Heat Thermal Energy Storage System Research Articles

Simulation of Heat Storage and Heat Regeneration in Phase Change Material

The present study explores numerically the energy storage and energy regeneration during Melting and Solidification processes in Phase Change Materials (PCM) used in Latent Heat Thermal Energy Storage (LHTES) systems. Transient two-dimensional (2-D) conduction heat transfer equations with phase change have been solved utilizing the Explicit Finite Difference Method (FDM) and Grid Generation technique. A Fortran computer program was built to solve the problem. The study included four different Paraffin's. The effects of container geometrical shape, which included cylindrical and square sections of the same volume and heat transfer area, the container volume or mass of PCM, variation of mass flow rate of heat transfer fluid (HTF), and temperatures difference between PCM and HTF were all investigated. Results showed that the PCMs in a cylindrical container melt and solidify quicker than the square container. The increase in mass flow rate and/or temperature difference decreases the time required for complete phase change. Paraffin's solidify quicker than they melt and store more energy than they release

Numerical study on melting process and heat transfer analysis of a multitube combination latent heat storage unit with innovative harpoon-type fins

The heat transfer rate of a coupled system combining a passive residual heat removal system and a latent heat thermal energy storage system is directly related to worker safety in nuclear power plants. To enhance the heat transfer performance of the coupled system, in this study, the melting process of phase change material in the latent heat thermal energy storage system is numerically investigated by inserting innovative harpoon-type fins. A new assessment index is also proposed to evaluate the comprehensive heat transfer performance of fins. More than thirty cases with different harpoon-type fins are designed, and the impacts of various efficient structural parameters of the harpoon-type fin on the melting process are evaluate. The response surface method is used to optimize the structure. The results demonstrated that the handle length and the number of fins significantly improve the heat transfer performance of the harpoon-type fin. The optimal geometrical parameters (arc angle θ = 45°, handle length Lha = 10 mm, fin number Nf = 8, and arc number Na = 1) of harpoon-type fins are obtained. The heat transfer rate of the optimal fin structure is six times that without fins, and the total melting time is shortened by 85.9%. Furthermore, the longitudinal extension of the fins is more important than the complex horizontal extension of fins. The harpoon-type fin not only shows better performance in the coupled system but can also be used in shell-and-tube latent heat thermal energy storage systems.

Effect of fin length and angle on the melting process of phase change materials in vertical latent heat storage unit

The installation of fins offers an effective solution for addressing the poor thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems. This paper aims to investigate the combined effects of unequal fin length arrangements and the inclination angle of fins on the performance of an LHTES system during the charging process. The LHTES system consists of a cylindrical container filled with paraffin (RT55) serving as the PCM. Numerical models are established and validated, followed by simulating various fin structures to analyze the complete melting time of the PCM. The characteristics of the melting process are further examined in four representative cases, including the full melting time, evolution of the melt fraction, average maximum velocity, streamline contours, temperature uniformity, and average Nusselt number. The results reveal that the optimal case, featuring unequal length and downward annular fins, achieves a significant 49.8% reduction in the complete melting time of the PCM compared to the benchmark case with ordinary annular fins. Moreover, the optimal configuration increases the largest average maximum velocity of the PCM by 35.36%, resulting in a more uniform temperature distribution and a higher Nusselt number.

Performance Improvement of a Solar-Assisted Absorption Cooling System Integrated with Latent Heat Thermal Energy Storage

Phase change materials (PCMs) have emerged as promising solutions for latent heat thermal energy storage (LHTES) systems, offering considerable potential for storing energy derived from renewable sources across various engineering applications. The present study focused on optimization of solar cooling system by integrating LHTES with different PCM tank configurations. TRNSYS simulation software was selected for the study, and the collected experimental data from laboratory system prototype were used for system validation. The results indicate that the use of PCM led to a noteworthy decrease of 6.2% in auxiliary energy consumption. Furthermore, the time during which the heat carrier temperature flow exceeded 90 °C from the storage tank to the auxiliary fluid heater was extended by 27.8% when PCM was utilized compared to that of its absence. The use of PCM in LHTES is more effective under variable weather conditions. On the day when changes in weather conditions were observed, around 98% of the cooling load was provided by produced sun energy. The results of the research can be used to optimize the solar cooling system, which will help reduce the environmental impact of cooling systems running on non-renewable fuels.

Understanding the effects of variable permeability along the cross-section of packed beds of encapsulated phase change materials for latent heat thermal energy storage systems

This work analyzes the impact of variable porosity along packed beds of encapsulated phase change materials for Latent Heat Thermal Energy Storage (LHTES) systems on their charging performance. A novel model encompassing variable permeability along the cylindrical bed’s cross-section due to geometrical constraints and a smooth phase change that is consistent with calorimetry measurements was adopted. A Finite Volumes code is used to solve the governing equations, while unknown phase change parameters are estimated using experimental data and the Levenberg-Marquardt inverse analysis algorithm. The aggregate result of the in situ estimation of the parameters related to the non-isothermal phase change and the proposed variable porosity model is a deviation of their results of at most 10% in comparisons involving temperature measurements for both the heat transfer fluid and phase change material. The significance of accounting for the variable permeability and the associated channeling effect is shown, as a considerable portion of the packed bed does not contact an enough amount of the hot heat transfer fluid to efficiently charge the LHTES system. The constant porosity model can overpredict the duration of the full conversion of heat input into heat stored by roughly 27 min and underestimate the full charging time by more than 200 min, which may lead to an erroneous sizing of the thermal energy storage unit. The usage of smaller capsules can enforce a more uniform heating of the packed bed, which allows for the heat transfer performance to approach the limit predicted by the constant porosity case.

Dynamic discharging performance of a latent heat thermal energy storage system based on a PID controller

A PID controller is introduced into a latent heat thermal energy storage unit to compose a coupling system in order to control the discharging performance. Outlet temperature of the working fluid can be precisely regulated by means of its inlet velocity variation based on the PID controller. The theoretical model is built through combining heat transfer of the latent heat thermal energy storage unit with the PID controller. Experimental results are used to validate the proposed theoretical model. PID control analysis indicates that its parameters have obvious effects on performance of the coupling system. Kp of −0.02 m/(s·K), Ki of −0.15 m/(s2·K) and Kd of −0.001 m/K are further optimized according to dynamic response of the transient outlet water temperature. System parameter analysis exhibits that higher target temperature produces larger heat discharging rate, which then reduces the outlet water flow rate accordingly. The discharging rate and total discharging energy of the latent heat thermal energy storage unit decrease with augment of the target outlet temperature. Increase of PCM melting point, thermal conductivity and latent heat is favorable of elevating the working fluid velocity. The discharging rate is improved by the PCM melting point, thermal conductivity and latent heat. The latent heat thermal energy storage units can separately obtain maximum discharging rates of 257.691, 294.437 and 257.603 W at 200 min for PCM melting point of 327.15 K, PCM thermal conductivity of 0.8 W/(m·K) and PCM latent heat of 250 J/g. It is apparent that PCM melting point, thermal conductivity and latent heat are conducive to enhancing the total discharging energy. The largest discharging energy at 200 min is respectively determined as 1280.409, 1060.105 and 974.153 kJ. Temperature and phase change contours can also be substantially affected by the system parameters. In conclusion, the built coupling system is beneficial to efficiently regulate and control discharging performance of latent heat thermal energy storage units.

Thermo-fluid performance enhancement in a long double-tube latent heat thermal energy storage system

Thermodynamic analysis and flow rate optimization for the long double-tube latent heat thermal energy storage systems (LHTESS) are performed. Computer modeling is carried out using created software and is based on a developed 3D non-steady non-linear coupled thermo-fluid mathematical model that combines the apparent heat capacity method and finite volume method for the sodium nitrate (NaNO3) phase change materials (PCM) and for the Syltherm800 heat transfer fluid (HTF). The mathematical model and numerical algorithm are verified through comparison with experimental data. It is found that the laminar flow of HTF ensures the uniform temperature in PCM and in HTF and this temperature is equal to the PCM melting temperature. It is proved that the PCM and HTF average temperatures along the LHTESS can be equalized using spatial and temporal velocity variations of the HTF. Mutual impact of the heat transfer and fluid mechanics parameters in the long double-tube LHTESS was studied by correlation between Nusselt numbers and Reynolds numbers. The optimal HTF flow rate parameters were analyzed based on the non-equilibrium thermodynamics method. It is discovered that the laminar regime 0 < Re < 2000 and the turbulent regime 12000<Re<15000 are the most optimal for long double-tube LHTESS of the described geometry.

Impact of innovative fin design on phase change material melting for thermal energy storage system

Among the main types of thermal energy storage, Latent Heat Storage System has the advantage of storing heat due to the small size temperature changes and the high stored energy. These benefits are attributed to the use of phase change material. However, the most fantastic drawback of phase change material is its low thermal conductivity. To further improve the weak thermal conductivity of phase change materials in these systems, it is imperative to look at different thermal enhancement techniques. This paper discusses two primary thermal improvement approaches for a rectangular thermal energy storage system: fins and a metal matrix. The rectangular enclosure is filled with n-eicosane and the bottom surface is subjected to constant heat flux. A comparison of different structures (conventional fin, Y-shaped fin, and honeycomb structure) with a reference configuration that contains only pure phase change material was discussed. The comparison between these structures is based on the charging time, which is one of the main objectives of this work. Outcomes reveal that adding a hexagonal Y-shaped fin and honeycomb structure can help improve the thermal performance of the latent heat thermal energy storage system and uniformize the temperature compared to the reference configuration. However, the effect of natural convection is not significant for the honeycomb structure but is crucial for the reference configuration. An optimization study was done to study the effect of varying the number of the hexagonal Y-shaped fin, PCM types, and heat flux. Results show that deploying four Y-shaped hexagonal fins is the best convincing argument in favor of improving the performance of the latent storage system. The RT44HC is the predominant coolant at lower heat fluxes, whereas the RT28HC was the best choice at higher heat fluxes. These results could be beneficial in applying phase change material to the thermal management of electronic components.

Performance enhancement of latent heat thermal energy storage system by using spiral fins in phase change material solidification process

Latent heat thermal energy storage systems (LHTESS) have recently gained attention due to the critical demand for clean energy production and storage. The influence of spiral fins on the performance augmentation of a vertical tube-shell LHTESS in the solidification process was studied numerically. Different formation of fins which includes the quadruple, triple, double and single fins were studied. Amount of phase change material (PCM) mass inside the PCM enclosure was preserved equal in all cases and the length of the fins were adjusted for different fin numbers to keep the surface of heat transfer constant to find the optimized fin number. The phase change process was simulated by adopting the enthalpy-porosity technique. It was observed that the triple fin case outperformed other cases and the single fin case showed the least enhancement. When comparing the different cases while the heat transfer surface was kept constant, the triple fin case shows better performance in terms of time averaged Nusselt number and total solidification time respectively. It was revealed that the performance enhancement was not directly proportional with the number of fins and there was a trade-off between fin number and length of each fin.

Effects of molten salt multi-thermophysical properties on performance of the latent heat thermal energy storage system and synergetic optimization investigation

Effects of molten salt multi-thermophysical properties on performance of the latent heat thermal energy storage system and synergetic optimization investigation

Investigation of energy costs for incorporating a latent heat thermal energy storage system into a South African cold room

Investigation of energy costs for incorporating a latent heat thermal energy storage system into a South African cold room

A numerical evaluation of a latent heat thermal energy storage system in the presence of various types of nanoparticles

Due to the high demand for using phase change materials (PCMs) in thermal systems and to the goal of improving the thermal efficiency of solar systems, herein, the heat storage performance of nano PCM (nPCM) was numerically scrutinized. For this purpose, a vertical double-tube heat exchanger containing paraffin and five different nanoparticles was simulated. By originating scientific results, 31 radial fins were considered on the tube side of the heat exchanger. RT35 paraffin wax as PCM includes a melting point close to the ambient temperature, making it easy to investigate domestic usage's charging and discharging processes. It was found that nanoparticles be able to decrease the duration of melting and solidification processes. Adding 5 vol% of Cu, CuO, TiO2, Carbon nanotube (CNT), and Graphene nanoplatelet (GNP) to the PCM caused 6.6%, 10.2%, 10.7%, 33.4%, and 56.4% of the melting time reduction, while time reductions of 20.3%, 13.4%, 13.2%, 43.1%, and 69.7% for solidification were observed, respectively. The results showed that thermal conductivity, density, and heat capacity properties affect the melting process, whereas thermal conductivity was the most critical parameter in the solidification process. Thus, despite the better performance of CuO and TiO2 compared to Cu in the melting process, it diminished the solidification time greater than the others. Also, the presence of nanoparticles was more significant in the solidification process. Moreover, the heat transfer coefficient of GNP-PCM was the highest among others (66.63 W/m2.K for 5 vol%), while it was 24.68 W/m2.K for 5 vol% of Cu-PCM. This comprehensive study yielded beneficial results for preparing more efficient thermal energy storage systems.

Experimental study of a latent heat thermal energy storage system assisted by variable-length radial fins

Societal demands for energy are only increasing due to the global increase in electronics, infrastructure, and transportation. With this demand, it is necessary to improve the storage and retrieval techniques of renewable energy. Latent heat thermal energy storage (LHTES) may be an effective storage method, but the low thermal conductivity of phase change materials (PCMs) hinders their response time. In the current study, the use of variable length radial fins was experimentally compared against uniform length radial fins on the charging and discharging processes of a LHTES system with RT-55 PCM. Four cases of variable radial fins, two with four fins and two with eight fins, were analyzed against four equivalent thickness uniform length radial fin configurations. The fin configurations were attached to a central copper pipe in a shell and tube LHTES system where the PCM was contained. The charging and discharging times of the PCM when enhanced with fins were compared to a benchmark case with no fins. The benchmark case with no fins took 47.87 h to fully charge and 42.50 h to discharge. The configuration with four variable length fins extending the furthest into the PCM decreased charging and discharging times by 79.34 % and 49.53 % compared to the benchmark which was the highest decrease in total time compared to all fin configurations.

Exergy Analysis of a Shell and Tube Energy Storage Unit with Different Inclination Angles

To optimize the utilization of solar energy in the latent heat thermal energy storage (LHTES) system, this study conducts exergy analysis on a paraffin-solar water shell and tube unit established in the literature to evaluate the effects of different inclination angles, inlet temperatures, original temperatures, and fluid flow rates on the exergy and exergy efficiency. Firstly, the thermodynamic characteristics of the water and the natural convection effects of the paraffin change with different inclination angles. When the inclination angle of the heat storage tank is less than 30°, the maximum exergy inlet rate rises from 0 to 144.6 W in a very short time, but it decreases to 65.7 W for an inclination angle of 60°. When the inclination angle is increased from 0° to 30°, the exergy efficiency rises from 86% to 89.7%, but it decreases from 94% to 89.9% with the inclination angle from 60° to 90°. Secondly, under the condition that the inclination angle of the energy storage unit is 60°, although increasing the inlet temperature of the solar water enhances the exergy inlet and storage and reduces the charging time, it increases the heat transfer temperature difference and the irreversible loss of the system, thus reducing the exergy efficiency. As the inlet water temperature is increased from 83 to 98 °C, the exergy efficiency decreases from 94.7% to 93.6%. Moreover, increasing the original temperature of the LHTES unit not only reduces the exergy inlet and storage rates but also decreases the available work capacity and exergy efficiency. Finally, increasing the inlet water flow rate increases the exergy inlet and storage rates slightly. The exergy efficiency decreases from 95.6% to 93.3% as the unit original temperature is increased from 15 to 30 °C, and it is enhanced from 94% to 94.6% as the inlet flow rate is increased from 0.085 to 0.34 kg/s with the unit inclination angle of 60°. It is found that arranging the shell and tube unit at an inclination angle is useful for improving the LHTES system’s thermal performance, and the exergy analysis conducted aims to reduce available energy dissipation and exergy loss in the thermal storage system. This study provides instructions for solar energy utilization and energy storage.

A Review on Active Heat Transfer Enhancement Techniques within Latent Heat Thermal Energy Storage Systems

Renewable energy resources require energy storage techniques to curb problems with intermittency. One potential solution is the use of phase change materials (PCMs) in latent heat thermal energy storage (LHTES) systems. Despite the high energy storage density of PCMs, their thermal response rate is restricted by low thermal conductivity. The topic of heat transfer enhancement techniques for increasing thermal performance of LHTES systems has mainly focused on passive heat transfer enhancement techniques with less attention towards active methods. Active heat transfer enhancement techniques require external power supplied to the system. In this paper, recent advances in active heat transfer enhancement techniques within LHTES systems are reviewed, including mechanical aids, vibration, jet impingement, injection, and external fields. The pertinent findings related to the field are summarized in relation to the charging and discharging processes of PCMs. Suggestions for future research are proposed, and the importance of additional energy input for storage is discussed.

Thermo-economic analysis of a low-cost greenhouse thermal solar plant with seasonal energy storage

Reduction of greenhouse gas emissions is today mandatory to limit the increase of ambient temperature. This paper provides a numerical study of a thermal solar plant using a seasonal dual-media sensible heat thermal energy storage system for supplying the total energy demand of a greenhouse located in the South of Italy, avoiding the use of the gas boiler. The aim of the work is to assess the technical and economic performance of a low-cost pit storage system, made of gravel and water, placed under the greenhouse to save surface. The study provides an original analysis of the charging and discharging phases during one year of operation on the basis of the real hourly heating demand and on real weather data. A sensitivity analysis of the levelized cost of heat is carried on with respect to the solar-collector area and to the storage-pit volume. The analysis shows that a minimum-cost design solution exists to cover 100% of the heat demand with an estimated levelized cost of heat of 153.3 EUR/MWh. The results demonstrate that dual-media thermal energy storage systems with solar thermal collectors represent a viable solution for reducing the environmental impact of greenhouses.

Investigation of thermal energy storage system based on mining by-products for the recovery of Moroccan mining industrial waste heat

Implementing thermal energy storage system for energy intensive industrial processes such as mining industry is regarded as viable alternative to increase the energy efficiency by capturing waste heat, storing it, and then using it to produce power during night or for daily demand-supply matching. The present work aims at examining the integration of thermocline packed-bed system to recover waste heat for a Moroccan mining industry from numerical, technical and economic viewpoints. The storage single tank uses thermal oil as the heat transfer fluid, and the mining by-product (Porcellanite) issued from the same industry as storage material. An earlier developed and validated model is deployed to simulate the thermocline behavior of the storage tank and assess the performances of the investigated storage material. The mining by-product undergone extensive experimental characterization including chemical and structural composition, thermophysical properties, mechanical behavior, and durability testing, before and after thermal cycling. Porcellanite is predominantly composed of quartz with a porosity of around 0.31 and a bulk and skeletal densities of 1650 and 2420 kg/m3, respectively. Thermal cycling impacts positively its heat capacity by raising it from 0.4 J/g.K to 0.98 J/g.K resulting in a considerable increase of energy density. The thermal stability of the storage material was also demonstrated. Less than 2% of mass loss are reported after heating tests. These results revealed the suitability of the by-product for medium-temperature range. Furthermore, numerical outcomes demonstrate the great potential of the storage material to store and/or release energy with a charge efficiency of 87% and discharge efficiency of 88%. Finally, the proposed solution to recover waste heat (heat exchanger and thermal energy storage system) was economically evaluated for the Moroccan mining industrial process. Findings demonstrate an economic profitability of the proposed solution opening an important prospect for circular economy.

Cesaro fins parametric optimization for enhancement in the solidification performance of a latent heat storage system with combined fins, foam, and nanoparticle

The use of Phase Change Materials (PCMs) for latent thermal energy storage enhances the availability of solar energy. PCMs can store a large amount of energy in a small volume using almost entirely isothermal processes. Despite this, the poor thermal conductivity of PCMs is a significant disadvantage of current PCMs, severely limiting their energy storage capabilities. As a result, the solidification/melting rates are reduced to an unacceptable level, and the system reaction time is increased unreasonably. By combining the novel fin arrangement, nanoparticles, and metal foam, the current study improved the solidification rate of the PCM in the Latent Heat Thermal Energy Storage System (LHTESS). LHTESS was numerically evaluated in ANSYS Fluent 18.1 using a solidification and melting model. The addition of cesaro fins, nanoparticles, and metal foam significantly improved PCM solidification in the LHTESS. PCM solidification time was reduced by 42.42% and 39.39% in Type-3 and Type-5 fin configurations, respectively, when compared to Type-4 fin configuration. Furthermore, a temperature difference of 27 K between the Heat Thermal Fluid (HTF) and the PCM ensures the best solidification performance. By incorporating nanoparticles into PCM and metal foam, the solidification time is reduced by 73.68%. Depending on the foam structure and volume fraction of the nanoparticles, dispersing nanoparticles in PCM with metal foam saves up to 75% of the time.

Experimental investigation of the performance attributes of a thermal energy storage unit using different system configurations

One of the goals engineers pursue in the energy production and recovery field is to design a heat exchanger that can store a large amount of thermal energy in a shorter time. This work practically tests the performance attributes of a latent heat thermal energy storage system in a vertical shell-tube heat exchanger configuration. Water flows in the tubes that are arranged as circular layers at certain radii in the shell, which is occupied by organic paraffin phase change material (RT60). The experiments consider the effects of the tube area ratio, layer radius ratio, number of tube layers, and distribution of the tubes (inline/staggered), besides incorporating semi-circular tubes instead of complete circular ones. These experiments are conducted by employing heating water (65 °C to 75 °C) during the charging process and cooling water (25 °C) during the discharging process. The key findings from this work are that increasing the radius ratio from 1/3 to 2/3, employing semicircular tubes instead of complete ones, increasing the area ratio from 2.4% to 4.3%, and distributing the same number of tubes in two layers rather than one layer provide reductions in the charging time of 7.2%, 7.3%, 17.6%, and 11%, respectively. The corresponding augmentations in the charging/discharging effectiveness are 8.1%/2.6%, 7.4%/3.3%, 19.7%/5.7%, and 8%/4.5%, respectively. Moreover, by applying a staggered distribution of the tubes instead of an inline one, the charging effectiveness is amplified by 5.3%. Finally, a set of experimental correlations is developed to predict the charging effectiveness of the storage system.

Numerical study on latent heat thermal energy storage with phase change material and metal foam in shell and corrugated tube with external heat losses

In the present work, a numerical investigation of the Latent Heat Thermal Energy Storage system (LHTESs) is performed on a vertical shell and tube geometry, made of a porous medium filled with a phase change material (PCM). The LHTESs is a cylinder with a corrugated inner surface at a constant temperature above the PCM melting temperature; on the external surface there are heat losses to the outside and the top and bottom surfaces are adiabatic. The PCM used is a pure paraffin wax, the metal foam, instead, is made of aluminum. The phase change process is modelled with the enthalpy-porosity theory, while the Local Thermal Non-Equilibrium (LTNE) and the Darcy-Forchheimer models are adopted to analyse the heat transfer between the paraffin and the metal foam. The solutions of the governing equations are computed with Ansys-Fluent commercial code. The survey considers different conductivity variations on the external wall and distinct corrugated wall geometric parameters, with different wavelengths and wave amplitudes. The results of the numerical simulations, concerning the LHTESs charging phase, are reported as a function of time and compared in terms of melting time, enthalpy stored, and energy loss.