamic therapy (PDT) transformation and oxygen supply for multimodal synergistic therapy of bacterial biofilm infections is presented. This approach combines a eutectic mixture of natural phase‐change materials (PCMs) and an aggregation‐induced emission (AIE) phototheranostic agent TPA‐ICN to form colloidally stable nanopartcicles (i.e. AIE@PCM NPs). The reversible solid−liquid phase transition of PCMs facilitates the adaptive regulation of the aggregation states of TPA‐ICN, enabling a switch between the energy dissipation pathways for enhanced PDT in solid PCMs or enhanced PTT in liquid PCMs. Additionally, oxygen‐carrying thermoresponsive nanoparticles are also introduced to alleviate the hypoxic microenvironment of biofilms by releasing oxygen upon heating by AIE@PCM NPs with enhanced PTT. The nanosystem exhibits outstanding therapeutic efficacy against bacterial biofilms both in vitro and in vivo, with an antibacterial efficiency of 99.99%. This study utilizes a self‐regulated theranostic nanoplatform with adaptive PTT/PDT transformation via the phase transition of PCMs and heat‐triggered oxygen release, holding great promise in the safe and efficient treatment of bacterial biofilm infections.

Numerical modelling of thermal hysteresis in melting and solidification of phase change materials

This research focuses on exploring the impact of thermal hysteresis effects on the performance of Phase Change Materials (PCMs) used in thermal storage or buffering applications. Computational Fluid Dynamics modeling in ANSYS Fluent is employed to investigate thermal hysteresis phenomena during solid-liquid phase change. The traditional enthalpy-porosity method is extended by introducing an alternative relationship between the liquid fraction and PCM temperature, implemented in Fluent through User Defined Functions. The study demonstrates the developed model by simulating a rectangular PCM enclosure with a heated wall featuring a time-dependent temperature boundary condition. Considering convective heat transfer, a comparison is made between the newly developed hysteresis model and the default solidification-melting model of ANSYS Fluent. The new model facilitates numerical analysis of thermal hysteresis during partial and complete melting and solidification processes, enabling the study of hysteresis effects on the part-load operation of PCM systems.

Natural convection and field synergy principle analysis of the influence of fins redistribution on the performance of a latent heat storage unit in a successive charge and discharge

The present study focuses on analyzing the impact of enhancing the heat exchanges on the shell side by surface extension on the kinetics of melting/solidification in a latent heat thermal energy storage (LHTES) unit. Particular attention is paid to the influence of fins redistribution on the performance of the LHTES unit, natural convection, and Phase Change Material (PCM) melting/solidification kinetics. The particularity of this study lies in the improvement of the LHTES unit performances in a successive charging-discharging operation by only redistributing the fins while keeping the same total heat transfer surface, PCM volume, and compactness. The first part of the study consists of evaluating the impact of fin redistribution for the same total heat transfer surface on the LHTES unit performance. Attention was paid to the fully charging and discharging times and the heat duty absorbed or released during the melting or solidification process. For this purpose, 4 configurations of LHTES units having 4 and 8 radial fins with the same total transfer surface were analyzed, with the aim of ensuring a maximum performance on charging process. In a second part, an improved configuration was proposed in order to minimize the successive charging and discharging time for a cyclic operation of the LHTES unit. The coordination factor derived from the field synergy principle, PCM liquid fraction, the heat duty exchanged, phase change kinetics, and liquid PCM velocity were used as performance key factors. They were used to analyze and compare the different configurations in order to find the best configuration for a successive charging-discharging operation. The selected improved configuration has been found to enhance both the charging and discharging processes. It leads to the reduction of the successive charging-discharging overall duration by 10 % to 47 % compared to the other configurations investigated with the same heat transfer surface. The enhanced LHTES unit developed in the present study is intended to improve the thermal comfort of buildings by valorizing and storing renewable and waste energies.