Model Of Phase Change Material Research Articles

Effect of Buoyancy Force in Phase Change Material-Based Metal Hydride Reactor

Abstract In Phase Change Material (PCM) simulations, buoyancy force is used to capture the melting contour. However, for the sake of simplicity, most of the PCM-based Metal Hydride (MH) simulations have ignored the influence of buoyancy in PCM which is crucial in analyzing the heat flow within PCM. This study incorporates the buoyancy term in mathematical models to capture the contour of a melted PCM and also its heat transfer capacity during the hydrogen absorption process. A PCM model with buoyancy force is validated against the experimental values and applied to the MH-PCM models. Incorporating the buoyancy force improves the heat transfer rate in the PCM during melting which benefits in better heat removal from the MH bed. Two designs of MH-PCM models having PCM placed in ring-type and tube-type configurations are discussed. Further, the design optimization in ring-type models was done by changing the PCM-MH volume and sandwiching ratios.

A new approach for selecting and implementing phase change materials in Kuwaiti Buildings: Practical considerations

This study focuses on practical considerations regarding Phase Change Materials (PCMs) for energy-efficient buildings in Kuwait's hot climate. Its objective is to fill gaps in the existing literature by providing experimental validation, which has been lacking in previous research that heavily relies on numerical simulations. The selection of a PCM with an appropriate melting point is crucial to achieve balanced melting and solidification cycles. To address this, two identical portable cabins were constructed at the Australian University of Kuwait. One cabin served as the base case, while the other was used to investigate various energy-saving methods. Indoor weather and energy monitoring devices were installed, enabling the collection of wall and roof temperature data at 10-minute intervals. Analysis of the temperature distribution revealed that a PCM with a melting point of 24 °C remained in a melted state for approximately 8 h and solidified for 16 h within a 24-hour cycle, particularly on the hottest days in Kuwait. Furthermore, a TRNSYS Type399 PCM model was developed to examine the impact of PCM parameters on the annual energy performance index of the portable cabins. The results indicate that utilizing a PCM with a melting point of 24 °C on interior walls and ceilings can result in annual energy savings of up to 20 %, while the thickness of the PCM does not significantly affect performance. In a broader context, this research seeks to tackle the real-world challenges linked to the deployment of PCMs in energy-efficient buildings within Kuwait's hot climate. It highlights the significance of confirming findings through practical experimentation aimed at improving the utilization of PCMs.

Hybrid battery thermal management system of phase change materials integrated with aluminum fins and forced air

AbstractDue to its high self‐heat rate, most researchers have avoided using lithium cobalt oxide (LiCoO2) in their work, although, major car companies use it to power some car models because of its high‐power density. A thermal management system benefits from phase change material (PCM) and serves as a reliable cooling system to ensure the safety, performance, and lifespan of Li‐ion batteries. In this study, we conducted an experimental investigation of a new hybrid battery thermal management system (BTMS) using PCM combined with aluminum fins and forced air to enhance the cooling performance of Li‐ion battery type 18 650 LiCoO2. Furthermore, the hybrid model's thermal behaviors are compared with other models that use only air or PCM for cooling. The cooling performance of different BTMS models was tested under a high temperature of 40°C and various discharge rates, as well as, various air velocities. The results demonstrate that the hybrid model effectively minimizes the battery heat accumulation and can reduce the maximum operating temperature by 1.5°C, 5.5°C, and 9.5°C compared to the air‐cooling model and by 2.8°C, 5.1°C, and 16.1°C compared to the PCM model for discharge of 1C, 2C, and 3C rates, respectively. Furthermore, the maximum temperature difference within the battery pack did not surpass 3.1°C with our hybrid model. Moreover, the use of our model has a significant advantage in minimizing the air‐cooling power consumption by 89%.

Experimental and numerical investigation on the cold harvest of composite phase change materials for building energy conservation

This paper investigates the cold energy storage of a horizontal shell-tube latent heat thermal energy storage (LHTES) unit for the cold harvest during night time. An experimental apparatus containing a horizontal circular tube with circumferential heating/cooling was designed and developed. Paraffin based phase change material (PCM) with a melting temperature of 27 °C was adopted as the cold harvest media. To improve the heat transfer rate, multi-walled carbon nanotubes (MWCNTs) were mixed with the paraffin to form a composite PCM with high thermal conductivity. A corresponding model of the composite PCM was developed and verified against the experimental data. Numerical simulations were performed for different boundary temperatures and concentrations of MWCNTs. The results show that when the heat transfer temperature difference is 20 °C, 0.05 wt% nanoparticles increase the melting rate of PCMs. When the heat transfer temperature difference was 40 °C, 0.10 wt% nanoparticles significantly affect the PCM melting rate. For low or high temperature (heat transfer temperature difference of 10 °C and 80 °C), the addition of nanoparticles is not conducive to improving the melting rate.

A hybrid battery thermal management system coupling with PCM and optimized thermoelectric cooling for high-rate discharge condition

The lithium-ion battery is now abundantly available in the market due to its excellent performance. However, battery overheating is increasingly prominent when the battery discharges at high speed. In this study, an active-passive BTMS (Battery Thermal Management System) combining PCM (Phase Change Material) and TEC (Thermoelectric Cooler) was proposed. The effects of different TEC currents and delayed cooling at different PCM melting rates were analyzed under the 4C discharge condition to enhance the thermal performance. The results demonstrate that battery temperature gets effectively controlled as the TEC current increases, but the temperature difference and PCM utilization are poor. However, applying a delayed current after the PCM melting rate reaches 80% reduces energy consumption and provides better temperature uniformity. Considering the large battery heat under 4C discharge, combined with the transient supercooling effect of TEC, a continuous pulse current was used to provide additional cooling power. Results show that the battery with TEC pulsed current operates 57.8% longer at 40 °C with a temperature difference maintained at 2.5 K under 4C discharge conditions compared with the PCM model.

Conventional and nano-enhanced Phase Change Material melting simulation by using Lattice Boltzmann method: A comprehensive review

Phase Change Materials (PCMs) are latent heat energy storage mediums that have received considerable attentions regarding their high heat capacity and applicability for other purposes such as thermal management. Numerical simulation has been applied for these materials to investigate their heat transfer characteristics such as the rate of phase change and energy storage capacity. Lattice Boltzmann method is a promising approach for modeling and simulation of PCMs in both charging and discharging processes. In this article, studies on the melting (charging) of PCMs, with and without existence of nanomaterials, are reviewed and their results are represented and summarized. Corresponding to the findings of the reviewed studies it can be concluded that this approach is able to properly simulate the melting process of various PCMs. Simulation of charging process by means of this method showed that the melting rate is improvable by employing different ideas namely adding nanomaterials, using fins and heat pipes. Applying these ideas have significant impact on melting rate under specific conditions, i.e. more than 52% improvement in the melting rate for adding Cu nanoparticles with 4% concentration. Finally, some recommendations are suggested for the forthcoming studies in this field.

Volumetric quantification of melting and solidification of phase change materials by in-situ X-ray computed tomography

Solid–liquid phase transitions in phase change materials (PCM) usually exhibit a complex dynamics, which critically determines the performance of latent heat thermal energy storage systems (LHTES). Experimental approaches enabling to track the dynamics of the entire PCM solid–liquid phase transition are thus crucial to provide relevant data for PCM material development and to validate PCM-models used to design efficient LHTES. In this work, we show how in-situ dynamic X-ray computed tomography (XCT) can be used to track the dynamics of the solid–liquid phase transition in PCMs. The method based on time-lapse XCT is illustrated based on data collected for two PCMs (ice/water and calcium chloride hexahydrate) during melting and solidification processes, respectively. Key enabler of the method is the density difference between solid and liquid PCM, which facilitates a clear identification of the solid and liquid PCM phases and, thus, tracking their spatial evolution in time. Analysis of the transient liquid fraction curves reveals a volumetric melting rate of 0.55 (% vol)/min for ice with a total melting time of 165 min, whereas calcium chloride hexahydrate undergoes a partial solidification at −0.30 (% vol)/min, with an overall volumetric shrinkage of 12.7 %. Furthermore, an image-based approach to quantify the time-dependent liquid volume fraction curve from the sequences of XCT imaging data, is presented. The extracted liquid volume fraction curves capture the entire dynamics of the solid–liquid phase transition and can either be directly inserted in the mass and energy balance equations of currently existing PCM models to predict LHTES performance or used for PCM-models validation.

Numerical models of heat storage with respect to phase change materials considering hysteresis

Phase change materials (PCMs) absorb and release thermal energy that corresponds to the latent heat absorbed and released during phase changes. Thus, by efficiently utilizing solar heat, they are expected to stabilize the room temperature, resulting in reduced heating loads. The accurate prediction of the energy-saving effect of PCM utilization is important for designing buildings, and it is essential to adequately evaluate the influence of the hysteresis phenomenon, which occurs when the heating and cooling cycles of PCMs are repeated. This study examines the precise calculation modeling of PCMs that demonstrate complex hysteresis behaviors to accurately predict the PCM effect. The proposed approach includes a simple model with two temperature–enthalpy curves, a complex model with multiple curves, and a subcooling model. The accuracy of the proposed model is verified by comparison with the measurement results, and the models can be integrated into a heat load calculation program.

Enhancement of phase change material hysteresis model: A case study of modeling building envelope in EnergyPlus

Nowadays, buildings are expected to offer demand side services to the power grid to enhance the electrical load flexibility, which leads to the concepts of grid-interactive efficient buildings (GEBs). Phase change material (PCM)-based thermal energy storage has seen increasing attention in recent years for peak load shifting of grid-interactive efficient buildings (GEBs). Numerical models are critical tools for design and evaluation of PCM-integrated systems. Most industrial-grade PCMs are reported to melt/freeze over a temperature range instead of at a unique temperature. Such thermal hysteresis effect significantly affects the reliability of simulation results because not only the heat transfer process depends on melting and freezing temperatures, the PCM thermal properties change significantly during the phase change process as well. This study is aimed to develop a model for the PCMs used in the building envelope with the capability to accurately simulate hysteretic behaviors. This model is based on a two-phase assumption and is implemented in a whole building energy performance simulation program (i.e., EnergyPlus). A comparison between numerical results and experimental data shows that during a complete phase transition, the two-phase model could achieve a good agreement with the experimental data. During a partial phase transition, the two-phase model could lead to significant improvements compared to other alternative PCM models, including the existing PCM model in EnergyPlus. Last, whole building simulations were performed to study this model's performance regarding heating/cooling loads and zone mean air temperature of a given building. The results show that the difference in hourly heating/cooling loads introduced by the models was less than 1% in design conditions, while significant changes were observed in both hourly heating/cooling loads and zone mean air temperature when the PCM envelope underwent partial phase transition processes.

In-duct phase change material-based energy storage to enhance building demand flexibility

This paper presents a novel energy storage solution by incorporating phase change material (PCM) panels in supply ducts to increase a building’s thermal storage capacity and demand flexibility. During off-peak hours, the system runs at a supply air temperature (SAT) below the PCM solidification point to charge the storage unit with “cooling” energy. During on-peak hours, a higher SAT is utilized so that the stored “cooling” energy can be discharged into the supply-air as a means to reduce the peak air-conditioning power usage. To evaluate the potentials of peak demand reduction and utility cost savings, a numerical model for a PCM panel prototype and its heat exchange with the air flow in the duct was developed and calibrated using experimental data. Whole building energy simulations were conducted in a co-simulation environment that has integrated the developed PCM model, EnergyPlus Department of Energy (DOE) prototypical model for a medium office building and a calibrated model for variable-speed direct-expansion cooling systems. The simulations covered five cities in different U.S. climate zones over a three-month cooling season and used actual time-of-use (TOU) rate schedules offered by the local electric utility companies. The simulation results have shown the PCM storage could reduce the on-peak energy consumption by 23–32% and the seasonal cooling electricity cost by up to 16%, with a simple rule-based control strategy. A simple payback analysis resulted in payback periods from 7.5 to 27 cooling months.

Impact of domain discretization on the accuracy of a 2D model of PCM module for ventilation application

Optimal selection of domain discretization for numerical Phase Change Material (PCM) models is useful to establish confidence in model predictions and minimize the time consumption for conducting design analysis. Very detailed and geometrically complex models are usually applied utilizing several million cells. A 2D numerical PCM model of a climate module for thermal comfort ventilation is investigated. The mesh independence was conducted on 22 different mesh sizes ranging from 70 to 10.870 nodes. Convergence criteria was evaluated based on average air supply temperature and total heat transfer between the PCM and the air within the simulation time interval. Less than 0.1 % change in the air supply temperature and the heat transfer between the PCM and the air was achieved with 5250 and 9870 nodes, respectively. Thereby highlighting that a relatively small amount of nodes can be considered to achieve sufficient accuracy to conduct analysis of PCM applications.

A complete numerical model for low temperature composite form-stable phase change material slab based on dynamically simplified temperature transforming method

ABSTRACT Phase change material (PCM) that is used in the roof top slab can minimize the heat infiltration into the living space from the building envelope and increase the indoor thermal comfort level. The major disadvantage of PCM is leakage at liquid state. Expanded graphite (EG) is used here as supporting material for PCM to prevent the leakage and maintains the form stability. The composite PCMs are prepared by adding the EG with various mass ratios, i.e. 3%, 6%, and 9%. The thermal properties of all composite PCMs are determined by DSC and thermal conductivity analyzer. The optimum PCM composition was found at 9% of EG. In this study, the shape-stabilized PCM-integrated roof top was analyzed by simplified temperature transforming (TT) numerical model. The main advantage of this model is that it is used to combine the equivalent enthalpy and heat capacity. The numerical results are validated with experimental values and show the lower mean absolute percentage error (MAPE), i.e. 6.91%. This indicates that present model is well suitable to predict the thermal performance of composite PCM incorporated roof top. The effect of various parameters like thickness of the PCM slab, wind velocity, percentage of EG mass ratio, and location of PCM are investigated by simplified TT model. The results showed that the maximum inner surface temperature reach up to 53°C for BG model (concrete and gypsum) by distributing constant heat flux, i.e. 1,000 W/m2 for 180 min. At this same condition, the inner surface temperature of other PCM models PBG (PCM, concrete, gypsum) and BPG (concreate, PCM, Gypsum) reaches to 50°C and 41°C, respectively. PBG model exhibits excellent thermal performance compared to BPG model. The thermal performance of PCM slab is also investigated by varying the thickness of the PCM layer and found that time lag is raised with the thickness of the PCM slab.

Evaluation of shape-stabilization phase change material sheets to improve the heating load reduction based on the indoor application method

The effectiveness of the phase change material (PCM) application method was measured in three identical test huts using a shape-stabilized phase-change material (SSPCM) sheet made of paraffin-based PCM. Based on these results, the accuracy was verified by comparing the measured values with the calculated values using each PCM model in EnergyPlus and ExTLA (Excel-based Thermal Load Analysis) software. Annual loads were simulated under various conditions to optimize the efficiency of the SSPCM sheets. A similar reduction in heating load was observed, regardless of the installation area until the capacity of the SSPCM sheet reached a certain value. However, above this value, the efficiency increased or decreased depending on the installation area. This shows that there is an optimum capacity according to the installation area of the PCM. To evaluate the performance of the PCM according to the shape of the building, a target building and climate were selected using the ASHRAE standard (90.1 and 169), and the heating load was simulated under the same conditions. When the volume of the building and the size of the window receiving solar radiation were constant, it was confirmed that the shape of the building did not significantly affect the heating load compared to the installed capacity and area of the PCM. However, depending on the installation area, there was a difference in annual heating loads up to approximately 12%. This study confirmed that there are optimum installation capacities and areas that maximize the efficiencies of PCMs.

Applicability of phase change material according to climate zones as defined in ASHRAE standard 169-2013

The improvement of the heating load reduction effect through indoor temperature stabilization and the possibility of applying phase change materials (PCMs) in various climates were examined. The indoor temperature and heat flow of each wall are measured in three identical test huts using a shape-stabilized phase-change material sheet made of a paraffin-based PCM. The results obtained are compared with calculated results using a PCM model fabricated basing a specific heat to verify the accuracy. The annual heating load reduction is confirmed by conducting simulations of 429 cases in various conditions of PCM capacity, building shape, and installation area for representative cities in each climate zone of ASHRAE standard 169–2013. In addition with this result, the relationship among the PCM installation method, building form, and climate factors are analyzed to obtain a correlation equation for annual heating load reduction. Comparing the simulation results and correlation equation results of the annual heating load reduction rate, it is confirmed that the error of the two results is below 2.7%, and the coefficient of determination is above 0.8. This correlation equation can be a measure of the approximate heating load reduction effect due to the PCM installation and the performance of indoor application methods without complex simulations early in the design or before the construction of the PCM.

Experimental evaluation of the optimal position of a macroencapsulated phase change material incorporated composite roof under hot climate conditions

This paper experimentally investigates the optimal position of a phase change material (PCM) incorporated composite roof under Iraq climatic conditions. The roof composed of Isogam (4 mm), concrete (50 mm) and gypsum board (8 mm) which is an Iraqi popular roof combination. Four models are installed and tested; one represented the reference roof (Model A) and the others incorporated with PCM. The PCM placed between Isogam and concrete (Model B), in the middle of concrete (Model C), and between the concrete and gypsum board (Model D). Set of indicators are introduced to compare among models considering the test room temperature, outside and inside roof surface temperatures. These indicators are the room maximum temperature reduction (RMTR), average temperature fluctuation reduction (ATFR), decrement factor (DF), time lag (TL) and heat flux reduction (HFR). Results showed that Model B verified the best thermal performance, and the PCM was effectively working at high outside temperatures. The maximum room temperature of PCM models was reduced by up to 9 °C compared with the reference model. Moreover, a maximum of 12.9%, 8.4–9.5 °C, 0.44–0.49, 140–180 min, 47.9–64.6% of respectively RMTR, ATFR, DF, TL, and HFR, are obtained for Model B under high outside temperatures.

Thermal reliability-based design optimization using Kriging model of PCM based pin fin heat sink

This paper deals with the thermal reliability optimization of a pin fin heat sink (HS) filled with phase change material (PCM) in order to study the heat transfer performance for cooling of electronic devices. Aluminium is taken to carry out the pin fin heat sink with a constant volume fraction of 9% by choosing 72 pin fins. Paraffin wax is used as PCM inside the heat sink to retain the heat produced by the electronic device. A reliability-based design optimization (RBDO) is addressed to determine the optimum thermal configuration of the pin fin heat sink that satisfies the desired reliability. The presented methodology is summarized by the combination of the 3D finite element simulation (FES), the Kriging substitution model and the optimization procedure. The surrogate model is built and validated using two metrics such as error predictions and cross validation (CV). A comparison of the number of training points shows that the Kriging predictor with 100 Latin hypercube sampling (LHS) points provides a better approximation of the original model. Thermal optimization results show that the time taken by the latent heating phase of the optimal design is higher than that obtained by the baseline model. With the reliability optimization, the maximum temperature of the optimal design was reduced by 30%.

Investigation of a cascaded CO2 refrigeration system using phase change materials for energy-saving potentials

A high-pressure lift often triggers an increased power input to the vapor compression systems. The increased power consumption becomes a bottleneck in R-744 refrigeration systems for freezing and refrigeration applications. Meanwhile, phase change materials (PCM) offer operation flexibility in the form of the compressor run-time from the energy storage potential. In this article, the energy-saving potential of the PCMs on a cascade refrigeration system using CO2 is investigated focusing on the impacts of charge amounts and the thermal resistance of the PCM. The validated dynamic model in Simscape™/MATLAB for an R-744 vapor compression system is adopted for a cascade refrigeration system together with the validated PCM model. In the studied system, the PCM is installed in the storage compartment as a thermal buffer. The comprehensive model employed an acausal, object-oriented, and equation-based paradigm adopting detailed heat transfer characteristics. The effect of PCM on the compressor running time was investigated under the cyclic steady-state operating conditions. The results showed that the compressor “On-time” ratio decreases when using the PCM; subsequently, the power reduction. The system consumes about 6.76 kWh (without PCM) and 5.93 kWh with PCM; thus, the power consumption decreases by 12.3%. The threshold PCM charge ratio is observed to be 1. Increasing the PCM charge value above this threshold does not trigger a significant decrease in power reduction. The increase in the overall thermal resistance of PCM has a negative impact on the “On-time” ratio and power consumption. The benefit of PCM is insignificant for thermal resistance above 0.02 K W−1. Despite the shortcomings of several assumptions involved, the present results clearly highlight the positive impacts of the PCM in terms of power savings for low-temperature refrigeration applications using R-744.

Lattice Boltzmann simulation of melting heat transfer in a composite phase change material

Thermal performance enhancement of the phase change material (PCM) is of particular significance to the energy storage applications. The composite PCM with metal particles is introduced here for maximizing the thermal performance. Based on the description of a composite PCM by the QSGS method, a lattice Boltzmann model of the melting composite PCM was developed and numerically solved. The melting front evolution and transient temperature response in the composite PCM are analyzed and compared to the pure PCM. Furthermore, the effects of the dispersity, volume fraction, and diffusion direction of the metal particles on the melting performance of composite PCMs are comprehensively analyzed. The results indicate that the presence of metal particles benefits the thermal performance enhancement of PCMs. The melting evolution and the heat transfer in the composite PCM are much quicker due to the enhanced thermal conduction. Besides, the melting front morphology maintains an approximate line during the whole melting process arising from the natural convection suppression. For maximizing the melting heat transport, the metal particles in the composite PCM are recommended to present a larger dispersity, and their diffusion direction is suggested to be in the same direction as the heat flow. Interestingly, even though the volume fraction of the metal particles is identical, the melting performance of composite PCM is also relevant to the dispersity and diffusion direction of the metal particles.

A design protocol for enhanced discharge exergy in phase change material heat battery

Thermal energy storage using phase change materials (PCMs) is finding a plethora of emerging applications, yet it suffers from the detriment of asymmetric discharging where the temperature of the heat transfer fluid (i.e. water) often drops significantly below the melting temperature of the PCM. This phenomenon significantly impacts the servicing value of the stored thermal energy and would eventually result in over-reliance on the auxiliary fossil fuel input. In this paper, we have studied the heat discharge issue using a validated PCM model (shell-n-tube heat exchanger) and characterized three distinctive heat discharge regimes; each is featured with a unique thermal barrier profile which constrains hot water production within a certain temperature range. These heat discharge regimes are attributed to the formation of a solid PCM layer around the water pipe throughout the discharge phase. Such layer completely isolates the water flow in the tube from the molten PCM in the annulus and acts as a thermal barrier that constrains the maximum achievable temperature. The development of thermal barrier could be minimized by changing the PCM design parameters/vairables. In this work, we have proposed a computational design framework that does not rely on the traditional trial-and-error approach while capable at generating a PCM system design with minimal thermal barrier development. For a solar water heater (SWH) case-study, the result shows a significant improvement in the PCM system exergy efficiency and translates to 18% reduction in fossil fuel consumption for a PCM integrated solar hot water system.

Energy and exergy analysis of wind farm integrated with compressed air energy storage using multi-stage phase change material

One of the most common issues associated with wind energy penetration as a viable resource is high instability under diverse amplitudes and frequencies. Compressed air storage systems (CAES) and thermal energy storages (TES) not only are promising alternative solution for renewable resources generally, but they are also used with the aim of peak shaving to provide cleaner and affordable power. Due to high storage density with low temperature gradient between storing and retrieving in comparison with sensible heat storage, phase change material (PCM) is selected considering their thermophysical properties. This work, presents a recovery approach by using PCM during 12 h’ compression periods to retrieve it in 12 h’ expansion as a case study in November for Baladeh (a city in north of Iran). It is worthy to mention that, in order to use PCM in multiple mentioned stages, auxiliary heaters facilitate system to provide constant heat load in each used stage. This concludes system to be more efficient, sustainable and can reduce irreversibilities. Temperature of PCMs and amount of heat stored and released versus time are modeled. A good agreement between PCM model and reported results of related articles was seen. Following to the energy and exergy balances calculation, round-trip efficiency (RTE) and total exergy efficiency of system, reach 70.83%, 80.71%. Exergy analysis showed that near 60% exergy destruction occurred in PCMs with major contribution of second ones in both charge and discharge times. Sensitivity analysis is also investigated assuming the effect of number of wind turbines which shows a reduction in RTE, steeper slope in increasing TES volume for PCM3 and amount of heat stored, by increasing them.