Bed Latent Heat Storage System Research Articles

An integrated machine learning and metaheuristic approach for advanced packed bed latent heat storage system design and optimization

To tackle the challenge of waste heat recovery in the industrial sector, this research presents a novel design and optimization framework for Packed Bed Latent Heat Storage Systems (PBLHS). This features a Deep Learning (DL) model, integrated with metaheuristic algorithms. The DL model was developed to predict PBLHS performance, trained using data generated from a validated Computational Fluid Dynamics (CFD) model. The model exhibited a high performance with an R2 value of 0.975 and a low Mean Absolute Percentage Error (<9.14%). To enhance the ML model's efficiency and optimized performance, various metaheuristic algorithms were explored. The Harmony Search algorithm emerged as the most effective through an early screening and underwent further refinement. The optimized algorithm demonstrated its capability by rapidly producing designs that showcased an improvement in total efficiency of up to 85% over available optimized experimental PBLHS designs. This research underscores the potential of ML-integrated approaches in laying the groundwork for generalized design frameworks for TES systems, offering efficient and effective solutions for waste heat recovery.

A comprehensive material and experimental investigation of a packed bed latent heat storage system based on waste foundry sand

The EU's industrial sector discards about 18.9% of its energy as waste heat, much of which has the potential for recovery. This study addresses the challenge by focusing on the advancement of latent heat thermal energy storage (LHTES) using phase change materials (PCMs) encapsulated within industrial waste foundry sand (WFS). WFS, a problematic by-product, is repurposed as a supportive matrix for NaNO3 and solar salt PCMs, tailored for effective integration into high-temperature industrial processes. The paper provides a thorough mechanical and thermal examination of the WFS-salt PCMs, highlighting their improved thermal stability, performance, and compatibility with direct thermal energy systems. The composite PCMs demonstrated melting points well-suited for industrial waste heat applications and achieved an energy density of 542.0 ± 8.3 kJ/kg for NaNO3 and 516.0 ± 4.5 kJ/kg for solar salt, An experimental cascade PBLHS, based on these CPCMs, with a capacity of 262 MJ, designed to mimic an industrial heat source at 450 °C, was systematically tested to assess its energy density and efficiency over repeated charging/discharging and free cooling cycles. Its overall system efficiency is found to be 68.5%. These findings position WFS-salt PCMs as a promising and environmentally beneficial approach to enhance industrial energy efficiency and utilisation.

Design analysis and performance prediction of packed bed latent heat storage system employing machine learning models

In recent years, the goal of becoming energy independent of fossil fuels has gained prominence. Solar energy is an excellent choice because it has a very less environmental impact in comparison to fossil fuels. The variability of solar radiation creates a divergence between energy demand and supply, making it necessary to implement efficient thermal energy storage systems to bridge the gap and enable solar thermal power plants to become viable solutions for uninterrupted power generation to meet the present and future energy needs. In this study, various data-driven machine learning (ML) models were used to analyze the design and performance of the packed-bed thermal energy storage (PBTES) system. Six different ML models, including linear regression (LR), support vector regression (SVR), K-nearest neighbors (KNN), decision trees (DT), random forests (RF), and extreme gradient boosting (XGB), were employed to evaluate the performance of PBTES. The models were trained and tested using experimental data reported in the literature on PBTES performance. The results of the study showed that the XGB ML model provided the best performance for PBTES analysis and prediction, with a maximum R2 value of 0.982, and minimum MAE, MAPE, and RMSE values of 0.057, 0.182, and 0.16, respectively. The study demonstrated the effectiveness of data-driven approaches in designing and analyzing PBTES performance, which can be useful for developing more efficient and sustainable energy systems. Overall, this study provides valuable insight into the potential of data-driven ML models for the design and performance analysis of PBTES, which could have significant implications for the utilization of renewable energy sources.

Influence of tank-to-particle diameter ratio on thermal storage performance of random packed-bed with spherical macro-encapsulated phase change materials

Thermal energy storage material is always filled in the packed bed system in a random accumulation manner, and there is an interrelationship between the tank-to-particle diameter ratio (TPDR) and the porosity. Therefore, in this paper, the packed bed latent heat storage system is constructed based on spherical macro-encapsulated phase change materials (PCM). To study the influence of TPDR on the thermal performance of a randomly packed bed, a transient two-dimensional axisymmetric symmetry continuous solid phase model is developed. The experimental and numerical results are compared to verify the accuracy of the model. The heat transfer and pressure drop characteristics between air and PCM capsules are analyzed in detail. The results indicate that the average porosity reaches the maximum at around TPDR≈1.7 position, which is about 0.7. In the same packed bed, when the TPDR is larger, the pressure drop is more affected. The diameter of the heat storage ball changes from 25 mm to 75 mm, the TPDR is reduced by 66.7%, the heat storage of the PCM is almost unchanged, and the heat storage capacity of the stainless-steel spherical shell is reduced by 72%, and the heat storage capacity of the entire heat storage ball is reduced by 12%.

A novel bionic packed bed latent heat storage system filled with encapsulated PCM for thermal energy collection

• A bionic structure brings a more homogeneous temperature difference and a smaller pressure drop compared with conventional systems. • The parameters related to heat transfer and phase transition acquired from numerical study were validated by experiments. • A non-local thermal equilibrium model was employed to characterize the temperature distribution of PCM and HTF in porous media. • The enhancement of flow resistance and heat exchange performance was evaluated. The main content of this work is to propose a novel bionic solution to overcome the nonuniformity of flow and temperature distribution, which is an inherent problem and restriction for conventional latent heat storage devices. By learning from animal circulatory systems, the inner space and flow channel network are distributed hierarchically as arteries, veins, capillaries and ventricles. A conceptual configuration of the bionic system is presented, and its numerical model is established to demonstrate the flow and heat transfer phenomena. The encapsulated PCM that is used in this study is fabricated and parameters related have been measured by experiments. A numerical model of a 3D continuous PCM bed is established to help research the flow of HTF through the surfaces of PCM particles and the heat transfer between them. Then, a model of a simplified bionic device is developed where the PCM region is set as a porous domain. The results show the flow and temperature fields are distributed uniformly, along with a much smaller global pressure drop. By allocating the thermal load on cascaded layers with stepwise PCMs, a more homogeneous global temperature difference can be achieved.

Performance analysis of packed bed latent heat storage system for high-temperature thermal energy storage using pellets composed of micro-encapsulated phase change material

High temperature latent heat storage has gained increasing attention owing to its potential in the integration of renewable energy sources. This study is a novel experimental investigation on the heat storage performance of a horizontal packed bed containing composites comprising Al-Si-based microencapsulated phase change material in a high-temperature air heating system. The pellet type composites with 3 mm is tested here in a 1L scale packed bed heat exchanger at airflow rates between 75 and 150 L min−1. The composite exhibited a narrow phase change temperature range and high heat storage/release characteristics. As the airflow increased, the phase change time of the composite decreased, and the heat exchanging rate increased. The heat exchange efficiency during charging and discharging ranged from 71.0 % to 98.3 % and 69.0 %–90.2 %, respectively. In the discharging mode, although supercooling which comes from the microencapsulated phase change material, was observed, this did not noticeable effect on the heat transfer.

Thermal performance of structured packed bed with encapsulated phase change materials

Packed bed latent heat storage system with simple construction and efficient heat transfer has been extensively applied in the field of renewable energy. This study aimed to select a proper structured packing format by comparing the thermal performance of different structured packed bed thermal energy storage (TES) configurations, with encapsulated paraffin as the phase change material (PCM). The 3D numerical models of the structured packed beds were constructed, and the numerical results are in agreement with the experimental ones. The performance indexes, including the average heat storage rate, total energy, discharging time and construction cost, were evaluated under consistent working condition. The analysis results indicate that the packed bed TES configuration with face centre cubic packing (FCC) possesses superior characteristics, such as high charging rate, low investment cost, large total heat storage energy and stable output temperature, compared with that with body center cubic packing or simple cubic packing. A detailed parametric investigation of the packed bed TES configuration with FCC is implemented to analyse the effect of Reynolds number (Re), inlet temperature and Prandtl number (Pr) of the heat transfer fluid (HTF). Results showed that the uniform extraction of heat is obtained by the packed bed with small inlet Re. The larger the temperature difference between PCM and HTF is, the faster the discharging rate is and the bigger the total heat recovery energy is. By selecting water, fuel oil JP-4, ethylene glycol and hydraulic oil as HTFs, the change in the HTF's Pr is determined to be irrelevant to the thermal characteristic variations of the structured packed bed TES configuration, whereas the thermal conductivity of the HTF positively affects the heat transfer inside the structured packed bed.

Performance of a medium temperature eutectic solder packed bed latent heat storage system for domestic applications

Abstract A packed bed latent heat storage system consisting of aluminum encapsulated eutectic solder (Sn63Pb37) capsules is experimentally evaluated during charging and discharging cycles. Sunflower Oil is used as the heat transfer fluid in the experiments. The effect of the flow-rate on the charging performance is evaluated using three charging flow-rates namely; 4 ml/s (low), 6 ml/s (medium) and 8 ml/s (high). The storage system is also evaluated with three different set heater charging temperatures (260 °C (low), 280 °C (medium) and 300 °C (high)). Discharging experiments are performed with the three different flow-rates to evaluate the effect of the flow-rate on the discharging characteristics. Charging and discharging results are presented in terms of the axial storage tank profiles, the energy rates and the exergy rates. The overall performance of the storage system is evaluated in terms of the energy and exergy storage efficiencies. The charging energy and exergy rates are seen to increase with the charging flow-rate at the expense of a greater charging duration since higher flow-rates tend to cool down the heater. The best charging flow-rate of 6 ml/s is suggested which ensures a reasonable duration of charging, reasonable thermal stratification and reasonably high energy and exergy charging rates. The effect of the set heater temperature on the charging energy and exergy rates is insignificant as compared to the effect of the flow-rate. The best set charging temperature of 280 °C is also suggested by the experimental tests. Increasing the flow-rate results in faster heat transfer with higher peak energy and exergy rates during discharging. However, the stored energy and exergy is utilized for a shorter duration as compared to the lowest flow-rate. Energy and exergy storage efficiencies decrease with an increase in the flow-rate and the highest flow-rate shows the lowest values due to the longer charging duration and the shorter discharging duration. The set heater charging temperature shows only a marginal effect on the energy and exergy storage efficiencies. A comparison of the energy and exergy rates of the solder during charging and discharging with adipic acid shows slightly better performance during charging cycles for adipic acid. For discharging cycles, the solder shows a better performance.

Cold energy storage in a packed bed of novel graphite/PCM composite spheres

The low thermal conductivity of phase change materials (PCMs) are hindering wider use. To enhance the thermal conductivity of PCM (water), a novel approach of encapsulated water in a high thermal conductivity graphite sphere was investigated. For a single graphite/water composite sphere, the results showed that the effective thermal conductivity of the PCM (water) is increased by 12 times, and hence the freezing and melting times of the PCM is reduced by 53.7% and 44.4% respectively, compared to a non-graphite sphere filled with the same amount of water. In addition, a graphite/water composite sphere exhibits minimum super-cooling, indicating that the graphite matrix material plays a good role as a nucleating agent for water freezing. The thermal behaviour of a packed bed filled with 50 graphite/water composite spheres was tested. The influence of heat transfer fluid (HTF) inlet temperature and volumetric flow rate on the thermal behaviour of the packed bed latent heat storage system are experimentally investigated. The results showed that both had a significant effect on freezing time. The freezing time at HTF inlet temperature of −3.5 °C and volumetric flow rate of 1000 mL/min is 5.3 h. However, it is decreased by 45% and 65% when the HTF inlet temperature is decreased from −3.5 °C to −5.5 and −7.5 °C, respectively. It is observed that by adjusting the HTF inlet temperature and volumetric flow rate during the discharge process, the required output temperature and average melting rate can be achieved in practical applications. The developed ice storage system can be easily adapted to a variety of cooling applications.

Thermal Stratification Performance of a Packed Bed Latent Heat Storage System during Charging

Experimental thermal stratification evaluation of a packed bed latent heat storage is done during charging cycles. The packed bed latent heat storage system consists of adipic acid encapsulated in aluminum spheres. Sunflower oil is used as the heat transfer fluid during charging cycles. Stratification number profiles are used to evaluate thermal stratification in the storage system. Charging experiments are carried out with three different flow-rates (4 ml/s, 8 ml/s and 12 ml/s). Charging experiments are also done using the same flow-rate (8 ml/s) with three different set heater temperatures (220 °C, 240 °C and 260 °C). The lowest charging flow-rate (4 ml/s) shows the best variation of the stratification number profile since it shows the least drop from the peak value and the shortest charging interval. Different set heater temperatures show almost identical stratification number profiles. The effect of the charging flow-rate is more significant than the effect of the charging set heater temperature when evaluating thermal stratification for this particular system.

Melting of PCM in Capsule by Forced Convection for Packed Bed Latent Heat Storage System.

Melting of PCM in Capsule by Forced Convection for Packed Bed Latent Heat Storage System.

Numerical and experimental investigation of a fixed bed latent heat storage system during charging processes

Heat transfer analysis of a packed bed-phase change material (PCM) latent heat thermal energy storage system is presented in this article. The spherical capsules, containing water with a nucleation agent as a PCM, fill the thermal storage tank used for an air-conditioning commercial application. The heat transfer fluid that circulates through the tank and around the capsules is an aqueous solution of ethanol. In this study, the experimental model is tested to use for analysing the thermal performance of packed bed-PCM latent. The governing equations are based on energy balance in the spherical capsules where the results are compared numerically using simple, explicit and finite difference technique. The results obtained are used only for charging process. The effects of mass flow rate and inlet heat transfer fluid temperature are investigated on the time duration for solidification. The contribution of this article is using ethanol as transfer fluid in thermal storage system.

Numerical investigation of packed bed storage unit filled with PCM encapsulated spherical containers – A comparison between various mathematical models

There are several methods adopted by the scientists in modeling the heat transfer phenomenon during solid–liquid phase change. However, the validity of the various models developed and the complexity required for a given problem is not well reported in the literature. This paper presents a comparative study of three different mathematical models for the packed bed latent heat storage system, comprised of a cylindrical storage tank filled with paraffin encapsulated spherical containers. The enthalpy formulation technique is used in the models to accommodate the phase change behavior of the paraffin over a range of temperatures. The results obtained by solving the models using the fully explicit finite difference method are initially validated with experimental results. Further numerical analysis is performed using the models for two different heat transfer fluids of air and water at different mass flow rates and ball sizes and the validity of the models are compared and reported. It is found that one model is sufficient when air is the heat transfer fluid and another model is recommended when water is the heat transfer fluid.

Erratum to “Numerical heat transfer analysis of the packed bed latent heat storage system based on an effective packed bed model” [Energy 35 (2010) 2022–2032

Erratum to “Numerical heat transfer analysis of the packed bed latent heat storage system based on an effective packed bed model” [Energy 35 (2010) 2022–2032

Numerical heat transfer analysis of the packed bed latent heat storage system based on an effective packed bed model

Due to the complexity of the fluid flow and heat transfer in packed bed latent thermal energy storage (LTES) systems, many hypotheses were introduced into the previous packed bed models, which consequently influenced the accuracy and authenticity of the numerical calculation. An effective packed bed model was therefore developed, which could investigate the flow field as the fluid flows through the voids of the phase change material (PCM), and at the same time could account for the thermal gradients inside the PCM spheres. The proposed packed bed model was validated experimentally and found to accurately describe the thermo-fluidic phenomena during heat storage and retrieval. The proposed model was then used to do a parametric study on the influence of the arrangement of the PCM spheres and encapsulation of PCM on the heat transfer performance of LTES bed, which was difficult to perform with the previous packed bed models. The results indicated that random packing is more favorable for heat storage and retrieval as compared to special packing; both the material and the thickness of the encapsulation have the apparent effects on the heat transfer performance of the LTES bed.

Numerical and experimental study of spherical capsules packed bed latent heat storage system

A numerical model to simulate a storage system composed of spherical capsules filled with PCM placed inside a cylindrical tank fitted with a working fluid circulation system to charge and discharge the storage tank. The simplified transient one-dimensional model is based on dividing the tank into a number of axial layers whose thickness is always equal or larger than a capsule diameter. It is also assumed that the temperature of the working fluid is uniform and equal to the average temperature of the layer. The solidification process inside the spherical capsule is treated by using a conductive one-dimensional phase change model with convective boundary condition on the external surface. The convection present in the liquid phase of the PCM is treated by using an effective heat conduction coefficient in the liquid region of the PCM. The solution of the differential equations is realized by the finite difference approximation and a moving grid inside the spherical capsules. The geometrical and operational parameters of the system are investigated both numerically and experimentally and their influence on the charging and discharging times was investigated.