Latent Heat Energy Storage System Research Articles

Performance enhancement of phase change materials in triplex-tube latent heat energy storage system using novel fin configurations

Phase change material (PCM) has promising applications as an energy storage material in thermal energy storage (TES) systems. However, the low thermal conductivity of PCM limits its applications. To reduce the response time of TES systems, various configurations of fins are used to improve the heat transfer performance of PCM. The Y-structured fins utilize the Y-structure, a common structure in nature, and this study investigates the different structures of Y-shaped fins and the effect of HTF on melting time. A numerical research method based on the enthalpy-porosity method is adopted used for the study. The numerical model of the study is validated using previous experimental data. The simulation results have been obtained, including solid–liquid interface contours, isotherm contours, and evolution of the PCM liquid fraction. The results show that the melting process of the PCM is divided into three main stages and integrated solid fins within the PCM effectively reduce the melting time. Under certain operating conditions, reducing the fin thickness, increasing the fin angle, and increasing the HTF temperature can effectively reduce the PCM melting time. Transient heat transfer rates and dimensionless quantities are analyzed based on numerical results. This study provides potential applications of novel fin structures for new industrial products related to thermal energy storage and management.

Melting behavior and heat transfer performance in a modified PCM-filled enclosure with fins under hypergravity conditions

The latent heat energy storage (LHTES) system has been suggested for the thermal management of airborne equipment due to its superior thermal energy storage capability. The enthalpy-porosity method is used to investigate the melting heat transfer characteristics of phase change material (PCM) in embedded fin enclosures under hypergravity. The effects of different hypergravity values and directions on the melting process are analyzed. The results indicate that the melting is greatly accelerated by the fin due to its high thermal conductivity. Compared with the enclosure without fins, the addition of fins reduced the melting time by a maximum of 46.0%. Under the hypergravitational environment, natural convection is significantly enhanced, which leads to a more than 5 times increase in the maximum velocity of the liquid PCM as the gravity value increases from 1 g to 9 g. The direction of hypergravity also affects the heat transfer performance. Under hypergravity values of 5 g, the total melting time at θ = 0° is reduced by 60.24% compared to the case of θ = 90°. The findings of this study may contribute to the design of the LHTES system in aerospace applications.

Thermal performance of latent heat energy storage system with/without enhancement under solar fluctuation for Organic Rankine power cycle

Thermal energy storage (TES) is an effective method to buffer solar fluctuation and enable Organic Rankine Cycle (ORC) to operate under steady and design conditions. Heat transfer and energy storage characteristics of TES systems under solar fluctuation need to be studied to better understand the practical energy storage process and provide guidance on design/optimisation of integrated TES-ORC systems. In this paper, the charging process of a shell-and-tube system containing molten salt as phase change material with/without ceramic foam enhancement over a whole sunny and cloudy day was investigated. For the same full charging cases, the total stored energy is different according to solar fluctuation, with a maximum difference of 17.9%. Strong solar radiation not only accelerates the energy storage rate but also improves the total stored energy. Rising solar radiation can also cause large total stored energy while the energy storage rate is slow. Oscillating solar radiation generates the least total stored energy among full charging cases, however, the energy storage rate is higher than that under rising solar radiation. Falling solar radiation leads to small total stored energy. Ceramic foam-enhanced molten salt is more sensitive to solar fluctuation while the total stored energy over the whole working day is improved by 33.2% on a sunny day and 29.1% on a cloudy day respectively.

Effects of Flow Rate and Inlet Temperature on Performance of Annulus Type Low-Temperature Latent Heat Thermal Energy Storages

Solar energy is one of the largest energy potentials that Indonesia has, which can be utilized in solar heater that are integrated with latent heat energy storage (LHTES). This research aims to investigate the effects of the operating conditions of flow rate and inlet temperature on the performance of the annulus type Low-Temperature LHTES using Computational fluid dynamics method in which the enthalpy-porosity is used as the solidification model. The results indicate that the increase of performance can be obtained by increasing the flow rate and inlet temperature. The increase in flow rate will promote higher heat transfer thus produce better performance up to 11.91% and 24.91% during charging and discharging, respectively. Meanwhile, increasing the inlet temperature will increase the performance up to 192.72% during charging and 13.07% during discharging of the Low-Temperature LHTES system.

Effect of Ball-Milled Steatite Powder on the Latent Heat Energy Storage Properties and Heat Charging-Discharging Periods of Paraffin Wax as Phase Change Material.

Phase change materials (PCMs) serve as an advantage in thermal energy storage systems utilizing the available sensible and latent heat. The PCMs absorb the thermal energy during the charging process and release it into the environment during the discharging process. Steatite is low cost and eco-friendly, with a thermal stability up to 1000 °C, and it is abundantly available in nature. This study investigates the steatite–paraffin wax-based PCM and the effect on the cyclic loads using a horizontal triplex-tube latent heat energy storage system. The thermal conductivity value of the milled steatite-based PCM composite was 7.7% higher than pure PCM. The PCM with the ball-milled steatite-fabricated composite exhibited better discharging characteristics, increasing the discharge time by 50% more than that of the pure paraffin wax. Moreover, the milled steatite-based PCM outperformed that incorporated with non-milled steatite with paraffin.

Experimental investigation during the melting process of a vertical and horizontal tube-in-shell Latent Heat Energy Storage System

Thermal energy storage systems with the application of Phase Change Materials have been in practice for many years due to their ability to store latent heat energy and have been applied for energy storage and thermal comfortability. It is essential to constantly explore various methods to enhance the performance of such Latent Heat Energy Storage Systems to develop a more effective system. Research in improving the performance of these storage systems through different orientations of the system has been limited. There has been little mention of the effectiveness of the different orientations of Latent Heat Energy Storage Systems at a system level. The study filled the research void by applying an effectiveness technique to explicitly quantify and evaluate the performance of the systems with different orientations from the perspective of a heat exchanger. An experimental investigation was performed on the static melting process of vertical and horizontal tube-in-shell Latent Heat Energy Storage Systems to investigate the effect of the different heat transfer fluid flow rates and the system orientations. Experiments were performed for 3 different heat transfer fluid flow rates (0.35 l/min, 0.7 l/min, and 1.4 l/min). From the experimental investigations, it was deduced that the horizontally oriented Latent Heat Energy Storage System had a higher melting rate in comparison to the vertical orientation, causing the phase change material to melt in a shorter period at all heat transfer fluid flow rates investigated. By examining the performance of the system as an effective heat exchanger, the horizontal Latent Heat Energy Storage System was observed to be at least 36 %, 30 %, and 47 % more effective than the vertical systems for the heat transfer fluid flow rates of 1.4 l/min, 0.7 l/min, and 0.35 l/min, respectively. The performance variation of the horizontal and vertical Latent Heat Energy Storage System was attributed to the variation in the convective heat transfer mechanism driven by the buoyancy forces within the phase change material as it melts.

Performance study of transcritical CO2 heat pump integrated with ejector and latent thermal energy storage for space heating

This study proposes a new transcritical CO2 heat pump integrated with ejector and latent heat energy storage system, and compares the performance of the system with and without energy storage equipment based on TRNSYS and experimental results. The results show that the new system operates more stably and is more conducive to space heating. Compared with the transcritical CO2 heat pump system with only ejector, the new system is more affected by the water flow rate and its performance can be improved by 18.53% when the water flow rate is 0.103 kg·s−1. The new system has more energy saving potential in low temperature environment, for which the utilization rate of primary energy and the primary energy ratio could reach 15.33 kgce·m−2 and 1.24, respectively. After thermo-economic optimization, it can be found that the minimum life-cycle cost of the new system is about 51.91 thousand CNY, which is reduced by 11.46% compared with the only ejector system. Therefore, the new system is superior to the previously transcritical CO2 heat pump systems both in terms of thermodynamic performance and economic performance. The research results are helpful to further promote the research and application of air source heat pump for space heating in low temperature area.

Innovative ladder-shaped fin design on a latent heat storage device for waste heat recovery

Latent heat energy storage system provides an alternative solution to solving the imbalance problem of energy supply and demand. To improve the phase change efficiency, a novel ladder-shaped fin is proposed to accelerate melting process. Under the same mass of fin materials, two groups of fin shapes (totally eight cases) are innovatively designed. Upon being verified by experiments in literature, numerical models account for comprehensive descriptions on melting front propagation with emphasizing temperature development and free convection in the liquid phase. Results demonstrate that the ladder-shaped fins can better optimize the melting channel of phase change material than the straight fin. Compared to the original straight fin case, a maximal 52.2% of the total melting time can be saved. The angle change of fins has a significant effect on reducing the melting time of the whole PCM. In Group I where fins are arranged vertically and horizontally, the total melting time is much shorter than that of each corresponding case in Group II (45° from the vertical axis). For the original straight fin in Group II, a 36.8% reduction in total melting time is obtained if turning fins by 45°clockwise. To be conclusive, it is more beneficial to add fins to mobile heat accumulators than to have no fins, saving more energy charging time.

Performance analysis of melting phenomena in an ice-freezing type direct-contact heat exchanger

The present study endeavours to represent a latest concept of utilizing similar heat transfer fluid (HTF) and phase change material (PCM) in a direct contact type PCM heat exchanger (DCHEX). This technique has been found more effective during melting process. In the following investigation, a segment of the heat exchanger is numerically modelled to analyse the temporal behaviour of the latent heat energy storage system during the cycle of discharging. The transient numerical computation incorporates an iterative, finite volume method based on enthalpy-porosity technique for numerically model the phase change phenomena. For the analysis, water is used as working fluid. To show the performance enhancement of this technique during melting process, a series of simulations are performed to examine the impact of varying HTF inlet condition and flow rates. The changes in the configuration of the heat exchanger are studied. Heat exchanger parameters such as difference between inlet and outlet temperature (ΔT), heat release rate (Q), temperature effectiveness (θ) and volumetric heat transfer coefficient (Uv) are evaluated for all such cases. A uniform exit temperature of the HTF is observed for most of the time with significant increase in the heat transfer in the direct contact type heat exchanger. Three distinct stages namely initial, intermediate and final phases are observed during the melting process. During the initial phase the parameters exhibits uniform behaviour. In the intermediate phase there is significant drop and rise in the parameters while during the final phase the value of parameters diminishes except for Uv. Increasing HTF flow rate promotes increment in heat transfer rate while increasing the inlet temperature of HTF is more desirable to increase the overall heat transfer coefficient.

Study of melting of paraffin dispersed with copper nanoparticles in square cavity subjected to external magnetic field

The addition of high thermal conductivity nanoparticles in a phase change material (PCM) is an effective way to improve the thermal performance of the latent heat energy storage system. The present work uses paraffin wax as a PCM, and copper (Cu) nanoparticles are added for thermal conductivity enhancement. The thermal performance of the PCM dispersed with Cu nanoparticles in a square cavity during the melting process is numerically investigated. The enthalpy porosity approach is used to capture the melting of the PCM in the enclosure. The effect of orientation of the heated wall of the square cavity and volume fraction of the Cu nanoparticles on the melting rate and energy storage capacity is evaluated. Subsequently, a uniform external magnetic field in the horizontal direction is imposed on the square cavity filled with nano-enhanced PCM. Further, a parametric study on the strength of the magnetic field based on Hartmann number is performed to analyze the heat transfer and fluid flow characteristics of the PCM during the melting process. The melting rate of PCM and the energy storage capacity of nano-enhanced PCM are found maximum at 2% and 0.5% concentration of Cu nanoparticles, respectively. Additionally, with the increase in the strength of the external magnetic field, a decline in the melting rate and energy storage capacity is observed.

Analysis of Heat Transfer Rate for Different Annulus Shape Properties-Enhanced Beeswax-Based Phase Change Material for Thermal Energy Storage

Thermal exploration of melting phenomena of four different annulus shapes’ (circular-circular, circular-rectangular, rectangular-circular, and rectangular-rectangular) beeswax-based phase change material for latent heat energy storage system is discussed here. To overcome the low efficiency in heat transfer because of low thermal conductivity of beeswax (the energy storage material in the current study), the composite-beeswax approach has been investigated numerically. Three metal oxides (Al2O3, MgO, and SiO2) with different volume concentrations (1%, 3%, and 5%) containing high thermal conductivity are dispersed into the pure beeswax. The 2-d continuity and momentum as well as energy transport mathematical model inside the composite-beeswax system have been adopted for the study, and we validated the model by available results in the literature. The obtained results revealed that both the melting rate and heat transfer are improved slightly in the case of rectangular-rectangular annulus shape. It was also shown from the result that the melting rate and heat transfer are improved significantly with the presence of metal oxide particles. Moreover, it was obtained that the types of particles have not affected noticeably the melting rate and heat transfer. For the three investigated nanoparticles, temperature of the system attained 346.4 K at 15000 s of process; at the same time, it is 341 K as noted for the beeswax, which shows an improvement of 1.4% in the case of circular-circular annulus and Al2O3. In the same conditions, melt fraction increases from 0.58 for beeswax to 0.91 for composite unit, thus showing 56.8% of improvement in the melting rate.

Experimental analysis of the heat transfer rate of phase change material inside a horizontal cylindrical latent heat energy storage system

Latent heat thermal energy storage system can help in the smooth operation of energy supply and demand. In the present work, experimental study was performed to analyze the heat transfer rate of phase change material inside an annulus. A copper pipe (centrally loaded) runs the length of a cylindrical container during both discharging and charging modes. The overall heat transfer rate is enhanced during phase change process by adding longitudinal fins with the copper pipe. These longitudinal fins were tilted at an angle of 120⁰. Paraffin wax is used as phase change material. The main objective of the experiment is to analyze the heat transfer rate during the solidification and liquefaction of PCM. Also, the effect of mass flow rate and inlet temperature of heat transfer fluid was analyzed. Conduction was found to be the primary heat transfer mechanism during the initial stages of charging. Once the PCM get liquefied inside the system, natural convection gets dominated. During the solidification of PCM conduction heat transfer get dominated. Also, it was observed that melting duration is strongly affected by the inlet temperature of HTF while the flow rate slightly affects the melting duration.

Numerical Study for the Tube Rotation Effect on Melting Process in Shell and Tube Latent Heat Energy Storage LHES System

Although renewable energy systems have become an interesting global issue, it is not continuous either daily or seasonally. Latent heat energy storage (LHES) is one of the suitable solutions for this problem. LHES becomes a basic element in renewable energy systems. LHES compensate for the energy lack when these systems are at low production conditions. The present work considered a shell and tube LHES for numerical investigation of the tube rotation influence on the melting process. The simulation and calculations were carried out using ANSYS Fluent software. Paraffin wax represents the phase change material (PCM) in this work, while water was selected to be the heat transfer fluid (HTF). The calculations were carried out for 9 rpm tube rotation case as well as the stationary case. The results show a slight increase in the liquid content of phase change material PCM due to tube rotation. The enhancement percentage in liquid content was 3.5% for 6 hrs charging process. The heat transfer in the axial direction was small relative to that in the radial direction.

Optimum design of a double elliptical latent heat energy storage system during the melting process

This paper concerns the optimum design of double elliptical latent heat storage units during the charging process using three-dimensional numerical simulation. Water and RT35 are employed as the heat transfer fluid and phase change material, respectively. The orientations of both inner and outer elliptical tubes, the number of inner tubes, and the comparison between the straight and wavy configurations for the inner tubes are examined to find the maximum melting rate. Moreover, the sensitivity analysis on the operating conditions, including the Reynolds number and inlet water temperature, is performed. The results show that the best performance is found when the inner and outer tubes are oriented vertically and horizontally, respectively. The performance of the unit enhances as the distance between the inner tube and the bottom wall of the outer tube reduces. Besides, the optimum place for positioning the inner tube is where the minimum distance of the ellipses is 2 mm. It is found that the implementation of double wavy inner pipes increases the heat transfer surface area, which accelerates the melting time by 2.17. The delivered energy rate to the PCM using double wavy inner tubes is 218.75 W/kg, while it is 180.4 W/kg using double straight inner tubes. Eventually, the sensitivity analysis confirms the system is more sensitive to the variations of inlet temperature compared to the Reynolds number regarding the tested operating conditions.

Performance enhancement of a maple leaf-shaped latent heat energy storage unit by adding nanoparticles and leaf vein fins

In this paper, the solidification process of a phase change material (PCM) in a maple leaf-shaped Latent Heat Energy Storage (LHES) system applying fins in the form of leaf veins and nanoparticles as direct and indirect heat transfer enhancement methods is investigated numerically. These systems are used to balance energy supply and need. In this research, both methods are used to solve the problem of pure PCM, ie low thermal conductivity. The innovative fins used in this work are geometrically optimized using the Response Surface Method (RSM). The goal of optimization is accelerating the solidification process and reducing the full solidification time (FST). In the second method, nano-enhanced phase change material (NEPCM) is made by adding MWCNT nanoparticles to PCM (water). Standard Galerkin Finite Element Method (SGFEM), along with adaptive grid refinement, has been used to simulate the solidification process. The two methods were examined separately and simultaneously (Hybrid method), and the results were compared. Although the hybrid use of the two aforementioned methods is excellent with a 56.9% reduction in FST if the two methods are used separately, the method of using optimized fins in the form of leaf veins with a 42.6% reduction in FST is much more effective than making NEPCM with a 25.5% reduction in FST.

Enhancing the thermal performance of PCM in a shell and tube latent heat energy storage system by utilizing innovative fins

The main obstacle of the PCMs which restricts their usage for thermal energy storage (TES) applications is their poor thermal conductivity. Utilizing metal fins is the most popular solution to enhance the performance of PCM-TES. In this work, PCM thermal performance enhancement in a shell and tube heat exchanger (STHX) was numerically investigated. Tee shaped fins is suggested as an innovative fin shape to accelerate the PCM melting process in the STHX. The tee fin was compared with the traditional longitudinal fin shape to evaluate its thermal performance. In this test, many heat exchangers with various fin shapes were tested and compared. These heat exchangers were: heat exchanger without fins, heat exchanger with six tee fins, heat exchanger with six longitudinal fins and heat exchanger with six tree fins. 2D numerical models were developed. The melting process was considered during the simulation. The results showed that the case without fins had about 15% of the PCM melted after 6 h, while, with the tee fins the PCM totally melted after 3.5 h. The total PCM melting time reduced by 33% when the tee fins were used, as compared to utilizing the longitudinal fins. It is observed that the geometry of the fins has an important influence on the PCM melting.

Theoretical design of solar-powered vapor absorption refrigeration system coupled with latent heat energy storage

In this work, the vapor absorption refrigeration system (VARS) with a cooling capacity of 1kW is designed. VARS is designed to be driven by hot water available from the solar thermal collector during the day. In the Sun’s absence, the system is designed to run by a coupled latent heat energy storage system. The unit has three major components: evacuated tube collector, latent heat energy storage, and VARS. The system is designed for a cooling capacity of 1 kW. The size of other components has been calculated by adopting the heat exchanger design approach and the relevant equations presented in the published works. The corresponding size of absorber, generator & condenser comes out to be 1.412kW, 1.46 kW & 0.96 kW, respectively for the cooling capacity of 1 kW. The evacuated tube collector of 100 LPD capacity is sufficient to provide the required heat to run the VARS and charge the thermal energy storage. Latent heat energy storage of 2.25 kW charging and discharging time of 3 hours kW is coupled with the system. The designed system gives the COP of 0.875.

Heat-Storage Performance Optimization for Packed Bed Using Cascaded PCMs Capsules

The design, in which the capsules are packed in the bed at different sections based on the Phase Change Material (PCM) melting temperature, is an effective method to improve the heat-storage performance of the latent heat energy storage system. A latent heat storage system was established in the present study in order to optimize the arrangement of cascaded PCM capsules. Four kinds of paraffin with different melting temperatures were selected as the PCM for the experiment. The effects of stage number, cascade ratio and melting temperature on the heat-storage performance of the latent heat storage system were investigated during the charging and discharging operations. The complete time of charge and discharge, heat storage-release capacity, energy efficiency, exergy efficiency and entransy dissipation (based on a new entransy theory) were computed for different arrangement cases, in order to analyze and evaluate the heat-storage performance of the system under different stage numbers and cascade ratios of PCMs. The results revealed that the arrangement of cascaded PCM capsules has an obvious effect on the heat-storage performance of the system. When more high melting PCMs are adopted, the heat storage-release capacity, energy efficiency and exergy efficiency increases, while the entransy dissipation decreases. However, the temperature increase becomes slow, and the charging or discharging process becomes long.

The effect of the inlet temperature of the heat transfer fluid in a rectangular latent heat energy storage

Solar energy is available during the day only. The excess heat energy collected during sunshine hours can be stored in the thermal energy storage and it can be reused during off sunshine hours. Latent heat energy storage systems by using phase change materials (PCMs) can be used effectively for storing thermal energy. It has high-energy storage density and the constant temperature storage process. In this paper, the performance of the latent heat storage system and phase change characteristics of PCM inside a rectangular latent heat energy storage unit will be presented. In this study, purified water is used heat transfer fluid (HTF) which is passed through the copper tubes inside the test unit and commercial-grade paraffin wax is used as PCM and indirect contact heat transfer method is used to heat exchange from the HTF to PCM. It was found that the PCM at the upper layer of the test section first melted during the melting process. Moreover, the effects of inlet temperature of HTF on the charging process was investigated. It can be concluded that increasing the inlet temperature of HTF effectively decreases the total charging time of the melting process. The amounts of heat storage for the inlet temperature of HTF 70 °C and 80 °C are 7400 kJ and 6555 kJ respectively during the melting process.

Latent heat energy storage system using phase change materials and techniques for their performance improvement: A Review

Entire world is struggling to explore newer methods to overcome the energy crisis. With limited and exhausting energy resources researchers around the world are finding efficient ways to store thermal energy. One of the efficient ways is to store thermal energy in the form of latent heat energy using phase change materials (PCMs). Latent heat storage (LHS) units have been widely adopted owing to superior energy storage density and constant operating temperature. But the thermal performance of these systems is limited due to low thermal conductivity of the PCMs. Researchers across the globe working on approaches to improve the thermal performance of these systems. The present review paper is concerned with a review on PCMs, methods to improve performance of LHS system using PCMs with special emphasis on use of various additives such as nano particles and porous materials to increase the thermal performance of PCMs and types of PCMs for specific applications. The factual data presented in this paper would be helpful in selection of appropriate PCM for specific application, and to adopt suitable performance enhancement technique to obtain most optimal LHS system