Melting Time Of Phase Change Material Research Articles

Accelerated charging dynamics in shell-and-multi-tube latent heat storage systems for building applications

Thermal energy storage (TES) is an emerging technique to store the surplus energy generated during periods of excess supply and utilise it when demand arises. Phase change material (PCM) stands out as a highly efficient TES system. Enhancing heat transfer during phase change is a major challenge in creating effective PCM-based TES systems. This study focuses on enhancing the melting performance of a shell-and-tube latent heat thermal energy storage (LHTES) system. This improvement is achieved by conducting an extensive parametric study involving various geometric factors including tube position from the bottom, vertical tube spacing, tube diameter, different heat exchanger shell aspect ratios, PCM temperature, tube temperature, and PCM type. A three-dimensional model is simplified to a two-dimensional geometry for numerical simulation. The results indicate that the PCM melting time decreased by 20.6 % and 4.4 % with a 20 mm vertical tube distance compared to 15 mm and 25 mm. Among the considered scenarios, the configuration with a doubled number of tubes in width consistently exhibits a higher melt fraction throughout the entire duration. Regarding the aspect ratio, the square-shaped system demonstrates both quicker melting times and a higher energy storage rate. When comparing PCM types, it is evident that RT 35 exhibits a 3.2 % higher heat storage rate and a 44.7 % shorter melting time compared to RT 35 HC.

Empirical Investigation of Thermal Features of Phase Change Material as Thermal Storage System

This paper presents an empirical investigation of the melting processes of phase change material (PCM) in a tube and shell heating exchanger utilizing solar thermal energy. The experiments were conducted outdoors in Al-Mussaib city, Babylon, Iraq (Lat 32.5° North, long 44.3° East), utilizing a north-south (N-S) collector oriented at a tilt angle of 32.5° from the horizontal. This work utilized pure Iraqi black paraffin with 12 kg as PCM. The main empirical rig involves a vacuum tube solar collector (VTSC) utilizing a tube and shell heating exchanger to melt PCM in the shell regime. Different rates of water flow inside the internal heating exchanger's tube, namely (3.5, 5, and 8.5 L/m), were utilized for each season from August 2022 to January 2023. The empirical findings concluded that the internal tube inlet and surrounding temps significantly influence the melting process compared to the rates of water flow. It was found that the melting process of PCM needs about (3 to 4) hours in the summer season. Still, winter needs a longer time, about 14 to 16 hours. Increasing surrounding temp and solar radiation reduces the melting time of phase-change material. The findings of the present work were compared with the earlier investigations and agree with increasing the present work by 23.5 %. The findings from the present study are of practical importance for industries requiring storage materials to improve thermal storage system performance.

Improving heat storage performance of shell-and-tube unit by using structural-optimized spiral fins

Spiral fins have been widely used to enhance the heat transfer of latent heat thermal energy storage (LHTES) systems. However, owing to the inhomogeneous melting of solid-liquid phase change materials (PCMs) driven by convective heat transfer, the uniform spiral fins always have poor enhancing performance. In the present work, we proposed structural-optimized spiral fins, including optimized fin thickness, optimized fin height, and optimized fin pitch, to uniformly and efficiently transfer the heat from fins to PCM. By comparing their melting results with the original-uniform model, we found that negative models with larger fin volume at the bottom are more efficient in accelerating the melting process, and they can maximally reduce the complete melting time of PCM by 15.01% compared with the original one. On the contrary, the positive model with a smaller fin volume at the bottom slows down the melting of the LHTES unit. The heat transfer mechanism along the whole melting process is analyzed by comparing the thermal parameters (including liquid fraction, average temperature, average liquid velocity, and heat flux) of the original and optimized models. The enhancements of the negative models are owing to their benefits to the developments of convective heat transfer in the top region and conductive heat transfer at the bottom. According to the results of this paper, researchers can design novel high-performance LHTES systems using optimized spiral fins.

Performance comparison and enhancement of the thermal energy storage units under two expansion methods

To improve the performance of the basic thermal energy storage unit, two expansion methods, modular combination and linear structural expansion, are proposed and compared through numerical simulations. The impacts of the two expansion methods on the performance of the storage units are compared by investigating the thermal storage and release processes. Following the numerical study, both expansion methods can increase the heat storage capacity and airflow rates compared to a basic phase change material (PCM) storage unit linearly. However, the linear structural expansion method will increase the PCM melting time from 147 min to 367 min when the heat storage capacity of the basic unit is increased two times, which is about 2.5 times longer duration than using the modular expansion method. As for the heat release process, the results indicate that thermal release performance using linear structural expansion is lower than that of the modular combination along with a decrease in heat release efficiency of about 32.53 %. In conclusion the modular combination method is proved to be more efficient compared to the linear structural expansion method for improving the performance of the PCM storage units.

A novel thermal management system for cylindrical lithium-ion batteries using internal-external fin-enhanced phase change material

This study introduced a phase change material (PCM)-based battery thermal management system (BTMS) using an innovative combination of internal and external fins to create PCM silos around the battery surface, addressing the low thermal conductivity of PCM. The lumped-capacitance thermal model and enthalpy-porosity approach were employed for the battery heat generation and PCM melting process, respectively. The BTMS was evaluated under transient and constant heat generation of the battery at various discharge rates. The effects of fin quantity on thermal management performance, energy density, heat storage capacity, and PCM melting time were investigated. The developed BTMS showed superior performance compared to the battery system with natural air convection cooling and the PCM cooling system without fins. At the end of the PCM complete melting process, the BTMS with 4 internal-external fins decreased the battery surface temperature by 9.90 and 17.45 K compared to the PCM cooling system without fins at the discharge rates of 3C and 5C, respectively. The BTMS with 4 internal-external fins kept the battery surface temperature under the optimum temperature of 318.15 K even at a high ambient temperature of 308.15 K while providing up to 10.02% higher energy density, 11.11% higher heat storage capacity, 32.79% higher fin efficiency, and only 1.08% lower overall fin effectiveness compared to greater fin quantities. The proposed BTMS provided an almost uniform cooling effect on the battery surface compared to the system without fins, which has been largely overlooked in previous studies on BTMSs. Various heat transfer regimes were identified during the PCM melting process. Correlations for predicting the PCM liquid fraction and Nusselt number were proposed as a function of a group of dimensionless numbers. These findings provided valuable insights for designing efficient PCM-based BTMSs.

Simulation and optimization of square fin concentric tube heat storage exchanger

The square fin was used to improve the heat transfer rate of the concentric tube phase change heat exchanger. The effects of fin spacing, fin arrangement, and fin length on the melting process of phase change material (PCM) were studied. The influence and mechanism of non-uniform fin arrangement were discussed in detail. The liquid phase distribution and temperature distribution of PCM with time were analyzed. The results indicated that the heat exchanger with square fins can significantly improve the heat storage rate and shortened the complete melting time of PCM. Compared with heat exchangers without fins, the melting time of PCM in a 40 mm equidistant fin heat exchanger was shortened by 15.85%, and that in a 70 mm, non-uniformly spaced fin heat exchanger was shortened by 36.79%. Due to the different distances between the square fins and the outer boundary of the concentric tube, the temperature distribution near the square fin showed anisotropy, which enhanced the melting rate of PCM. The sensitivity order was fin arrangement > fin length > fin spacing. The research results can provide a reference for the design of phase change heat exchangers.

Experimental study on heat transfer and storage of a heating system coupled with solar flat heat pipe and phase change material unit

Using renewable energy, especially solar energy, is essential to achieve a low-carbon society. PCMs suffer from low thermal conductivity, which hinders the efficiency of phase change thermal storage systems. Heat pipes exhibit vastly superior thermal conductivity, making them a promising candidate for enhancing PCM-based systems. To solve the contradiction between building insulation and importing solar energy into buildings in winter, this study proposes a new building heating ceiling system consisting of a flat-plate heat pipe (FHP) coordinated with a phase change material (PCM), and establishes a platform for a heat stockpiling device integrating the FHP and PCM. This research investigates the impact of heating power and bending angle on the heat transfer efficiency of the heat pipe and phase change heat storage system. The experimental findings demonstrate a direct relationship between increasing heating power and the enhancement of the FHP's heat transfer efficiency. When the FHP is bent at a 5° angle and heating power is increased from 20 W to 80 W, to store heat energy into the PCM cavities, the effective thermal conductivity rises significantly, escalating from 7.26 × 104 W/(m·°C) to 15.1 × 104 W/(m·°C), marking a remarkable 108 % rise. Moreover, although increasing the bending angle leads to heightened effective thermal conductivity of the FHP under constant heat input, and the heat transfer in PCM cavities will be weakened within a bending angle of 15°, experimental results demonstrate that the melting time of PCM still decreases with the increase of bending angle; the heat transfer inertia of phase change materials is dominant.

Numerical simulation and structural optimization of spiral finned tube thermal energy storage

Thermal energy storage (TES) has emerged as a promising solution to enhance nuclear safety by passively removing decay heat during reactor shutdown and accidents, thus preventing overheating of the reactor core and protecting the integrity of containment barriers. The research of TES with different structures has broad application prospects and practical significance. In this study, the melting process of phase change material (PCM) in various TES structures was simulated by the numerical simulation method in two and three dimensions. The mechanism of gravity-driven natural convection enhancing heat transfer was revealed. The effects of different TES structures, fin pitch, fin height, and fin thickness on heat transfer performance were studied. The results showed that many vortices formed by liquid PCM are the main reason for enhancing the natural convection. Adding fins could greatly accelerate the heat storage process. The melting time of PCM in annular and spiral finned tube TES was 47.3% and 61.3% less than that in smooth tube TES, respectively. In the present study, the heat transfer effect was enhanced as the spiral fin pitch became small, the fin height increased and the fin thickness increased. Two opposite effects of fin structure on the natural convection were revealed: (1) positive effect provided by heat transfer enhancement and (2) negative effect produced by blockage.

Enhanced thermal performance of shell and tube phase change heat accumulator with novel biomimetic spider web fins

Shell and tube phase change heat accumulator (STPCA) has many advantages such as flexible arrangement, simple structure and high operation temperature and pressure. However, there are some limitations such as the low thermal conductivity of phase change material (PCM) and much un-melted PCM at the bottom of STPCA. In this contribution, in order to solve aforementioned problems of STPCA, we firstly designed novel biomimetic spider web fins and applied the enthalpy-porosity method to solve the problem of phase transition and obtain the liquid fraction and location of the solid–liquid interface at different times. Then, we compared the enhance heat storage effect of the novel fins with that of normal radial fins. In addition, we further analyze the effects of three different fin arrangements and four different fin radial angles on the thermal storage performance. The results show that the novel biomimetic spider web fins can accelerate the melting of PCM at the bottom of the accumulator, uniform the temperature distribution and greatly improve the heat storage rate of the accumulator. The complete melting time of PCM of the accumulator with the novel web fins is only 48 s, but the radial fins is 140 s, which is much longer than that of the accumulator with the novel web fins. Moreover, the radial angle mainly affects the later melting period, because the angle can affect the natural convection. In this work, the model with a radial angle of 75° shows the better thermal storage performance. This contribution can provide a guidance for STPCA design to improve the heat storage performance.

Improving energy storage by PCM using hybrid nanofluid [(SWCNTs-CuO)/H2O] and a helical (spiral) coil: Hybrid passive techniques

The aim of this study is the numerical analysis of the melting process of the phase change material (PCM) in a spiral coil. The space between the inner tube and outer shell is filled with RT-50 as PCM. Moreover, the hybrid nanofluid (with a carbon component) flows through the inner tube. The novelty of this work is to use different configurations of fin and different percentage of hybrid nanoparticles (SWCNTs-CuO) on the PCM melting process. In the numerical model created by ANSYS-Fluent, the effect of various inlet temperatures is investigated. The results indicate that the extended surface created by extra fin has a dominant effect on melting time, so by adding the third fin, the melting time is reduced by 39.24%. The next most influential factor in PCM melting is the inlet temperature of the working fluid, so that 10°C increment of temperature result in the PCM melting time decreased by 35.41%.

Numerical feasibility study of improving the melting performance of horizontal and vertical double-pipe latent heat storage systems using ultrasonic field

The present research is devoted to the numerical study of the effect of ultrasonic waves emitted from an ultrasonic transducer on the melting performance of a double-pipe latent heat exchanger system (LHS). In the considered LHSs, hot water passes through the inner tube and the phase change material (PCM) located in the annulus melts by taking heat from the water. The performance of the LHS systems including the ultrasonic waves were compared with the performance of common LHS systems in both horizontal and vertical situations. In contrast to conventional methods for enhancing the heat transfer, integration of ultrasonic source with LHS is the novelty of current research. It is followed by evaluating the effect of transduce position and power on thermal energy absorption. The ultrasonic transducers were installed in various positions to find the most suitable location for improving the heat transfer. The melting time of PCM decreased up to 56.63 % and 74.59 % by applying the ultrasonic field for horizontal and vertical LHS, respectively. In addition, the effect of the transducer power on the performance of the best horizontal and vertical LHS cases was investigated. It was found that the increase in the transducer power from 20 W to 150 W is associated with a decrease up to 40.83 % in the charging time of PCM. The obtained improvement of heat charging of LHS can be attributed to the intensifying the convective heat transfer through ultrasonic field.

Strengthening of melting-solidification process in latent heat storage through sine wave shaped fins

Phase change materials (PCMs) offer an effective way to store thermal energy and balance the supply-demand mismatch in time and space. The melting-solidification process in PCMs is of main importance for the performance of the storage. To improve this process, numerical analyses are performed with PCM in a 2-D square-form cavity with two discrete heat sources and wavy sinusoidal shaped fins. The influence of different period and amplitude is analyzed to find the better fins arrangement. For the melting process, when the fin period is 20 and the amplitude is 2, the complete melting time of PCM is the shortest. In addition, fins with larger heat transfer area do not show better performance. For the solidification process, the optimal arrangement of fins is fins with period of 10 and amplitude of 5. The complete melting time can be shortened by more than 20.8 % and the complete solidification time could be shortened by more than 19 % compared to the case without any fins. Furthermore, in this study, the natural convection in the melting process is greatly affected by the fin area. When the fin area is large, the average value of natural convection is small, resulting in the maximum and minimum shortening of PCM melting time of 35.6 % and 20.8 %, respectively. The increase of fin area shows good heat transfer enhancement at the beginning of both melting and solidification process, but this strong strengthening effect does not continue throughout the melting/solidification process.

Heat transfer and storage characteristics of a hexagonal close structured packed-bed thermal storage system with molten salt phase change materials

The phase change material (PCM) spheres using 316SS as the ball shell and solar salt (NaNO3-KNO3, 60–40 wt%) as the PCM were arranged in an orderly pebble-bed arrangement. The charging performance, energy and exergy of PCM spheres in the packed ball thermal energy storage system (PBTES) were investigated using CFD simulation in order to solve the problem of heat storage at 300 °C–500 °C. The results show that the total melting time of PCM spheres slightly decreases from 1455 s to 1319 s with the inlet velocity increasing. The average heat storage efficiency of PCM spheres and PBTES are improved with the inlet temperature increasing. When the inlet flow rate increases from 0.01 m/s to 0.10 m/s, the energy efficiency of PBTES increases approximately 5.06 times, and the exergy efficiency increases from 17.91 % to 99.55 %. However the heat energy storage and exergy efficiency of PCM spheres are not affected by the inlet velocity changing. The energy efficiency of PBTES increases about 2.09 times, and the exergy efficiency increases from 30.29 % to 70.93 % with the inlet temperature grows from 300 °C to 500 °C. It provides an idea for the design of the medium-high temperature and high-efficiency molten salt PCM heat storage system.

Numerical simulation study of the effect of mechanical vibration on heat transfer in a six-fin latent heat thermal energy storage unit

The optimization of heat transfer in latent heat thermal energy storage units (LHTES) has received a lot of research during the past decade, and the use of fins to enhance heat transfer in phase change materials (PCM) is one of the efficient ways. However, the existing studies do not consider the influence of mechanical vibration which widely exists in LHTES. To fill the research gap in this important topic, a horizontal shell-and-tube six-fin latent heat thermal energy storage unit is investigated in this study, and the effects of mechanical vibration are investigated by numerically simulating the PCM charging process in LHTES using the Enthalpy-porosity technique. In this paper, the charging rate of PCM, variation of key parameters such as Nusselt number, temperature and liquid fraction are analyzed in detail under vibration conditions. And the following conclusions can be obtained. (1) Mechanical vibration can significantly increase the charging rate of PCM, under the condition of vibration amplitude of 10mm and frequency of 1Hz (the melting time of PCM is reduced by 46.6%). (2) The enhancement effect of mechanical vibration on the melting rate of PCM increases with the increase of amplitude and frequency, but the enhancement efficiency keeps decreasing. These observations result from that the mechanical vibration changes the velocity of the liquid PCM, so the forced convective heat transfer of the PCM is significantly enhanced. Furthermore, the melting process of PCM is sensitively affected by increasing the amplitude than by increasing the frequency. Increasing the amplitude or frequency alone (amplitude from 10mm to 40mm; frequency from 1Hz to 4Hz) can reduce the total melting time of PCM by 75% and 68.7%, respectively.

A novel numerical study on the melting process of phase change materials in a heat exchanger for energy storage

In this article, a new model with a different geometry is presented for application in systems of energy storage that contain phase change materials (PCMs). The main innovation of this research is designing two tubes instead of one tube inside the heat exchanger and investigation of its impact on the melting process of the PCM. Also, the influence of extended surfaces is studied to evaluate the reduction of melting time, and the changes of related geometrical parameters, including the number and length of fins, are examined in detail. The finite volume commercial code has been employed for numerical simulation and the obtained outcomes have very good agreement with a published experimental study. Results indicate that the utilizing of two tubes and reduce the distance between these tubes has a considerable influence on energy storage and reduction of melting time. Further, it can be concluded that for a certain number of fins, the melting time of PCM reduces by enhancing the fin length.

Performance enhancement of latent heat storage unit by the multiple chambers

AbstractThe thermal conductivity of phase change material (PCM) is one of the essential variables for the fast heat transfer process for latent heat energy storage (LHES) units. The thermal characteristics of a novel LHES rectangular enclosure based on multiple chambers separated by insulating and rigid walls are numerically investigated. The enthalpy‐porosity strategy supported by the finite volume method is implemented to perform the simulation. Simulation results exhibited that thermal charging and discharging performance was enhanced without affecting the system's total heat storage capacity by creating multiple chambers. Liquid fraction, mean temperature, heat flux, contours of liquid fraction and temperature of PCM are demonstrated as a function of the melting time. The thermal charging time of PCM is diminished by increasing the number of chambers. Although, the consequences of the number of chambers on the melting time of PCM are diminished by surging the number of chambers. It was also found that continuously raising the heating temperature is not beneficial for reducing the total time of liquid fraction during melting. Thermal discharging performance is poor than that of the thermal charging process.

Effect of phase change material tubes inclination angel on the performance of indirect hybrid thermal energy storage system: An experimental approach

• A modular indirect hybrid thermal energy storage tank is designed and investigated. • Temperature evolution of the PCM and the water in the tank are studied. • Thermal performance of the water tanks with and without PCM tubes are compared. • Effect of the PCM tubes inclination angel on the thermal performance is discussed. For an efficient use of indirect hybrid thermal energy storage, it is necessary to investigate the heat transfer characteristics of its charging and discharging processes. However, in previous studies, the inclination angel of phase change material (PCM) units is fixed. The influence of PCM units inclination angel on the thermal performance of the indirect hybrid thermal energy storage has not attracted much attention. To address this research gap, this study proposes a modular indirect hybrid thermal energy storage tank in which the PCM tubes inclination angel can be changed freely. The heat transfer characteristics of the tanks with horizontal, inclined, vertical PCM tubes, and without PCM tubes are studied by experiments. The experimental results show that the melting time of horizontal PCM tube is the shortest, which is 25% less than that of vertical PCM tube. However, the solidification time for all the three different inclination angel tubes is the same at 96 min. Compared to the tank without PCM tubes, the average overall heat transfer coefficient of the heat exchanger during charging/discharging processes for the tanks with PCM tubes are increased by 7.18%/7.58% (horizontal), 1.37%/10.05% (inclined), and 4.43%/8.96% (vertical), respectively. The maximum average thermal storage rate of 1.31 kW is observed in the tank with horizontal PCM tubes, which is an increase of 5.65% compared with the tank without PCM tubes. For the discharging process, the difference of the average thermal release rate among the four tanks is not noticeable. The results indicate that the PCM tubes inclination angel has significant impacts on the melting time of PCM, the heat transfer coefficient of the heat exchanger and average thermal storage rate of the tank. Optimizing the PCM tubes inclination angel is an effective way to improve the thermal storage rate of the indirect hybrid thermal energy storage system.

Assessment on the effect of longitudinal fins upon melting process in a latent heat thermal energy storage unit

Latent heat thermal energy storage(LHTES) unit are an effective technical means to balance the demand and supply of energy. To enhance the heat transfer efficiency of the phase change material(PCM) in the LHTES unit, a series of novel three-tube heat exchangers with longitudinal fins was designed. The study was carried out in terms of the number, length, thickness, and arrangement of fins. Results demonstrate that the thickness change of fins has a significant effect on reducing the melting time of the whole PCM. The thin long fins have a higher melting rate. The complete melting time of the thin long fins was 10.6 % faster than that of the short thick fins. By studying the effect of fin length on the heat storage performance, it was found that the structure appeared to be more reasonable at L = 30 mm and the heat storage time was shortened by 18.0 %. In addition, the use of the lower long and upper short fin arrangement can strengthen the heat transfer. Considering that the amount of heat storage capacity decreases as the number of fins increases, N = 20 is considered as the best fin number. Therefore, we give an optimal combination of fin design parameters (N = 20, L = 30, W = 1), which shortens the total melting time of PCM by 71.2 %. To be conclusive, it is more beneficial to add fins to heat transfer enhancement than to have no fins, saving more energy charging time.

Enhancement of phase change material melting using nanoparticles and magnetic field in the thermal energy storage system with strip fins

In this work, the numerical analysis of heat transfer and the enhancement of the melting of phase change material (PCM) in a three-dimensional cylindrical thermal energy storage system has been investigated. The RT82 is as PCM and the finite volume method is as the numerical solution method. Porosity-enthalpy method has been used to simulate the phase change melting process. The effects of strip fins, Fe3O4 nanoparticles, and uniform and non-uniform magnetic fields on the PCM melting are studied in details. Different modes have been considered for the non-uniform magnetic fields, both constant and variable with location. The predicted results display that the PCM melting time of the energy storage system using the new arrangement of strip fins is reduced by about 51 % compared to the that without fins. The addition of nanoparticles in PCM with volume fractions of 2.5 % and 5 % has improved the melting time by about 15 % and 22 % compared to those without nanoparticle. The use of a uniform magnetic field does not have much effect on the melting process without fins. But in the finned cases, in the initial melting (<1000 s), it has a noticeable effect on the amount of releasing energy in the desired system compared to the that without magnetic field, the mount of releasing energy is almost doubled. Using a variable magnetic field has a positive effect on the melting process of thermal energy storage and has improved the phase change process by about 39 % compared to the case without a field. It has also been concluded that in the case where the changes of the origin of the variable magnetic field (electric voltage) in the z-direction are parabolic, >60 % reduction in the melting time is noted.

Numerical analysis of the thermal energy storage in cellular structures filled with phase-change material

This paper reports the results of a numerical study on the thermal performance of metal cellular structures that can be obtained by additive manufacturing (selective laser melting) when they are impregnated with phase change material (PCM) for possible applications in electronic cooling. Two body-centered cubic (BCC) periodic structures with cell sizes of 5 mm and 10 mm and a porosity of 87%, made of two solid materials (aluminum alloy and copper), and two paraffins with characteristic melting temperatures of 55 and 64 °C were considered. The numerical simulations are carried out using the commercial code ANSYS Fluent and are based on a previously validated purely conductive heat transfer model. The computational domains include just small repetitive portions of the considered composite structures, thus allowing substantial savings of computational time. Computed results show that, with both paraffins, the copper made finer BCC structure (5 mm) yields the best thermal performances, i.e, the shortest PCM melting time and the highest rate of thermal energy storage during transients.