Melting Process Of PCM Research Articles

Numerical investigation on flow characteristics and thermal performance of phase change material in spherical capsules with smooth or dimpled surfaces

The utilization of phase change spherical capsules with dimpled surfaces in a packed-bed latent thermal energy storage (PLTES) system provides a novel approach to addressing the intermittency and fluctuation in solar thermal utilization processes. In the context of accounting for wall effects, a comparative analysis of the flow characteristics and thermal performance of smooth and dimpled spherical phase-change capsules is conducted using the Large Eddy Simulation (LES) and an enthalpy-porosity method. Results show that the dimpled spherical capsule exhibits a substantial improvement in thermal performance compared to the smooth spherical capsule, with a maximum increase of 28.3 % in time-averaged Nusselt number when the difference in time-averaged drag coefficient is within 2 %. Compared to the smooth spherical capsules, the transient characteristics of dimpled spherical capsules exhibit significant changes, with the fluctuation amplitude of the drag coefficient and the fluctuation frequency of the lift coefficient both increasing by approximately twice. The local heat transfer performance also exhibits significant differences. The increase in surface temperature enhances the melting rate of PCM inside spherical capsules, but with the temperature rise, the enhancement efficiency decreases. The dimpled structure has a promoting effect on the melting process of PCM inside spherical capsules, and with the increase in surface temperature, this promoting effect becomes more pronounced. The time for PCM to achieve complete melting can be reduced by up to 19.07 %. The work contributes a novel idea for the application of non-smooth structures in PLTES systems.

Research on the performance failure of phase change materials thermal management for lithium battery

Lithium batteries are highly favored in the industry due to their high efficiency performance and long service life, but their thermal safety has always been a major challenge. The application of phase change materials (PCM) can effectively ensure the thermal safety. However, the inability to immediately dissipate heat from the PCM will result in their performance failure. The purpose of this study is to obtain the optimal parameter range considering the critical melting state of PCM through reverse analysis, to overcome the thermal issues during the discharge process of lithium batteries. The experiment and simulation of PCM thermal management are operated by considering input parameters, including liquidus temperature, discharge rate, thermal conductivity, filling thickness, and late heat. An explanation was provided for the entire melting process of PCM. The results showed that the simulation is reliable. The temperature of battery cooled by PCM is 15.4 K lower than that of battery not cooled for a discharge rate of 2C. The PCM with high liquidus temperatures is less likely to result in performance failure for conditions with high discharge rate. The cooling performance increases with the increase of discharge rate under the premise of effective thermal management. There is an optimal value for the filling thickness of PCM in terms of cooling performance and economic benefits. When the latent heat increased from 195 to 275 kJ/kg, the battery temperature decreased from 311.54 K to 311.02 K and the liquid fraction decreased from 83.16 % to 63.61 % at a discharging rate of 2C. This study provides an important insight for the application and further study of PCM in lithium batteries.

Analysis of heat transfer and fluid flow during the melting process of PCM within tubular thermal energy storage unit

In the present paper, a numerical and experimental study is implemented to analyze the melting behavior of a Latent Heat Thermal Energy Storage System (LHTES) in a horizontal cylinder with using paraffin 27 as the Phase Change Materials (PCM). By varying the internal diameter and wall temperature of the horizontal cylinder, the liquid fraction and mean heat transfer coefficient are adopted to evaluate the effect of Stefan number (Ste) and Grashof number (Gr) on the phase change process of PCM. The results indicate that both the effect of wall temperature and internal diameter on the melting process is significant. Furthermore., the dimensionless analysis results show that the heat flux decreases monotonically during the whole melting period when Ste number less than 0.093, this means that the natural convection cannot significantly promote the melting process of PCM. It is found that increasing the Grashof number from 2.28 × 104 to 1.54 × 105 with a constant Stefan number enhances the heat transfer, also for a constant Grashof number the PCM melts at a faster melting rate when the Stefan number increases from 0.046 to 0.313. Besides, with the Gr number increasing by 97 % and 238 % while the Ste number stays constant, the melting rate with respect to the dimensionless time (Ste∙Fo) is increased by 19 % and 31 %; by contrast, with the Ste number increasing by 73 % and 239 % while the Gr number stays constant, the melting period is decreased by 50 % and 76 %. Finally, correlations for the melt fraction and Nusselt number (Nu) with a combination of the Fourier, Grashof and Stefan numbers are developed for designing the LHTES appropriately.

A phase change material based annular thermoelectric energy harvester from ambient temperature fluctuations: Transient modeling and critical characteristics

Annular thermoelectric power generator has been increasingly considered in application of ambient energy harvesting owing to the advantages of simple structure and no pollution. To improve thermal stability and energy harvesting performance of this system, the latent heat of phase change materials to improve thermal management and the high thermal conductivity of the heat sink to enhance heat transfer with the ambient are harness to annular thermoelectric power generator. Motivated by this, a phase change material based annular thermoelectric energy harvester (PCM-ATEH) with fins is developed for ambient energy harvesting and its three-dimensional transient model is also built up through jointly with thermo-electric and phase change processes. This paper considers the influence of key parameters such as temperature fluctuation amplitude, temperature fluctuation period, height ratio of PCM and thermoelectric generator (TEG) and melting temperature on liquid fraction, temperature difference, voltage and power density. Moreover, the comparison of PCM-ATEH and PCM based thermoelectric energy harvester (PCM-TEH) with/without fins is further conducted in this study to explore thermal management and energy harvesting performance. The energy harvesting characteristics of PCM-ATEH with fins is developed concerning the combination of power generation of TEG and melting process of PCM. Based on the results, it is found that the temperature difference and power density of PCM-ATEH with fins vary periodically with the sinusoidal temperature boundary, and results show that increasing temperature fluctuation period is not always feasible. Additionally, the comparative results indicate that the peak power density and energy efficiency of PCM-ATEH with fins are increased by 0.126 W/m2 and 0.02 % compared with PCM-TEH with fins, and increased by 0.195 W/m2 and 0.041 % compared with PCM-ATEH without fins. The results of energy harvesting characteristics show that a maximum of 0.77$ per watt can be reached to power generation cost of PCM-ATEH with fins. This paper can provide theoretical guidance for thermal management and energy conversion of energy harvesting system.

Experimental and numerical study on the effect of the intelligent memory metal fin on the melting and solidification process of PCM

Experimental and numerical study on the effect of the intelligent memory metal fin on the melting and solidification process of PCM

Numerical simulation of fin arrangements on the melting process of PCM in a rectangular unit

Innovative fin arrangements were proposed to enhance the thermal performance of latent heat storage units. The enthalpy-porosity approach was employed to optimize the fin distribution and predict the transient melting behaviors of N-octadecane. The unit with horizontal fins of uniform length was set as the base condition for comparison. It was found that the dead space of heat transfer and melting due to natural convection was not effectively eliminated by the conventional fin set. The region persisted at the bottom of the unit until the end of the melting process. In light of these observations, the fins were repositioned and resized. Three alternative fin configurations were proposed and evaluated: angled fins, asymmetrically located fins, and stepped fins. Results illustrated that fin structures significantly influenced the heat transfer characteristics and melting behaviors of latent heat storage units. Generally, greater enhancements were attained with downward angles and downward offset distances. The downward angle −20°led to an accelerated melting rate of 18.3 % compared to the base condition. In case 9, where the fins were moved down by 12 mm, the heat transfer enhancement ratio reached 32.5 %. However, introducing inhomogeneity in the fin length had only a minimal impact on the melting process.

Experimental investigation of thermal characteristics of phase change material in finned heat exchangers

A significant challenge to the widespread use of practical latent heat energy storage systems based on phase change materials is the inherent low thermal conductivity of these materials. Inserting fins is considered one of the effective methods of heat transfer enhancement. In the present paper, an experimental investigation of the melting process of PCM in finned and unfinned heat exchangers is conducted. The experimental setup was constructed, and the measurement system was used to monitor the transient progress of the melting process. The heat exchanger comprises annular horizontal concentric double pipes, where the inner tube is heated by flowing water as heat transfer fluid (HTF), and the outer shell is thermally insulated. Four configurations of fins of the same fin/PCM volume ratio are attached to the inner tube. These configurations are longitudinal fin (LF), circular fin (CF), longitudinal perforated fin (LPF), and circular perforated fin (CPF). The effect of inlet HTF temperatures of 60, 70, and 80 °C is tested. The experimental findings indicate that the thermal performance of finned heat exchangers exceeds that of unfinned heat exchangers. Also, the perforated finned heat exchangers showed a higher thermal feature than the unperforated ones. In addition, the CPF achieved the lowest melting time and the highest melting rate, followed by LPF, CF, and LF. The maximum reductions of melting time are 71.1 %, 70.6 %, and 70.2 % due to using CPF HE instead of UF HE for inlet HTF temperatures of 60, 70, and 80 °C, respectively.

Study on melting and solidification performances improvement of phase change material using novel branch fin structure

A novel fin structure was proposed to improve the heat transfer characteristics of triple-tube latent heat storage system (TTLHSS). Ansys Fluent software is used for two-dimensional numerical calculation, and the model adopts melting/solidification model. The innovation of this paper is to develop a new type of fin that can simultaneously improve the solidification and melting process of PCM and optimize the structure of the new fin so that it can significantly shorten the time required to complete a heat storage and release cycle. Initially, the melting process of the case without fins and the case with new fins were compared. It was observed that compared with the case without fins, the melting and solidification time was shortened by 67.7 % and 74.8 %, respectively. Then the effects of the thickness, the length ratio, and the angle of the new fins on the melting and solidification process of PCM were studied. The liquid fraction contour of PCM in different cases and the liquid fraction curve of PCM with time were analyzed. The results show that the addition of new fins can significantly improve the heat storage and release rate of PCM in TTLHSS. Compared with rectangular fins, melting time and solidification time are reduced by 32.7 % and 52.9 % respectively. The new fins distribute the fin volume in the central area of the PCM which is difficult to melt, which improves the melting and solidification speed of the PCM and makes the overall rate more uniform. Finally, the geometric parameters of the fins are optimized by the response surface method (RSM), and the fin configuration with the cross fin thickness of 0.8 mm, the fin length ratio of 1, and the fin angle of 63.1° is optimal for shortening the total time. At this time, the time required to complete a heat storage and release cycle is reduced by 84.5 % compared with the case without adding fins. The corresponding regression equation is also obtained, which provides a basis for the design of fins.

Lattice Boltzmann simulation of the melting enhancement of composite phase change material with highly conductive additives - Effect of discrete particulate phase and continuous conductive network

The melting process of paraffin-aluminum composite PCM in a 2D enclosure is numerically investigated by means of an enthalpy-based lattice Boltzmann method. The aluminum is deployed in discrete particles with size around 100 μm and the continuous fibrous network in the composite PCM, respectively. The effects of equivalent particle diameter, the volume fraction of aluminum additives as well as the local structural rearrangement are systematically investigated. The results demonstrate that the appending of discrete aluminum particles at a low volume fraction (ϕ ≤ 0.2 in this work) even has a negative effect on the melting process, because of the inhibition of the natural convection. By concentrating the particles in either back and top area, the melting performance could be slightly promoted. However, the improvement is very limited. Instead, it is more effective to utilize the continuous conductive fibrous network structure to accelerate the melting, which is suggested to be bespread over the entire PCM with larger local space in the direction of temperature gradient. Furthermore, it is discovered that the critical melting time reduces exponentially with the increase of fiber volume fraction. This work gives a comprehensive understanding of the differences between the discrete particles and continuous structures in the heat transfer enhancement of composite PCM, and offers an optimization strategy in the fabrication of fiber/foam structures.

Numerical study on n-octadecane PCM melting process inside a pear-shaped finned container

This work numerically explores the melting process of a nano-enhanced phase change material (NePCM) in thermal energy storage (TES) system. The TES unit is pear-shaped and filled with n-octadecane PCM loaded with Al 2 O 3 nanoparticles and fitted with copper fins. The heat transport governing equations are solved using the finite element method's enthalpy-porosity approach. The melting and heat transmission processes were investigated in terms of the impacts of a variety of factors, including the volume percentage of nanoparticles, the passage of time, the number and the dimensions of the fins. The findings show that the addition of nanoparticles improves the melting process of PCM. For example, adding 6% Al 2 O 3 into PCM decreases the melting time by 12.5%. Furthermore, longer and thinner fins are advised to increase melting rate due to decreased thermal resistance enhanced heat propagation in the deeper regions of the thermal storage unit.

Experimental study of thermal energy battery working with nano-enhanced phase change material

The increasing use of renewable energy sources during the last two decades has increased the importance of research and development of energy storage systems. In this study, a new design of a thermal energy battery (TEB) was fabricated and experimentally investigated. This battery is composed of an aluminum finned tube heat exchanger inserted within a tank in plexiglass filled with 2.5 kg of nano-enhanced paraffin. Water was used as heat transfer fluid (HTF). To evaluate the influence of aluminum nanoparticles on the thermal behaviour of the TEB, the melting process of PCM was monitored using thermocouples. A series of experimental measurements were conducted and analysed. It was shown that the TEB's charging time is enhanced with increasing flow rate and temperature of HTF. The charging process of the TEB was found to be expedited by up to 30% using 1.0 wt% nanoparticles of aluminum with the paraffin Wax.

Melting of hybrid nano-enhanced phase change material in an inclined finned rectangular cavity for cold energy storage

The aim of this paper is to study the potential of two heat transfer enhancement techniques, namely adding fins and hybrid nanoparticle (Cu and Al2O3), for improvement of the melting process of PCM (water) in an inclined rectangular enclosure as model of cold energy storage systems. Phase change and heat transfer of PCM are modelled using an in-house built code based on Lattice Boltzmann Method, which is validated with experimental and numerical results from literature. Enhancement effect is investigated through the main parameters including number of fins, fin length ratio (W/H) and nanoparticle volume fraction (ϕ). Heat transfer and fluid flow, liquid fraction, transient evolution of melting front, required time for full melting, and thermal energy storage are analysed in detail. The results show that the melting rate is about two times higher for the fin length ratio of W/H = 0.75, compared to W/H = 0.25. Besides, nanoparticle loading further enhances the melting rate. The highest melting rate is attained in the case of 3-fins and nanoparticle concentration of ϕ = 6 vol% with a 33.5% reduction in the complete melting time. Incrementing the fin length ratio increases the thermal energy stored, and the melting time can be shortened by up to 64%.

Preliminary design of safety system using phase change material for passively cooling of nuclear reactor containment building

The new application of phase change material for passively cooling the containment building of a nuclear power plant provides many benefits such as minimized wall penetration, low maintenance cost, and the possibility of installation in currently operating power plants with a minimal design change. In this study, the applicability of PCM as a passive containment cooling system is verified through design and evaluation of the PCM condenser. In addition, the effective heat capacity method is verified for simulating the melting process of PCM in the condition of a reactor accident. The PCM condenser design is optimized with five design parameters; melting point, volume, heat transfer area, effective thermal conductivity, and total heat absorbed. The performance of the PCM condenser is evaluated by containment safety analysis and is compared to that of an active containment cooling system. Although the PCM condenser had a limitation for absorbing only a fixed amount of thermal energy due to the absence of an external heat sink, the PCM condenser shows better performance in the early stage after the accident initiation compared to the single spray system and finally maintains the integrity of the containment building.

Modeling of convection-dominated melting in rectangular enclosures

A validated CFD by ANSYS model is built for a melting process of PCM (gallium), inside rectangular enclosure heated from one side and cooled from another. This was carried out by enabling the solidification and melting model in addition energy model of ANSYS. Regression model of melting front results from CFD model by ANSYS is utilized and integrated inside numerical approach by MATLAB to generate constants for Nusselt correlations and effective conductivity during different melting stages that can be used to define melting front locations and temperature at grid different locations. In addition, effect of the wall temperature and model aspect ratio variation on melting process have been simulated by ANSYS and analyzed in details. Enthalpy method and conduction equations for 2-D model were used to describe the predicted share of convection in melting process, with trial and error by assuming the constants automatically. Accordingly, melting process can be predicted in a simple and a conservative time way at the same time, the results are mainly indicating that convection heat transfer affects the melting process and melting behavior which is in coherence with previous experimental and analytical literature. Also, the effect of aspect ratio were investigated to assure that the more the aspect ratio, the better is the temperature homogeneity.

Numerical study on enhanced melting heat transfer of PCM by the combined fractal fins

The melting heat transfer characteristics of PCM were studied in different combined types of heat exchangers. The effect of combining two different bifurcation level fractal fins was considered for PCM melting heat transfer in a phase change heat exchanger. Based on fractal theory and enthalpy-porosity method, a PCM melting model of two-dimensional unsteady heat transfer was established in a combined fractal fin heat exchanger. The influences of some factors, such as combined types of fractal fins, bifurcation level, heat transfer area of the fins and the spacing of the fins, were discussed for the melting heat transfer process. The results show that the complete melting time of PCM in a combined fractal fin heat exchanger is reduced by 68% compared with the traditional fractal fin heat exchanger. The melting time shows decreasing first and then gradually stabilizing as the bifurcation level number and heat transfer area of the combined fractal fins increase. The melting rate of PCM is the fastest in the Case 4 heat exchanger, and the complete melting time of PCM is the shortest in the Case 3 heat exchanger. Fin spacing and heat transfer area have a significant impact on the complete melting time. On this basis, the thermal performance coefficients between the fins zone and PCM zone are defined. The complete melting time of PCM is found to be exponentially negatively correlated with the thermal performance coefficient by curve fitting. The temperature distribution uniformity coefficient is proposed to evaluate the temperature distribution uniformity during the melting process of PCM. It is found that the temperature distribution uniformity of Case 2 has the best at the end of melting. The above results provide a theoretical basis for structural design of the heat exchanger with combined fractal fins to enhance PCM melting heat transfer.

The effect of aspect ratio on PCM melting behaviour in rectangular enclosure

ABSTRACT The effect of Aspect ration on melting process of PCM (polyethylene glycol 1500 (PEG 1500)) in a rectangular encloser was investigated using CFD modelling. The CFD model was validated by experimental measurement performed for one case of aspect ratio of 2.31 with height = 155 mm, width = 67 and depth = 200 mm. The study was conducted in two phases: i) constant height enclosure, ii) constant volume enclosure. The main conclusions from this study are: i) the conduction heat transfer is the only mode of heat transfer in the first 250 secs from the start of heating of PCM. Then, the evolution of natural circulation starts at the hot wall and developed to a complete steady cycle after 2000 secs. ii) the results indicate a clear effect of the aspect ratio (AR) on melting percentage with peak at AR = 2,31 for both cases of constant heght and constant volume. iii) the results also show that there is a limiting width of the encloser where the circulation velocity reduced to low values (<0.3 mm/s) regardless of the enclosure heht.

Melting performance enhancement of thermal storage system by utilizing shape and position of double fin

In present study, a 2D rectangular enclosure was considered as a latent thermal energy storage (LTES) system. Lauric acid was used as PCM material. The aim of this study was to use fins to enhance melting process of PCM. Position and shape of double fins were considered as investigating parameters. At first stage three different positions were considered for fins of rectangular shape. Results indicated that amongst aforementioned cases, best results were achieved when double fins were located at lower half of enclosure. Results revealed that up to 1800s could be saved during whole melting process. At second step, two trapezoidal form and one triangular shaped double fins were used to evaluate the effect of fin shape. In these cases, fins were placed at optimum position concluded from previous stage. Results presented that up to Fo = 0.15, best values of Nusselt numbers were related to triangular shaped fins. After Fo = 0.15, the case with triangular fin has least Nu number. The best melting performance was related to triangular fins at which 1000s less melting time was observed. Enhancement ratio results presented better performance for triangular fins after second of 2500s.

Experimental and numerical investigations on the effects of different tilt angles on the phase change material melting process in a rectangular container

This paper presents the experimental and the numerical investigations to examine the effects of different tilt angles on the melting characteristic of the PCM as a passive cooling material inside a rectangular container. The experimental and the numerical tests are performed at four different angles, namely, 0o, 30o, 60o, and 90o, by applying heat on one of the rectangular container's walls filled with PCM at a constant temperature of 373 K. The purpose of the numerical study is to assess the possibility of analyzing the PCM melting characteristics accurately using a simulation model in ANSYS Fluent. The experimental and numerical results show good agreement with the satisfactory error ratios ranging between 4% and 6%. The results also show that the decrease in the PCM container tilt angle leads to the increase in the time taken for the melting process of PCM to complete. This is due to the diminishing effects of the convection heat transfer as the tilt angle is reduced. In general, a shorter time taken for complete melting of the PCM indicating a better cooling performance. Therefore, in this paper we have concluded that the PCM's cooling performance can be improved by increasing the tilt angle closer to the vertical angle (90o).

Melting performance analysis of phase change materials in different finned thermal energy storage

This study proposes helical-fin as an innovative structure for latent heat thermal energy storage systems. A three-dimension numerical model considering natural convection was established to research the melting process of PCM in finned LHTES units. To evaluate the new fin structure, the melting process of PCM in conventional finned LHTES systems was firstly simulated and compared with the innovative LHTES unit at the same heat transfer surface area. The results indicate that the fin structure has a remarkable effect on the charging process. Embedding the double-helical fin into phase change materials area can achieve the best thermal performance in a vertical LHTES. Meanwhile, quadruple-helical finned LHTES can achieve the best thermal performance in a horizontal thermal energy storage unit. Compared with the conventional finned LHTES units, the complete melting time is reduced by 31.0% in vertical LHTES. Moreover, the effects of HTF inlet direction and velocity on the thermal performance were investigated. The results reveal that the LHTES unit exhibits a uniform temperature field and better thermal performance when the direction of HTF inlet is opposite to the direction of gravitational acceleration. Increasing the inlet velocity of the HTF greatly affects the charging process of the finned LHTES unit.

Examining effects of special heat transfer fins designed for the melting process of PCM and Nano-PCM

In this study, a new heat transfer fins design, which may improve melting in thermal energy storage, is proposed. First, the melting process in the thermal energy storage without fins is discussed. Then, heat transfer fins are designed to allow the melting of the non-melting regions in TES. These fins are compared with the most widely used fin types in the literature. Melting processes of Base and Nano PCMs with different heat transfer fins are also investigated. The results showed that the development of heat transfer fins has a positive contribution to enhance melting in thermal energy storage systems such as reducing the weight of TES and reducing costs of TES. It is observed that adding fin 2 reduces notably the melting time, but in terms of geometry, fin 1 is more effective in the melting process. In addition, it is found that when inserting fin 1, the PCM melts faster. The melting time has decreased by 63% with the placement of the designed fin in the heat storage tank. However, in the case without fin1, the Nano-PCM is partially melted. The melting ratio at t = 120 min is 98% and 36% for PCM and Nano-PCM, respectively.