Phase Change Thermal Energy Storage Research Articles

Numerical Investigation of Heat Transfer Characteristics of Trapezoidal Fin Phase Change Thermal Energy Storage Unit

Abstract: In order to enhance the heat transfer performance of a phase change thermal energy storage unit, the effects of trapezoidal fins of different sizes and arrangement modes were studied by numerical simulation in the heat storage and release processes. The optimal enhancement solution was obtained by comparing the temperature distribution, instantaneous liquid-phase ratio, solid–liquid phase diagram and comprehensive heat storage and release performance of the thermal energy storage unit under different fin sizes. During the heat storage process, the results show that when the ratio of the length of the upper and lower base of the trapezoid h1/h2 is 1:9, the heat storage time is shortened by 9.03% and 18.21% compared with h1/h2 = 3:7 and 5:5, respectively. During the heat release process, the optimal heat transfer effect is achieved when h1/h2 = 5:5. To further improve the heat transfer effects, the energy storage unit is placed upside down; then, the least time is achieved when h1/h2 = 2:8. When heat storage and release are considered together, the energy storage unit with h1/h2 = 2:8 takes the shortest time to melt in upright placement and then to solidify in upside-down placement.

Multiscale Porous Architecture Consisting of Graphene Aerogels and Metastructures Enabling Robust Thermal and Mechanical Functionalities of Phase Change Materials

AbstractPassive thermal energy storage systems using phase change materials (PCMs) are promising for resolving temporal‐spatial overheating issues from small‐ to large‐scale platforms, yet their poor shape stability due to solid–liquid transition incurs PCM leakage and weak resistance against mechanical disturbance, limiting practical applications. While foam‐stable templates for PCMs have shown complement, they reveal massive leakage and collapse of liquefied PCMs under external loads or impacts. Herein, a multiscale porous architecture consisting of graphene aerogels (GAs) and meta structures enabling robust thermal‐mechanical functionalities of PCMs (3D‐MPGA) toward sustainable phase change thermal energy storage composites is reported. 3D‐printed mechanical metamaterials employing octet‐truss cells provide supportive strength and directionally‐assisted leakage reduction, while GAs serve as porous templates with surface‐interfacial contacts, thereby fixing paraffin wax as PCM inside their nano/micropores. The 3D‐MPGA shows intrinsic thermal characteristics of bulk PCMs, and improved thermal‐mechanical‐chemical stability, confirmed by long‐term heating‐cooling cycle tests over 10 h. Moreover, it exhibits highly reinforced strength (200–5000%) within a low density across ambient and melting temperatures, and maintains original shapes in the liquefied PCMs without severe leakage, against external loads. This work inspires rational strategies for advancing robust thermal‐mechanical functionalities for PCM‐based thermal energy storage systems.

A Numerical Investigation of the Influence of Humid Environments on the Thermal Performance of a Phase Change Thermal Storage Cooling System in Buildings

Phase change thermal energy storage (PCTES) technology has garnered significant attention in addressing thermal management challenges in building HVAC systems. However, the cooling performance of PCTES systems in humid scenarios remains unexplored, which is crucial in subtropical regions, high-humidity underground areas, and densely populated spaces. Taking the mine refuge chamber (MRC) as an example, this study focuses on a passive temperature and humidity control system by employing cold storage phase change plates (PCPs) for 96 h. First, an improved and simplified full-scale numerical model including PCPs and MRC parts is established. Then, the model is validated through the experimental results and solved using a numerical method. Finally, the influence of various factors within the system is investigated and an optimization method involving batch operation is proposed. The results indicate that (1) within 40 h, the use of cold storage PCPs leads to an indoor temperature reduction of 4.8 °C and a 7% decrease in relative humidity; (2) the PCPs show asynchronous states in sensible and latent heat transfer rates; (3) for every 50 additional PCPs, the average indoor temperature increases by 0.6 °C and the relative humidity decreases by 1.5%; (4) implementing batch operation of PCPs ensures that the indoor Heat Index drops by 10 °C, which is vital for human survival. The findings will play a crucial role in the global expansion and application (including geographical and functional aspects) of phase change thermal storage technology.

Initial experimental testing of a hybrid solar-dish Brayton cycle for combined heat and power (ST-CHP)

The Solar Turbo Combined Heat and Power (ST-CHP) project developed a novel solar-gas hybrid prototype for combined heat and power generation in Pretoria, South Africa. A vacuum-membrane faceted parabolic dish with a large-pipe open-cavity receiver was coupled to a counterflow recuperator, a combustion chamber, a micro gas turbine with air bearings and a phase change thermal energy storage unit containing solar salts. This study aimed to validate the electrical output of the full-scale dish-Brayton prototype, addressing the literature gap on micro-scale dish-Brayton plants' in-field power generation. Solar hybridization of micro gas turbine technology can significantly reduce combustion fuel consumption. A performance analysis under relevant conditions revealed a late afternoon micro gas turbine output intermittently peaking at 0.4kWe and subsequently stabilizing to a steady state of 0.145kWe at 130krpm. A SimuPact numerical model and an analytical model supplemented the telemetry data to reduce interference in the experimental setup and fully characterize the ST-CHP prototype performance, estimating a steady-state turbine isentropic efficiency of 57%, a compressor efficiency of 71% and a collector efficiency of 17% due to the late afternoon steady-state point. Analytical case studies revealed that fuel savings of between 12% and 33% at the combustion chamber were achievable from the solarized preheating. A subsequent test of the micro gas turbine without solar hybridization or a recuperator resulted in 1.05kWe being generated. The study confirms the dish-Brayton prototype's viability for combined heat and power generation, producing an initial full-scale performance characterisation during in-field testing, and highlighting the impact of solar hybridization on turbine electrical output. Optical efficiency, insulation effectiveness, pressure losses, and turbine operating conditions were identified as critical areas requiring optimization to improve electrical output. The lessons learned, and the calibrated numerical model may be used to optimize the performance of the dish-Brayton plant in future work. The successful in-field full-scale power generation of the ST-CHP prototype adds to the available literature on dish-Brayton technology and brings the technology closer to a commercial product.

Research on compressed air energy storage systems using cascade phase-change technology for matching fluctuating wind power generation

The wind speed varies randomly over a wide range, causing the output wind power to fluctuate in large amplitude. An isobaric adiabatic compressed air energy storage system using a cascade of phase-change materials (CPCM-IA-CAES) is proposed to cope with the problem of large fluctuations in wind farm output power. When the input power is lower than the minimum energy storage power of the compressor, the gradient phase-change thermal energy storage is utilized to broaden the operating range of the system. Second, the system design method and operation rules are elaborated. The storage/release characteristic curve is obtained by constructing the system components and the overall variable operating condition model. A matching system scheme is designed according to the characteristics of a wind farm in a port in China. The case study shows that the wind farm configured with the CPCM-IA-CAES system reduces the wind abandonment rate by 5.7%, recovers 4,644.46 kW h of wind power abandonment, and improves the storage power index by 16.67% compared with that of IA-CAES. Meanwhile, the system efficiency is increased from 65.96% to 74.68%, and the energy storage density is increased from 8.69 to 9.89 kW h m−3.

An IGDT-Based Energy Management System for Local Energy Communities Considering Phase-Change Thermal Energy Storage

An IGDT-Based Energy Management System for Local Energy Communities Considering Phase-Change Thermal Energy Storage

Low temperature phase change material for cold storage and its application to refrigerated transportation

This paper applies the phase-change cold storage technology to refrigerated transportation to reduce the energy consumption. Experiment data showed that the electronic expansion valve can be randomly adjusted to simulate the temperature within negative 25?C to negative 5?C, and a system for defrosting at low temperature and auxiliary refrigeration based on phase-change thermal energy storage of diethylene glycol were developed to guarantee the reliability of the cold chain system.

Case Study of Optimized Cascaded Phase Change Thermal Energy Storage Unit

Phase change materials are paid increasing attention by the scholars in the past decades. For maintaining a relatively constant renewable energy output as a competent alternative for fossil fuel replacement, phase change storage unit are widely studied. However, for better pursuit of thermal energy performance and energy efficiency, only single staged phase change storage unit is not enough for increasing thermal requirements. Therefore, a triple staged phase change thermal energy storage unit have been proposed in this study. Meanwhile, correspondent comparison with single staged counterpart have been conducted along with related optimization. It has been concluded that the proposed thermal storage unit achieved 334.95 J/s & 41.54% / 186.37 J/s & 53.22 % in thermal energy exchange rate & exergy efficiency during endothermic/exothermic respectively. 3/21.4 L/min are the optimal circulating heat transfer fluid flowrates for endothermic/exothermic (better discharging rate)/ exothermic (better energy efficiency). Moreover, 100/9/15 are the best temperatures of circulating water for endothermic/ exothermic (better discharging rate)/ exothermic (better energy efficiency).

Energy storage and hydrophobicity characteristics of cement-based materials containing paraffin-pumice at low air pressure

Pumice is an environmental friendliness and low-cost carrier material for development of paraffin-pumice phase change energy storage composites (PP) at low air pressure in this work. PP was incorporated into cement to obtain CBM-PP. Microstructural, chemical, and thermal characteristics of PP were investigated by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) tests. Moreover, thermal energy storage and hydrophobicity characteristics of CBM-PP were performed by thermal conductivity, drip, and water absorption experiments. Results show that paraffin is effectively impregnated into pumice pores. There exists a physical interaction between paraffin and pumice. And PP possesses excellent compatibility and thermal stability, while its phase change temperatures and thermal energy storage capacities are in the ranges of 51.84–54.69 °C and 77.22–110.60 J/g, respectively. Furthermore, CBM-PP possesses excellent thermal energy storage and hydrophobicity at low air pressure in plateau areas, thus exhibiting a good application prospect in building thermal management and impermeability. Moreover, the thermal conductivity variation of CBM-PP is studied by the thermal conductivity model, which can predict the thermal conductivity with an error of no >9 %.

Experimental Validation of Switched Moving Boundary Modeling of Phase Change Thermal Energy Storage Systems

Abstract Thermal Energy Storage (TES) devices use Phase Change Materials (PCMs) to store and release thermal energy. Control-oriented models are needed to predict the behavior of TES devices and experimental validation is necessary to demonstrate the predictive capabilities of these models. This paper presents an experimental validation of a switched Moving Boundary (MB) approach for modeling TES devices, where the dynamics of the device are captured with fewer states than traditional models. A graph-based modeling approach is used to model heat flow, while the moving boundary captures the time-varying liquid and solid regions of the TES. The model uses a Finite State Machine (FSM) to switch between four modes of operation based on the State-of-Charge (SOC) of the TES. Results show that the switched MB approach has similar accuracy and lower computational cost compared to traditional modeling approaches when predicting the SOC of an experimental TES device.

Simplicity is the ultimate sophistication: One-step forming for thermosensitive solid–solid phase change thermal energy harvesting, storage, and utilization

In light of the growing recognition of low-carbon initiatives, renewable energy is gradually assuming a dominant role within the energy framework. Phase change materials can enhance the efficiency of renewable energy utilization by energy peak shaving and time shifting. However, leakage and inherent rigidity signify that a significant amount of energy input is required for scale-up applications of phase change materials to enhance shape stability and processability during industrial installation. In conventional enhancement strategies, high-quality encapsulation means more intricate processes and higher energy consumption. Here we propose a simplified thermally-initiated encapsulation and molding strategy, which involves grafting the phase change materials onto thermosetting polymer backbones by covalently integrated, to construct self-supported phase change materials with complex three-dimensional geometry. The encapsulation process is macroscopically manifested as a transformation from solid-liquid to solid–solid phase change. Therefore, by imposing restrictions on liquid materials, any ultra-high-precision complex structure can be molded, and mechanical properties are imparted through curing to achieve shape stability, ultimately enables the integration of phase change material encapsulation and casting. The complete process requires no curing agents or organic solvents, and no pollution emissions, making it highly maneuverable and environmentally friendly. Furthermore, we demonstrate the universal high value applications of new materials in different fields. In the ancient thermotherapy experiment, the sample exhibited sustained heat release for 8 min. In the advanced chip cooling simulation, the chip exhibits superior heat dissipation performance, as evidenced by its operating temperature being 50 °C lower than that of natural cooling within 20 min. It confirms the remarkable potential of phase change materials constructed through this approach for thermal energy applications.

Experimental study of thermal performance in a rectangular finned-tube latent heat storage device with composite polyethylene wax/expanded graphite

Phase change materials and geometric structure of latent heat storage (LHS) devices constitute crucial factors affecting the performance of phase change thermal energy storage systems. In this study, focusing on the LHS system with a heat source temperature of 150 °C, a rectangular finned-tube latent heat storage device was designed and fabricated. Polyethylene wax (PEW) with a 10% mass fraction of expanded graphite was adopted to prepare the composite phase change material. A series of experiments was conducted to evaluate the thermodynamic performance of the device with varying inlet temperatures and mass flow rates. The experimental results showed that the process of heat storage and release was predominantly governed by thermal conduction due to the high viscosity of PEW. Although the temperature variations in various directions within the LHS device remain nearly consistent, the heat transfer in the non-fin regions on the rectangular LHS device walls and corners was comparatively inferior due to the absence of natural convective heat transfer. In comparison to the mass flow rate, the inlet temperature exerts a more significant impact on accelerating the heat storage/release processes. While an increase in the mass flow rate enhanced the heat transfer capacity, its slightly accelerates the heat transfer duration. Moreover, the heat release ratio of the device exhibits an initial increase followed by a decrease with an increasing mass flow rate. In practical applications, prioritizing an increase in inlet temperature difference proves to be more effective than adjusting mass flow rate to enhance the heat storage performance.

The impact of non-ideal phase change properties on phase change thermal energy storage device performance

Phase change materials have been known to improve the performance of energy storage devices by shifting or reducing thermal/electrical loads. While an ideal phase change material is one that undergoes a sharp, reversible phase transition, real phase change materials do not exhibit this behavior and often have one or more non-idealities – glide, hysteresis, supercooling – associated with them. Experimental and modeling techniques to characterize these non-ideal properties are reasonably well understood, however, their impact on the performance of a thermal energy storage system is not fully understood. Here, we analyze the performance of a heat exchanger with a phase change material as a function of the different non-idealities, for a heating and a cooling application. We focus on the impact of these non-ideal behaviors on different modes of operation of the thermal energy storage device, which will serve as a useful guide to researchers on the relative importance of the non-ideal properties, along with the necessary accuracy required during an experimental characterization.

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.

A control method combining load prediction and operation optimization for phase change thermal energy storage system

Due to the high latent heat and load-shifting capacity, phase-change thermal energy storage technology is an effective way to reduce energy costs under time-of-use electricity pricing. A favorable operation strategy is essential to exploit the advantage of the phase change thermal energy storage system. Previous studies on the operation strategy lack consideration of load prediction, which could reduce the matching degree of heat supply and demand. This study proposed a control method combing load prediction and operation optimization based on an electric boiler-phase change thermal energy storage heating system. A deep learning-based heating load prediction model was built; on this basis, an operation optimization method using dynamic programming was formulated subsequently. The proposed method was applied to a case building located in Beijing, China. By applying the proposed control method, the energy costs of the system were saved by 10% compared to the original operation strategy in the whole heating season, and the matching degree of heat supply and demand could be close to 100%, demonstrating that the method can provide users with cheaper and the best thermally comfortable heating. The proposed method is capable of achieving optimal operation of a phase change thermal energy storage system in practical applications.

Experimental and Numerical Optimization Study on Performance of Phase-Change Thermal Energy Storage System

Promoting the use of solar energy resources has always involved the challenges of instability and supply–demand mismatch. The key to solving these issues is to efficiently store and utilize solar energy resources using high-performance heat storage devices. This study designed a high-performance shell-and-tube phase-change thermal storage device and established a numerical model using ANSYS software to summarize the device’s dynamic melting law. To verify the accuracy of the numerical simulation, a performance testing platform for the phase-change thermal storage device was built to investigate the impact of various factors, such as the inlet water temperature, inlet water flow rate, type of heat storage, and initial temperature of the device, and to reveal the change law of the device’s performance. The results show that the inlet water temperature has the most significant impact on the device’s heat storage and release performance. When the device’s heat storage or release is used for heating, changing the inlet water flow rate has a weak and limited effect on the device’s performance. However, when the device’s heat release is used to provide domestic hot water, increasing the make-up water temperature and reducing the inlet water flow rate can significantly improve the device’s effective heat release. Furthermore, based on the experimental validation of the model’s correctness, this study further simulated and studied the impact of different factors on the device’s heat storage process to optimize its structural design and provide technical references for the device’s actual operation and installation. The results show that the placement of fins has a negligible effect on the performance of the heat storage device while reducing the fin spacing and increasing the fin thickness can significantly improve the melting efficiency of the phase-change material (PCM). Additionally, the heat storage characteristics of the device are significantly better in the vertical installation mode than in the horizontal installation mode. This study provides theoretical guidance and technical references for the design and use of phase-change thermal storage devices.

Advanced Materials and Additive Manufacturing for Phase Change Thermal Energy Storage and Management: A Review

AbstractPhase change materials (PCMs) can enhance the performance of energy systems by time shifting or reducing peak thermal loads. The effectiveness of a PCM is defined by its energy and power density—the total available storage capacity (kWh m−3) and how fast it can be accessed (kW m−3). These are influenced by both material properties as well as geometry of the energy systems; however, prior efforts have primarily focused on improving material properties, namely, maximizing latent heat of fusion and increasing thermal conductivity. The latter is often at the expense of the former. Advanced manufacturing techniques hold tremendous potential to enable co‐optimization of material properties and device geometry, while potentially reducing material waste and manufacturing time. There is an emerging body of research focused on additive manufacturing of PCM composites and devices for thermal energy storage (TES) and thermal management. In this article, the fundamentals and applications of PCMs are reviewed and recent additive manufacturing advances in latent heat TES for both the PCM composite and associated heat exchanger are discussed. A forward‐looking perspective on the future and potential of PCM additive manufacturing for TES and thermal management is provided.

Thermal property optimization and shape stabilization of sugar alcohols phase change thermal energy storage materials reinforced by sintering synthesized alumina porous ceramics

Sugar alcohols phase change thermal energy storage materials have many advantages such as high latent heat, non-toxicity and abundance, which are extremely potential in the field of thermal energy storage. However, the application of sugar alcohols in thermal energy storage is greatly restricted by high supercooling. In this work, alumina porous ceramics (APC) were successfully prepared by replication template method, and then the prepared APC were modified by 3-aminopropyltriethoxysilane to obtain APC-SiX. The APC and APC-SiX were used to improve the thermal properties of erythritol (ET), d-mannitol (DMT) and d-dulcitol (DDT), respectively. Based on the results, the supercooling degree and solidification stability degree of sugar alcohols were suppressed observably, among which, the supercooling suppression for ET was the most significant. The supercooling degree and solidification stability degree of ET were suppressed to 3.3 ± 0.1 °C and 0.7 ± 0.2 °C, respectively. Besides, the thermal conductivity of the sugar alcohols was also obviously enhanced. Furthermore, the high latent heat, excellent cycling thermal stability and anti-leakage of sugar alcohols composite phase change materials (PCM) are also available. This conclusion is important for supercooling regulation and thermal property optimization of sugar alcohols, and indeed, can promote the utilization of sugar alcohols in thermal energy storage.

Boiling sodium and melting salt: Evaluation and optimisation of a novel solar–thermal system concept

The phase-change phenomenon facilitates efficient heat transfer and the storage of a large amount of heat close to an upper-bound temperature limit. In this paper, a novel solar-thermal system configuration is evaluated and optimised, where liquid sodium is boiled in a receiver and energy is stored through the melting and freezing of NaCl salt. Polar and surround field configurations of a 1 MWe sodium-boiler plant were investigated where co-optimisation of solar multiple, field parameters, receiver geometry and storage parameters was performed to obtain lowest possible levelised cost of electricity (LCOE); this compared to a 100 MWe two-tank molten salt plant optimised via the same method. The LCOE values obtained for the 1 MWe sodium-boiler plant was 128.3 USD/MWh for a polar field configuration and 144.9 USD/MWh for a surround field configuration, compared to 107.1 USD/MWh for the 100 MWe two-tank molten salt system. Whilst promising for smaller-scale systems, the analysis identifies limitations and challenges associated with high operating temperatures and low receiver flux limits, which opens the possibilities for the investigation of lower-temperature phase change materials (PCMs) and alternative PCM geometries. • Phase change thermal energy storage is coupled with a boiling sodium solar receiver. • A detailed physical model is used to optimise the design for lowest energy cost. • The system achieves 128 USD/MWhe at 1 MWe scale with 14 h of storage.

Phase Change Thermal Energy Storage Enabled by an In Situ Formed Porous TiO2.

Uneven and insufficient encapsulation caused by surface tension between supporting and phase change materials (PCMs) can be theoretically avoided if the encapsulation process co-occurs with the formation of supporting materials in the same environment. Herein, for the first time, a one-pot one-step (OPOS) protocol is developed for synthesizing TiO2 -supported PCM composite, in which porous TiO2 is formed in situ in the solvent of melted PCMs and directly produces the desired thermal energy storage materials with the completion of the reaction. The preparation features straightforward operation and high environmental metrics with no emission, requires only stirring and heating without the addition of organic solvent or catalyst. Moreover, the preparation process can be easily scaled-up at the laboratory. Because of the OPOS protocol and porous TiO2 inside, the as-obtained PCM composite possesses a 66.5% encapsulation ratio and 166.8% thermal conductivity enhancement compared to pristine unsupported PCMs, with 94.7% light-to-thermal conversion efficiency and promising bacterial inhibition activity without any leakage.