Phase Change Energy Storage System Research Articles

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.

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.

Thermodynamic and Exergoeconomic Analysis of a Novel Compressed Carbon Dioxide Phase-Change Energy Storage System

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system.

Experimental research on the effect of graphite on heat transfer performance of a latent heat storage system

Phase change materials (PCMs) provide a good resolution for the latent heat storage system which can be used in many application fields such as solar energy utilization and waste heat recovery. This study aims to experimentally investigate the impact of graphite powder on the thermal characteristics and heat transfer performance of paraffin with ceresin (PC) as a PCM, using water as the heat transfer fluid. Experimental tests were conducted to analyze the heat transfer performance of PC and the influence of graphite powder on its thermal characteristics. Different masses of graphite powder were employed to assess their effects on the heating rate and the time required for PC to reach its melting temperature. The experimental results revealed that the addition of graphite powder improved the heating rate of both PC and water, attributed to its high thermal conductivity. Furthermore, the time for PC to reach the melting temperature was decreased with varying amounts of graphite powder, achieving a maximum reduction of 17.2% with the addition of 40 g of graphite powder. However, the effectiveness of graphite powder in enhancing heat transfer efficiency was found to be limited, with the optimal promotion effect observed at around 40 g of graphite powder for 500 g of PC. The findings of this investigation provide valuable insights for the design of phase change energy storage systems, with potential applications including heat pump drying units, greenhouse energy storage in modern agriculture, and solar energy storage utilization technology. The theoretical basis established can contribute to the development and optimization of PCM-based systems in diverse practical scenarios.

Numerical Study of a High-Temperature Latent Heat Thermal Energy Storage Device with AlSi12 Alloy

This paper explores the potential of thermal storage as an energy storage technology with cost advantages. The study uses numerical simulations to investigate the impact of adding porous material to the HTF side during solidification to improve the heat transfer effect of TES using AlSi12 alloy as the phase-change material. The research also examines the effects of adding porous dielectric materials and increasing air velocity on the discharge temperature, discharge power, and discharge time of high-temperature phase-change energy storage systems. The study found that the temperature difference of the PCM (increased), solidification time (reduced more than 85%), the outlet temperature of the air, and heat discharge power of the LHS did not vary significantly across different porous materials (copper foam, nickel foam, and silicon carbide foam) added to the HTF tube. These findings offer important information for the design of high-temperature phase-change energy storage devices and can guide future developments in this field.

Numerical investigation of the influence of unsteady inlet temperature on heat storage performance of a novel bifurcated finned shell-tube heat storage tank

Due to the change of solar radiant intensity with time, the melting process in the phase change energy storage system connected to the solar collector occurs under the unsteady inlet temperature. Three unsteady inlet temperature conditions have been proposed, and their average inlet temperature has been used as the corresponding steady inlet temperature conditions to form three comparative working conditions. Under different comparison conditions, a three-dimensional numerical comparison analysis has been conducted on the heat storage performance of a novel bifurcated finned shell-tube heat storage tank. Compared with the corresponding steady inlet temperature condition, the unsteady inlet temperature condition can accelerate the melting process and improve the temperature uniformity of the phase change material. The liquid fraction differences of TA and Ta, TC and Tc at the end of the reaction are 9.5% and 7.5% respectively, and the difference in the time required for the liquid fractions of TB and Tb to reach 1 is 17.7%. The evaluation coefficients for the three comparative working conditions are 3.1, 1.3 and 3.6 respectively. The results can provide a certain reference value for the performance optimization and practical application of the latent heat storage system.

Melting characteristics of concentric and eccentric inner elliptic tube in double tube latent heat energy storage unit

Thermal energy storage is critically necessary for most solar energy applications. The phase change energy storage systems are the most promising; however, the poor thermal conductivity of the material is a major disadvantage. This work aims to simulate the melting process and investigate the optimum design parameters for a stable and high melting rate of phase-change energy storage systems. A 2-D axisymmetric numerical model has been developed using ANSYS 17. The model was validated by published experimental data. A new elliptical design of the inner tube was investigated; and the main parameters considered were eccentricity (0, 0.1, 0.2, 0.3, 0.4, and 0.5), aspect ratio (1, 0.9, 0.8, 0.7, 0.6, and angle of 0.5), and inclination (0°, 30°, 60°, and 90°) of the inner tube. The outcome of this investigation revealed that the maximum enhancement of the average melting rate was 19.14%, 42.65%, 71.3%, 105.51%, and 150.1%, for eccentricity of 0.1,0.2,0.3,0.4, and 0.5, respectively, for an aspect ratio of 1. The maximum and minimum average melting rate were 0.00516 and 0.00417 kg/min for the vertical inner elliptical tube (θ = 90°) and the horizontal inner elliptic (θ = 0°) respectively for an aspect ratio of 0.5.

Effects of hollow skeleton on melting process in copper foam

The compositing of porous medium and phase change material is an effective way to improve the heat transfer performance of solid-liquid phase change energy storage system. In this paper, we reconstruct the three-dimensional numerical structure of the copper foam by using the micro computed tomography, and then conduct the pore-scale numerical simulation of the melting process in a cubic cavity filled with the phase change material comprised of the copper foam via the lattice Boltzmann method. The effects of the hollow skeleton on the melting process are discussed in detail under different Rayleigh numbers and ratios of thermal conductivity of the copper foam to that of the phase change material. The results show that the hollow skeleton copper foam possesses a lower average Nusselt number along the left wall at the early stage of the melting process, a slower melting rate, and a higher energy storage efficiency than the solid skeleton copper foam. Comparing with the skeleton region of the copper foam, the heat transfer rate entering the cubic cavity through the hollow region of the skeleton is almost negligible. Because of the competition between heat conduction and natural convection, the heat transfer enhancement efficiency of copper foam first increases, then decreases, and then increases again with the increase of the Fourier number. When the Rayleigh number decreases, the energy storage efficiency increases, and the natural convection also weakens. Meanwhile, the fluctuation of the heat transfer enhancement efficiency decreases as the Fourier number increases, and the gap of the heat transfer enhancement efficiency between the hollow skeleton copper foam and the solid skeleton copper foam becomes smaller. When the ratio of the thermal conductivity of the copper foam skeleton to that of the phase change material increases, the energy storage efficiency is relatively high at the early stage of the melting process but becomes relatively low when the melting process is completed. With a larger thermal conductivity ratio, the heat transfer rate entering the cubic cavity through the skeleton region of the copper foam becomes dominant, which reduces the effect of the hollow skeleton on heat transfer, and thus the gap of the heat transfer enhancement efficiency between the hollow skeleton copper foam and the solid skeleton copper foam becomes relatively small.

Thermal assessment on solid-liquid energy storage tube packed with non-uniform angled fins

The solid-liquid phase change energy storage system promoted the efficient and sustainable utilization of dispersive and intermittent renewable energy. Low energy storage rate and unbalanced thermophysical characteristics existed in the vertical shell-and-tube heat storage tubes. To improve thermal properties and melting uniformity, this paper proposed a non-uniform angled fin type considering the optimization by the non-uniform arrangement and angled fins with small angles. A visual experimental platform was designed and built, and the reliability of the numerical model was verified by the experimental results. Numerical simulations of a single shell-and-tube heat storage tube regarding maximizing phase change rate were carried out. The development of the phase change interface and transient temperature field during the charging process of the non-uniform angled fins with downward 10° were obtained. Results showed that, compared with the uniform straight fin tube, the non-uniform angled fin can effectively promote the melting process of the whole fin tube, especially in the bottom area, leading to a 69.59% reduction in complete melting time. This provided a reference for the performance optimization of the shell-and-tube finned phase change heat storage tube. • Non-uniform angled fins are designed for improving energy storage. • A 69.59% reduction in full melting time is obtained compared with uniform straight finned tube. • Unbalance of thermophysical characteristics are effectively reduced by non-uniform design. • Non-uniform angled fins achieved heat flux improvement of TES unit as large as 29.19%.

Melting performance assessments on a triplex-tube thermal energy storage system: Optimization based on response surface method with natural convection

The low thermal conductivity of phase change materials significantly affects the heat storage and release performance for a phase change energy storage system. To alleviate this issue, a novel triplex-tube latent heat thermal energy storage system is designed and the melting behavior of phase change materials is studied numerically. On the premise of a fixed total volume of phase change material, the multi-parameter optimization design of the system is carried out by the response surface method. The fluid-structure coupling function of each parameter is fitted. Compared with the original model for the triplex tube, the melting performance of the optimized model is improved by 23.87%. The internal temperature fluctuation is found by dynamic temperature response, and the mechanism is explained by dynamic flow rate study. The improvement of melting performance by natural convection after optimization is also studied. The influences of the physical parameters (fin length, initial temperature of phase change material, inner and outer tube wall temperature, and fin material) of the optimization model on the melting performance of the system are quantified, as well. The effect of fin length (30-35-40 mm) on melting performance is found to be less than 11.47% and the effect of thermal conductivity of fin on the melting process is not obvious.

Numerical investigations of thermal performance enhancement in phase change energy storage system effective for solar adsorption cooling systems

Solar cooling systems requires an uninterrupted heat input for their continued operation. Thermal energy storage systems using phase change material (PCM) has the ability to deliver heat near isothermally and are effective for solar cooling applications. But these high energy dense storage systems exhibits poor thermal performance due to the low thermal conductivity of PCMs and are bulky. The main objective of this study is to design a phase change energy storage system (PCES) unit with different fin configurations, and to select a proper PCM for solar adsorption cooling systems (SAC). It projects the Preference Selection Index (PSI) method as the effective way to select the PCMs, and the result suggests the commercial PCM SavE-HS89 as a potential candidate among the different materials considered. This study also numerically investigates the thermal performance of different fins shapes, namely, positively tapered, negatively tapered and straight fins; among these the negatively tapered fins are found to be capable of compensating the slow melting process at the bottom region of the storage unit. It has been found that the negatively tapered fin improves the thermal performance of the PCES unit by reducing the melting time by up to 13% and 36% in comparison with the conventional straight fin and positively tapered fin, respectively. A case study of actual plant data of a SAC with different fin shapes shows that the storage system with the desirable configuration can save up to 46% of heat storage cost as compared to PCES without fin.

Constant-Volume Vapor-Liquid Equilibrium for Thermal Energy Storage: Proposal of a New Storage System for Concentrated Solar Power Plants

The development of thermal energy storage systems is key to increasing the deployability and reliability of concentrated solar power plants. Previous work from the authors studies the possibility of exploiting vapor-liquid phase change in closed and constant volumes as a thermal energy storage mechanism because of the higher heat transfer coefficients of the phenomenon with respect to solid-liquid phase change energy storage systems. The objective of this paper is to propose a new thermal energy storage condition based on vapor-liquid systems for concentrated solar power plants. The reference case of the Khi Solar One power plant in Upington, South Africa is taken. Results show that increasing the critical temperature of the storage fluid allows for increased temperature differences and higher volume-based energy storage, while the decrease of critical pressure allows lower mechanical stresses on the energy storage system. The use of high critical temperature fluids such as ethylene glycol allows for an increase of the volume-based energy storage of around 95% at same pressure conditions with respect to the base case. The use of low critical pressure siloxanes such as D6 results in a decrease of around 26% in the volume-based energy storage. The use of D6 on the other hand leads to a substantial decrease in the maximum pressure of the storage system, which drops from 8.2 MPa to 1 MPa, allowing the use of cheaper and less complex equipment. Both cases lead to a relevant increase in the maximum storage temperature, increased of 130 K and 55 K respectively.

Review on solar collector systems integrated with phase‐change material thermal storage technology and their residential applications

This article reviews the design of solar phase-change energy storage systems and their applications in residential buildings. The solar thermal collection system has high heat collection efficiency, no pollution, and it is also widely used in the field of building heating. In order to improve the efficiency of the solar collector system, the researchers found that integrating phase-change materials (PCMs) into the solar thermal collector system can achieve this goal, but there will be a problem of PCM leakage. Some researchers have solved this problem by microencapsulating PCMs, the thermal conductivity and energy storage efficiency of the PCMs after microencapsulation will be greatly affected. Adjusting the solar collector to an appropriate inclination angle can achieve the highest heat collection efficiency. Choosing the PCM in the appropriate temperature zone can improve the system efficiency. For the separated solar collector system, the parts that need to be considered include the type of heat exchanger, the structure of the energy storage heat exchanger, the shape of the heat exchanger fins, the type of solar collector, and so on. All in all, coupling PCM into the solar collector system can improve energy efficiency reduce carbon emissions and have good economics, the maximum internal rate of return of solar collectors integrated with PCMs in residential and industrial applications is 22% and 17.2%.

Comparison of different approaches for thermal performance improvement of a phase change energy storage system

Performance improvement of a phase change material (PCM) thermal storage system is numerically investigated. A finite volume solver is employed to simulate the melting process of the PCM in different geometrical and boundary conditions. The numerical predictions are initially validated against available experimental data. Afterward, four different scenarios are investigated to improve the thermal characteristics of the phase change process. These scenarios include insertion of radial fins with different radial lengths, insertion of a porous layer on the PCM side of the heat transfer fluid (HTF) tube, doubling the HTF mass flow rate, and also increasing the HTF inlet temperature. The results indicate that all of these scenarios expedite the melting process, but at different rates. The insertion of the porous medium is shown to be more effective than using of radial fins. Moreover, according to the second-law analysis of the thermal storage system, using the porous layer provides a superior exergy efficiency compared to other enhancement scenarios. Overall, the addition of a metallic porous layer around the HTF tube is proven to be the most effective as well as the most efficient approach to improve the thermal characteristics of the energy storage system.

Semi-analytical thermal modeling of transverse and longitudinal fins in a cylindrical phase change energy storage system

Inclusion of fins in phase change energy storage systems has been widely investigated for improving the rate of energy storage. Despite significant past experimental research in this direction, there is a lack of comprehensive theoretical models for fin-based enhancement in energy storage, particularly for cylindrical geometries. This is a considerably challenging, non-linear problem. This paper presents a semi-analytical model for temperature distribution and energy storage in an annular phase change material (PCM) material around a hot cylinder in the presence of transverse and longitudinal fins extending into the PCM. Two distinct pathways for heat transfer into the PCM are analyzed separately and expressions for total heat flux into the PCM are determined for both fin types. The perturbation method is used for analyzing the non-linear phase change problem and determining the heat flux into the PCM through the fin. The dependence of total energy stored on fin thermal properties and geometrical parameters is determined. Results indicate key similarities and differences between cylindrical fins and recently-reported Cartesian fins. It is shown that even a thin fin results in considerable heat transfer enhancement. Results also indicate diminishing results when the fin size is further increased. Theoretical modeling presented in this paper improves the fundamental understanding of an important heat transfer enhancement strategy for phase change based energy storage systems. Results discussed here may help improve the practical design of finned, cylindrical phase change energy storage systems that are commonly used for harnessing renewable energy.

Experimental analysis of defrosting and heating performance of a solar‐assisted heat pump integrated phase change energy storage

This thesis investigates a novel solar-assisted heat pump integrated phase change energy storage system. The defrosting performance of this system was studied experimentally and the results were compared with two traditionally used methods: reverse cycle defrosting (RCD) method and hot gas bypass defrosting (HGBD) method. The results show that the phase change energy storage system has superior performance compared with traditional defrosting methods. The indoor temperature drop recorded was relatively small and the defrosting time was 75% of the RCD system and 53% of HGBD system. The phase change energy storage system increased the condensation temperature which consequently increased the temperature difference of heat transfer resulting in higher conductivity in the defrosting progress. Compared with the method of RCD and the method of HGBD, the recovery time of the system was shortened by 90 and 160 seconds, respectively. The system works with low-temperature heat source and circulating water, which considerably reduces energy consumption, thereby improving the performance of the defrosting system. A further experimental study was also conducted on the heating performance and the results also indicated that the value of COP can reach up to 3.6 in daytime, and the indoor temperature can be stably maintained above 18°C throughout the day. Novelty Statement A new defrosting method for energy storage defrosting is proposed, and the defrosting performance is compared with two common defrosting methods. In addition, the performances of the heating system over the day were experimentally investigated. The experimental results show the system meets the heating needs of the building. Finally, the influence of the outdoor temperature on the exergy efficiency of the system was discussed. It shows that this system can improve the operational stability, the system economy and energy saving.

Development of a math module of shell and tube phase-change energy storage system used in TRNSYS

Due to the lack of phase-change energy storage modules in the TRNSYS software, this paper applies the numerical simulation method to develop a TRNSYS module. Research has been conducted on the characteristics of the shell-and-tube phase-change energy storage system in order to provide a reasonable basis for its application in practical engineering. According to the principles of energy conservation, a numerical model has been proposed to calculate the temperature field and fluid temperature field of the phase-change unit, and a mathematical model is applied to guide the editing of the TRNSYS module. A Fluent model was established to compare the TRNSYS simulation results and verify the physical validity of the module. In terms of the thermal outlet temperature of the HTF, the maximum relative error between the two in the melting phase is noted to be 1.17%, and the maximum relative error at the solidification stage is 1.83%.Different flow parameters of the system have been studied. The results of the study indicate that differences in inlet temperatures have a greater influence on the average temperature and outlet temperature of the PCM, whereas differing inlet flows have a negligible influence on the phase-change unit.

Numerical Study on Enhancement of Heat pipe-nickel foam to High Temperature Phase Change Thermal Storage

High temperature phase change thermal energy storage could be widely applied in the fields of solar power systems, industrial waste heat recovery, etc., while the drawback of low thermal conductivity constrains the application of phase change thermal energy storage. The enthalpy-porosity technique was employed to analyze the performance of a thermal energy storage unit with square container and high melting temperature phase change material enhanced by heat pipes and nickel foam. The melting performance of the phase change material with different thermal enhancement methods has been studied. The obtained results reveals that heat pipe is more effective than the nickel foam, and the heat pipe-nickel foam mode could effectively shorten the melting process and decrease the temperature difference within the phase change material in the container. The simulation could provide a significant reference to the phase change energy storage system enhanced by heat pipes.

Plate type heat exchanger for thermal energy storage and load shifting using phase change material

The study presents an experimental investigation of a thermal energy storage vessel for load-shifting purposes. The new heat storage vessel is a plate-type heat exchanger unit with water as the working fluid and a phase change material (PCM) as the energy storage medium. The thermal characteristics of the heat exchanger such as heat transfer coefficient, effectiveness, efficiency, water exit temperature, heat storage rate, total energy storage capacity and storage time were experimentally evaluated as a function of various inlet conditions. The compact parallel plate design showed an enhanced the performance compared to conventional storage systems with an effectiveness up to 83.1% even when a PCM of low thermal conductivity is used. The proposed phase change energy storage system not only can deliver substantial benefits as a thermal energy storage medium, but also provides cost savings in infrastructure, equipment, and maintenance/operations compared to conventional systems.

Experimental and Scale Analysis of a Solid/Liquid Phase Change Thermal Energy Storage System

ABSTRACTA detailed experimental study has been carried out to evaluate the heat transfer performance of a solid/liquid phase-change thermal energy storage system. The phase-change material, 99% pure eicosane with a melting temperature of 36.5°C, was contained in a vertically oriented test cylinder that was cooled or heated at its outside boundary, resulting in radially inward freezing or melting, respectively. Detailed quantitative time-dependent temperature distributions and melt-front motion and shape data were obtained. In the freezing case study, a mathematical model was developed based on a one-dimensional analysis, which considered heat conduction as the only mode of heat transfer. In the melting case study, a heat transfer scale analysis was used to help interpret the data and development of heat transfer correlations. In the melting scale analysis, conduction heat transfer in the solid and natural convection heat transfer in liquid were considered. Comparison of experimental data with scale analysis predictions of the solid-liquid interface position and temperature distribution was performed. The analytical results agreed, in the worst case, within 10% of the experimental results in both melting and freezing cases. In the case of melting, scale analysis results agreed within 5% (after initial superheat disappeared in 50 minutes) with experimental results, and experimental results confirm the existence of four melting regions.