Phase Change Energy Storage Research Articles

Evaluation into the effect of lignocellulosic biochar on the thermal properties of shape stable composite phase change materials

Biochar is suitable for preparing shape stable composite phase change materials (sscPCMs) due to the advantages of cost-effective, environmentally, and sustainability. However, the heat properties of biochar-based sscPCMs were not consistent. To investigate how different types of biochar influence the thermal properties of sscPCMs, three types of sscPCMs were successfully prepared using peanut shell biochar (PSC), poplar wood biochar (PWC), and corn straw biochar (CSC) as framework materials and combined with stearic acid (SA). A comprehensive analysis of the thermal properties of three sscPCMs was performed, taking into account thermal conductivity, phase change latent heat, encapsulation efficiency, crystallization rate, and energy storage efficiency. The study indicated that among the three types of sscPCMs, SA/PWC sscPCMs demonstrated excellent comprehensive performance. The phase change latent heat of SA/PWC reached 100.13 J/g, and the thermal conductivity was 0.38 W/mK. Compared to SA/PSC, the phase change latent heat of SA/PWC increased by 45.96 %, with only a 28.30 % reduction in thermal conductivity. In comparison to SA/CSC, the thermal conductivity of SA/PWC improved by 18.75 %, while the phase change latent heat decreased by only 14.02 %. In addition, the proportions of cellulose, hemicellulose, and lignin played a crucial role in determining the thermal properties of sscPCMs. This study clarified the mechanism by which biochar influences the thermal characteristic of sscPCMs, offering valuable insights for choosing biochar framework materials.

Injected phase change seismic source construction and monitoring experiment

Scientific assessment of the transport channels and distribution of oil, gas, water, and other fluids is the key to enhancing oil and gas production capacity and ensuring the safe and efficient development of mineral resources. Traditional microseismic monitoring has been suffering from limitations such as ambiguous attribute characteristics of the seismic source and low signal-to-noise ratios of the data, leading to poor location accuracy and large uncertainties. We develop a phase change seismic source monitoring method that allows for a detailed characterization of the spatial distribution of subsurface fluid transport by accurately locating the equivalent seismic source within supportive fractures. A phase change seismic source is developed and constructed based on the phase change material, enabling control over phase change temperature, source energy, and source scale through the principle of phase change energy storage. The source introduces an active approach to seismic signal generation, diverging from the conventional passive method reliant on rock rupture. Then, 3D homogeneous models are constructed for ground monitoring and in-well monitoring using impulse source propagation theory. The numerical simulation of the wavefield uses the finite-difference method, and the equivalence of discrete sources is confirmed using the Pearson correlation function. The reliability of the monitoring method is verified through a seismic monitoring experiment and comprehensive feasibility analysis.

Experimental study on the melting characteristics modulation of cubic ice cubes with different trace air contents under natural convection condition

Ice as a typical phase change material has the advantages of low cost, high latent heat and environmental friendliness, and the ice melting process under natural convective conditions is a fundamental study that has received wide attention. For the cubic ice cubes having different air contents, their melting characteristics becomes more complicated. The melting model of cubic ice under natural convection conditions was developed, which can accurately predict the time of the entire melting process. To validate the accuracy of the model, a series of melting experiments on cubic ice cubes are conducted and analyzed, with mass and air contents varied from 20 g to 50 g, and from 0 to 3.9 %, with a model error of less than ±20 %. Based on the maximum melt rate and the change in shape to a pyramid of cubic ice, the melting process can be divided into the initial melting, frustum-shaped, and pyramid-shaped stages. Varying the air content of the ice regulated the total melting time and the time proportion of the initial melting stage and the frustum-shaped stage of the ice. The proportion of time in the pyramid-shaped stage decreased from 64.3 % to 51.5 % for bubble ice with an air content of 3.9 % compared to clear ice. The proportion of time in the pyramid-shaped stage during the ice melting process is not significantly related to the air content and mass, and remains at approximately 27 %. Results of this study are meaningful for regulating the melting process and optimizing phase change energy storage technologies.

Hydrophilic Ultra-Fine SiC Nanowires Enhance the Performance of Hydrated Salt Phase-Change Energy Storage Materials.

In this study, ultrafine linear nanostructured SiC with high wettability and large specific surface area were synthesized via the carbothermal reduction method. These nanowires were impregnated with Na2SO4 ⋅ 10H2O, CaCl2 ⋅ 6H2O, MgCl2 ⋅ 6H2O, and CaMg2Cl6 ⋅ 12H2O to obtain composite phase change materials (CPCMs), which demonstrated improved phase separation and significantly reduced supercooling. In particular, the supercooling degree of CaCl2 ⋅ 6H2O was minimized to 0.1 °C. The SiC nanowires effectively prevented issues of dehydration and deliquescence in hydrated salts. The thermal storage capacities of the CPCMs exceeded 90 %, with Na2SO4 ⋅ 10H2O and MgCl2 ⋅ 6H2O reaching 107.10 % and 103.35 %, respectively. Furthermore, the CPCMs exhibited greater sensitivity to changes in temperature compared with the pure hydrated salt phase change materials (PCMs). These results indicate that ultra-fine SiC nanowires can act as a versatile carrier for hydrated salt PCMs at low and intermediate temperatures.

MUF-n-Octadecane Phase-Change Microcapsules: Effects of Core pH and Core-Wall Ratio on Morphology and Thermal Properties of Microcapsules.

Phase change energy storage microcapsules were synthesized in situ by using melamine-formaldehyde-urea co-condensation resin (MUF) as wall material, n-octadecane (C18) as core material and styryl-maleic anhydride copolymer (SMA) as emulsifier. Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis were used to study the effects of emulsifier type, emulsifier dosage, core-wall ratio and pH on the morphology and thermal properties of microcapsules. The results show that the pH of core material and the ratio of core to wall have a great influence on the performance of microcapsules. SMA emulsifiers and MUF are suitable for the encapsulation of C18. When the pH is 4.5 and the core-wall ratio is 2/1, the latent heat and encapsulation efficiency of phase transition reaches 207.3 J g-1 and 84.7%, respectively. The prepared phase-change microcapsules also have good shape stability and thermal stability.

Bacterial cellulose-based Janus energy storage phase change composite aerogel for efficient interfacial solar vapor generation

Interfacial solar evaporation systems based on Janus structures exhibit potential application prospects in terms of salt tolerance. However, intermittent and unstable light conditions limited the evaporation rate and water production performance of the evaporators. The introduction of energy storage phase change (ESPC) composite materials into the interface solar evaporators can effectively solve this problem. In this work, bacterial cellulose (BC) is selected as the matrix material, sodium alginate (SA) and multi-walled carbon nanotubes (MWCNTs) are added as functional fillers, and porous composite aerogels are prepared using direct freeze-drying. On this basis, Janus porous composite aerogel (J-BCS/CNT) with ESPC function is further constructed by depositing paraffin onto the upper layer of the aerogel through a unilateral vacuum impregnation method. The aerogel exhibits strong photothermal conversion capabilities and excellent thermal management properties. The addition of appropriate amount of MWCNTs enables it to obtain high latent heat storage and release functions, providing energy for operation in dark conditions. Under the solar irradiation of 1.5 kW m−2, J-BCS/CNT40% aerogel exhibits a high evaporation rate of 1.95 kg m−2h−1 in pure water and 0.67 kg m−2h−1 under dark conditions. The salt evaporation resistance test shows that the aerogel has excellent purification capabilities in high-concentration salt water (20 wt%) solutions. More importantly, the long-term energy storage-release tests of J-BCS/CNT in 3.5 wt% saline water indicate that the aerogel reveals excellent sustainability and latent heat release functions.

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.

Experimental and numerical investigation of a double spiral tube heat exchanger in a novel composite phase change material

Phase change energy storage technology effectively harnesses energy, and phase change materials have been garnered significant attention due to their high latent heat capacity. The heat transfer capacity and phase transition of HCNT − CH3COONa·3H2O/Na2HPO4·12H2O composites in a double spiral tube heat storage unit were investigated. The effects of different flow rates and temperatures on the heat transfer characteristics of phase change materials were studied, and the thermal performance of the storage units was evaluated by calculating the power, energy and energy efficiency ratios. The phase change process of the composite during heat transfer was further revealed via simulation, and the heat storage and heat release of the composite were compared with those of other phase change materials. The results show that the effects of the flow velocity on the transformation time and power of the phase change material are negligible. However, an increase in flow rate can significantly increase the heat storage and heat release of the phase change unit. In particular, when the flow rate is 4 LPM, the energy efficiency ratio can reach 76.6 %. When the temperature increases from 80 °C to 90 °C, the melting time decreases by 30.23 %, indicating that increasing the temperature has a significant effect on the phase transition process. Through simulation calculations, the composite phase change material shows significant performance advantages under the same working conditions; its heat storage capacity is 108 % greater than that of the other materials, and the heat release capacity is 206 % greater, which indicates that it has greater energy storage and release efficiency and a better thermal energy conversion capacity. In addition, the experimental and simulation results also reveal the existence of a diagonal region of slow phase transition in the heat storage unit. In summary, this paper analyses the heat transfer performance of a double spiral tube heat storage device, provides a theoretical basis for practical application, and provides an important reference for improving the performance of a phase–change energy storage system.

Experimental Study on Phase Change Energy Storage Flooring for Low-Carbon Energy Systems in Grassland Pastoral

Phase change energy storage technology enhances the integration of renewable resources into low-carbon energy systems for grassland pastoral settlements, further addressing the balance between energy needs and environmental sustainability. This study examines a heating system using an experimental platform in an environmental chamber, where the thermal storage and release processes of phase change energy storage flooring were monitored. The results revealed that phase change energy storage flooring exhibits higher heat transfer efficiency and faster heating rates. Under 40 °C heating conditions, the heating rate of the thermal storage layer increased by 12.5% within 1 h. The flooring also demonstrated superior heat release performance, with the peak heat flux of the thermal storage layer delayed by 15 min. Higher heating temperatures shortened the heating time and extended the heat release duration of the phase change energy storage flooring. Under 45 °C heating conditions, the heat transfer efficiency of the surface temperature of the thermal storage layer increased by 38% within 1 hour and by 24.7% over 4 h. In addition, energy consumption in different tests was analyzed, and thermal conductivity was discussed according to the heat transfer model. Phase change energy storage flooring, when coupled with the abundant solar energy resources available in grassland pastoral areas, presents a viable option for the construction of low-carbon energy systems in grassland pastoral settlements.

Photo-thermal effects initiate multi-level energy conversion in “solid-solid” phase-changing fibers

The current textiles primarily employ passive heat barriers to minimize heat loss and achieve effective thermal insulation for human beings. Accordingly, intelligent fibers with energy storage and temperature control capabilities have garnered significant attention due to their potential to revolutionize textile technology. The study integrates the photo-thermal effect and phase change energy storage materials onto a fiber, thereby fabricating a fully intelligent energy storage fiber. This innovation enables the multi-level conversion of sunlight: “Optical energy - Thermal energy - Phase transition energy - Thermal energy”. The intelligent fiber efficiently converts solar energy into heat energy through the photo-thermal coupling of CuNPs, subsequently inducing a spatial conformational change in the solid-solid phase change material within the fiber for effective heat storage. The hybrid fiber possesses enhanced mechanical properties but also exhibits a significantly high phase transition enthalpy value of 49.75 J g−1 and a phase transition temperature suitable for human body temperature (20.19–30.21 °C), especially the fiber is more durable. The photo-thermal conversion test vividly demonstrates the systematic transformation of four distinct forms of energy within the composite fiber. This approach holds significant potential for advancing the field of smart fiber technology.

Heat transfer mechanism of superabsorbent polymers phase change energy storage cold-formed steel wall under fire

The superabsorbent polymer phase change materials (SAP materials) exhibit exceptional water absorption and retention properties, offering substantial potential for fire protection in steel structures, thereby reducing the need for sheathing boards and fire-retardant coatings, while minimizing energy consumption. Understanding the heat-mass exchange theory of SAP materials is crucial for enhancing their application in the building industry. This study develops a comprehensive theoretical model for heat-mass exchange in cold-formed steel (CFS) walls incorporating SAP materials. An equilibrium phase change model and a simplified thermal radiation model were developed to capture the water loss and dynamic heat exchange processes in SAP materials. These models were integrated into a transient fluid-solid-thermal coupling model using Ansys Fluent and User Defined Functions. In the case study, the newly developed numerical models can accurately predict temperature field changes in CFS walls with SAP materials, demonstrating the heat transfer mechanisms of hot and cold flanges at different temperature rise stages. The developed numerical model was used to investigate the effects of factors such as the moisture content of the SAP material, web depth, and flange width on the fire resistance of the CFS wall. Results indicated that increasing the wall stud height improves fire resistance, while increasing flange width has little effect on hot flange temperature. These findings provide a theoretical foundation and practical guidelines for the application of SAP phase change insulation materials in the building industry, promoting energy reduction and supporting sustainable construction practices.

Self-assembly and energy storage potentials of biphasic phase change azobenzene liquid crystalline block copolymers

Flexible polymeric materials with potentials in energy storage have attracted extensive attention in today's sustainable society. Here, we reported a series of crystalline-liquid crystalline biphasic phase change block copolymers, poly(ethylene oxide)-b-poly(11-(4-(4-cyanophenylazo)phenoxy)undecane methacrylate) (PEO-b-PMAAzo), and studied the UV and Li+ ions coordination-mediated self-assembly for the potentials in phase change energy storage and solid electrolytes. The PEO-b-PMAAzo BCPs possess both the solid-liquid phase transition of PEO and the photo-chemical-thermal energy transition of PMAAzo block. Meanwhile, PEO has the capability to coordinate with the Li+ for the ionic conductivity. We explored the binary phase change behaviors and thermal energy density of the BCPs with different lithium ion concentrations before and after UV irradiation. The addition of LiTFSI salts increases the interaction parameters (χ) of the BCPs leading to phase transition of the self-assembled nanostructures. The phase diagram covering LAM, HEX, GYR, Fddd and HPL nanostructures facilitating ion transport was demonstrated. The PMAAzo block enabled the solid feature of the BCPs and ensured the high energy density and high conductivity. This work demonstrates that the combination of the functional polymers in one BCP not only provides multiple morphology tunabilities but also enables multiple functionalities from energy conversation and storage to ionic conductive electrolytes.

Experimental Study on the Effect of Additives for Phase Change Hysteresis Performance

Phase change energy storage materials are the core of phase change energy storage technology. Phase change hysteresis can cause phase change materials not to store and release thermal energy as expected, and most studies have not focused on this. A low-temperature eutectic phase change material CaCl2·6H2O–MgCl2·6H2Omaterial prepared was investigated, and some influencing factors of the phase change hysteresis phenomenon and its regular characteristics were aspired to be obtained. The melting-solidification curves were obtained using a step-cooling test bench, and the latent heat values and heat absorption and exothermic curves of materials with different proportions were measured by a differential scanning calorimeter. The experimental results show that the temperature difference of the phase change hysteresis tended to increase gradually with the increase of the mass fraction of the nucleating agent, and the hysteresis temperature difference increases from the initial 3.9 °C–15.02 °C when SrCl2·6H2O was added by 2.4%. The temperature difference of the phase change hysteresis increased gradually with the increase of the mass fraction of the thickener. This paper provides a new idea for optimizing the properties of phase change energy storage materials and provides a possibility for realizing the parametric control of phase change hysteresis factors.

Analysis of the Applicability of a Phase-Change Energy Storage Wall for Public Buildings in Hot Summer and Cold Winter Climate Zones

The effects of applying a phase-change energy storage wall in office buildings in hot summer and cold winter climate zones were analyzed by comparing several factors based on numerical calculations, specifically focusing on the internal and external wall temperature, delay time, attenuation multiple, and building load. It was found that the most effective phase-change temperature was 30 °C and the optimal thickness for the phase-change layer was 30 mm. The adoption of the outer phase-change wall layout improved the heat insulation performance during the summer. This effectively enhanced the energy-saving effect of the phase-change layer thickness and layout, which aligns with the influence law of phase-change wall heat transfer.

A 3D self-floating evaporator loaded with phase change energy storage materials for all-weather desalination

Today, humanity is confronted with two interrelated crises: water and energy scarcity. The utilization of solar energy to evaporate seawater enables the acquisition of freshwater resources while minimizing energy consumption. However, the solar energy hitting the ground is associated with different weather patterns and the alternation of day and night. This work is based on chitosan (CS) aerogel, loaded with phase change material octadecane (ODE) and coated with epoxy resin glue and electrospinning fiber photothermal layer for continuous evaporator operation. Using the characteristics of phase change materials, the ODE undergoes a change from solidification to liquefaction, during which it absorbs and stores energy at elevated temperatures. Conversely, when the temperature decreases, the ODE reverts to solidification and releases stored energy. This enables the evaporator to be utilized in a broader range of scenarios, thereby enhancing the continuity of evaporation. The temperature of the evaporator remained higher than the initial temperature 2 h after the light source was switched off, achieving a light absorption of 94 % and an evaporation rate of 1.74 kg m−2 h−1. Furthermore, it exhibits purification capabilities for different kinds of solutions. The interfacial evaporator is capable of facilitating all-weather evaporation, and it has the potential to become a pivotal instrument in the domain of seawater desalination, with a vast array of applications.

Preparation of coconut oil/aluminum nitride/expanded graphite composite phase change materials with high thermal conductivity and stable shape for thermal energy storage

Preparation of coconut oil/aluminum nitride/expanded graphite composite phase change materials with high thermal conductivity and stable shape for thermal energy storage

Comparative analysis of radiant air-conditioning systems combined with two different types of solar-powered dehumidification methods

Abstract This paper proposes a solar liquid desiccant radiation air-conditioning system(SLDRS) and a solar desiccant wheel radiant air-conditioning system(SDWRS) that combine with a phase change energy storage radiation terminal, solar energy, and heat pump system. The models of the two systems are simulated with the transient system tool (TRNSYS) to compare the refrigeration and dehumidification effects and energy saving of the two systems. The results show that the total refrigeration capacity of the SLDRS is reduced by 20.45% compared with the solar desiccant wheel radiation air-conditioning system, the monthly average dehumidification capacity is increased by 37.09%, and the total energy consumption is reduced by 712.9 KW·h. It is evident that the cooling and dehumidifying effect and energy efficiency of the SLDRS are superior to those of the SDWRS.

Research and optimization of heat transfer characteristics of heat pipe-coupled phase change energy storage system

Abstract Heat pipe coupled Latent Heat Thermal Energy Storage (LHTES) is a commonly used technique for improving heat storage, due to its advantages such as heat conduction, isothermal, and uniform temperature. Adding fins to the heat pipe can enhance energy storage efficiency and system performance. Although previous research has looked into how heat pipe layouts affect LHTES, there is still a dearth of research on fin geometry optimization for boosted heat transfer. In this work, we used ANSYS Fluent to simulate the consequence of fin placement upon the heating capacity of a Phase Change Material (PCM) based LHTES system. Through an in-depth analysis of the heat transfer mechanisms, in an effort to quicken the PCM’s solidification process, we adjusted the fins’ length and spacing. The LHTES system’s overall solidification time was greatly shortened by the optimized model, going from 18800 seconds to 8500 seconds, achieving a 54.79% enhancement in thermal transfer efficiency.

A Study of Asymmetric Hyperbolic Heat Storage Unit

ABSTRACTDue to the advantages of high energy density and constant temperature, phase change energy storage technology has attracted much attention in energy saving and efficient utilization of energy. In this paper, Fluent software is used to simulate and analyze the heat storage characteristics of six new thermal storage units: corrugated tube, hyperbolic‐shape, non‐hyperbolic‐shape, symmetric frustum‐shape, non‐frustum‐shape, and bow‐shape. The results show that the melting rate of the non‐hyperbolic‐shape phase change unit is significantly higher than that of the circular tube, the heat storage time is shortened by 22.52%, and Ra* reaches 0.0086. Second, the effects of the radius difference (δ) between the inlet and outlet of the non‐hyperbolic‐shape phase change unit and the asymmetric position (s) on the heat storage process are studied. The results show that when δ increases from 2 to 10 mm, the melting time of phase change material (PCM) is shortened by 22.89%, that is, the average heat transfer rate between PCM and heat transfer fluid increases with the increase of δ. On the other hand, the average heat storage rate of the heat storage unit decreases first and then increases with the increase of s. When δ = 10 mm, s = 35 mm is the best working condition, the average heat storage rate of the non‐hyperbolic‐shape thermal storage unit reaches 34.3 J/s. This study can provide new ideas and references for the optimization design of latent heat storage units and the progress of experiments.

Multi-objective optimization of L-shaped fins in rectangular phase change energy storage units based on genetic algorithm

Phase change energy storage technology holds immense potential in the field of energy storage, and enhancing the efficiency of energy storage systems has long been a focal point of industry attention. This study aims to optimize the design of an L-shaped fin structure to improve the melting rate of the phase change material (PCM) within a rectangular phase change energy storage unit and enhance the overall system performance. Through the utilization of numerical simulations and the response surface method (RSM), the influence of fin design parameters - specifically, the length and thickness of the main segment and the length and thickness of the branch segment - on the energy storage per unit mass (Em) and energy storage efficiency (Pt) of the energy storage unit is evaluated. The results reveal that the length of both the main and branch segments of the L-shaped fin significantly impacts the melting rate of the PCM, whereas the thickness of these segments has a comparatively lesser effect. Additionally, when the length of the main segment reaches a sufficient value, increasing the length of the branch segment effectively addresses the challenge of PCM melting difficulties at the bottom of the rectangular phase change cavity caused by natural convection. The Non-Dominated Sorting Genetic Algorithm-II (NSGA-II) is employed for the multi-objective optimization of the L-shaped fin shape, and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) with entropy weighting is applied for decision-making to determine the optimal solution. Notably, when the weights of Em and Pt are set at 44.9 % and 55.1 % respectively, the overall performance of the energy storage unit is optimized. The Pareto-optimal decision solution exhibits a significant improvement of nearly threefold in Pt compared to the case without fins, while the reduction in Em is only 5.24 %. This design approach presents a novel perspective for determining fin parameters in phase change energy storage devices and is expected to drive advancements in phase change energy storage technology.