Heat Transfer In Phase Change Material Research Articles

Numerical phase change model considering crystal growth under supercooling

The supercooling of phase change material (PCM) significantly affects the heat release characteristics of heat storage systems. Therefore, accurate numerical modeling of the solidification process is key for studying heat storage. Few models considering the crystal growth of supercooling PCMs have been established; however, their accuracy under slight supercooling conditions is unsatisfactory. In this study, the implicit finite difference method was used to establish a two-dimensional PCM heat transfer model that considers the crystal growth process in detail. The growth rate of the crystallization front was used to control the crystallization start time at each node, and the solidification speed was used to manage the heating process once the crystallization was triggered. The accuracy of the model was verified by the experimental results obtained by melting, cooling, and triggering crystallization in a stable supercooled state and during cooling. Based on the simulations of a concentric tube PCM heat exchanger, the effects of several parameters on the heat release rate were investigated, such as the supercooling degree, the PCM initial temperature, and the inlet temperature of Heat transfer fluid (HTF). The results show that a large supercooling degree will accelerate the heat release rate of the PCM heat exchanger after the crystallization is triggered. An increase in the initial PCM temperature reduces the sharp increase in HTF outlet temperature caused by crystallization; a decrease in HTF inlet temperature also has the same effect. A comparison of various models demonstrated that the use of the crystallization front to calculate the PCM temperature directly causes up to 3% of the heat to be released earlier or later. Moreover, ignoring the crystal growth process causes up to 9% of the heat to be released in advance, and ignoring the supercooling causes an even greater error.

Unconstrained melting of phase change material in cylindrical containers inside hot water tanks: Numerical investigation and effect of aspect ratios

In this study, a numerical model with variable mushy zone constants was developed based on the enthalpy-porosity method for the unconstrained melting of phase change material (PCM) encapsulated in cylindrical containers inside hot water tanks. In particular, a method for dynamically determining mushy zone constants was established. Mushy zone constants were explicitly calculated for each element in the solid region and updated at each iteration in the solution procedure of the model. The model showed satisfactory performance, with a mean absolute relative error of 5.2% between experimental measurements and numerical results. Based on this model, the unconstrained melting process of PCM and the influence of the aspect ratio of the cylindrical container were investigated. Results showed that contact melting accelerated the heat transfer of PCM at the bottom region and further enhanced the natural convection of liquid PCM at the side region. Moreover, the aspect ratio exerted little influence on the heat transfer coefficient at side wall surfaces. The correlation between the total melting time and aspect ratio was also calculated. The peak total melting time occurred for an aspect ratio of 5.49, and the smallest total surface area corresponded to an aspect ratio of 2. Clearly, larger total surface areas do not necessarily result in shorter total melting time. Further analysis indicated that flatter containers likely to be preferable to slenderer containers in practical designs. In addition, increasing the percentage of the bottom surface area to the total surface area can increase the average heat transfer coefficient of latent heat storage units.

Nature-inspired triply periodic minimal surface-based structures in sheet and solid configurations for performance enhancement of a low-thermal-conductivity phase-change material for latent-heat thermal-energy-storage applications

Low-thermal-conductivity phase-change materials (PCMs) are often hybridized with high-thermal-conductivity metal matrices to achieve improved heat-transfer performance in latent-heat thermal-energy-storage (LHTES) applications. Owing to recent developments in additive-manufacturing technology that allow any complicated topology to be manufactured with ease, triply periodic minimal surfaces (TPMS) have gained considerable attention. These nature-inspired TPMS structures have already shown promising results in a variety of applications. TPMS structures can be developed in either sheet or solid configurations, both of which exhibit distinct architectures. Herein, a numerical study is presented whereby an organic PCM (docosane) is hybridized with two TPMS structures, namely, gyroids and I-graph-and-wrapped-packages (IWPs) in both sheet and solid configurations. The effective thermal conductivity of each resulting TPMS-PCM composite was calculated using steady-state simulations. Moreover, transient simulations were conducted under isothermal and isoflux conditions to assess the structures' heat-transfer performance. The obtained results were compared with those obtained using PCM only, and the incorporation of gyroid and IWP structures in both sheet and solid configurations was found to significantly improve the PCM's heat-transfer performance. For isothermal case under pure conduction, sheet-based configurations outperformed the solid-based ones with IWP sheet configuration being the best configuration with a PCM melting time of 118 s. However, upon taking buoyancy into account, IWP solid showed best performance with a PCM melting time of 108 s. Furthermore, the performance of each TPMS-PCM composite was found to depend on the type of structure incorporated into it and the value of the applied boundary condition. For isoflux case, IWP sheet showed the best performance in terms of temperature homogeneity in PCM domain as compared to the rest of the TPMS structures under both pure conduction case and the case with buoyancy effects. The PCM melting time in isoflux case was not found to have a strong dependence on TPMS structure type. In both isothermal and isoflux cases, Gyroid solid based TPMS-PCM composite showed the least performance. Moreover, the effects of PCM buoyancy are more pronounced in solid configurations than the sheet ones. Therefore, this study may serve as a design guideline to select appropriate TPMS configuration based on the applied boundary conditions/application.

Effect of copper foam fin (CFF) shapes on thermal performance improvement of the latent heat storage units

To overcome the poor thermal change of Phase Change Material (PCM), Copper Foam Fin (CFF) was innovatively utilized to enhance the PCM heat transfer capability and improve the thermal performance of vertical shell-and-tube latent heat storage units (LHSUs). Three CFF shapes, including annular CFF (ACFF), longitudinal CFF (LCFF) and compound CFF (CCFF), were designed with the same filling ratio of 30%. A contrastive experiment with three flow rates was conducted to evaluate the heat transfer capacity of LHSUs integrated with three CFF shapes. Experimental results showed the CFF shape had the large effects on the thermal performance of LHSU and that ACFF showed the most excellent thermal performance. Compared with LCFF and CCFF, adding ACFF could increase the melting rates by 14.1% and 3.9%, the solidification rates by 10.1% and 2.7%, and the thermal efficiency by 21.9% and 42.0%, respectively. And ACFF and CCFF units showed better performance in the liquid interface distribution and the temperature uniformity. Moreover, the volume flow rate had the small influence on the temperature response rate, but could improve the thermal efficiency significantly.

Phase change material heat transfer enhancement in latent heat thermal energy storage unit with single fin: Comprehensive effect of position and length

In this study, the comprehensive effect of position and length of the fin in a latent heat thermal energy storage (LHTES) unit with a single fin on the melting and solidification of the phase-change materials (PCMs) was explored by transient numerical simulations. By analyzing the liquid-solid interfaces, temperature distributions, velocity vector and phase change rate, the melting and solidification characteristics of PCM and heat transfer enhancement mechanism of the fin with various length ratios and height ratios were understood in detail. The results illustrated that the total melting time was significantly reduced by increasing the fin length and lowing the fin position simultaneously. On the other hand, lowering the fin position would result in non-uniform temperature distribution during the solidification process. More importantly, considering the contradiction in fin position between melting and solidification, an optimal position of the fin corresponding to different fin lengths was suggested. Besides, a disparity between heat storage/release and phase transition was quantitatively discussed.

Simulation and analysis of heat dissipation performance of power battery based on phase change material enhanced heat transfer variable fin structure

The further development of battery thermal management phase change material (PCM) cooling technology is limited by the low thermal conductivity of a single PCM. In order to enhance the performance of thermal conductivity of phase change materials and improve the heat dissipation capacity of power battery, the fin with high thermal conductivity is used as a style of enhance heat transfer to phase change materials. The computational fluid dynamics (CFD) method is used to study the effect of parameters, such as shape, number and material of high thermal conductivity fins added in PCM as well as the air convection coefficient of shell on the heat dissipation performance of lithium ion power battery. The results show that the maximum temperature of the battery decreases the most, which is 5.57 K, when the oblique-oblique fins are added, compared with the fin without enhanced heat transfer in PCM. In the limited available space, the decrease rate of the maximum temperature of the battery does not increase with the increase of the number of oblique-oblique fins. When four oblique-oblique fins are added, the rate of decrease in the maximum temperature of the battery is the maximum, which is 0.47%. According to the thermal physical properties of each fin material and the simulation results, aluminum is the best choice for fin material. As for the convection coefficient of the air, the greater the value, the better the heat dissipation effect of the battery is.

Study on the influence of tank structure and fin configuration on heat transfer performance of phase change thermal storage system

Owing to the intermittent and fluctuating nature of solar energy, thermal energy storage (TES) plays a vital role in solar energy utilization. The structural and geometric limits of the traditional heat storage systems, as well as the low thermal conductivity of phase change materials (PCMs), decrease the heat storage and exothermic efficiency of TES severely. To alleviate these shortcomings and improve the TES heat storage and release efficiency, the geometrical structure of TES and fin structure of the heat storage system need to be optimized. This study established a 2D model of the phase change TES unit with a single tank and auxiliary electric heating based on the experimental findings. The heat transfer performance of the truncated cone model with different taper configurations was also analyzed numerically. The influence of long and short fins on PCM heat transfer was analyzed under the premise of a certain fin volume. The influence of fins with different inclinations on the heat transfer process was also analyzed. The results show that the truncated cone with a taper of 0.37 performs best in the charging and discharging process. Compared with long fins, most short fins showed to have a more significant effect on accelerating the charging process. The enhancement effect of the different fin on the heat transfer process was divided into two categories, and the analysis shows that the fins with an inclination angle of −15° have the most significant enhancement effect. These findings of the study will guide the optimization design of the heat transfer structure of TES with a single tank configuration.

Numerical study of melting and heat transfer of PCM in a rectangular cavity with bilateral flow boundary conditions

The melting of phase change material (PCM) in a rectangular cavity with heat transfer fluids (HTFs) flowing at both sides from bottom up (bilateral flow boundary conditions) are numerically studied. A parametric study is performed by changing the Reynolds number (Re) of HTF in a range of 1 × 104, 3 × 104, 5 × 104, 7 × 104 and the Rayleigh number (Ra) in a range of 3 × 106, 4 × 106, 5 × 106, 6 × 106. The results show that the formation of natural convection is due to the impacts of non-uniform heat transfer of HTF and cooling between solid-liquid interface and liquid PCM. The asymmetric flow boundaries lead to various skew forms of the PCM melting process and effect the heat transfer and thermal energy storage. The melting process can be divided into three melting stages, the first two stages are mainly ruled by Re and the last stage by Ra. A set of introduced dimensionless parameters are analyzed to elaborate the heat transfer mechanism and the general rule of melting characteristics. The various dimensionless correlations are applied to describe the evolution of melting volume fraction, dimensionless average temperature and thermal energy storage fraction during the melting process.

CFD simulation for heat transfer enhancement in phase change materials

In this research work, a two dimensional CFD approach is presented to analyze the heat transfer phenomenon in Phase Change Materials (PCM). In this research study a rectangular shell type heat exchanger filled with PCM is selected and rectangular tubes are inserted to flow a heat transfer fluid. PCM is used as thermal energy storage material to store heat energy and a CFD simulation has been done to analyze the melting process of PCM and optimized the geometry of rectangular tubes inside the shell. Two geometries of rectangular tube, tubes without fins and tubes with four fins, are used to investigate the effect of geometry on heat transfer and melting of PCM. In this research work, CFD approach based on enthalpy porosity model is used for the enhancement of heat transfer and to reduce PCM’s melting time by inserting fins on circumference of the rectangular tubes in which a hot temperature fluid is flowing. The aim of this research is to optimize the geometry for increasing heat transfer in PCM and analyze the results in terms of liquid fraction at an applied temperature of 80 °C on the rectangular tubes. It can be seen from the analysis that fins incorporated to the tubes increases the heat transfer to the PCM and reduce the PCM’s melting time.

Study of Natural Convection Melting of Phase Change Material inside a Rectangular Cavity with Non-Uniformly Heated Wall

In the present numerical study, the convection diffusion phenomena associated with solid-liquid phase transition processes during phase change material (PCM) melting within a rectangular cavity is studied. The cavity is heated from left wall with a sinusoidal temperature distribution. Initially the enclosure was filled by solid gallium at melting temperature 29.78°C. The enthalpy-based lattice Boltzmann method (LBM) with D2Q9 particle velocity model is used to solve density, velocity and temperature fields. Influence of Rayleigh number ranging from 103 to 4×105 on streamlines, isotherms and liquid fraction is analyzed. The results indicate that natural convection of liquid phase change material (PCM) plays a significant role in the melting heat transfer of PCM. It is found that the rate of the melting increases with the increase in the values of the Rayleigh number.

Dynamic performance of a novel air-soil heat exchanger coupling with diversified energy storage components—modelling development, experimental verification, parametrical design and robust operation

A novel vertical air-soil heat exchanger (VASHE) is proposed, coupling with diversified energy storage components, i.e., both annular and tubular phase change material (PCM) components. Compared to traditional air-soil heat exchanger systems, advantages of the new VASHE include the space-saving, higher energy efficiency, centralized discharge of condensate water and smaller fluctuation of outlet air temperature. An enthalpy-based model is developed to characterise the underlying heat transfer mechanism of the sophisticated sensible and latent heat transfer in PCMs. An experimental platform is thereafter constructed for the calibration of the developed enthalpy-based numerical model. Systematic parametrical analysis has been conducted on PCM types, PCM structure and PCM locations. Research results indicated that, the developed enthalpy-based model was accurate to predict the system performance with the maximum relative error at 1.98%. Systematic parametric analysis indicates that, within various PCM types, the RT 20 in the tubular PCM is the most promising with the smallest outlet temperature amplitude. Furthermore, accurate PCM location is an effective solution to the contradiction between daily cooling storage capacity and outlet temperature amplitude. This study demonstrates a novel air-soil heat exchanger with diversified energy storage components, which can provide concrete guidance and pave path for the geothermal energy utilisation.

Experimental investigations of phase change material filled rectangular enclosure with inclined top and side heating mode

Abstract An experimental examinations has been conducted on an inclined top and side heating mode phase change material (PCM) filled rectangular enclosure to understand its applicability in various thermal applications like: photovoltaic (PV) thermal management systems, concentrated PV systems, building thermal management and so on. The basic objective of this research work is to experimentally analyze the melt front propagation and temperature distribution of the PCMs in rectangular enclosure with the top heating mode; which is very rarely available in the literature. Lauric acid and paraffin wax are used during an experimentations as the PCMs. The inclination angles of PCM enclosure are varied with 30°, 60° and 90° with the horizontal. Constant heat flux are applied on the heater surface using halogen lamp assembly. The heat input to the 30° and 60° inclined systems are from top side and for 90° system, the heat input is from the right side. Solid-liquid interface transition of the PCMs and its various heat transfer characteristics are explained in the present research work during the charging period. The result shows that the convection currents inside the PCM container plays the major role on PCMs heat transfer characteristics at different inclination angles. The melting rate of PCMs increases with the increase in the inclination angles; however, the heater plate temperature is observed to be smaller at high inclined systems. Heat transfer from the heater plate to the PCMs are very high during the initial period and it decreases as the time progresses.

Experimental study of storage capacity and discharging rate of latent heat thermal energy storage units

The key performance indicators of thermal energy storage (TES) units are the effective storage capacity and discharging rate. As it happened in building cooling applications, a latent heat thermal energy storage (LHTES) unit, which is a TES unit using phase-change-materials (PCM), when not properly designed, could have an effective storage capacity significantly lower than that of a stratified-water-storage (SWS) tank. This study experimentally demonstrates how the effective storage capacity and discharging rate of PCM-based TES units can be improved by enhancing heat transfer in PCM. To do this, four basic components of shell-and-tube LHTES units were filled with four different PCM composites, respectively, and tested under both laminar and turbulent flow conditions (Re: 500–14,500). The four selected PCM composites were composed of pentadecane and expanded graphite (EG), and achieved effective thermal conductivities (keff) of 0.21 W/(m·K), 1 W/(m·K), 8.6 W/(m·K) and 20 W/(m·K)), respectively. It was found that the test unit using pentadecane-EG composite with keff = 8.6 W/(m·K) can have an effective storage capacity twice that of an ideal SWS tank operating under Re = 4300 for the radiant cooling application condition. It has long been known that enhancing heat transfer in PCM could improve the performance of PCM based TES units. However, this is the first experimental confirmation that a PCM based TES unit can achieve an effective storage capacity higher than that of an ideal SWS tank; and the discharging rate of a PCM based TES unit could be improved under a realistic, practical operating condition.

Phase change heat transfer in an L-shape heatsink occupied with paraffin-copper metal foam

The enormous transient heating loads can be occurred in various electronic components, and hence, the thermal management of such loads is a curial task. The current research aims to address the flow and heat transfer of Phase Change Materials (PCMs) embedded in metal-foams heatsink under pulse heating conditions. The heatsink is made of an L-shape enclosure with a mounted hot element at the vertical side. The element produces a pulse heat flux while the heatsink is cooled at its top wall by an external flow. As a result, the heatsink changes the direction of heat transfer by absorbing the heat from a vertical surface and dissipating through a horizontal surface. The governing equations for the phase change flow and heat transfer of PCM in a metal foam are present and transformed into a non-dimensional form to generalize the study. The finite element method with an automatic time-step and grid adaptation is adopted as the solution method. Due to the presence of unsteady heat flux, the PCM in the heatsink experiences both of the solidification and melting phase change phenome. The outcomes show that the PCM-heatsink enhances the cooling rate of the element on the activation of the heat pulse. The heatsink provides a uniform and constant efficiency during the pulse. The higher the pulse power, the higher the heatsink efficiency. The growth of the element heat flux to fourfold and sixfold of the steady heat flux results in a heatsink efficiency of η = 1.75 and η = 2.4, respectively.

Performance optimization for shell-and-tube PCM thermal energy storage

Abstract Phase change material (PCM) based latent heat thermal energy storage (LHTES) systems have been a technology of increasing interests. Extensive experimental and numerical studies on the heat transfer enhancement of PCM have been reported. However, a thorough analysis of the effects of PCM heat transfer enhancement in combination with geometric optimization on the overall storage performance of an LHTES system is still lacking. In this work, a performance index, the effective energy storage ratio Est, based on the effectiveness-NTU theory, which set up a standard to compare TES systems, was adopted to evaluate the effective energy storage density of an LHTES system. Using the conjugate heat transfer analysis, we investigated the impact of the key parameters and flow conditions, including the geometric parameters (tube length-diameter ratio L/di, PCM volume ratio λ), turbulent versus laminar flow conditions of HTF, and the effective PCM thermal conductivity keff, on the performance indicator Est. It was found that the effective energy storage ratio increases with tube length-diameter ratio, and an optimal PCM volume ratio exists. Increasing the effective PCM thermal conductivity is only effective in enhancing the effective energy storage ratio when PCM volume ratio is above certain value. Over 500 sets of parametric studies were performed to optimize the PCM volume by maximizing the effective energy storage ratio. The results show that for both laminar and turbulent flow, optimal PCM volume ratio and maximal effective energy storage ratio increases with tube length-diameter ratio and effective PCM thermal conductivity. The enhancement of effective PCM thermal conductivity only noticeably increases maximal effective energy storage ratio when tube length-diameter ratio is above a certain threshold, i.e., around 800 for laminar flow and around 600 for fully turbulent flow. The fully turbulent flow greatly enhances the charging rate by 50 times and increases the capacity effectiveness at optimal PCM volume ratio to 0.6-0.9 from 0.2-0.8 at laminar flow conditions, but the maximal effective energy storage ratio of fully turbulent flows are generally lower than those of laminar flows. This work is the first systematic numerical analysis of the complete ensemble design factors of a shell-and-tube LHTES system, and it is recommended that the method could be a standard one for the engineering design of an LHTES system.

Recent progress in phase change materials storage containers: Geometries, design considerations and heat transfer improvement methods

• The different geometries of PCM storage containers and their design considerations are presented. • Recent advances of different heat transfer improvement techniques in PCM storage containers are reviewed. • Various designs of PCM-finned storage systems and their key design parameters are deeply discussed. • Discussions for current systems design and recommendations for future research are illustrated. The potential for phase change materials (PCMs) has a vital role in thermal energy storage (TES) applications and energy management strategies. Nevertheless, these materials suffer from their low thermal conductivity and hence heat transfer enhancement techniques should be applied to enhance their thermophysical properties. This review focuses on the geometrical configurations of PCM containers and their design considerations, aims to improve the performance of TES systems. Various methods for enhancing heat transfer of PCMs (the main challenge in container design) include microencapsulated PCMs, insertion of fins, the combination of fins and nanoparticles, the use of metal foams and graphite, and the doping of high photothermal materials are also extensively discussed as well. Moreover, this paper highlights various designs of PCM-finned storage systems and discusses deeply their key parameters to find out the suitable design for optimum melting and solidification rate of PCM. The reviewed results showed that the rectangular PCM container is the effective container for the bulk storage due to its high melting rate and storage efficiency. Moreover, the use of longitudinal finned geometry within PCM integrated triplex tube heat storage units significantly achieved better heat transfer performance compared to the other finned geometries. Additionally, the improvement of the heat transfer of PCM by the deployment of fins is more effective than the hybrid combination of fins and nanoparticles. Further optimization and experimental studies are recommended to explore new hybrid compound intensification techniques such as the triple combination of fins, expanded graphite, and heat pipes with multiple PCMs that augment the thermal performance of TES systems.

FEM Applied to Building Physics: Modeling Solar Radiation and Heat Transfer of PCM Enhanced Test Cells

In passive solar buildings, energy can be stored using either sensible heat materials or latent heat materials. Phase change materials (PCM) can contribute to temperature control in passive solar buildings when melting occurs near to comfort temperature required for building’s interior spaces. The use of finite element method (FEM) as a numerical methodology for solving the thermal problem associated with heat transfer in current building materials and PCMs make sense, as it is a well-known technique, generalized and dominated, however, still little applied to the domain of building physics. In this work, a solar model was developed and applied in order to simulate numerically the effect of solar radiation incidence on each face of the test cells (with different solar exposures) without neglecting the main objective of the recommended numerical simulation: the study of the action of PCM. During the experimental campaign, two test cells with distinct inner layers were used to evaluate the effect of solar radiation: (i) REFM test cell (without PCM) with a reference mortar; (ii) PCMM test cell (with PCM) with a PCM mortar. The temperatures monitored inside the REFM and PCMM test cells were compared with the values resulting from the numerical simulation, using FEM with 3D discretization and the explicit modeling of the solar radiation, and the obtained results revealed a significant coherence of values.

Investigation of heat transfer of wall with and without using phase change material

As part of reducing energy use for building application like cooling and heating, the phase change material (PCM) plays a vital role, it be incorporated into building structure and materials in an effective manner. In this research concentrated to find the effect of heat transfer of PCM filled hollow block (wall) and unfilled one, tested in a natural climatic condition of Chennai. In this regard Organic Material OM29 PCM is chosen based on average temperature persists on the selected location, it acts as thermal barrier also minimize the heat entering to the room. Heat gain of the building wall is respective to seasonal variations based on that the selected OM29 is to be effective only where the clear sunny days, over the period the PCM performance is to be optimized. The result shows that temperature drop of 5.7% and heat gain reduction of 33% are observed across the dimensions of the hollow block in the indoor surface, the temperature at various points in a surface is similar. The results showed the selected PCM have great influence in reduction of heat transmission from external face to internal face in hot climates, however for a moderate climate, the solar intensity differs from day to day so cooling transmission loads it varies, so employability of PCM influenced by ambient factors. The numerical simulations were performed thus the results are validated with experimental, in the incorporated PCM was effective in the months of April to July.

Melting and solidification of PCMs inside a spherical capsule: A critical review

Abstract To date, numerous phase change materials (PCM) have been developed for application in latent heat storage systems. There are many issues in the process from the development of PCM to using them in storage systems, which should be resolved. The problem of heat transfer in PCMs during the phase change process is the most important one. Latent heat storage containers usually have simple geometrical forms such as a sphere, cylinder, cylindrical annulus, rectangular enclosure, etc. A large number of papers were published on melting and solidification processes in PCMs. Therefore, there is a pressing necessity for generalizing the art of the state in this field and establish how accumulated knowledge meets practical requirements. The present review considers the current state in investigations of heat transfer in a spherical shell. Heat transfer in PCMs during constrained melting (solid PCM fixed inside the vessel), unconstrained (unfixed) melting and solidification, and phase change in finned shells are analyzed. It is shown that currently, there is no satisfactory description of the constrained melting process. For unconstrained melting and solidification, some correlations are suggested, describing these processes. The applicability range of the proposed correlations, as well as their accuracy were investigated and established. To intensify the process of phase change inside the spherical container, the use of orthogonal fins is appropriate option compared to the employ of circumferential fins.

Thermal analysis of an inclined heat sink with finned PCM container for solar applications

This paper explores the dynamic thermal performance of Phase Change Materials (PCMs) melting in an inclined finned rectangular container with the top heating mode. Internal external fins are provided to the back surface of the PCM tank considering its applications in the large duty cycle photovoltaic thermal management systems, top heating mode heat sinks and so on. Internal-external fins attached to the back surface of PCM container are proposed for: (a) to lengthen the melting time of PCMs during charging period specifically for peak sunshine hours in the solar applications (b) to enhance PCMs solidification during the discharging period and (c) to improve the heat transfer from the molten PCM to outside after complete melting; so as to reduce heat trapped. RT 42 is used as a PCM in the present study. Unsteady numerical investigations are performed with changing PCM thicknesses, inclination angles and number of extended surfaces. The PCM layer thicknesses are varied with 20 mm, 30 mm and 40 mm for the inclination angles of 30°, 45°, 60° and 90°. PCM container configurations with 2 fins, 3 fins and 4 fins are investigated. The effect of natural convection current is also included in the present numerical simulation using Boussinesq approximations. Control volume approach is used for the estimation of melting time, temperature distribution, velocity magnitude and Nusselt number enhancement. The result shows that the melting time for all the PCM systems increases with decreases in inclination angles and addition of a number of extended surfaces. The average PCM temperature and average velocity magnitude of the PCM decreases with decreasing inclination angle. Incorporation of additional fins than three does not add any significant enhancements in the melting time, although it drastically improves the PCM heat transfer performance. During the completion phase of melting process; using extended surfaces, Nusselt number is increased by 6–9 times for 30° inclined systems and 2–3 time with other inclination angles.