Phase Change Material Heat Exchanger Research Articles

Advancing thermal performance in PCM-Based energy Storage: A comparative study with Fins, expanded Graphite, and combined configurations

Phase Change Material (PCM) thermal energy storage systems have emerged as a promising solution for efficient thermal energy storage from low to very high-temperature applications. This paper presents an investigation into the utilization of medium temperature range PCM-based systems for domestic hot water application, focusing on different techniques to overcome the low thermal conductivity of the PCM. Five shell and tube heat exchangers were fabricated employing different heat transfer enhancement methods including fin, expanded graphite (EG), and a combination of fin and EG. The combination of EG and circular fins exhibited the best performance in terms of charging and discharging, maintaining a uniform temperature distribution throughout the system due to extensive conductive network provided by the combination of EG and circular fins. When the PCM/EG/fin heat exchanger system is fully charged, the energy stored in the system is 109% higher than that of the PCM heat exchanger at the same elapsed time. Furthermore, the PCM/EG/fin system demonstrated a faster discharging response compared to other thermal energy storage (TES) configurations, with over 160% higher discharging power than a system without any enhancement methods. These findings emphasize the practical viability of integrating PCM/EG composite materials into thermal energy storage systems, offering a viable solution for meeting high heat demand requirements in domestic hot water applications. Furthermore, the enhanced discharging response observed in the PCM/EG/fin system has significant implications for improving energy efficiency and reducing operational costs in real-world applications.

Experimental and numerical investigation of a real-scale air to multiple PCM heat exchanger

Energy consumption by residential sectors has proliferated due to urbanization and lifestyle changes. Passive cooling and heating systems can reduce energy consumption and CO2 emissions in residential and commercial sectors. Phase change materials provide an efficient solution for passive energy storage, addressing a building's needs for free cooling and heating. These materials absorb and release heat energy, enhancing the overall efficiency of the energy management system. By employing energy storage devices, it becomes feasible to reduce and shift peak loads to off-peak hours. This study optimized the size and configuration of air-to-multiple PCM heat exchanger through the utilization of a 2D ANSYS (Fluent 19.2) model. This study employs multiple phase change materials (PCMs) with varying melting temperatures as a heat transfer technique to reduce the melting and solidifying times of the PCMs. Furthermore, it was observed that the arrangement of PCMs in series affected melting and solidification times, so two scenarios have been examined. The air-to-multiple PCM system has been investigated through numerical simulations and experimental analyses, focusing on the liquid fractions within the PCM and the outlet air temperatures across the air channels. The total time for entirely melting PCMs RT25HC and RT21HC is less than 4 h, but the solidification time for PCM-RT21HC needs more than 12 h. In both scenarios, PCM-RT21HC melted first, while PCM-RT25HC solidified first.

Numerical investigation of heat transfer in wire and tube-based phase change material heat exchanger

The utilization of latent heat storage units with their high energy density and isothermal heat transfer behavior can enhance the performance of thermal energy systems. This study aims to investigate the effect of fin placement on the melting time of a wire and tube-based Phase Change Material (PCM) heat exchanger using numerical simulations. The study introduces a new complex geometry for the heat exchanger, and numerical analysis of heat transfer was conducted in Ansys Fluent software using an established solidification and melting model. The numerical results were validated against experimental data, and it was found that the position of the tubes and fins had a significant impact on heat transfer within the PCM. The model was able to predict temperature data with a maximum discrepancy of 3%.

Development of PCM-based shell-and-tube thermal energy storages for efficient EV thermal management

Electric vehicles face significant challenges in cold climates. Battery efficiency decreases, and cabin heating demands additional electricity, which diminishes the energy available for vehicle propulsion. In this context, a thermal energy storage system based on a phase change material (PCM) with diverse designs of shell-and-tube heat exchangers is investigated to meet cabin thermal load demands independently. A simulation model for a two-phase PCM heat exchanger is developed and validated using experimental data. The comparison revealed average temperature differences of 1.59 K and 1.61 K for the melting and solidification processes, respectively. Compared to the single tube design, the heat transfer performance of finned multitube design improved the melting process and reduced the melting time by 92.9% and reduced the solidification time by 87.6%. The average heat transfer rate of the finned multitube during the solidification process is 2.9 times higher than that of the single tube. Additionally, the use of PCM incorporating different types of nanomaterials is explored to enhance the melting and solidification performance through increased thermal conductivity. The graphene nanoplatelet PCM exhibited the most substantial improvements in thermal conductivity, resulting in melting and solidification time reductions by 54.2% and 48.9%, respectively.

Experimental investigation on the use of PCM heat exchangers in Geo-energy piles and walls

The current paper aims to experimentally investigate the thermal performance of geo-energy piles and walls fabricated with Phase Change heat exchangers. Four prototype concrete geo-energy structures (i.e., piles and walls) were tested using two distinct types of heat exchangers, including standard heat exchangers and PCM heat exchangers. The PCM heat exchangers utilized in the current study were filled up with two different types of Phase Change Materials (PCM) with melting points of 26 °C and 42 °C for geo-energy piles and walls, respectively. The thermal efficiency of the geo-energy piles/walls was experimentally assessed over 100 h of continuous operation under cycles of cooling and heating. The findings illustrated that using PCM heat exchangers led to enhancing the heat transfer efficiency of geo-energy piles by 75 % and 43 % in heating and cooling operations, respectively, compared to those achieved using a standard heat exchanger. Furthermore, the heat transfer performance of geo-energy walls with a PCM heat exchanger was enhanced by 43 % and 32 % in heating and cooling tests, respectively, compared to those achieved using a standard heat exchanger. Moreover, the findings indicated that the inclusion of PCM heat exchangers in geo-energy structures contributed to reducing: the impact on soil temperature and thermal interference radius as well as the potential structural damage due to thermal stress.

A numerical study on control mechanism of heat transfer in a double pipe PCM heat exchanger by changing eccentricity

The thermal analysis of a double pipe phase change material heat exchanger is studied numerically. The study is done for three cases as; a) Case A: a melting process when inner pipe is maintained at a constant temperature higher than melting point, b) Case B: a solidification process when the inner pipe temperature is constant but less than melting temperature, and c) Case C: for a cyclic thermal storage when the inner pipe surface temperature periodically changes between temperatures of Cases A and B. The aim of this study is to find the optimum position of the inner pipe for each studied cases and to investigate the differences in heat transfer mechanism of the above cases for various Rayleigh numbers. The obtained results show that for Case A, the best position of the inner pipe depends on Rayleigh number, but the bottom region provides the shortest melting time for Ra>105. For the Cases B and C, the center must be preferred for all Reynolds numbers since the conduction heat transfer controls the process. In spite of many reported studies in literature, it is better to study on the enhancement of heat transfer for solidification rather than melting process.

Experimental Investigation of Energy and Exergy Assessment of Vapor Compression Refrigeration Unit Enhanced via Encapsulated Phase Change Material

Energy and exergy performance of simple vapor compression refrigeration unit is investigated experimentally with and without coupling heat exchanger of phase change material before the condenser. The hot outside air is cooled before entering the condenser throughout the day by flowing over the cooled phase change material structure that previously solidified during nighttime. Phase change material SP24 is employed because its melting/freezing range is suitable for most selected countries' climates. An experimental set‐up of an air‐phase change material heat exchanger coupled with the unit is constructed to examine its performance, including pressure–enthalpy curve, coefficient of performance, exergy performance, and power consumption including inflow air temperatures and flow rates impacts. Results affirm that the coefficient of performance, cooling capacity, power usage, and exergy destruction are improved by using phase change material. Compared to the unmodified unit, the maximum percentage of saved power and exergy destruction enhancement for the modified refrigeration unit with phase change material is about 8.8% and 10%, respectively. The maximum coefficient of performance and exergy efficiency rise is about 15.1% and 14.2%, respectively. Increasing the temperature differential across the phase change material heat exchanger, either by increasing inlet temperature or decreasing airflow, enhances the refrigeration unit power saving.

Enhancing thermal performance and optimization strategies of PCM-integrated slab-finned two-fluid heat exchangers for sustainable thermal management

This research investigates the influence of phase change material (PCM) distribution, fin density, and PCM type on the thermal performance of a slab-finned cross-flow PCM heat exchanger (HEX). The aim is to develop a highly efficient PCM-HEX system for enhanced thermal intermittency management. Computational fluid dynamics (CFD) simulations are employed to analyze the dynamic behavior of the HEX. Three PCM configurations, 15 variations in fin densities, and three paraffin-based PCMs with distinct melting temperatures are considered. The results reveal that the Type II configuration enhances heating time at high set point temperatures (SPTs), while the Type I configuration extends heating time at low SPTs. Increasing the air mass flow rate (AMFR) reduces the overall discharged thermal energy by 18–19 % for Type II and III configurations and by 10 % for the Type I configuration, indicating the lower sensitivity of Type I to AMFR variations. It is also shown that decreasing the PCM domain's fin density extends the heating time at low SPTs. Additionally, using a PCM with a higher melting temperature enhances the heating time at high SPTs and increases latent energy discharge power. Tetracosane demonstrates the highest efficiency at 54.9 % and maximum total discharged energy reaching 112.4 kJ. The findings of this study have significant implications for the development of optimized PCM heat exchangers in various applications, enabling more efficient and impactful thermal management.

Prediction of transient melt fraction in metal foam - nanoparticle enhanced PCM hybrid shell and tube heat exchanger: A machine learning approach

Phase change materials (PCMs) have gained popularity in storing thermal energy due to their high energy storage capacity per volume. However, the low performance of the PCM heat exchanger (HX) is primarily due to poor thermal conductivity. The performance of these systems can be improved by using metal foams, nanoparticles, fins, etc. In the present work, the melt fraction (MF) in PCM shell and tube (ST) heat exchanger (HX) with a hybrid combination of metal foam + Graphene nanoplatelets (GNP) nanoparticles (NPs) is predicted using the Machine learning (ML) algorithms. This study analyzes 0.93, 0.95, and 0.97 porosity copper metal foams and 0.5% and 1% volume fraction GNP NPs considering the orientation (0°, 30°, 45°, 60° and 90°) effects of HX. Numerical simulations are carried out to collect the data, to train, cross-validate, and testing. Linear regression (LR), support vector regression (SVR), XGBoost (XGB), and K nearest neighbor (K NN) ML algorithms are used to predict the MF of the PCM in HX with respect to time. MF is predicted during both the melting and solidification processes. Among the ML models selected, the LR model has predicted the transient variation of MF with the highest accuracy during both melting and solidification.

Latent heat thermal energy storage solution for CSPs: Integration of PCM heat exchangers

In the last few decades, alternate and renewable energy harvesting techniques, such as Concentrated Solar Power (CSP), have attracted attention as a unique source of electricity. However, the intermittent nature of solar energy results in discontinuous electricity generation. Thus, the integration of a Latent Heat based Thermal Energy Storage (LHTES) system will help in managing this issue. This numerical study explores the heat storage and discharge abilities of Phase Change Material (PCM) to design an efficient energy storage system. In this study, a 2D novel geometrical model is introduced to enhance the performance of PCM based heat exchanger module. Finite Volume Method (FVM) has been used to simulate the complex phase change problem via ANSYS Fluent solver. The double pipe heat exchanger with concentric cylinders is considered as the base case and multiple design modifications with augmented heat transfer areas have been provided. Comparison of different configurations by varying geometrical parameters with base case is carried out. The improvement in the rate of phase change is observed as the base case tube is replaced by semi-circular tubes in the system. The reduction in sensible heat storage is large during initial stages of charging, a reduction is observed as 46%, 43.5% and 48.9% respectively for all three cases. The time taken to achieve a maximum storage and discharge effectiveness of 82%, 85% respectively is less for novel configurations as compared to base case. It is observed that both novel configurations can be useful to store and release faster which can be used in meeting the energy demand on time.

Effect of fin configuration and orientation of latent heat storage system on the melting and solidification performance

Phase change materials (PCMs) are used to store thermal energy. They possess high specific energy at nearly constant temperatures. The usage of the PCMs is limited due to their very low thermal conductivity, which results in poor heat transfer. To overcome this problem usage of fins is a potential technique. In the current analysis, the surface area of the heat transfer fluid (HTF) tube is increased by radial (R-type), spiral (S-type), and longitudinal (L-type) fins. A 3D numerical analysis of melting and solidification is carried out on R-type, S-type, and L-type shell and tube (S&T) PCM heat exchanger (HX) by considering the inclination effects. Lauric acid is used as PCM. Phase change time, energy ratio, and exergy efficiency are considered to analyze the performance of HXs. MOORA analysis is carried out to select the best HX. It is observed that R-type HX at the vertical position has shown better performance among the selected HXs. Among the considered geometries, the maximum average exergy efficiency is obtained for 45° inclination with R-type HX and minimum for horizontally positioned L-type HX during both melting and solidification. The charging time of the vertically positioned HX, when compared to 45o oriented HX with R type, S type, and L type HX is observed to decrease by 47.5%, 45.7%, and 23%, respectively.

Experimental study of vapor compression refrigeration system enhanced via tubular heat exchanger incorporating single/dual phase change materials

Vapor compression refrigeration (VCR) systems operating in hot climates suffer from high condenser temperatures that reduce their performance. One interesting approach being investigated to improve VCR performance is incorporating phase change materials (PCMs) into VCR systems that have not yet been expanded experimentally. So, this work experimentally studies the effect of using tubular PCM heat exchanger to cool the VCR condenser. The impact of two PCMs types suitable for warm climate conditions: SP24 and SP26, and combination of them on the VCR energy and exergy performance is investigated for two inlet ambient air temperatures. The impact on the exit air and PCMs temperatures, and VCR unit's pressure-enthalpy curve, VCR coefficient of performance, and power consumption is also examined. The results show that PCM-equipped systems significantly enhance the VCR exergy efficiency and coefficient of performance, especially at higher ambient temperature. Compared to the system without PCM, the power consumption can be reduced by up to 10.4% with PCM, while the exergy efficiency and coefficient of performance can be improved by 13.7% and 13.4%, respectively. While PCM SP24 provides the best performance, PCM SP26 has longer effective cooling period. A combination of SP24 and SP26 balances the performance and effective cooling period.

Numerical analysis of melting time and melt fraction for bottom charged tube in tube phase change material heat exchanger

Numerical analysis of melting time and melt fraction for bottom charged tube in tube phase change material heat exchanger

Performance evaluation of a solar thermal storage system proposed for concentrated solar power plants

This study aims to assess the performance of the Hybrid Solar Thermal Storage (HSTS) system, the storage system proposed for concentrated solar power (CSP) plants. The heat storage hybridisation concept is based on coupling latent phase change material (PCM) and thermochemical storage system containing paired metal hydride (MH) beds. One base design which uses only thermochemical heat storage mode and two designs of the HSTS system with two distinct PCM heat exchanger designs (i.e., shell-and-tube and cylinder with truncated hollow cones) are proposed and numerically investigated. To predict the dynamic behavior of the three storage systems, a bidimensional mathematical model is established and a numerical code written in Fortran-90 is developed. Key performance indicators used to evaluate the performance of the three storage systems include volumetric storage capacity, specific power, state of hydrogen charge, and energy storage efficiency. Comparing the performance of the three systems reveals that the HSTS system's energy storage efficiency increased by 36% due to the integration of a reaction heat recovery internal system based on Na3Al as PCM. The use of the PCM in truncated hollow cones resulted in a 36.4% reduction of the heat charging and discharging time, an 18.5% increase storage capacity, and a 54.1% increase in specific power. In addition, this study proves that the third design can be imlpemented as a HSTS system in a solar power plant with the following performance indexes: 128 W/kg- Mg2FeH6, 160 MJ/m3 and 88% for specific power, volumetric storage capacity and energy storage efficiency, respectively.

Mathematical modeling for transient thermal performance analysis of phase change material-based heat exchanger

Thermal energy storage (TES) provides a unique way for the thermal solutions to short-duration thermal load systems. TES system utilizes phase change material (PCM), wherein energy is stored in latent heat during the lean time and released during peak load. Conventionally, in a shell-and-tube PCM heat exchanger, PCM is stored in the shell and heat transfer fluid (HTF) flows in the tube. Numerical modeling based on computational fluid dynamics (CFD) tools like FLUENT and COMSOL are computationally intensive. Most numerical research is based on the enthalpy porosity model for solidification/melting problems. Enthalpy-porosity model requires a mushy zone parameter constant which significantly affects analysis results. The constant has no theoretical basis and is chosen based on experience. Analytical models in literature cannot give reasonably good results, which can be directly utilized for engineering purposes. This paper establishes a mathematical model based on the effectiveness-NTU (e-NTU) technique for transient analysis/rating of such PCM heat exchangers. Transient behavior of PCM heat exchanger due to phase transforming static PCM are modeled using an innovative concept of PCM zones, effective zonal length of heat exchange, and PCM zonal resistances. These functions are dependent on one dimension – total PCM liquid fraction ‘xf’ and a model is established for evaluating thermal performance analysis and optimization of PCM heat exchangers. The model is validated against published experimental results for cumulative energy stored in PCM of a PCM heat exchanger with air as HTF. The root-mean-square error for evaluated & predicted model results is less than 2.5%. The model proposed is uncomplicated and can be further utilized to optimize PCM heat exchangers. Transient analysis of inlet–outlet HTF temperature difference, PCM heat exchanger effectiveness, total PCM liquid fraction, PCM phase fractions, and zonal heat exchange length ratios of PCM heat exchanger for the respective experimental cases is further investigated.

Boosting the air conditioning unit performance using phase change material: Impact of system configuration

Boosting the energy efficiency of air conditioning (AC) systems will considerably impact on lowering domestic power consumption. Innovative methods are being developed to enhance AC performance. One promising method involves integrating phase change materials (PCM) with the AC systems. The significant PCM charging period is a primary limitation of coupling AC systems with PCM in the previous research. The current study aims to investigate the impact of coupling an AC unit with various PCM container configurations (e.g., parallel plates, staggered and aligned tubes, and elliptical tubes) on PCM charging and discharging, and AC performance. During the nighttime, the low ambient temperature is charged inside the PCMs. Then, during the daytime, the hot ambient air is cooled by passing through the cold PCM heat exchanger before passing over the unit condenser. A complete dynamic mathematical model for the proposed system is constructed and solved numerically using ANSYS software. Results indicate that applying the cylindrical arrangement lowers the solidification time of the PCM at night by approximately one-third compared to the plate arrangement. Also, raising the inflow air temperature of the air-PCM heat exchanger increases the air temperature difference through the heat exchanger and saving percentage of the AC's power and decreases the PCM's charging and discharging time. For inflow air temperatures of 318.15 K, 313.15 K, and 308.15 K, the maximum average percentage of saved power is around 25 %, 18.7 %, and 12.5 %, respectively for 2 h working and around 8.4 %, 7.2 %, and 6.3 %, respectively for 8 h working of the AC unit. Cylindrical configuration is preferable for daily use of AC systems as the charging process can be achieved through the nighttime.

Enhancement of thermal energy storage in a phase change material heat exchanger having elliptical and circular tubes with & without fins

The objective of this study is to examine the thermal performance of a heat exchanger having multiple elliptical tubes and a phase change material (PCM) filled in the cylindrical shell of a heat exchanger. To improve the heat transmission from elliptical tubes to PCM, two and four fins are incorporated on the circumference of the elliptical tubes. The use of elliptical tubes with fins in the enhancement of heat transfer is an innovative approach in thermal performance studies of heat storage systems. The geometry of heat exchangers having elliptical tubes without fin, with two fins, and four fins are compared with the geometry of heat exchanger with circular tubes having no fin, two fins, and four fins respectively. The current investigation is carried out with the use of a 2D CFD model using a physical enthalpy-porosity technique to explore the phase transition of the solid PCM. The effect of integrating a number of fins on heat transfer has also been explored, and outcomes of elliptical and circular tube geometries in terms of PCM mean temperature and liquid percentage at two different temperatures of 50 °C and 60 °C have been compared. Results show, that PCM melting time is being reduced to 550 s in PCM heat exchanger geometry having elliptical tubes with four fins compared to 585 s for the same heat exchanger with two fins and 665 s for heat exchanger without fin at 50 °C resulting 12 % & 17 % reduction in melting time by applying two and four fins respectively. Whereas PCM melting time is 515 s in PCM heat exchanger geometry having circular tubes with four fins compared to 560 s for heat exchanger with two fins and 655 s for heat exchanger without fin resulting 14.5 % and 21 % reduction in melting time by applying two and four fins respectively. It has been concluded that adding fins on the circumference of elliptical and circular tubes enhances the heat transmission and reduces melting time as well as more heat can be transferred by circular tube geometry compared to elliptical tube heat exchanger geometries. The findings of the investigations are validated with the available simulation data and show good agreement, suggesting a 3.8 percent deviation.

Preliminary experimental assessment of a vertical shell and tube heat exchanger based on phase change materials

The paper presents an experimental setup developed for phase change materials (PCM) testing inside a vertical shell and tube heat exchanger (VSATHE). The work presented part of a more complex one focusing on designing a PCM heat exchanger that could be used in the defrosting process of commercial and refrigeration systems. The phase change materials (PCM) were commercial paraffin RT54HC, while water was used as heat transfer fluid (HTF). This work was presented The impact of changing the temperature of the inlet water (70 °C, 75 °C, and 80 °C) and the change of flow rate (0.012kg/sec, 0.014kg/sec and 0.016kg/sec) in the solidification and melting of the PCM. The results of the experiments showed that when the inlet hot fluid temperature increases at the same flow rate, the melting time in VSATHE units decreases. At the same time, during the charging process, the increase of flow rate with the difference in inlet temperature has no effect on the total melting time.

Measuring the maximum capacity and thermal resistances in phase-change thermal storage devices

Thermal energy storage can increase the efficiency of the electric grid by adding flexibility to thermal systems. The value of thermal storage is a function of its energy and power density, which are driven by the capacity and thermal resistances in the storage device. Measuring these properties in-situ at the device level is an important step to understanding the performance and improving the design of thermal storage systems. In this paper, we present methods to measure the total capacity and thermal resistances in heat exchangers with integrated phase change materials. These methods are demonstrated on two thermal storage devices—a 570-kWh ice-based storage tank and a 0.35-kWh graphite-tetradecane composite device. The results show how thermal resistances evolve with the state of charge and discharge rate in these devices and quantify the impact of applied pressure on the contact resistance in composite phase change material heat exchangers. The proposed method allows for easy comparison between different systems and provides information on the thermal bottlenecks limiting performance. Ultimately, these measurements will allow designers to make robust, high-performance thermal storage devices for next-generation thermal systems.

Design for energy flexibility in smart buildings through solar based and thermal storage systems: Modelling, simulation and control for the system optimization

The present study investigates the use and implementation of energy efficient measures and strategies for building applications, toward the Nearly Zero Energy Buildings target. Specifically, objective of the study is to implement building integrated photovoltaic thermal devices coupled with a phase change materials heat exchanger acting as an active thermal storage building component, with the aim to add flexibility to the building while still maintaining indoor comfort conditions. To show the potentials of the novel configuration proposed in this paper, a multi-zone grey-box model is developed and validated to capture the thermal dynamics of a building, and a control strategy applied to the whole system is developed for energy management purpose. The whole simulation model, including thermophysical properties of the building-system and the control features, is implemented in a MATLAB environment. To assess the model and application potentials toward the optimal design and operation of the proposed system for energy efficiency and flexibility goals, a suitable case study analysis is conducted. Thus, a sensitivity analysis, using an evolutionary algorithm, is performed by considering economic and energy objective functions which focuses on the reduction of the building energy demand, load variability and economic aspects. In this regard, the optimal design configuration is underlined in a way that the operation of the components can be maximized to provide flexibility to the building: in average working conditions one single layer of PCM can provide around 186.3 Wh/K per unit of temperature and width. A rule-based management strategy is proposed to prove the possibility to shift and shave the energy peaks during high energy request periods, demand response events. Finally, by considering an approximate economic calculation, the simple payback, taking into account only the positive effects on the winter management, is around 13.5 years.