Melting Point Of Phase Change Material Research Articles

Enhancing Solar Water Heater Performance Using Phase Change Materials and Modified Encapsulation Geometry

ABSTRACTSolar energy's abundant availability in India makes it a potential solution to meet increasing energy needs without harming environment. Solar water heating (SWH) systems are effective in converting solar radiation into heat for domestic and industrial applications. However, their inability to provide hot water during nighttime or off‐sunshine hours due to the intermittent nature of solar energy presents a challenge. Thermal energy storage, particularly using phase change materials (PCMs), has emerged as a solution. In this study, spherical ball‐type encapsulated PCM, specifically RT60, was incorporated into a solar water heater tank under variable atmospheric conditions. The PCM stores excess energy during daylight and releases it when the water temperature drops below the PCM's melting point. The results reveal a significant reduction in the temperature drop of water from 4.5°C to 1.4°C when utilizing PCM compared to conventional storage water tanks without PCM. Additionally, energy storage capacity is enhanced by 5.13% with PCM incorporation. Furthermore, modifying the encapsulation geometry to a rectangular shape enhances heat transfer and reduces temperature drop even further to 0.9°C, making it a promising approach to improving SWH system performance. This study highlights the possibility of enhancing encapsulation shape and applying PCM to enhance SWH system performance. The results highlight the possibility of increasing solar thermal systems' energy efficiency and usefulness, which will support sustainable energy sources.

Investigation on Cooling Performance of Composite PCM and Graphite Fin for Battery Thermal Management System of Electric Vehicles

ABSTRACTModern electric vehicle (EV) batteries need phase change materials (PCM) that are capable of efficient battery cooling. In this work, a composite PCM is prepared by mixing Fe3O4 nanoparticles (1 wt.%) in paraffin, and the effects of these nanoparticles on the enthalpy and melting point of PCM are studied. It is found that the Fe3O4 nanoparticle additives reduce the onset of melting from 61.46°C to 57.03°C. The composite PCM is used for the cooling of a battery module of 6 substitute‐18 650 batteries, and the cooling performance is experimentally and numerically investigated. The hybrid battery thermal management system (BTMS) utilizing composite paraffin demonstrates a significant reduction of 11.2°C in lithium‐ion battery (LIB) temperature compared with natural convection cooling at a heat generation rate of 2W. The numerical results in this study are in good agreement with the experimental temperature values, with a modest mean absolute error of 1.35°C detected between experimentally obtained and simulated battery temperature values. In order to deal with the low thermal conductivity of liquid PCM after PCM melting, a numerical investigation is conducted to study the effect of a graphite fin on the battery temperature. The use of a fin in hybrid BTMS considerably reduces the temperature of LIBs and temperature difference in the module. The numerical simulations capture the behavior of the phase change phenomenon, showing the evolution of liquid PCM under constant heating. This work presents the dynamic melting patterns of PCM along the length of LIB with and without a fin, which is useful for the effective design of BTMS.

Thermal performance analysis of lightweight phase change envelopes

To improve indoor thermal comfort and achieve building energy saving, a new envelope structure based on phase change material (PCM) was proposed. Firstly, an experimental platform was built around the room model, and the effects of ambient temperatures and PCM layout on the room temperature at different times were explored. Subsequently, a room numerical model heat transfer was constructed and the experimental verification was completed. The effects of PCM thickness, position, arrangement, and melting point difference on the room temperature at each time were analyzed based on the latent heat utilization rate, temperature fluctuation amplitude, and delay time. The experimental results show that when the walls all around the room contain PCM, the maximum indoor temperature can drop to 29.5 °C, and the maximum temperature drop is 3.2 °C. In addition, the greater the heat flow, the less effective the PCM is at controlling the temperature in the room. The simulation results show that when the PCM with a thickness of 15 mm is placed on the interior side of the wall, the maximum indoor temperature can be reduced to 29 °C, the maximum temperature drop is 2.9 °C, and the peak indoor temperature is extended by 0.8 h. When the PCM is arranged in series and the melting point difference is 3 K, the temperature control effect is the best, the maximum indoor temperature can be reduced to 25.7 °C, the maximum temperature drop is 2.9 °C, and the temperature fluctuation is the minimum, 2.6 °C.

Machine learning accelerated the performance analysis on PCM-liquid coupled battery thermal management system

With the increasing prominence of thermal management issues in lithium-ion batteries, the performance of active-passive hybrid battery thermal management systems attracts extensive attention. In this study, a novel phase change material-liquid cooling coupled battery thermal management system was designed. The effects of battery arrangement structure, liquid flow direction, mass flow rate, startup temperature, phase change material melting point, and liquid cooling power consumption on the thermal management performance of the battery module during high-rate discharge were numerically investigated. The results show that the phase change material-liquid cooling system can effectively regulates battery temperature within safe limits under optimal operational conditions. Compared to the module without liquid cooling with an initial temperature of 40 °C, the maximum temperature is reduced by 15.18 °C and 27.5 °C during 3C and 5C discharge, respectively. Lower liquid cooling startup temperature and higher liquid flow rate contribute further to reducing the maximum module temperature, albeit with increased energy consumption. Compared to continuously operating liquid cooling at 0.01 kg/s, adjusting liquid cooling operating point with minimized power usage can drastically reduce energy consumption by up to 94.71 % during 5C discharge and ambient temperature conditions. Additionally, machine learning with three multi-objective regression prediction models were utilized to predict the temperature and energy consumption of the proposed coupled system. The error between the Random Forest model's predicted values and the simulation results was determined to be <5 %.

Experimental and numerical study on photovoltaic thermoelectric heat storage system based on phase change temperature control

To improve the thermal and electrical performance of photovoltaic (PV) systems, a novel system was proposed, in which the PV panel, phase change material (PCM), thermoelectric (TE), and thermal collection devices (PV-PCM-TEG-T) were combined. The experimental device of the PV-PCM-TEG-T system was put up, and its electrical and thermal characteristic was experimentally studied by comparing it with the standard PV panel on the condition of 3-hour radiation and 3-hour non-radiation. A heat transfer numerical model of the PV-PCM-TEG-T system is established and verified by experiments. The comparison of the PV-PCM-TEG-T system and standard PV panel and the effects of PCM thicknesses, and melting temperatures on the temperature of photovoltaic devices were numerically analyzed in 24-hour operating conditions. The results show that under an experimental condition of 3-hour solar radiance of 800 W/m2 and 3-hour non-radiance, the novel system has better temperature control performance, which could increase the PV panel’s output power and power generation efficiency by 10.4 % and 1.9 % respectively. Under 24-hour simulation conditions, the temperature of the novel system is significantly lower than that of the standard PV panel, with a maximum temperature difference of 10.1 °C. The PV-PCM-TEG-T system with thicker PCM has the same temperature as the system with thinner PCM, but higher TE power generation. And the temperature control is better with the lower PCM melting point. This study has a good promoting effect on the efficient utilization of solar energy.

Rotary Heat Recovery Wheel (RHRW) system with an embedded PCM: Proof of concept

This work presents the thermal performance of a novel Rotary Heat Recovery Wheel (RHRW) system incorporating a Phase Change Material (PCM) embedded in the solid structure of the matrix of a rotating recuperator. The main aim of this device is to increase the thermal efficiency of the RHRW in two ways: by storing large amounts of thermal energy in latent form, and by permitting approach temperatures (around PCM melting point) that are closer to the desired setpoint temperatures for heating/cooling purposesA numerical model of the RHRW system with an embedded PCM was developed, comparing its performance against an identical RHRW without the PCM. The numerical model was validated with experimental data from the literature. A sensitivity analysis was carried out, varying the content of PCM embedded and the rotating speed of the wheel. Under the conditions tested in this work, for intermediate rotating speeds (between 0.1 and 0.7rpm) the PCM increases the efficiency of the system. For n=0.3rpm the efficiency augments from 0.44 to 0.87 with an addition of 15% in mass of PCM. There is also a certain rotating speed, nmax, for which the efficiency is maximum as the phase change of the PCM limits the temperature change. A relationship is proposed between the rotating speed and the mass fraction of PCM to reach the maximum efficiency.

Numerical modeling and optimization of tube flattening impacts on the cooling performance of the photovoltaic thermal system integrated with phase change material

In this research, a computational fluid dynamics-based numerical simulation is performed to evaluate the influence of tube flattening on the cooling performance of a photovoltaic thermal system integrated with phase change material. Such a study is executed to obtain the four evaluation parameters, including average photovoltaic panel temperature, phase change material melting percentage, tube pressure drops, and the difference between the highest and lowest temperature points on the photovoltaic panel. To obtain the optimum percentage of tube flattening to optimize the cooling performance of the systems, multi-objective optimization by utilizing response surface methodology is done by considering some design requirements, including minimizing average photovoltaic panel temperature, maximizing phase change material melting percentage, minimizing tube pressure drops, and minimizing the difference between the highest and lowest temperature points on the photovoltaic panel. Finally, a parametric analysis is done to explore how certain critical factors (solar radiation, fluid mass flow rate, phase change material thermal conductivity, phase change material enthalpy of fusion, and phase change material melting point) affect the efficiency of the systems. The findings indicate that as tube flattening rises from 0 % to 75 %, the average photovoltaic panel temperature and the difference between the highest and lowest temperature points on the photovoltaic panel decrease which is a positive effect. Conversely, increasing the tube flattening results in an increase in the tube pressure drops and a reduction in the phase change material melting percentage. These changes adversely affect the cooling performance. Considering these impacts and conducting an optimization process, the ideal tube flattening value is 54.78 %. In this optimized state, the average photovoltaic panel temperature reaches 55.21 ˚C, phase change material melting percentage comprises 42.54 %, tube pressure drops is 184.8 Pa, and the difference between the highest and lowest temperature points on the photovoltaic panel is 33.42 ˚C.

Optimization of temperature distribution in building envelopes of Ahmedabad region using nano-encapsulated phase change material

The incorporation of Phase Change Materials (PCM) into the building envelopes helps to increase indoor thermal comfort while lowering energy usage. The selection of PCM is directly related to its performance and might be viewed as an optimization challenge. The manuscript highlights the optimization of temperature distribution in building envelopes (walls and roofs) of Ahmedabad by choosing the suitable PCM and Nano-particle. Three different PCMs (RT31, RT 35, and RT42) and Nano-particles (Al2O3, CuO, and ZnO) with different concentrations (12 %, 16 %, and 20 %) are considered for the optimization. The PCMs are encapsulated into the building layer thickness to examine their characteristics like effective thermal conductivity, concentration, melting point, etc. These parameters are evaluated in a room that measures 5 m x 4 m x 3.5 m (L x W x H). The design-builder software (Version 7.0.2.006) is used to carry out the steady-state numerical simulations for this building envelope. The results suggest that the integration of PCM reduces the building's overall energy consumption by 7.92 kWh/m2 per year. The optimal design is proposed by establishing a temperature difference (ΔT) in building envelopes and utilizing a hybrid optimization technique (a combination of Artificial neural network (ANN) and Genetic algorithm (GA)). This temperature difference of the building envelope is confirmed to be dependent on their PCM melting point, effective thermal conductivity, concentration (in%), and PCM layer thickness. Hybrid optimization is found to be the most stable strategy for predicting temperature dilation and energy storage in building envelopes. Thus this paper gives a systematic understanding of the selection of PCM and Nano-particles and identifies the suitable PCM layer thickness for encapsulation.

Enhancing Energy Efficiency in Buildings through PCM Integration: A Study across Different Climatic Regions

In the quest for sustainable and energy-efficient building solutions, the incorporation of phase change materials (PCMs) into building envelopes emerges as a groundbreaking strategy. PCMs, renowned for storing and releasing thermal energy during phase transitions, stand as a promising avenue to curtail energy consumption while enhancing thermal performance. This study rigorously explores the potential energy savings and thermal comfort benefits achievable through PCM integration into building envelopes. Multiple energy simulations are conducted on a residential building model in diverse locations, including Irbid, Amman, and Aqaba in Jordan, and the city of Oradea in Romania, utilizing the EnergyPlus simulation tool embedded in DesignBuilder software v7.0.2.006. The results reveal that BioPCM®, derived from renewable biomass, significantly elevates thermal performance owing to its heightened latent heat of fusion. Optimal outcomes materialize with a PCM melting point of 23 °C, a configuration closer to the interior surface, and a thickness of 37.1 mm. The study underscores the superior performance in moderate climates (Irbid and Amman) compared to hot-dry climates (Aqaba) and cold-wet climates (Oradea, Romania). Financially and environmentally, incorporating PCM in Amman demonstrates potential annual energy savings of 5476.14 kWh, translating to a cost reduction of 1150 USD/year, and a decrease in GHG emissions by 2382.31 kgCO2eq. The estimated payback period for PCM incorporation in external walls is four years, robustly emphasizing the feasibility and multifaceted benefits of this energy-efficient solution.

Numerical investigation of heat transfer mechanism in an embedded PCM-TEG for better overall performance under the fluctuating heat source

Using phase change materials (PCM) can effectively ensure the stable operation of semiconductor thermoelectric generators (TEGs). Conventional PCM-TEG structures exhibit relatively poor output performance due to energy barriers caused by low thermal conductivity. The embedded PCM-TEGs proposed in this study can address this issue well by adopting variable structure composite forms of PCM and TEG, resulting in a more complex heat transfer mode than traditional systems. To evaluate embedded systems' characteristics and performance enhancement methods, this paper first establishes a multiphysics mathematical model for embedded PCM-TEGs. Then, employing the TOPSIS method, an optimal embedded structure that considers system output and stability is obtained. Finally, we investigate the effects of key parameters on system performance, including PCM volume, latent heat, melting point, and metal-added composite materials. The CCC PCM-TEG (embedded PCM-TEG with PCM closer to the cold side) exhibits superior performance with a 28.6 % increase compared to conventional structures. For a given PCM volume, embedded structures with equal heights show better performance due to weak influence from asymmetric configurations on internal heat flow direction. Unlike traditional PCM-TEGs, metal-added composite PCMs in embedded structures reduce the temperature difference range across TEGs and thus deteriorate system performance.

Experimental and numerical study on temperature control performance of phase change material heat sink

With the increasing power consumption of electronic products, the rising temperature leads to the deterioration of working environment and the reduction of service life. In order to control the temperature rise of electronic products, in this paper, the heat sinks with phase change material (PCM) and honeycomb metal were designed. And their performance was compared with that of the original heat sink (without PCM and honeycomb metal) then studied under various working conditions. Paraffin (n-eicosane) and prepared low melting point alloy were filled into the heat sink with honeycomb metal. The temperature control performance of heat sink was tested experimentally under different heating power. A two-dimensional heat transfer mathematical model of honeycomb metal PCM heat sink was established and solved numerically. The numerical results were compared with experimental data to verify the mathematical model. The results demonstrate that PCM heat sinks effectively controls the temperature of electronic devices and the low melting point alloy makes heat sink better performance than paraffin. Honeycomb metal further decreases the temperature of the paraffin heat sink by up to 3.6 °C, and extends the effective working time of the alloy heat sink by 14 %. The performance of the low melting point honeycomb metal heat sink is superior to that of the paraffin honeycomb metal heat sink at high heating power, and is close to the latter at low heating power. The effective working time of PCM honeycomb metal heat sink is significantly extended when the PCM melting point is close to the limit temperature, especially at high heating power and for the PCM with low thermal conductivity. This study provides valuable reference for temperature control design of electronic products.

Numerical study on using multichannel tube and PCM for improving thermal and electrical performance of a photovoltaic module

The electrical efficiency of a crystalline silicon module drops with increasing cell temperature. Phase change material (PCM) was commonly used to perform the thermal management of a PV module, while its poor thermal conductivity may act as a barrier to wide application. In the current study, an innovation design that utilizes excellent heat storage capacity (HSC) of PCM and high thermal conductivity of multichannel tube is introduced into a PV module (MPCM-PV). Computational Fluid Dynamics (CFD) modeling of the MPCM-PV together with experimental validation was conducted. It was determined that the established model can predict the performance of the MPCM-PV at reasonable accuracy. The effect of the structural and physical parameters on the operating performance of the MPCM-PV module was analyzed. The electric energy production was increased by 4.75 % when the number of channels was increased from 1 to 5. Additionally, the rectangular-shape channel rather than triangular shape was more beneficial for the MPCM-PV temperature reduction. Further, it was found that the low melting point and large HSC of PCM lead to the higher electric energy production. The electrical energy increments of 1.71 % and 0.32 % were respectively achieved when the HSC was increased from 240 kJ/kg to 560 kJ/kg and the melting temperature was decreased from 44 °C to 38 °C. The sensitive analysis suggested that the channel shape and the HSC have the most significant impact on electric energy production. These findings provide insight into the design the MPCM-PV system and can guide the development of efficient PV system.

Potential evaluation of energy flexibility and energy-saving of PCM-integrated office building walls

Building energy flexibility is important for reducing peak-to-valley differences in air-conditioner loads. Integrating phase change material into office building envelopes and precooling can effectively reduce peak load, but precooling may increase total energy consumption. Therefore, it is imperative to investigate its energy flexibility and energy consumption features. In present work, a heat transfer model of phase change material (PCM)-integrated office building walls was established firstly and verified by experiments. Then, the energy flexibility and energy-saving potential of the PCM-integrated wall under different precooling strategies were studied, and the effects of various PCM parameters on energy flexibility and energy-saving potential were evaluated. Finally, the influence of different peak-to-valley electricity tariff differences on electricity costs was analyzed. The results show that the optimized precooling strategy and peak-to-valley electricity tariff difference make the energy flexibility index of the PCM-integrated wall up to 69.7% at a total load reduction of 1.3% and save the electricity cost by 51%. The PCM location and melting point have the most significant effect on the energy flexibility and energy-saving potential of the PCM-integrated wall under precooling operating conditions. This study guides the selection of energy flexibility and energy-saving precooling strategy and PCM parameters for PCM-integrated office building walls and the formulation of time-of-use tariff policies.

Multi-objective optimization of a metal hydride reactor coupled with phase change materials for fast hydrogen sorption time

Recently, the utilization of phase change materials (PCM) for the heat storage/recovery of the metal hydride's reaction heat has received increasing attention. However, the poor heat management process makes hydrogen sorption very slow during heat recycling. In this work, the H2 charging/discharging performance of a metal hydride tank (MHT) filled with LaNi5 and equipped with a paraffin-based (RT35) PCM finned jacket as a passive heat management medium is numerically investigated. Using a two-dimensional mathematical model validated with our in-house experiments, the effects of design parameters such as PCM thermophysical properties and the fin size on hydrogen charging/discharging times of the MHT are investigated systematically. The results showed that the PCM's melting point and apparent heat capacity have a conflicting impact on the hydrogen sorption times, i.e., the low melting point and high specific heat capacity reduce the H2 charging time. In contrast, the hydrogen discharging time follows the opposite trend. As a result, a multi-objective optimization was conducted to simultaneously minimize the H2 charging/discharging times using the thermal properties and size of the PCM. The optimum solutions selected from the Pareto front show that the PCM melting point should be around 42–43 °C for fixed hydrogen ab/desorption pressures of 10/1.5 bar. Moreover, the comparison between the MHT-PCM using the optimized PCM and reference PCM showed that the former reduced the hydrogen charging/discharging times by 48.6 % and 4 %, respectively. At the same time, the hydrogen storage efficiency of the optimal design is 100 % as compared to 96 % for the reference design. Besides, among the practical PCMs, inorganic PCMs (salt hydrates and eutectics) display favorable hydrogen charging time below 3000 s at the expense of hydrogen discharging time (above 7000 s) in our case study.

Numerical investigation of photothermal performance of glazed window integrated with airflow channel and phase change material

ABSTRACT Double-glazed window coupled with phase change material (PCM) improves the thermal inertia and heat storage capacity, but the inefficient utilization of latent heat stored in PCM restricts the application in cold regions in winter. To surmount the deficiencies, a PCM ventilation window (PCMVW) with an airflow channel installed outside is proposed, in which the external ambient air enters the room after being heated by the PCM layer to realize the adequate utilization and recovery of the energy stored in the PCM. A two-dimensional model was established to investigate the photothermal performance of PCMVW in winter. Then, the effects of airflow rate and PCM melting point on the photothermal performance of PCMVW are analyzed. The results show that the thermal performance of the structure achieves significant enhancement with the airflow channel installed, which saves 521 kJ/d of energy, and the temperature fluctuation is 0.68 times that of the traditional PCMW. Meanwhile, the airflow improves the dynamic transmittance of the window at certain times. Remarkable enhancement of the thermal performance and optical performance of the PCMVW is achieved by adjusting the air mass flow rate and PCM melting point, which provides solutions for the application of PCMVW in cold regions.

Experimental investigation in the selection of phase change materials based on thermal stratification effect in thermal energy storage system

AbstractThis study aims to evaluate the effects of thermal stratification on thermal energy storage (TES) systems during the charging process and choose suitable phase change materials (PCMs) for various layers. The research revealed that fiberglass insulation of 60 mm thick significantly decreased natural convection losses and increased the TES system's potential for energy recovery. For constant heat load, the charging time increased with increasing HTF inlet temperature, but remained constant for the first TES layer at a specified flow rate, resulting in increased storage capacity with minimal heat loss to the surroundings. The solar collector efficiency was shown to be dependent on solar radiation and collector efficiency, with peak efficiency seen at specified periods. The lowest melting point of PCMs at each layer 68°C, 62.7°C, 57°C, and 50°C was chosen based on temperature graphs. For comparing stratification behavior, the “MIX” number versus non‐dimensional charging time plot was effective. Additional experiments are needed to assess the selected PCMs' charging and discharging properties.

Experimental study on pressure-enhanced close contact melting with PCMs for stable temperature control of high heat flux electronic devices

Phase change material (PCM) demonstrates great potential for the thermal management of electronic devices. However, stable temperature control is hardly achieved because of the moving melt front during the phase change process. This study presents the pressure-enhanced close contact melting method for PCM, from the application aspect via visualization study. The overheated liquid PCM can be rapidly removed from the heat source, thus achieving stable temperature control for electronic device when operating under high heat flux. The transient performances of paraffin and low melting point alloy are evaluated, respectively, under various heat loads and pressures. It is recognized from the visualization test that the conventional PCM-based and metal foam-enhanced heat sinks fail to achieve stable temperature control since the continuously elevated liquid thickness between melt front and heat source results in increasing thermal resistance. However, the pressure-enhanced close contact melting method might continuously squeeze melted liquid, thus promoting the contact of melt front with the heat source. The effects of applied pressures and heat loads on the transient thermal management performance over time are virtually investigated. As the result, the surface temperature of heat source can be stabilized around the melting point of PCM. When applying the pressure of 2250 Pa, the thermal resistance can be minimized to lower than 10−4 K·m2·W−1. It is also noted that the thermal management performance remains unchanged when the pressure exceeds 1250 Pa.

Impact of PCM type on photocell performance using heat pipe-PCM cooling system: A numerical study

The effectiveness of a hybrid cooling system consisting of flat heat pipes (HP) and a heat sink of phase change material (PCM) for the temperature regulation of the photocell (PV) is studied. The system is mathematically modeled and numerically solved by using MatLab software. The impact of the type of PCM (RT25, RT35, and RT42) in summer on the performance of the hybrid photocell cooling system is analyzed. Results prove that the HP-PCM cooling system performs better than the natural photocell cooling. PCM with a low melting point is more efficient for electric performance than a high melting point. For a given PCM thickness of 4 cm, the maximum temperature of the photocell is reduced by 8.7 °C when PCM RT25 is used as a heat sink compared to 7.5 °C and 7.3 °C for RT35 and RT42, respectively. RT25-based PV/HP-PCM system outperformed a conventionally cooled photocell in terms of electrical efficiency by 5.3%. In comparison, RT35 and RT42 yield incremental gains of 5% and 4.5 %, respectively. As the PCM melting point is lowered, the hourly thermal efficiency increases with a peak of 48.9% for RT25, 33.7% for RT35, and 32.2% for RT42, respectively.

A review of phase change materials in multi-designed tubes and buildings: Testing methods, applications, and heat transfer enhancement

Phase change materials (PCMs) can be used as a latent heat storage system which is a very cost-efficient and affordable method for conserving thermal energy for future use. They are capable to store and release a vast amount of energy. In the past decade, PCMs are used widely for thermal insulation in buildings. A literature search revealed that various reviews have been conducted in recent years, although most of them have focused on PCM applications in a specific field, such as thermal comfort and building energy efficiency. Very few of them investigated PCMs in tubes with multiple designs and their testing methods simultaneously. This study thus investigates the recent development of thermal energy storage systems incorporating PCMs in multi-designed tubes and buildings, as well as their testing methods, other applications and heat transfer improvement. The melting point of PCM varies depending on the type. For instance, the RT23 PCM has a melting point of only 23o C, making it an excellent choice for home insulation. A 31-finned tube shows the maximum energy efficiency for commercial paraffin and reduces the PCM melting time by 65 %. However, the expansion of PCM applications is typically restricted by the reliability, efficiency, overall cost, and performance of the technology. A significant improvement is still needed in the phase transition, thermal conductivity, and compatibility of the materials. When dealing with inorganic PCMs, it is very important to take steps to prevent subcooling, supercooling, and phase separation by adding nucleating agents.

Optimization design and performance investigation on the cascaded packed-bed thermal energy storage system with spherical capsules

Most of the previous researches on the cascaded packed-bed latent heat storage (CPTES) system are the thermal performance optimization based on numerical calculation. Experimental studies are few and mainly focus on single design parameter at low-temperature conditions. Lack of the detailed temperature - flow field experimental data and optimization scheme for the CPTES system. In this paper, an optimized two-layered filling structure of packed-bed heat storage system (OT-PTES) was proposed, which considers melting temperature of phase change material (PCM), capsule diameter, and filling volume ratio. The heat transfer process of PCM capsule and heat transfer fluid (HTF) during charging/discharging process were studied in detail by experiments. Under consistent working conditions, the average charging/discharging rate, total heat capacity, overall efficiency, and exergy efficiency was evaluated. And the influences of HTF inlet flow and the volume filling ratio of two-layered on thermal performance were analyzed. Finally, the concentric diffusion model was used to simulate the system to further optimize its hierarchical structure. The results are concluded as follows: (1) The temperature difference between PCM capsule and HTF at the interface changes continuously, and there is also an obvious temperature gradient in the radial direction of HTF, which improves the heat transfer efficiency. (2) Through experiments, the packed-bed with single large/small size PCM capsules are compared with the OT-PTES system. The overall efficiency of the latter is 74.2%, increased by 3.38% and 8.28%, and the exergy efficiency is 62.7%, increased by 7.5% and 52%. It is proved that the OT-PTES system has better charging/discharging performance. (3) When the volume filling rate = 1/2, the system has the best thermal performance (75.04%) and exergy efficiency (67.1%). (4) The numerical simulation results show that the overall performance of the packed-bed is optimal when the capsule size composition is 20–30 mm and the temperature difference of PCMs melting point is 60 ℃. In summary, OT-PTES is an optimized system with better heat storage performance. This study can provide experimental data support for the optimal design of the PLTES system and useful guidance for industrial applications.