Solid Phase Change Material Research Articles

High energy storage density titanium nitride-pentaerythritol solid–solid composite phase change materials for light-thermal-electric conversion

To achieve the goal of carbon neutrality, efficient use of solar energy is feasible and imminent. The selection of phase change materials (PCMs) as energy storage media is an effective way to achieve practical utilization to solve the uncontinuity and unstability of solar energy. Solid-solid PCMs (SS-PCMs) have attracted attention due to their advantages of stable shape, no phase separation, and no corrosion. In this paper, cheap raw material pentaerythritol (PE) is selected as the energy storage medium. Titanium nitride (TiN) with localized surface plasmon resonance is used as light absorber and thermal conductive filler. The results show that phase transition enthalpy of 0.2 wt% TiN-composite phase change materials (CPCMs) is still as high as 287.8 J/g, which maintains 96.06 % energy storage density of PE. In addition, thermal conductivity of 0.2 wt% TiN-CPCMs is increased by 109.48 %, and photo-thermal conversion efficiency is as high as 90.66 %. Simultaneously, a thermoelectric harvester integrating thermoelectric generator (TEG) with SS-PCMs is proposed. The average maximum power of the TiN-CPCMs-TEG system is 59.26 % higher than that of the PE-TEG system. Total energy of system is also increased by 58.99 %, which lays the foundation for the application of mid-temperature heat collection engineering.

Effect of Different Soft Segment Contents on the Energy Storage Capacity and Photo-Thermal Performance of Polyurethane-Based/Graphene Oxide Composite Solid-Solid Phase Change Materials.

A series of polyurethane/graphene oxide (PU/GO) solid-solid phase change materials (SSPCMs) were synthesized by using GO as a light-absorbing filler and polyethylene glycol (PEG) as a phase change matrix. The effects of PEG content on the energy storage capacity, thermal stability and photo-thermal conversion performance of PU were investigated. The results show that the form-stability of PU/GO decreases while the phase change enthalpy and photo-thermal conversion efficiency of PU/GO increases with the increasing PEG content. The introduction of a very low content of GO can maintain comparable energy storage density and greatly improve light absorption by reasonably modulating the soft segment contents. The PU/GO composite with 92 wt% PEG has a phase change enthalpy of 138.12 J/g and a high photo-thermal conversion efficiency (87.6%). The composite solid-solid PCMs have great potential for effective energy storage and solar energy utilization.

Structure optimization of tree-shaped fins for improving the thermodynamic performance in latent heat storage

Tree-shaped fins have widely been approved to enhance heat transfer performance in the field of latent heat storage. However, the structure of tree-shaped fins should be optimized to amplify its performance advantages, which are rarely addressed in previous studies. An unsteady numerical model is established to study the thermal performance advantages of tree-shaped fins. A method by coupling a genetic algorithm and a CFD simulation is utilized to optimize the structure of the tree-shaped fins based on the melting and solidification processes of a Phase Change Material (PCM). The results indicate that structural optimization is important and necessary for the application of tree-shaped fins especially in latent heat storage systems. Compared with the radial fins, the optimized tree-shaped fins reduce the phase transition time by 38.83%in the melting process and by 32.71% in the solidification process. Also, the optimized tree-shaped fins increase the average heat transfer rate and average heat transfer coefficient by 65.70% and 65.54% in the melting process while 51.51% and 51.00% respectively in the solidification process. The optimization results also shows that the optimized tree-shaped fins based on different heat transfer processes all show the characteristics of gradually increasing branch length and decreasing branch angle, that is, L0<L1<L2, β1>β2. Interestingly, the optimized structure of the tree-shaped fins based on PCM melting differs from that of the PCM solidification process because of the difference in heat transfer mechanisms. This study provides a method for the structural optimization of tree-shaped fins and increases the application prospect of tree-shaped fins in the field of latent heat storage.

Output power leveling of on-chip thermoelectric generator using a solid–solid phase change material

Energy harvesting technology using thermoelectric generators (TEG) is a promising solution to environmental energy problems. Moreover, an on-chip TEG, which can improve the net power consumption of electronic devices, is attracting attention. However, thermal or electrical control is required to stabilize the TEG output for unsteady heat sources, such as electronic chips. In this study, we focused on output power-stabilization technology by thermal control using phase-change materials (PCM). A vanadium dioxide (VO2) sintered body, a solid–solid PCM, was used as the PCM and compared to paraffin, a typical solid–liquid PCM. The power generation performance of the TEG with these PCMs mounted on a thin heat-generating chip was evaluated. The TEG with VO2 exhibited higher power generation and output power leveling performance than paraffin, mainly because it has a higher thermal conductivity than paraffin. Furthermore, in the TEG with VO2 case, the maximum temperature of the heat-generating chip was 14.4 °C lower than that without the PCM, indicating that the on-chip TEG with VO2 could level the temperature of the electronic chip while generating electricity.

Melting processes of phase change materials in a horizontally placed rectangular cavity

This paper revisits the melting process of phase change materials (PCMs) enclosed in a horizontally placed rectangular cavity, with isothermal and adiabatic conditions subjected to the vertical and horizontal walls, respectively. First, numerical simulations based on an improved lattice Boltzmann method are conducted to illustrate and to inform the theoretical modelling. It is shown that, compared with the traditional two-stage conduction–convection melting description, it is more reasonable to include a third stage in terms of the heat transfer behaviour. During the third stage, the remnant solid PCM is located in the corner formed by the cold and bottom walls of the cavity, and an increasing part of the input energy will be transferred directly out of the cavity without compensating for the melting latent heat, thus inducing a continuously decreasing melting rate until the end of the melting process. Then theoretical predictions are derived piecewise for the melted liquid fraction during the entire melting process, and the corresponding transitions between two successive stages are also discussed. The results are validated successfully via the available experimental and numerical data in the literature, and could guide the design and operation of latent heat storage systems.

Enhancement of thermal energy storage in a phase change material heat exchanger having elliptical and circular tubes with & without fins

The objective of this study is to examine the thermal performance of a heat exchanger having multiple elliptical tubes and a phase change material (PCM) filled in the cylindrical shell of a heat exchanger. To improve the heat transmission from elliptical tubes to PCM, two and four fins are incorporated on the circumference of the elliptical tubes. The use of elliptical tubes with fins in the enhancement of heat transfer is an innovative approach in thermal performance studies of heat storage systems. The geometry of heat exchangers having elliptical tubes without fin, with two fins, and four fins are compared with the geometry of heat exchanger with circular tubes having no fin, two fins, and four fins respectively. The current investigation is carried out with the use of a 2D CFD model using a physical enthalpy-porosity technique to explore the phase transition of the solid PCM. The effect of integrating a number of fins on heat transfer has also been explored, and outcomes of elliptical and circular tube geometries in terms of PCM mean temperature and liquid percentage at two different temperatures of 50 °C and 60 °C have been compared. Results show, that PCM melting time is being reduced to 550 s in PCM heat exchanger geometry having elliptical tubes with four fins compared to 585 s for the same heat exchanger with two fins and 665 s for heat exchanger without fin at 50 °C resulting 12 % & 17 % reduction in melting time by applying two and four fins respectively. Whereas PCM melting time is 515 s in PCM heat exchanger geometry having circular tubes with four fins compared to 560 s for heat exchanger with two fins and 655 s for heat exchanger without fin resulting 14.5 % and 21 % reduction in melting time by applying two and four fins respectively. It has been concluded that adding fins on the circumference of elliptical and circular tubes enhances the heat transmission and reduces melting time as well as more heat can be transferred by circular tube geometry compared to elliptical tube heat exchanger geometries. The findings of the investigations are validated with the available simulation data and show good agreement, suggesting a 3.8 percent deviation.

Energy and daylighting performance of a building containing an innovative glazing window with solid-solid phase change material and silica aerogel integration

Responding to the appeal of realizing carbon neutrality in response to the field of buildings, minimizing the energy demand and improving the energy management of the buildings by the development of energy saving technologies related to transparent components are considered as promising means. In this paper, an innovative glazing window integrated with solid-solid phase change material and silica aerogel is proposed, and a parametric study is conducted with a focus on evaluating the implementation potential of our innovative window in the severe cold region of China. Firstly, to address the issue that the transparent media such as phase change material and silica aerogel cannot be directly incorporated into glazing elements of EnergyPlus software, an equivalent model of the innovative window compatible with the modeling capabilities of EnergyPlus is developed. Then, the contributions of the thermal and optical properties of phase change material to energy savings are quantitively distinguished via sensitivity analysis. Additionally, the energy performance of the building containing the innovative window under different thermal and optical properties of phase change material is numerically investigated aiming to provide guidance to the design strategies of phase change material parameters adopted in the innovative window. Finally, in light of counterbalancing the need for energy saving and daylighting performance indoors, the optimal silica aerogel thickness employed in the innovative window is studied. The results show that the phase change material properties of melting temperature, latent heat, absorption coefficient, and refractive index are of remarkable relevance to the energy performance of the buildings in conditions of 10 % property variations. In comparison to the 4 mm single glazing window installed, the maximum energy saving of the building containing the innovative window can be realized by 18.22 % within the realistic range of phase change material properties. Moreover, for the sake of providing the maximum possibility of energy saving under the premise of meeting the daylighting design standards in China, the thickness of silica aerogel is recommended to be selected as 10 mm in the innovative window.

Influence of low-temperature polyurethane solid-solid PCMs particles on the pavement performance of asphalt mixtures

In order to slow down the cooling rate of the mixture and reduce the low temperature cracking of asphalt pavement in large temperature difference areas, low-temperature polyurethane solid-solid phase change materials (LPSPCMs) were prepared by prepolymer method. The researches show that LPSPCMs have good phase change heat storage performance and thermal stability performance, and can be applied to hot mix asphalt mixtures. The LPSPCMs particles were incorporated into the asphalt mixture, and the road performance of the LPSPCMs particulate asphalt mixture was tested and analyzed and found: as LPSPCMs particles change the abrasion resistance and embedded effect between asphalt mixes, with the increase of LPSPCMs particles, the high-temperature performance of asphalt mixes first increased and then decreased. The water stability of asphalt mixtures gradually decreases with the increase of LPSPCMs particles content because relative to limestone aggregates, LPSPCMs particles adhere poorly to asphalt. The thermal stress restrained specimen test (TSRST) showed that the cracking temperature of the asphalt mixture gradually decreased with the increase of LPSPCMs particles contents because of the phase change temperature control effect of LPSPCMs particles indicated that LPSPCMs particles improve the low-temperature performance of asphalt mixtures. On this basis, the correlation between the evaluation index of the phase change temperature adjustment effect and the improvement effect of the low-temperature performance of the mixture was established.

A Smart Photothermal Nanosystem with an Intrinsic Temperature-Control Mechanism for Thermostatic Treatment of Bacterial Infections.

Photothermal therapy (PTT) has attracted extensive attention in disease treatments. However, conventional photothermal systems do not possess a temperature-control mechanism, which poses a serious risk to healthy tissues and/or organs due to inevitable thermal damage. Herein, a smart photothermal nanosystem with an intrinsic temperature-control mechanism for thermostatic treatment of bacterial infections is reported. The smart photothermal nanosystem is constructed by loading a thermochromic material into a hollow-structured silica nanocarrier, in which the thermochromic material is composed of naturally occurring phase-change materials (PCMs), a proton-responsive spirolactone, and a proton source. The resulting nanosystem shows strong near-infrared (NIR) absorption and efficient photothermal conversion in solid PCMs but becomes NIR-transparent when PCMs are melted upon NIR irradiation. Such an attractive feature can precisely regulate the photothermal equilibrium temperature to the melting point of PCMs, regardless of the variation in external experimental parameters. In contrast to conventional PTT with severe thermal damage, the reported smart photothermal nanosystem provides an internal protection mechanism on healthy tissues and/or organs, which remarkably accelerates the recovery of bacteria-infected wounds. The smart photothermal nanosystem is a versatile PTT platform, holding great promise in the safe and efficient treatment of bacterial infections and multimodality synergistic therapy.

Experimental investigation of air-based active-passive system for cooling application in buildings

• The cooling effect of the interior PCM wall and ceiling was experimentally studied. • The PCM plates provided a cooling effect at constant and transient daily cycles. • Complete solidification of PCM is achieved at an air gap flow rate of 400 m 3 /h. • Complete solidification of PCM is achieved at an inlet temperature of 16°C. • The system is adequate for Mediterranean summer conditions and not for summer heatwaves. Due to the consequences of global warming, cooling of lightweight buildings is one of the main future challenges. The study presents an active-passive system (APS) with phase change material (PCM) plates integrated into the internal wall and ceiling substructure which during the day cools the indoor space passively. During the night, the air gap is ventilated actively to improve the PCM solidification process. The APS was experimentally tested in two identical test cells, PCM modified (cell-A) and reference cell (cell-B). Two different types of scenarios were investigated. First type tested the cooling effect of the PCM during the daytime cycle, determined by the temperature difference between the cell-B and cell-A. The same amount of heat was simultaneously added to both cells which was navigated by the setpoint air temperature in the cell-B (26°C, 30°C, 30°C with background ventilation, 35°C, TRY Ljubljana, TRY Rome and heatwave Ljubljana). Second type tested the PCM solidification time during the nighttime cycle (inlet air temperature ( T ai ) of 15°C, 16°C, and 17°C). The results showed that PCM plates provided the largest cooling effect at in 35°C-scenario. The complete solidification of PCM was achieved at T ai of 16°C. The system is adequate for Mediterranean summer conditions.

Multi-objective optimization of a phase change material-based shell-and-tube heat exchanger for cold thermal energy storage: experiments and numerical modeling

• PCM-based cold thermal energy storage is numerically and experimentally analysed. • The experimental outcomes show room for optimization in the PCM discharging phase. • Charging/discharging time and heat transfer area/melting difference are optimized. • Multi-objective genetic algorithm allows to exploit up to 72% PCM latent heat. • This optimal solution implies a 69% increase in minimum heat transfer area. In recent years, significantly increasing demand for air conditioning systems has led to higher power consumption during on-peak hours. If optimized, latent heat thermal storage for chiller systems – thanks to its high storage density and compact structure – can reduce installed cooling capacity and allow the chiller to operate more continuously. Starting from the existing design, this work presents a multi-objective optimization framework to improve the storage performance of a phase change material (PCM)-based shell-and-tube heat exchanger. To address this issue – based on experimental data – a 2D axial-symmetric transient numerical model is first developed. To investigate the overall performance of the system – depending on geometrical features and chiller operating conditions – a parametric analysis is performed. Then, by coupling the numerical model developed in COMSOL Multiphysics environment with MATLAB, the system performance is optimized through the genetic algorithm (GA), i.e., minimizing PCM charging/discharging time, by varying the chiller operating conditions. The optimal solution is achieved under a water mass flow rate of 0.095 kg/s, implying a reduction in the inlet temperature of 1.25 °C with respect to the reference case. Results are further validated through experimental tests and discussed looking at the PCM melting and solidification processes for better exploitation of this storage technique. As the main outcome of the model optimization on user’s demand, the maximum amount of PCM that can be fully exploited is equal to 40 % of the initial one. Therefore, based on this value, a further optimization step by GA is performed to define the minimum heat transfer area, resulting in a shell diameter reduction of 12 cm to exploit 72 % of the PCM potential.

Light-Responsive Solid-Solid Phase Change Materials for Photon and Thermal Energy Storage.

We report a series of adamantane-functionalized azobenzenes that store photon and thermal energy via reversible photoisomerization in the solid state for molecular solar thermal (MOST) energy storage. The adamantane unit serves as a 3D molecular separator that enables the spatial separation of azobenzene groups and results in their facile switching even in the crystalline phase. Upon isomerization, the phase transition from crystalline to amorphous solid occurs and contributes to additional energy storage. The exclusively solid-state MOST compounds with solid-solid phase transition overcome a major challenge of solid-liquid phase transition materials that require encapsulation for practical applications.

Enhancement of the part-load thermal charging performance of a latent heat thermal energy storage unit with variable length fins at effective locations

Rapid thermal charging of the latent heat thermal energy storage unit (LHTESU) based on phase change material (PCM) is restricted by the material's low thermal conductivity. The numerical investigation for the thermal charging process of LHTESU considering a rectangular enclosure under the high-temperature gradient is presented. Constant and variable length fins with different locations are considered inside the enclosure with one vertical sidewall at a constant temperature. For various part-load thermal charging operations, a two-dimensional transient model with enthalpy-porosity technique is employed with natural convection current to evaluate the thermal charging rate and melting characteristics. The simulation outcomes manifest that convective heat transfer significantly impacts PCM melting in the case of variable length fins. Uniform distribution of Variable length fins with the most extended fin near the base of the container has 20% superior thermal charging performance than of constant length in full load thermal charging operations. However, in half-load thermal charging operations, constant-length fins with uniform distribution in the enclosure reduce the maximum thermal charging time and the average temperature of the PCM domain. Further, the result indicates that Cases VF-2 (most extended fins placed significantly close to the bottom and remaining fins inserted with equal gap) and VF-3 (fins insertion only in the lower half of the container) minimized the sensible heating of liquid PCM by directing the heat towards solid PCM. Case VF-3 demonstrated the most robust thermal charging performance by taking the least melting time in all cases for a 90% thermal charging of the system.

Thermal storage properties of polyurethane solid-solid phase-change material with low phase-change temperature and its effects on performance of asphalt binders

Preparing phase change materials (PCMs) with appropriate phase-change temperatures is of great significance in preventing the low-temperature disease in pavements. In this study, several polyurethane solid-solid PCM (PUPCM) samples were prepared via a two-step condensation reaction of polyethylene glycol, polytetramethylene ether glycol, 4,4′-diphenyl methane diisocyanate, and 4,4′-methylenebis-(2-chloroaniline). Considering the phase-change temperature and thermal stability, a PUPCM sample with a suitable molar ratio was used for the asphalt modification. The prepared materials were characterised by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, three indices of asphalt and viscosity tests, rotational viscometer tests, and other techniques. PUPCM samples with different soft and hard segment ratios exhibit different phase-change temperatures and enthalpies, and their physical, chemical, and phase-change properties are stable. When the ratio of soft and hard segments is 8:2 (PU-14), the freezing and melting temperatures were −2.7 °C and 12.9 °C, and the enthalpy was 46.8 J/g. The PUPCM modification of asphalt only involves physical miscibility. Adding PUPCM negligibly affects the high- and low-temperature performances of the modified asphalt binder. The viscosity of the PUPCM-modified asphalt binder is slightly higher than that of the original asphalt binder, and the storage stability of the modified asphalt binder is satisfactory. The addition of PUPCM improves the anti-ageing performance of asphalt, and the improvement becomes significant with increasing PUPCM content. Moreover, the phase-change energy storage properties of PUPCM in asphalt were found to be satisfactory. Hence, PUPCMs can potentially be used for asphalt modification to further improve the low-temperature performance of pavements.

Effect of processing on microstructure and mechanical properties of pentaglycerine based solid-solid phase change materials

The present work addresses the lack of reported information about the mechanical properties of solid-solid PCMs, and how these are affected by their processing, considering that they usually incorporate fillers to increase their thermal conductivity. To this end, this work analyzes pentaglycerine (PG) based composites, which are of great interest in TES intended for 80 °C. These composites are also doped with various contents of expanded graphite (EG) with two different particle sizes. With these combinations, the effect of two typical processing methods, pressing and casting, on the microstructure of the composites is evaluated. Furthermore, the mechanical behavior of these composites in both crystal and plastic phases, as well as their thermal expansion during the transition process, is also reported in the current study. Besides demonstrating the important role that processing plays in these properties in PG/EG-based composites, it has been found that the use of EG is also beneficial for mitigating the permanent deformations experienced by these composites during thermal cycling. Finally, the exposed results give the first evidence of the interesting effect these processing methods have on the thermal properties of the composites.

Applications of phase change materials in smart drug delivery for cancer treatment.

Phase change materials (PCMs) are materials that are stimulated by the external enthalpy change (temperature) to realize solid-liquid and liquid-solid phase transformation. Due to temperature sensitivity, friendly modification, and low toxicity, PCMs have been widely used in smart drug delivery. More often than not, the drug was encapsulated in a solid PCMs matrix, a thermally responsive material. After the trigger implementation, PCMs change into a solid-liquid phase, and the loading drug is released accordingly. Therefore, PCMs can achieve precise release control with different temperature adjustments, which is especially important for small molecular drugs with severe side effects. The combination of drug therapy and hyperthermia through PCMs can achieve more accurate and effective treatment of tumor target areas. This study briefly summarizes the latest developments on PCMs as smart gate-keepers for anti-tumor applications in light of PCMs becoming a research hot spot in the nanomedicine sector in recent years.

Emerging Solid-to-Solid Phase-Change Materials for Thermal-Energy Harvesting, Storage, and Utilization.

Phase-change materials (PCMs) offer tremendous potential to store thermal energy during reversible phase transitions for state-of-the-art applications. The practicality of these materials is adversely restricted by volume expansion, phase segregation, and leakage problems associated with conventional solid-liquid PCMs. Solid-solid PCMs, as promising alternatives to solid-liquid PCMs, are gaining much attention toward practical thermal-energy storage (TES) owing to their inimitable advantages such as solid-state processing, negligible volume change during phase transition, no contamination, and long cyclic life. Herein, the aim is to provide a holistic analysis of solid-solid PCMs suitable for thermal-energy harvesting, storage, and utilization. The developing strategies of solid-solid PCMs are presented and then the structure-property relationship is discussed, followed by potential applications. Finally, an outlook discussion with momentous challenges and future directions is presented. Hopefully, this review will provide a guideline to the scientific community to develop high-performance solid-solid PCMs for advanced TES applications.

Solidification performance analysis of bionic spider web vertical latent heat system based on response surface method optimization

The vertical sleeve phase change heat storage unit filled with RT55 is taken as the research object. Aiming at the low thermal conductivity of phase change materials, a vertical latent heat storage sleeve (LHTES) with spider web structure optimized by response surface method is proposed to improve the solidification performance of latent heat storage system, and the phase change heat transfer process is simulated by numerical simulation method. The enhanced heat transfer characteristics of phase change material (PCM) unit in casing with different spider web fin sizes are studied. The results show that reasonably changing the fin spacing, main fin thickness and branch fin thickness of spider web shape fins can reduce PCM solidification time and evaluation temperature correspondingly, and increase the heat dissipation of LHTES. Combining PCM solidification time, heat release of LHTES and PCM average temperature as evaluation indexes, the solidification heat performance of LHTES is comprehensively analyzed, and the geometric parameters of fins are optimized by response surface method (RSM), and the optimal solution is obtained as follows: the spider web fin spacing (H) is 30.00 mm, the spider web main fin thickness (m) is 3.91 mm, and the spider web branch fin thickness (L) is 2.64 mm. Finally, the economic analysis finds that the spider web structure LHTES has high economic efficiency.

Numerical Modeling of the Effect of Nanoparticle Concentration on Solidification Rate of Phase Change Materials in Thermal Energy Storage Systems

Considering the growing rate of energy consumption as well as significant enhancement in worldwide energy demand, it is necessary to improve the performance of energy storage, i.e., melting and solidification rates in thermal energy storage systems. Phase change materials (PCMs) with high latent heats of fusion and proper melting points can be used as alternatives in energy storage systems. The most serious shortcoming in the existing PCMs is low thermal conductivity which confines the rate of energy storage. This issue can be tackled using nanoparticles with much higher thermal conductivities conjugated with the existing PCMs. In this research, effect of nanoparticle addition into PCMs along with copper fins inside both un-finned and finned triplex-tube thermal energy storage systems on PCM solidification rate was investigated numerically. Furthermore, various parameters including nanoparticle type (Al2O3, Ag, CuO, and Cu), concentration (1 and 3%) and diameter (20 and 80 nm) were analyzed for augmentation of the solidification time. The obtained results revealed that the simultaneous presence of fins and 3% of nano-Al2O3 with a 20 nm average diameter can save solidification time up to 67.11%.

Graphene oxide/polyurethane‐based composite solid–solid phase change materials with enhanced energy storage capacity and photothermal performance

Graphene oxide/polyurethane‐based composite solid–solid phase change materials with enhanced energy storage capacity and photothermal performance