Phase Change Thermal Storage Research Articles

Thermal conductivity enhancement and shape stabilization of phase change thermal storage material reinforced by combustion synthesized porous Al2O3

The utilization of paraffin in latent heat storage system is limited by its leakage and low thermal conductivity. To address such challenges, we prepare composite phase change materials (PCMs) with enhanced thermal conductivity and shape stability. Paraffin is supported by porous Al2O3 which is synthesized by solution combustion synthesis (SCS). The porous structure of Al2O3 is quite influenced by the fuel species in SCS reactions. The glycine-induced Al2O3 shows highly hierarchical porous structure, which can improve the anti-leakage performance of the composites. The thermal conductivity of Al2O3/PW reaches 1.27 W/m•K with an Al2O3 mass ratio of 50 wt%, which is 5 times of pure paraffin. The composite also presents acceptable latent heat capacity of higher than 100 J/g and very good thermal cycling stability. These characteristics assure the promising application of Al2O3/PW composites for thermal energy storage.

NiTiHf shape memory alloys as phase change thermal storage materials

Motivated by the recent advancements demonstrating the effectiveness of NiTi shape memory alloys (SMAs) as high figure of merit (FOM) phase change materials (PCMs) for thermal management and storage, NiTiHf SMAs were explored as candidate solid-solid PCMs with high temperature capability. Differential scanning calorimetry and Archimedes’ method were used to determine the transformation temperatures, thermal hysteresis, enthalpy of transformation, and density of several different NiTiHf SMAs with varying compositions. Ni50.3Ti29.7Hf20 (at. %) demonstrated a high transformation enthalpy of 32.5 J/g, a relatively low thermal hysteresis of 31°C and a thermal conductivity of 11.19 Wm−1K−1 in the austenite phase. In general, NiTiHf SMAs exhibited FOM values an order of magnitude higher than traditional PCMs and up to about 120 % higher than the FOM value measured in binary NiTi SMAs. The clear trends relating transformation temperatures, transformation enthalpy, and thermal hysteresis to composition presented here provide for tunability of NiTiHf SMAs to specific thermal energy storage applications through composition control. High FOM values combined with transformation temperatures surpassing 500°C allows NiTiHf alloys to populate previously empty regions of FOM vs. transformation temperature property space for high FOM PCMs.

Study on the influence of tank structure and fin configuration on heat transfer performance of phase change thermal storage system

Owing to the intermittent and fluctuating nature of solar energy, thermal energy storage (TES) plays a vital role in solar energy utilization. The structural and geometric limits of the traditional heat storage systems, as well as the low thermal conductivity of phase change materials (PCMs), decrease the heat storage and exothermic efficiency of TES severely. To alleviate these shortcomings and improve the TES heat storage and release efficiency, the geometrical structure of TES and fin structure of the heat storage system need to be optimized. This study established a 2D model of the phase change TES unit with a single tank and auxiliary electric heating based on the experimental findings. The heat transfer performance of the truncated cone model with different taper configurations was also analyzed numerically. The influence of long and short fins on PCM heat transfer was analyzed under the premise of a certain fin volume. The influence of fins with different inclinations on the heat transfer process was also analyzed. The results show that the truncated cone with a taper of 0.37 performs best in the charging and discharging process. Compared with long fins, most short fins showed to have a more significant effect on accelerating the charging process. The enhancement effect of the different fin on the heat transfer process was divided into two categories, and the analysis shows that the fins with an inclination angle of −15° have the most significant enhancement effect. These findings of the study will guide the optimization design of the heat transfer structure of TES with a single tank configuration.

Effect of high-temperature-resistant epoxy resin/polyethylene glycol 2000 composite stereotyped phase change material particles on asphalt properties

In this study, epoxy resin/polyethylene glycol 2000 composite stereotyped phase-change material (EPPCM) particles were prepared. It was found that the phase change thermal storage properties were almost unchanged after heat treatment when the thermal decomposition onset temperature reached 230 °C according to Differential scanning calorimetry (DSC) analysis and Thermogravimetric analysis (TGA) test. Modified asphalt with increasing particle doping was prepared by high-speed shearing. Dynamic shear rheological (DSR) test, Bending beam rheometer (BBR) test, temperature regulation test and specific heat capacity test were carried out on modified asphalt. The results show that with the increase in EPPCM doping, gradual improvement of rheological properties of modified asphalt appeared, and there was an increasing trend occurred in the temperature regulation effect. The maximum temperature difference reached 4.3 °C and the specific heat capacity of asphalt increased as well.

A Review on Thermal Properties Improvement of Phase Change Materials and Its Combination with Solar Thermal Energy Storage

This article summarizes measures to enhance the solar phase change thermal energy storage (TES), starting from two key points in solar phase change TES research: solar phase change materials (PCM) and solar phase transition devices. First, different types of PCM and their advantages and disadvantages are introduced. To improve thermal performance, the research progress of different dimensional thermal conductivity additives, photothermal composite phase change materials (CPCM), and phase change microcapsules is reviewed. Then, the characteristics of commonly used solar phase transition TES devices and the research status of solar energy device improvement with fins and multistage phase transition TES are summarized for the past few years. It is hoped to provide methods and ideas for the design and research of solar phase change TES systems, and to increase the overall heat transfer properties through the combination of multiple optimization methods. Finally, the future direction and research focus of solar phase change TES technology are put forward.

Distributed Thermal Energy Storage Configuration of an Urban Electric and Heat Integrated Energy System Considering Medium Temperature Characteristics

Distributed thermal energy storage (DTES) provides specific opportunities to realize the sustainable and economic operation of urban electric heat integrated energy systems (UEHIES). However, the construction of the theory of the model and the configuration method of thermal storage for distributed application are still challenging. This paper analyzes the heat absorption and release process between the DTES internal heat storage medium and the heat network transfer medium, refines the relationship between heat transfer power and temperature characteristics, and establishes a water thermal energy storage and electric heater phase change thermal energy storage model, considering medium temperature characteristics. Combined with the temperature transmission delay characteristics of a heat network, a two-stage optimal configuration model of DTES for UEHIES is proposed. The results show that considering the temperature characteristics in the configuration method can accurately reflect the performance of DTES, enhance wind power utilization, improve the operation efficiency of energy equipment, and reduce the cost of the system.

Preparation and thermal storage performance of phase change ceramsite sand and thermal storage light-weight concrete

1. Abstract: In this study, preparation and thermal storage performance of phase change ceramsite sand and thermal of storage light-weight concrete are studied. Sintering-free ceramsite and ceramsite sand with high adsorption ability were prepared. Then, paraffin is incorporated into them to fabricate phase -change coarse aggregate and phase-change fine aggregate, respectively, which are used to prepare thermal storage light weight concrete. Brunauer-Emmett-Teller (BET), Mercury intrusion method (MIP) Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) and X-ray diffraction (XRD) are employed to analyze the specific surface area, pore structure, thermal properties, chemical composition and phase composition of phase change aggregate. The compressive strength and the temperature regulation performance of the thermal storage light weight concrete are studied. The results show that the porosity of the ceramsite sand is 58.27% when the content of expanded perlite and Aluminum is 30 g and 1 g, respectively. In addition, the adsorption rate of paraffin in the ceramsite sand is 42.75 wt% and the melting latent heat of the phase change ceramsite sand is 45.64 J/g. The compressive strength of the prepared thermal storage light-weight concrete meets the strength level of lightweight concrete 15 Mpa (LC15) Moreover, the prepared concrete shows light-weight character and good temperature regulation performance. The prepared thermal storage concrete shows a good application prospect in energy-saving and the use of renewable energy.

Phase change thermal storage: Cooking with more power and versatility

A 100 W solar panel directly powering an Insulated Solar Electric Cooker (ISEC) can slowly cook 5 kg of food over the course of a day. However, 0.4 kWh of the day’s energy can be stored in 2.5 kg of erythritol phase change material, allowing ISEC to cook more rapidly, as well as cook after sunset. We control supercooling by forcing crystallization, making erythritol an ideal thermal storage material for cooking and other thermal-storage processes, but the erythritol degrades in quality when cycled for several months over 180 °C. The efficiency of thermal storage is comparable to that of more expensive systems using battery storage and induction cooktops. ISECs can be built in low-income communities, and the best design varies depending on availability of materials, access to building technologies, and local preferences. A Global Learning Community of researchers, funding agencies, nonprofits, student groups, and local enterprises is collaboratively developing the open source technology with partners in low income communities to optimize designs, construction, and dissemination.

Design and performance evaluation of a dual-circuit thermal energy storage module for air conditioners

We present experimental results and a validated numerical model of a dual-circuit phase-change thermal energy storage module for air conditioners. The module incorporates a phase-change material encapsulated in compressed expanded natural graphite foam. We used n-tetradecane as the PCM with a transition temperature (~4.5 °C) suitable for air-conditioning applications. Heat exchange to and from the module is accomplished through two fluid loops operating as a heat source and sink embedded inside multiple slabs of the composite material. This dual-circuit design enables easier integration with air-conditioning equipment and provides enhanced flexibility in system operation as compared to the state-of-the-art thermal storage systems. When integrated with an air-conditioner, this design will enable peak-load shaving and enhances operational efficiency. The thermal storage device was designed for a nominal storage capacity of ~ 3.5 kWh. We evaluated the heat transfer and energy storage performance of this device using standalone heat transfer experiments to estimate key thermal resistances and identify design improvements before integration with an air conditioner. The numerical model of the heat exchanger uses a combination of discretized and lumped parameter approaches to maintain a balance between accuracy and computational expense. Our analyses show that the geometric features and integration of fluid tubes are key contributors to the thermal contact resistance between the fluid and the thermal storage material, and consequently, to the overall performance of the thermal storage module. Our standalone experiments also identified important operating scenarios in which this thermal storage module can be used for air-conditioning in buildings.

Numerical investigation of the optimization of phase change thermal storage units with air as heat transfer fluid

Phase change thermal storage units (TSUs) that use air as heat transfer fluid (HTF) are in huge demand in the fields of building heating, solar energy utilization, and flue gas heat recovery. Researchers have developed various air-based TSUs and used different methods to optimize their structure. In the current study, the structural parameters of a novel TSU with air as the HTF are optimized using a comprehensive method that combines overall thermal resistance analysis and numerical simulation. The influence of different HTF injection methods on the natural convection of a phase change material (PCM) and the effects of different structural parameters on the TSU's charge performance were investigated. Results indicated that the heat transfer thermal resistance of the developed TSU is mostly concentrated in the PCM side. When the depth direction of the flat tube was perpendicular to the direction of gravity and the HTF adopted side injection, the phase change completion time was shortened by 20.59% compared with that in the original TSU. Thermal resistance balance was achieved in the air and PCM sides when the rib height, pitch, and thickness of the flat tube were 0.03, 0.0232, and 0.00025 m, respectively. At this moment, the compact factor and effectiveness of the novel TSU were 1.63 times and 10.52% higher than those of the original TSU, respectively.

Thermal performance analysis of multi-slab phase change thermal energy storage unit with heat transfer enhancement approaches

A novel multi-slab thermal energy storage (TES) unit with NaNO3 as PCM is designed for concentrating solar thermal power plants due to its easy manufacture and high energy storage density. A numerical model, based on the k−ε turbulence model, is used in studying the thermal performance of the system. To enhance the efficiency, two heat transfer enhancement methods are compared with the original unit, which is adding plate fins or 10 wt%EG into NaNO3. The numerical model is validated to be reliable for simulating the heat transfer with natural convection by a lab-built rig. The numerical results show that adding fins shortens the phase change time by up to 18% with an HTF flow rate of 4.0 × 10−3 m3/s in each channel and adding 10 wt%EG is the most effective way to enhance the heat transfer. The role of natural convection in heat transfer is analyzed. In practical applications, the sensible heat during the charging/discharging process cannot be neglected, which occupies 45%–55% of the total heat stored/released. This paper is expected to provide a detailed investigation of the thermal performance of the unit with two different thermal enhancement methods to give some rational advice in optimizing the system design and operation.

Design and investigation of single tank phase change thermal storage domestic hot water system

Thermal energy storage (TES) is extensively applied in production and daily life. As a basic work, we designed a single tank phase change TES domestic hot water system using night valley power. Based on the single tank TES experimental platform, a 2D numerical model of the system was established. To optimize the performance of a single tank TES system, the effect of heat transfer fluid (HTF) inlet velocity and temperature on the heat release of the storage tank was analyzed based on simulation. The enhanced heat transfer effect of the radial cascade system and axial cascade system was also compared. The results showed that 0.8 m/s is the optimal HTF inlet velocity in the calculation range. The rule of the heat release about the HTF inlet temperature just meets the different hot water requirements in winter and summer. The heat release capacity of the radial cascade system and axial cascade system is higher than that of the conventional single-stage system, and the proportion of latent heat release in radial cascade is larger. This study will provide theoretical guidance for the optimal design of the single tank TES domestic hot water system in the future.

Novel and durable composite phase change thermal energy storage materials with controllable melting temperature

The development of high temperature phase change materials (PCMs) with great comprehensive performance is significant in the future thermal energy storage system. In this study, novel and durable Al-Si/Al2O3-AlN composite PCMs with controllable melting temperature were successfully synthesized by using pristine Al powder as raw material and tetraethyl orthosilicate as SiO2 source. The Al2O3 shell and Al-Si alloy were in-situ produced via the substitution reaction between molten Al and SiO2. Importantly, the crack caused by the incomplete encapsulation of the Al2O3 shell could repair itself by the nitridation reaction of internal molten Al and thereby forming a highly dense Al2O3-AlN composite shell. The produced dense Al2O3-AlN composite shell could significantly improve the thermal cycling stability of composite PCMs, and thus, the thermal storage density decrease of the Al-Si/Al2O3-AlN (59.8 J/g to 77.7 J/g) was far less than that of the Al-Si/Al2O3 (118.5 J/g) after 3000 thermal cycles. Moreover, the synthesized Al-Si/Al2O3-AlN still exhibited a controllable melting temperature (571.5–637.9 ℃), relatively high thermal storage density (105.6–150.7 J/g), great dimensional stability and structural stability after 3000 thermal cycles. Hence, the synthesized Al-Si/Al2O3-AlN composite PCMs, as promising preferential thermal energy storage materials, can be stably used in the energy utilization efficiency improvement of various systems for more than 6 years.

Rate capability and Ragone plots for phase change thermal energy storage

Phase change materials can improve the efficiency of energy systems by time shifting or reducing peak thermal loads. The value of a phase change material is defined by its energy and power density—the total available storage capacity and the speed at which it can be accessed. These are influenced by material properties but cannot be defined with these properties alone. Here we show the close link between energy and power density by developing thermal rate capability and Ragone plots, a framework widely used to describe the trade-off between energy and power in electrochemical storage systems (that is, batteries). Our results elucidate how material properties, geometry and operating conditions influence the performance of phase change thermal storage. This research sets a clear framework for comparing thermal storage materials and devices and can be used by researchers and designers to increase clean energy use with storage.

A turbidity titration procedure for the nucleation mechanism determination of sodium sulfate decahydrate (Glauber salt) in unseeded aqueous solution

As a noteworthy salt hydrate, sodium sulfate decahydrate or Glauber salt can be used as a phase change thermal energy storage material. Kinetic parameters of sodium sulfate decahydrate salt solution are evaluated experimentally. Instead of the traditional polythermal and isothermal methods, a novel constant temperature experimental method (based on the turbidity titration) was adopted to experimentally illustrate the induction time and metastable zone width, in unseeded batch crystallization for sodium sulfate decahydrate salt solution at different temperatures (7, 9, 10, 13, 16, 19, 22 °C) and supersaturation ratio (1.01–1.43). We determined crystallization thermodynamics parameters, solubility, and supersolubility, of sodium sulfate decahydrate salt solution under atmospheric pressure and at different temperatures. The solubility data could be well fitted by the solubility carve of sodium sulfate decahydrate in the phase diagram of sodium sulfate. Statistical analysis shows that there was consistency in the result data of solubility. Two models, classical nucleation theory (primary homogeneous) and secondary nucleation, were employed to analyze the experimental data. The secondary nucleation model helped determine the order of nucleation and nucleation kinetic constants.

Research on Performance and Safety of Composite Inorganic Phase-Change Materials (NaNO3/SiO2/C) under Low-temperature Cold Shock

This article studies the cold shock resistance and safety performance of NaNO3/SiO2/C composite inorganic phase-change thermal storage materials at extremely low temperatures. A low-temperature cold shock test system is built, and the composite inorganic phase-change thermal storage materials of different raw material particle sizes are carried out through the static cold shock and dynamic cold shock at − 40, − 60, − 80 and − 196 °C. The changes in quality, volume, surface morphology phase and thermal properties of the phase-change thermal storage materials are respectively analyzed by means of characterization methods such as scale, vernier caliper, DSC, SEM, and XRD. The results show that the thermal performance of phase-change thermal storage materials with different particle sizes is only 1.97-8.89%, especially under cryogenic shock at − 196 °C. The cold shock resistance is better with the increase in particle size. The physical properties, chemical properties and thermal storage capacity of the material under impact are basically stable, and it has good cold shock resistance. The cold shock of the two methods does not affect the thermal storage function of the material and does not cause thermal energy waste, and the safety performance is better.

Thermophysical characteristics and enhancement analysis of carbon-additives phase change mono and hybrid materials for thermal management of electronic devices

A novel zero-noise and clean thermal management technology (TMT), based on phase-change thermal energy storage (TES) technology, has turned out the new vision for researchers and industrialist involved in electronics industry. Therefore, this paper highlights a new direction by developing the nano-enhanced phase change materials (NePCMs) by combining the carbon-additives with phase change material. Four different types of carbon-additives of multi-wall carbon nanotube (MWCNT), graphene oxide (GO), reduced graphene oxide (rGO) and graphene nanoplatelet (GNP) were dispersed in RT-35HC, used as a PCM, with the combinations of mono (MWCNT, GO, rGO and GNP) and hybrid (GO+MWCNT, rGO+MWCNT and GNP+MWCNT) nanoparticles. A constant mass percentage of 1.0 wt.% was selected for both mono and hybrid combinations of nanoparticles to explore the best type and dispersion scheme for productive and effective thermal management applications. All the synthesized NePCMs were characterized using various characterization methods to study microstructural features, surface chemistry, lattice dimensions, stability, thermal and phase-change TES characteristics. The key findings reveal the best chemical and thermal stability, uniform dispersion of carbon-based nanoparticles in RT-35HC without modifying the molecular structure. The highest thermal conductivity enhancements of 182.7%, 183.8% and 185.3%, and optimum value of enthalpy of fusions of 237.42, 235.35 and 230.82 J/g were achieved for hybrid NePCMGO+MWCNT, NePCMrGO+MWCNT, and NePCMGNP+MWCNT, respectively in comparison of mono NePCMs. The phenomenon of thermal conductivity and specific heat capacity were explained systematically. Conclusively, the minimum subcooling, specific heat capacity enhancement and smaller phase-transition temperature reveal that GNP+MWCNT dispersed hybrid NePCM can be potentially used for thermal management applications.

Development and Validation of a Latent Thermal Energy Storage Model Using Modelica

An abundance of research has been performed to understand the physics of latent thermal energy storage with phase change material. Some analytical and numerical findings have been validated by experiments, but there are few free and open-source models available to the general public for use in systems simulation and analysis. The Modelica programming language is a good avenue to make such models available, because it is object-oriented, equation-based, declarative, and acausal. These characteristics have enabling the creation of component model libraries that can be used to build larger system simulations for design analysis. The authors have previously developed a numerical framework to model phase change thermal storage and have validated model predictions with experiments. The objectives of this paper are to describe the transfer of the numerical framework to an implementation in a Modelica component model and to validate the Modelica model with data from the experiment and the original numerical framework.

Enhancing discharging performance of a phase change thermal storage unit with a fractal space-filling matrix

The phase change thermal storage (PCTS) technique is essential for renewable energy utilization. To strengthen the heat-discharge performance, an innovative PCTS unit with a fractal space-filling matrix is proposed. Based on the established solidification model, the solidification interface transformation and temperature field evolution of the innovative PCTS unit are numerically analyzed and compared with those of conventional units. Moreover, the roles of the structural parameters of PCTS units are investigated in terms of the resulting solidification behavior, and the metal matrix is optimized in terms of the solidification duration. The results show that the fractal space-filling matrix effectively improves the heat-discharge performance. Compared to conventional PCTS units, the proposed PCTS unit with a fractal space-filling matrix produces a more uniform temperature field and enhances the solidification rate by approximately 40%. Regarding the trade-off between cost and performance, a fractal level of two is suggested to maximize the heat-discharge enhancement and minimize the manufacturing cost. To minimize the solidification duration, the optimal length and thickness ratios of the fractal space-filling matrix are found to be 0.4 and 0.5, respectively, for practical engineering applications.

Dynamic numerical study on phase change thermal storage heat transfer

Targeted at the poor heat transfer effect of the phase change thermal storage heat exchanger due to the low thermal conductivity of the phase change material, a fin-tube type phase change thermal storage heat exchanger has been proposed in the study. A 2-D model of the phase-change heat storage unit was established, and the dynamic heat transfer law of the melting and solidification of the phase change material, and the influence of the fin structure size on the heat storage/release performance of the heat exchanger were numerically analyzed. The results show that in the area close to the tube wall, the smaller the fin spacing, the larger the thickness, the faster the phase change heat storage/release speed, and the better heat transfer effect. In the central area of the phase change material, the greater the fin spacing and thickness, and the better the heat transfer effect of the phase change heat storage/release. The area close to the outer wall has the smallest temperature change, and the heat storage/release effect is the worst. Therefore, the use of energy storage heat exchangers with gradual fin thickness and spacing is an effective method to improve the heat transfer efficiency of existing equipment. In addition, in order to improve the heat exchange effect of the edge area of the phase change, its structure could be changed or the heat exchange form can be increased.