Phase Change Energy Storage Research Articles

Numerical simulation of heat transfer processes in shell and tube phase change heat exchangers for recovering industrial waste heat

Abstract This article combines phase change energy storage technology with shell and tube heat storage and exchange devices to establish a three-dimensional numerical model of the shell and tube phase change heat storage and exchange device. The hexahedral structured grid division is used to make the simulation results more accurate. Combined with the computational fluid dynamics software Fluent and the related principles of phase change heat transfer, the effects of different heat transfer fluid temperatures and flow rates on the phase change process of phase change materials and the fluid outlet temperature in the phase change heat exchanger were numerically simulated. The results show that under the set parameters, when the inlet water temperature increases from 70℃ to 90℃, the time required for the outlet temperature to increase from 20℃ to 60℃ is shortened by 23%, while when the temperature is constant, the inlet temperature of heat transfer fluid is shortened by 69%. Analysis shows that the influence of the inlet temperature of the heat transfer fluid on the heat storage and release of phase change materials is significantly greater than the inlet flow rate.

Biomimetic Nanostructured Polyimine Aerogels with Graded Porosity, Flame Resistance, Intrinsic Superhydrophobicity, and Closed-Loop Recovery.

Polymer aerogels, with their porous and lightweight features, excel in applications such as energy storage, absorption, and thermal insulation, making them a sought-after new material. However, the covalent cross-linking networks of current polymer aerogels result in unsustainable manufacturing and processing practices, persistently depleting our finite natural resources and causing significant global environmental impacts. Herein, we have constructed a high-performance dynamic covalent cross-linking aerogel network using biobased materials, with its structure and green sustainability akin to those of plants in nature. Abundant reversible cross-linking points endow the aerogel with ultrafast degradation capabilities, enabling allow for closed-loop chemical monomer recovery and reprocessing. Furthermore, utilizing the highly active reversible network, net-zero emission material reuse and reprocessing can be achieved. Additionally, the controlled dynamic aerogel network features a multilevel roughness nanostructured surface similar to lotus leaf and a biomimetic pore structure, contributing to significant anisotropy. The distinctive structure and composition endow the dynamic aerogel with high compressive strength (2.2 MPa) vertically, low thermal conductivity (0.0257 W/(m·K)) horizontally, and outstanding fire resistance (LOI is as high as 36%). Notably, the aerogel demonstrates the highest hydrophobicity among polyimine materials, with a contact angle of 154°. Furthermore, those dynamic aerogels have excellent performance in a variety of potential applications such as oil-water separation, directional transport, and phase change energy storage, and it is anticipated that these applications will greatly benefit from systematic upgrades in recyclability and reprocessing.

Multifunctional Polymer-Encapsulated Aerogel Fibers with Thermal Insulation, Active Heating, and Phase Change Energy Storage Abilities

Multifunctional Polymer-Encapsulated Aerogel Fibers with Thermal Insulation, Active Heating, and Phase Change Energy Storage Abilities

Comprehensive Energy System with Combined Heat and Power Photovoltaic-Thermal Power Stations and Building Phase Change Energy Storage for Island Regions and Its Coordinated Dispatch Strategy

Comprehensive Energy System with Combined Heat and Power Photovoltaic-Thermal Power Stations and Building Phase Change Energy Storage for Island Regions and Its Coordinated Dispatch Strategy

Wood-based phase change energy storage composite material with reversible thermochromic properties

With the continuous increase in global energy demand and environmental challenges, the efficient utilization and storage of energy have become critical areas of scientific research. This study presents the preparation and performance assessment of a wood-based phase change composite (TPW) with reversible thermochromic properties. Thermogravimetric analysis (TG) confirmed thermal stability across 26 °C to 270 °C, while differential scanning calorimetry (DSC) demonstrated that TPW has good thermal cycling performance, and suitable phase change temperature at about 34 °C. Thermal insulation tests showed that TPW can reduce heat exchange between inside and outside environment, maintaining the internal temperature for longer time. Below the transition temperature, the material displays a bluish-purple color, transitioning to light yellow upon heating, with a notable color difference (ΔE⁎) increase from 3.46 to 67.89. Since the phase transition temperature close to human body temperature, enhances TPW’s compatibility for applications in home decor, temperature indicators, and anti-counterfeit labeling. This research contributes novel insights and foundational data for advancing wood-based functional materials in sustainable applications.

Performance and Optimization of Novel Solar-Assisted Heat Pump System with Hybrid Thermal Energy Storage

In this study, a novel solar-assisted heat pump (SAHP) system with hybrid thermal energy storage is proposed. The system can address the problems of large space requirements and the unstable heating of solar heating systems and tackle the energy-efficient degradation of air source heat pumps (ASHPs) in winter. This study utilized TRNSYS18 software to establish a dynamic simulation model of the system, including the system’s model construction and the control scheme’s design. This performance study focused on analyzing the effects of the collector area and thermal energy storage (TES). The results show that with the increase in the collector area, the collector and power generation efficiencies decrease, and the system performance coefficient improves; the rise in the volume of TES leads to the collector and power generation efficiencies first increasing, and then they tend to stabilize, and the performance coefficient shows a trend of firstly increasing, and then decreasing. In terms of parameter optimization, a target optimization scheme and an evaluation model are constructed. The results indicate that the heating demand for a 116-square-meter building in the Tianjin area is met. The equivalent annual cost (EAC) of the system cost is the lowest, which is CNY 3963, when the collector area of the system is 31 square meters, the heat storage tank (HST) volume is 0.4 cubic meters and the phase-change energy storage (PCES) volume is 0.2 cubic meters. The payback period of the system is 10.59 years, which was compared to that of the ASHP. The further comparison of the economic feasibility of the system in the Lhasa, Shenyang, and Tianjin regions shows that the Lhasa region has the lowest EAC and payback period of CNY 1579 and 8.53 years, respectively, while the payback periods of Tianjin and Shenyang are 10.59 and 10.3 years, with EACs of CNY 3963 and CNY 5096, respectively.

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.

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.

Saponification residue–sodium nitrate morphologically stable phase-change materials for medium- and high- temperature thermal energy storage

Saponification residue (SR) is a by-product of the chlor-alkali process used to produce propylene oxide. Owing to its high porosity and large specific area, SR is suitable as a carrier in the preparation of composite phase-change materials (CPCMs). This approach not only addresses the leakage issues associated with phase-change energy storage materials but also utilises solid waste. Herein, a morphologically stable CPCM was prepared using industrial SR solid waste and a phase-change material (sodium nitrate) via a hybrid sintering method. Phase analyses by X-ray diffractometer showed good chemical compatibility between sodium nitrate and SR. Further, scanning electron microscopy showed that SR has a porous structure, and sodium nitrate can be stably adsorbed on the pores and surface of SR. The maximum compressive strength of SR-CPCM was 43.37 MPa. Moreover, the highest loading capacity of SR for sodium nitrate was 50 wt%, resulting in no leakage and remarkable morphological stability. Differential scanning calorimetry indicated that SR-CPCM exhibited adequate thermal stability and that the latent heat increased with rising nitrate content, reaching a maximum value of 99.24 J/(g·°C). Importantly, after 100 thermal cycles, SR-CPCM demonstrated good stability in terms of chemical compatibility and latent heat. These results demonstrate the potential of SR as a carrier material for energy storage applications.

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 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.

Simulation and experimental study on the performance of vacuum tube phase change collector with combined heat exchange of flat tubes and fins

This paper establishes a solar vacuum tube collector with flat tubes and fins as the heat transfer unit, and the thermal performance was tested under different environmental conditions. The results indicate that the paraffin in the vacuum tube collector showed the phenomenon of temperature stratification at the region of the high and low temperature when the system absorbed heat. Secondly, the daily average heat-taking efficiency can reach 30–45 % when the irradiance is 822.5 W/m2, 555.0 W/m2, and it only about 6 % under the irradiance 111.6 W/m2. In addition, the energy storage system was simulated, and the thermal storage stage was analyzed according to the different temperature distribution curves, temperature distribution nephogram and liquid fraction. The results show that when the running time is about 2500 s, the paraffin temperature reached the melting point, the paraffin begins to melt; when to 4500 s, the solid–liquid phase conversion is complete, after this time the temperature rise is relatively smooth; when the time is run to 14,000 s, energy-storage type solar vacuum collector has reached a stable state, the temperature tends to level off, then the temperature increase is not obvious. It will provide some theoretical and data support for the later combination of solar phase change energy storage technology and heat pump technology.

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 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.