Phase Change Material Storage Unit Research Articles

Enhancing Solar Thermal Efficiency: PCM Integration for Compact Energy Storage Systems

The optimal utilization of solar energy presents a challenge in meeting round-the-clock hot water demands while accommodating limited space in modern architectural designs. Solar collectors, operating solely during daylight hours and weather-dependent, necessitate efficient energy storage to meet evening and morning peak hot water consumption in households. Current architectural trends, marked by smaller boiler rooms, further compound the challenge of integrating conventional solar tanks, emphasizing the critical need for compact energy storage solutions. Addressing this challenge, this paper proposes a ground-breaking solution: a solar tank infused with phase change material (PCM). This innovative tank design not only boasts smaller dimensions but also significantly higher heat capacity compared to conventional counterparts. Crucially, the PCM solar tank enables solar collectors to operate at lower temperatures, potentially elevating the overall efficiency of the solar collector system. The proposed storage system comprises two synergistic heat-absorbing units: a solar water heater and a PCM-based heat storage unit. While the solar water heater fulfills the daytime hot water supply, the PCM storage unit accumulates and retains heat throughout the day, ensuring continuous hot water availability during night hours and overcast periods. Leveraging small cylinders filled with paraffin, serving as the PCM, integrated with solar collectors maximizes solar energy absorption and storage. This paper meticulously compares the performance of the PCM-based thermal energy storage system with conventional sensible heat storage systems, presenting insightful conclusions derived from the comparative analysis. The findings underscore the remarkable efficiency and efficacy of the PCM-based solution in meeting the challenges posed by solar energy intermittency and limited space constraints, offering a promising avenue for sustainable and efficient solar energy utilization in residential settings.

Experimental and numerical investigation on the charging and discharging process of a cold energy storage for space cooling of buildings

To address the current issue of the difficulty to use the hot outdoor environment during summer nights to provide coolness for phase change materials (PCM) and thus reduce building energy consumption in hot summer areas, a novel cold energy storage unit has been proposed. It replaces the hot outdoor environment with other free or cheap cold sources. An experimental setup is built to investigate the cold storage and release performance of the PCM storage unit. Later, the well-validated numerical model is conducted to further explore thermal performance of the PCM storage unit. The numerical result indicates that the cold storage process can be completed from 64.33 min to 96.56 min when the water inlet temperature varies from 10 °C to 16 °C. Further, during the cold release process, the PCM storage unit can reduce the temperature of the hot air by a maximum of about 8–12 °C when the air inlet temperature ranges from 32 °C to 38 °C. The cold release efficiency is varied between 81.65 % and 96.44 %. In conclusion, the findings provide a promising way for cold storage and space cooling of buildings in hot summer areas through the cold energy storage unit.

Enhanced honey badger optimization of performance analysis of evacuated tube heat pipe solar collector integrated with PCM storage unit

A hybrid method for improving the efficiency of heat pipe evacuated-tube solar-collector (HPETC) is proposed for incorporating the phase-change materials (PCMs) in both off-demand and regular operation. The proposed hybrid approach is called an improved honey badger algorithm (HBA). The crossover and mutation operator improves the honey badger's (HB) foraging habit. The proposed approach aims to generate hot air at various rates of airflow under incident and nonincident solar-radiation situations. The analysis is done on the effects of different energy-storage systems and the position of the heat pipe (HP). In a normal heat-pipe evacuated-tube solar collector, the HP is put within the glass tube that is closer to the upper-surface, and it is held in place through an aluminum fin. However, in the proposed method, the HP is rearranged in the tube's middle. In order to identify the PCM with the highest average-fin temperature, the temperatures of the area-weighted average-fin are measured and compared throughout the glass tubes under typical conditions. For maximizing the thermal-energy carrying capability, the average liquid fraction volume of PCMs is measured for a 24-h flow period. The average liquid-fraction volume of PCMs is continuously observed in stagnation mode till the glass tube reaches the maximal value. The structured mesh patch conforming method is used to invalidate the HPETC system's constituent parts, improving numerical stability and convergence. The proposed method efficiency is 0.43. The proposed method shows high efficiency compared with other existing methods.

Multi-objective grey wolf optimization and parametric study of a continuous solar-based tri-generation system using a phase change material storage unit

Considering the necessity of producing freshwater from seawater, especially in regions with high solar energy potential, this study proposes a novel system for tri-generation application using solar power through which high capability of freshwater production is available together with electricity and cooling. This system comprises a heliostat field and a phase change material storage unit for continuous production, a gas turbine cycle, a Kalina cycle, an absorption chiller, a humidification dehumidification desalination, and reverse osmosis desalination. The prediction of the behavior of the system has been accomplished utilizing a comprehensive parametric study; afterward, the method of grey wolf optimization has been utilized to optimize the simulation in different multi-objective cases. Regarding obtained results, the net power generation is obtained of about 4137 kW and 41.28 kg/s freshwater with 30.63 % exergetic efficiency and 57.55 $/GJ unit product cost. Also, applying the optimization declines the freshwater production rate, but it improves the other performance indexes. Under optimized condition an exergy efficiency of 32.90 % and a unit product cost of 48.98 $/GJ is achieved.

Performance Improvement of The Domestic Refrigerator Using Phase Change Materials

A growing environmental Impact of global warming and rapidly increasing cost of the electrical energy cause researchers in the field of refrigeration and air conditioning to develop the sustainable cooling technologies. This study investigated the influence of latent heat storage materials on the power consumption and the temperature distribution of a commercial domestic refrigerator. The 2 kg PCMs (Phase change materials) slab of thickness 5 mm, which consisted of a 2:1 by weight mixture of refined paraffin wax and kerosene oil, were located on the back side of the roll-bond evaporator and the copper coated steel tubing coils of the hot-wall condenser, in order to improve the higher performance of refrigerator and to decrease the operating cycle time of the compressor. The experimental and CFD (Computation fluid dynamics) simulation results indicated that the refrigerator equipped with the PCMs storage unit showed a significant enhancement of the system performance and a reduction of the temperature fluctuations in the refrigerator compartment compared to a conventional system. In this investigation, the electric power consumption and the compressor on-time ratio were reduced by 15.69% and 12.13%, respectively. Moreover, the COP (Coefficient of performance) of the refrigeration system was increased by 9.53%.

Apparent heat capacity method to describe the thermal performances of a latent thermal storage system during discharge period

In this work, a novel detailed dynamic model for latent cold thermal storage unit containing water as phase change material (PCM) is presented. The proposed dynamic model is based on transient energy balances for both PCM capsules and heat transfer fluid (HTF). The apparent heat capacity approach is used to model phase transition processes in PCM, where the PCM heat capacity is given as a temperature-dependent function. This method can be simply integrated into a variety of software to assess the energy efficiency of latent storage. The dynamic model of the PCM storage unit is validated using measured results from the literature and it is used to investigate the influence of multiple parameters on the storage thermal performance. The obtained result show that the PCM melting process varies in both axial direction and radial direction in the storage unit. It was also observed that the higher the height of the tank, the longer the discharge period. Increasing the diameter of capsules from 47 mm to 77 mm leads to increase the discharging period by about 30%. In addition, varying the storage tank initial temperature between −8 °C and −4 °C does not have a significant effect of on the discharging time. Finally, it was recommended that for improving the storage performance and minimizing water pumper energy consumption, a compromise between the HTF flow rate and the capsule diameter must be determined.

Experimental analysis of submerged coil and encapsulated slab latent heat storage

• Experimental data for slab encapsulation and submerged coil performance are obtained. • Storage with constant and time varying flowrates are evaluated. • Partial charging/discharging demonstrates higher mean thermal power. • Submerged spiral coil heat exchanger allows higher storage density. • Slab encapsulation can meet higher thermal power demand. Latent heat thermal energy storage (LHTES) has two primary LHTES packing methods, encapsulation and bulk PCM storage. Since there is still a lack of experimental comparison between these two methods, two types of LHTES units based on separated methods were built for direct comparison. Moreover, the impact of heat transfer fluid (HTF) flowrate on LHTES performance was evaluated. Unit one is a 0.38 m 3 tank containing slab-shaped macro-encapsulated phase change material (PCM); unit two is a 0.54 m 3 tank containing submerged spiral coil heat exchanger (SCHE) in PCM. PCM with a melting temperature of 58–60 °C was charged/discharged between 46 and 72 °C. Parametric studies on constant and time-varying HTF flowrates were conducted to test the impact on the thermal storage performance. The time-varying flowrate control enables the system to supply the needed power at different discharging stages. Moreover, partial charging/discharging demonstrates higher mean thermal power than full charge/discharge rendering this control strategy adequate under specific operating conditions. Finally, the comparison between the slab-encapsulated PCM storage unit and the SCHE based unit shows that the former requires a shorter completion time while the latter has a higher energy storage density.

Phase change material thermal energy storage design of packed bed units

Heat transfer enhancement and optimization are found to be essential for the PCM (phase change material) thermal energy storage design. In this work, the performance advantage of the packed bed PCM storage unit design is analyzed in comparison, and the impacts of key geometric parameters of a packed bed unit were numerically investigated. The optimized shell-and-tube design, based on the hexagonal circle configuration, serves as the benchmark for the comparison. The thresholds of the bed and PCM-capsule diameter ratio,D/d, is found, above which the effective energy storage capacity of the packed bed would be higher than that of an optimal shell-and-tube unit. The threshold of D/d can be quantitatively correlated to the superficial velocity of the heat transfer fluid, providing a pathway for the tailored design of a packed bed PCM thermal storage system. In conclusion, it was found that packed bed units are advantageous due to their larger surface-to-volume ratio, in particular in large-scale applications. This work proposes a numerical analysis based framework to design packed bed PCM storage units in comparison with shell-and-tube units so that a proper type of PCM thermal storage design can be selected under a specific geometric and operational condition.

Thermal and energetic behaviour of solid-solid-liquid phase change materials storage unit: Experimental and numerical comparative study of the top, bottom and horizontal configurations

Thermal energy storage technology with Phase Change Materials (PCM) is an attractive option to optimise energy resources and to recover and promote excess heat. The phase change behaviour of PCM requires advanced research to understand and better control the thermal energy storage using PCM, which is a crucial step to develop a powerful latent storage system. This paper aims to analyse the multiphysics phenomena of three regenerator configurations, horizontal case and two injection direction of Heat Transfer Fluid (HTF): top and bottom in vertical case. The study is done for the charge and discharge cycles of the solid-solid and solid-liquid phase transitions of PCM. First, the temperature dependence of the thermal and physical properties of paraffin as PCM is characterised. Second, an experimental study of an annular latent storage system was carried out. Also, an experimental mesh method was introduced to compare the energy behaviour of the three cases. Third, a numerical analysis of the experimental storage unit with low thermal diffusion is performed. The experimental results are confronted with the numerical results obtained with ANSYS Fluent and COMSOL Multiphysics commercial software. Last, the three configurations are compared to a reference case without gravitational field. The results show that specific mechanisms control the thermal and energetic behaviour of the regenerator. Furthermore, several parameters, such as storage density, distribution of energy storage rate in the different regenerator components (PCM, HTF, and heat exchanger), were analysed. Altogether, the results supply important information to understand the dynamics of passive storage systems.

Peak load shifting using a price-based control in PCM-enhanced buildings

Peak load shifting, a load management policy, has attracted widespread attention as it can minimize the impact of load variation on a system’s operation and reduce the electricity costs. Phase change materials (PCMs) can contribute to peak load shifting by storing the daytime solar energy in winter/free night cooling in summer or the low-rate energy provided at off-peak hours for use during the high electricity peak period. This study aimed to experimentally investigate the effect of an active PCM storage in combination with a price-based control on peak load shifting. The experiments were conducted using two identical test huts, which were equipped with an electric and solar air heater during cold seasons or an air conditioning unit during warm seasons. But in addition, one of the huts was equipped with an active PCM storage unit charged by the solar heater. A CompactRio data acquisition system, powered by LabView interface, was used to transfer data and communicate with a host computer. Results showed that the proposed system was successful in shifting both heating and cooling demands to the off-peak periods. Up to 47% of daily energy-saving (∼0.83 kWh) with a corresponding 65% of electricity cost-saving, in winter, and up to 23% daily energy saving (∼0.27 kWh) with a relevant 42% of cost-saving, in summer, were achieved.

Numerical simulation and validation of commercial hot water tanks integrated with phase change material-based storage units

Thermal energy storage (TES) allows to extensively exploit solar thermal technologies by effectively handling the mismatch between energy production and demand thus possibly causing a downsizing of generation units. Among thermal energy storage technologies, those based on phase change materials (PCM) are particularly interesting because relatively large latent heat values may guarantee more compact systems (as compared to sensible TES). In this work, we report a numerical and experimental investigation on a hybrid latent-sensible heat storage characterized by a commercial hot water tank integrated with macro-encapsulated phase change materials. Those hybrid systems are interesting as they can possibly increase the overall thermal capacity of a sensible water tank. Despite all this, we demonstrate that increasing the effective storage capacity is a non trivial task with standard conditions and materials. To this end, three different numerical models have been developed and experimentally validated. The first model is based on the enthalpy porosity method and simulates the charge and discharge of a PCM storage unit in a climatic chamber. The second model is a one-dimensional description of the water storage tank without PCM. Finally, the third model is obtained by coupling the previous two and simulates the whole PCM-water thermal storage. This final model was validated through an experimental test, which consisted in inserting 94 modules of PCM in the water tank and observing the resulting thermal behaviour for three days, applying the load curve of a detached house of 200m2. The model proved to be very accurate, with determination coefficients between 92.10% and 99.80% for the considered physical quantities (temperatures and thermal powers). As a main contribution of this work, we proved that the hybrid thermal storage system did not exploit the full latent heat potential of the PCM, since only 40% of it actually changes its phase, due to is thermal transport properties that negatively affect heat transfer.

Energy payback time, exergoeconomic and enviroeconomic analyses of using thermal energy storage system with a solar desalination system: An experimental study

In this study, the performance of solar still incorporated with thermal energy storage (TES) unit of phase change material (PCM) is evaluated based on energy and exergy methodologies. Energy payback time for solar still with and without PCM is quantified and compared. Furthermore, the performance of both configurations is also evaluated from exergoeconomic and exergoenvironmental points of view. Experiments for solar still with and without PCM are conducted in summer and winter seasons subjected to the weather conditions of Alexandria, Egypt. The findings showed that the addition of a PCM storage unit to solar still system increased the annual energy and exergy savings by 10% and 3%, respectively. The results indicated that the incorporation of PCM in solar still was found ineffective compared to traditional still based on energy payback time. Based on the exergy approach, the integration of PCM in the solar still system is not effective where the conventional still (without PCM) achieved more than 400% more CO2 mitigations compared to PCM-based solar still system. Also, the exergoeconomic and exergoenvironmental parameters of the modified system were very poor related to those of traditional still. Therefore, for PCM-based solar stills systems to become competitive from global energy and environmental approaches, attempts should be performed by industrialists and engineers to find storage materials with low embodied energy and with low cost in conjunction with its evaluation from energy and exergy outputs to get a complete picture about the effectiveness of the system. In this case, the potential of thermal energy storage techniques for low-temperature solar-powered desalination systems will be thermodynamically, economically, and environmentally effective.

Numerical and Experimental investigation of thermal energy storage in a conical finned tube in PCM storage unit

In modern world, use of phase change materials (PCMs) in a thermal energy storage system is an efficient way to store the energy. There are many applications of thermal energy storage system in which PCMs is used, namely, heat pumps, solar systems, spacecraft thermal applications etc. The purpose of this paper is to identify effect of geometrical changes on the melting process of PCM. Computational fluid dynamics (CFD) is used to analyze phase change process. Thermal energy storage tank consists of a vertical tube in tube geometry where outer tube consists of phase change material and inner pipe carrying hot fluid. Paraffin is used as latent heat storage material. Further, the paper describes the effect of inlet temperature of heat transfer fluid on the phase change process. Two types of geometries are used, namely cylindrical and conical shaped. Result shows that charging time is 2.56% less for conical shaped storage system rather than the same for cylindrical shaped system. The results of CFD and experimental analysis considering the parameters like flow rate and inlet temperature of heat transfer fluid are compared. The results of the numerical analysis and the experimental readings shows a good agreement between them. It is observed that as the mass flow rate increases, the effectiveness of the PCM based heat exchanger decreases.

An optimizer using the PSO algorithm to determine thermal parameters of PCM: A case study of grey water heat harnessing

The melting and freezing of Phase Change Materials (PCMs) is categorized as a moving boundary problem. For this reason the mathematical solution to study the behaviour of practical applications is only possible via complex numerical approximations. However for a preliminary design the main concern is to select the optimum thermal characteristics of the PCM storage unit, for both melting and freezing. This is to be done before the detailed design by integrating an optimization algorithm with a numerical simulation. The application of using PCMs to harness the waste heat from non-industrial grey water is investigated as a case of study. For this purpose, the 2-phase analytical solution to the Stefan problem is coupled with the particle swarm optimizer (PSO) to find the best combination of thermal characteristics within the prescribed boundary conditions of this case study. Results show that the optimum phase change temperature lies between 20 and 22 °C, depending on various sets of input parameters. At the same time the ratio of latent to sensible heat transferred by the PCM highly influences this optimum temperature for the combination of both melting and freezing. Similarly results show melting being faster and more intensive in term of latent heat charging compared to a higher sensible heat discharging while freezing.

Integrating Two-Stage Phase Change Material Thermal Storage for Cascaded Waste Heat Recovery of Diesel-Engine-Powered Distributed Generation Systems: A Case Study

Thermal energy storage using the latent heat of phase change materials (PCMs) is a promising technique to solve the time mismatch between the availability and usage of flue gas heat in distributed generation systems (DGSs). A diesel-engine-powered DGS integrated with two-stage tube-type PCM modules for exhaust gas heat recovery was developed and studied. Energy and exergy analysis for the PCM storage unit was carried out to verify the effectiveness of the PCM modules for heat recovery and to highlight the merits of the cascaded configuration through a practical engineering case. Furthermore, the performance of the DGS was evaluated to study the contribution of PCM storage to improving system efficiency. The results showed that 56.4% energy and 48.3% exergy of the input flue gas were stored by the two-stage storage unit. Additional integration of the low-temperature PCM module to the high-temperature module improved the average storage efficiency from 33.6% to 62.3% for energy and 33.1% to 50.8% for exergy. By utilizing the stored energy for heating water, the thermal efficiency of the diesel engine was increased from the original 35.8% to 41.9%, while the exergy efficiency was improved from 29.5% to 29.7%.

Energetic and exergetic performance assessment of the inclusion of phase change materials (PCM) in a solar distillation system

In this experimental work, the energetic and exergetic performance enhancement of solar distillation system (solar still incorporated with PCM storage unit) is performed by using two techniques. First, pin fins heat sink (PF) is embedded inside the PCM to act as a thermal conductivity enhancer. Second, black steel mesh fibers (SWF) are employed in the solar still basin with PCM. In this regard, four cases of the solar stills are studied and compared conventional still: conventional solar still (without PCM), still with PCM (With PCM), still with PCM and pin fins heat sink embedded in the PCM (With PCM-PF) and still with PCM and SWF in the basin (With PCM-SWF). The energetic and exergetic performance of the four cases is evaluated and compared under the meteorological conditions of New Borg El-Arab City, Egypt. The results show that the total daily cumulative yield of distilled water of still with PCM, still with PCM-PF, and still with PCM-SWF are greater than of conventional still by 9.5%, 16.8%, and 13%, respectively. Additionally, the inclusion of the fins heat sink in the PCM increases the average daily energy and exergy efficiencies by 17.9, and 13.2%, respectively compared to conventional one. Likewise, the energy and exergy efficiencies of still with PCM-PF are higher than those of solar still with PCM by 7.7 and, 6.8%, respectively. Furthermore, placing SWF in the basin of still with PCM significantly enhances the daytime energy and exergy efficiencies with a considerable reduction of these values in the nighttime. The total daily evaporative exergy for still with PCM-SWF is greater than those of conventional still, still with PCM, and still with PCM-PF by 13, 8, and 2%, respectively. Also, still with PCM, still with PCM-PF, and still with PCM-SWF exhibit an increment of the daily exergy efficiency 5.9, 13.2, and 17.3%, respectively compared to still without PCM. Still with PCM-PF achieved the highest accumulated daily water productivity and energy efficiency but still with PCM-SWF attained the highest daily exergy efficiency with nearly no additional cost.

Modeling horizontal storage tanks with encapsulated phase change materials for building performance simulation

The current article describes a model developed to simulate the performance of a horizontal storage tank filled with commercially available, slab-like, macro-encapsulated phase change material. The model is implemented as a component for the TRNSYS simulation program, and is intended for integration into whole building energy analysis. It is based on one-dimensional conduction and uses the thermo-physical properties of the phase change material to maps its thermal behavior, considering hysteresis in the enthalpy-temperature curve. The validity of the modeling assumptions is assessed using a detailed finite-element model and basic dimensional analysis. Experimentally measured thermal behavior of a full-scale phase change material storage unit is used to validate the model. A variety of flow rates, inlet temperature profiles and temperature intervals are evaluated in 13 distinct tests. Comparisons between measurements and simulations indicate the validated model can simulate the behavior of such phase change material storage tanks and be used to improve their design for specific applications.

A Comparative Study on the Effectiveness of Passive and Free Cooling Application Methods of Phase Change Materials for Energy Efficient Retrofitting in Residential Buildings

This study compared the effectiveness of passive and free cooling application methods of Phase change materials (PCMs) when used as energy efficient retrofitting in a residential building. A modern duplex residential building in Melbourne, Australia was considered for the case study. In passive application, PCM was installed in the ceilings of the house. In free cooling application, outdoor air was supplied to the indoor after passing it through a PCM storage unit. The study was carried out using building simulation software EnergyPlus V8.4 and computational fluid dynamics (CFD) software ANSYS V15.1. The developed simulation models of passive and free cooling applications were validated using relevant experimental data. The validated simulation models were then used to investigate the effectiveness of these PCM application methods in the selected building. The results showed that, for the studied house, free cooling application of PCM is more effective than the passive application in reducing the internal zone temperature. Under typical summer climatic conditions of Melbourne, free cooling application resulted in up to 1.8°C reduction in zone air temperature, compared to only 0.5°C when PCM was applied as passive heat storage system. The outcome of this study would be helpful in selecting the effective PCM application method for these types of residential buildings in similar climates.

Experimental investigation of a desiccant dehumidifier based on evacuated tube solar collector with a PCM storage unit

ABSTRACTA rotary desiccant dehumidifier based on an evacuated tube solar air collector with a phase change material (PCM) storage unit has been experimentally investigated. The PCM (acetamide) simultaneously stores and transfers the heat to the air during day hours. The stored heat of the PCM is utilized to produce hot air during night hours. The performance of the system is analyzed for different air flow rates at different rotational speeds (rph) of desiccant wheel. The dehumidification effectiveness (ϵA), regeneration effectiveness (ϵR), and dehumidification coefficient of performance are 8.17, 10.35, and 0.0327%, respectively, at 16 rph of the desiccant wheel with 127.23 kg/h air flow rate. The system is also used to generate dry air for 14 h a day with PCM, which shows that acetamide used as the PCM has an ability to store an adequate amount of heat to regenerate the desiccant wheel during off-sunshine hours.

Experimental investigation of latent heat storage in a coil in PCM storage unit

The thermal energy storage is very important because it provides the solution to problems related between the provided and the required energies. This work presents the experimental study of a PCM storage unit for storing latent heat thermal energy. Three different types of paraffin are tested as phase change material (PCM) and water is used as heat transfer fluid (HTF). The temperatures of PCM and HTF, solid fraction and thermal effectiveness are analyzed. The effects of inlet temperature of HTF, flow rate of HTF and the type of PCM used on the time for charging and discharging heat are discussed. The following conclusion can be drawn: (1) HTF flow rate does not have a great effect on the discharging phase compared to the charging phase. (2) Inlet temperature has a great effect on the exchanger performance. It can accelerate charging phase 54.5% and delay the discharging phase by 48.5%. (3) Adding the oil engine to the paraffin can improve the speed of the charging and discharging heat process by 42.4 and 66%, respectively. However, the latent heat of the PCM is considerably reduced.