Latent Heat Energy Storage System Research Articles

Numerical study and experimental validation of a porous biochar supported form stable composite for thermal energy storage

This study numerically investigates the performance of the melting process for a biochar-based phase change material latent heat energy storage system. The melting processes of a composite made from softwood biochar combined with paraffin RT28, were compared numerically using the equilibrium porous medium model in ANSYS Fluent. The set up was validated through results from previous literature and experimental work. The enhancement in melting was compared to the pure PCM melting scenario and the effects of different paraffins, boundary conditions and inclination angle were investigated for real world application. Softwood biochar composites significantly surpass the performance of paraffin alone, reducing the melting time by 79 %. Different paraffins within the softwood composite produced different melting times, ranging from 2565 s to 4790 s. In terms of inclination angle adjusting to 90° produced steadier heating and reduced the melting time by 63 % in the composite. These findings offer insights into optimising latent heat thermal energy storage systems for improved performance and reduced energy wastage, highlighting the potential of biochar composites in sustainable energy solutions.

Melting of PCM-graphite foam composites with contact thermal resistance: Pore-scale simulation

Latent heat energy storage systems have emerged as a solution to intermittency and instability in renewable energy sources, the phase transition of phase change materials (PCMs) within these systems is hindered by their poor thermal conductivity. Graphite foam, renowned for its superior thermal properties, stands as an ideal choice to improve the melting efficiency of PCMs. In the current study, the melting behavior of PCM-graphite foam composites is simulated by the pore-scale numerical simulation (PNS) by employing cubic idealized cells with spherical pores and cylindrical channels. The computed results demonstrate that the porosity and contact thermal resistance of graphite foam are key factors affecting the melting efficiency of PCMs. The full melting time (FMT) of PCMs increases with porosity, achieving a 53.1 % improvement as porosity decreases from 0.90 to 0.75. In addition, the absence of natural convection markedly diminishes the maximum melting rate of PCM, reducing it by 33.5 % to 50.3 % for porosity from 0.75 to 0.90. Notably, it needs to be emphasized that the melting rate of PCM is significantly reduced when the contact thermal resistance surpasses 1.0 × 10–4 m2·K·W−1. Compared to the idealized condition without contact thermal resistance, the dimensionless FMTs for porosities of 0.75, 0.80, 0.85, and 0.90 extend by 27.3 %, 27.1 %, 22.2 % and 23.9 % for a contact thermal resistance of 5.0 × 10–4 m2·K·W−1, respectively.

Enhancing melting performance in multi-tube latent heat exchangers: Investigating the effect of inner tube number and arrangement

The latent heat energy storage system holds promising application prospects in the field of energy. However, the critical bottleneck remains the melting speed of phase change materials (PCMs). In this study, the melting dynamics of PCM within a triplex-tube heat exchange system are investigated, focusing on the effects of varying the number and arrangement of inner tubes. The system performance with four, five, six, and seven inner tubes is compared, revealing a decrease in melting time with an increasing number of inner tubes. However, excessive numbers do not yield more significant enhancement. A novel arrangement scheme is proposed, recommending six inner tubes. Additionally, the effects of inner tube spacing, upper angle and lower angle are explored. Increasing these parameters initially decreases melting time but then exhibits a reverse trend. Specifically, appropriate spacing enhances coverage area, expediting rapid connectivity of melting areas and thereby augmenting natural convection. While an increase in the upper angle delays PCM melting in the upper half, optimal arrangement enhances lower half PCM melting. Balancing melting rates of three difficult-to-melt areas in the lower half with proper lower angle achieves optimal performance. Compared with the base case, the proposed arrangement with the tube spacing of 40 mm, upper angle of 92°, and lower angle of 62° reduces melting time by 44.8 %. These findings provide a theoretical and experimental foundation for enhancing PCM-based energy storage system performance, offering valuable insights for engineering applications.

Exploring the impact of tube rotation on the melting performance of multi-tube latent heat storage systems: A numerical investigation

This study explores the impact of tube rotation on the melting performance of a multi-tube latent heat energy storage system through numerical analysis. The system involves a phase change material (PCM) contained within a tube, which absorbs heat from hot water flowing through a tube surrounding the PCM, as well as two tubes enveloped by the PCM. The investigation considers the angle between the line connecting the centers of the two inner tubes and the horizon (α = 0°, 45°, 90°, and 135°), along with the direction of rotation of inner tubes. Results are compared with data from scenarios involving only outer tube rotation and stationary systems. Temporal variations in temperature and liquid fraction contours, along with the temporal evolution of average temperature and average liquid fraction of PCM are presented. It was determined that for each α, the melting performance varied from best to worst across the system configurations as follows: the system with all three rotating tubes, the system with only the outer rotating tube, and the stationary system. The minimum time required to complete PCM melting for cases at α = 0°, 45°, 90°, and 135° is respectively 44.92 %, 42.11 %, 41.32 %, and 40.62 % less than that of the stationary system.

Numerical Study of a Latent Heat Storage System’s Performance as a Function of the Phase Change Material’s Thermal Conductivity

The thermal conductivities of most commonly used phase change materials (PCMs) are typically fairly low (in the range of 0.2 to 0.4 W/m·K) and are an important consideration when designing latent heat energy storage systems (LHESSs). Because of that, material scientists have been asking the following question: “by how much does the thermal conductivity of a PCM needs to be increased to positively impact the design and performance of a LHESS?” The answer to this question is not straightforward as the performance of a LHESS depends on the PCM’s thermal conductivity, other PCM thermophysical properties, the type of heat exchange system geometry used, the mode of operation, and the targeted power/energy storage of the LHESS. This paper presents work related to this question through a numerical study based on a simplified 2D model of an experimental setup studied previously in the authors’ laboratory. A model created in COMSOL Multiphysics, based on conduction and accounting for the solid-liquid phase change process, was initially validated against experimental results and then used to study the impact of the PCM’s thermal conductivity (dodecanoic acid) on the discharging power of the LHESS. The results show that even increasing the thermal conductivity of the PCM by a factor of 50 only leads to a maximum instantaneous power increase by a factor of 2 or 3 depending on the LHESS configurations.

Study on melting process of latent heat energy storage system by nano-enhanced phase change material under rotation condition

The utilization of phase change material in latent heat thermal energy storage technology is hindered by its limited thermal conductivity. This research aims to enhance the melting properties of a triplex-tube latent heat thermal energy storage unit through active strengthening (rotation mechanism) and passive strengthening (nanoparticle, longitudinal fin) heat transfer methods. A numerical investigation is conducted to examine the influence of nanoparticle percentage and rotation speed on various melting properties, including melting time, liquid fraction, heat absorption rate, and temperature response. The results demonstrate that the inclusion of 2.5 % and 5 % Al2O3 nanoparticles can significantly reduce the melting time by 58.49 % and 57.59 % respectively, while also increasing the average heat absorption rate by 126.53 % and 123.37 % at a rotation speed of 0.1 rpm. The findings from the Taguchi method suggest that rotation speed has a greater impact on melting duration and heat absorption rate compared to nanoparticle concentration. Moreover, maintaining a constant rotation speed, and a higher nanoparticle proportion can lead to an increase in dynamic viscosity and the settling of nanoparticles, which adversely affects the melting process efficiency.

Supercooling suppression and thermal conductivity enhancement of erythritol using graphite foam with ultrahigh thermal conductivity for thermal energy storage

The application of erythritol to medium-temperature latent heat energy storage systems is limited by its low thermal conductivity and large supercooling. Three types of graphite foams (GFs) with different thermal conductivities were used as the porous skeleton for encapsulating erythritol via vacuum impregnation, and the erythritol/GF composites were investigated using different methods to solve the aforementioned problems. The GF pores were effectively filled with erythritol via vacuum impregnation, and the filling rate of erythritol reached more than 90%. The thermal conductivity of the erythritol/GF composites was 73.80, 35.05, and 13.30 W/m·K. The thermal conductivity of the erythritol/GFs was improved by 26–158 times over that of pure erythritol. The subcooling degree of the erythritol/GF composites was reduced from 64.1 °C to 59.4 °C, facilitating the release of latent heat. The erythritol/GF composites had remarkably boosted thermal stability compared with that of pure erythritol. The developed erythritol/GF phase-change composite material exhibits excellent heat transfer and storage properties, and it has broad prospects in the field of phase-change heat storage at intermediate temperatures.

Development of novel form-stable PCM-biochar composites and detailed characterization of their morphological, chemical and thermal properties

Storing heat with phase change materials has the potential for several modern-day applications such as building thermal regulation, isothermal solar drying, electronic cooling, etc. However, to suitably incorporate latent heat energy storage systems, the challenges of leakage and low thermal conductivity of these materials need to be addressed. In this direction, biochar derived from abundantly available biomass feedstocks has been explored to develop form-stable, environmentally compatible energy storage materials. Biochar has been derived from wheat straw and softwood and has been analysed for their surface structure and utilised in the preparation of form-stable phase change material. The biochar derived from softwood was found to have a superior porous structure with a surface area of 441 m2/g compared to wheat straw. Biochar and phase change material Rubitherm 28 (RT28) were blended at various wt% and tested for leakage. The composite with 50 wt% of softwood biochar and RT28 had the lowest leakage rate. The developed green phase change-bio composite with minimum leakage has been thoroughly evaluated for its chemical and thermal properties. The latent heat of fusion has been found to be 228.6 J/g, 132.3 J/g and 51.6 J/g, for the RT28, softwood biochar composite, and wheat straw biochar composite respectively. Thermal conductivity was also higher for the composites than that of RT28. The thermal cycling reliability is suitable for thermal storage applications as there is a minimal alteration in the thermal properties observed after 200 cycles. The melting enthalpy of the new and aged composites after 200 cycles has been found to be 136.6 J/g and 132.42 J/g, respectively. The composite with minimal leakage and high thermal conductivity can potentially revolutionise the area of low temperature latent heat storage. The properties of the form-stable phase change-bio composite synthesised in this work make it suitable for application in the field of thermal management of photovoltaic modules, electronic devices, and buildings.

Enhancing melting and solidification characteristics of a triple-pipe latent heat energy storage system via a wavy central wall with a sinusoidal fixed wavelength

This study aims to improve the melting and solidification characteristics of a triple-pipe heat storage unit by introducing a wavy middle plate with a sinusoidal fixed wavelength. The inner and outer tubes facilitate the flow of heat transfer fluids (HTFs), while the middle tube houses the phase change material (PCM). Various scenarios are examined to gauge the impact of the wavy central wall on the PCM's phase change performance, comparing liquid fraction and mean temperatures with cases featuring a straight middle plate. The primary goal is to pinpoint the optimal scenario with the shortest discharging/charging times and the highest rates of heat release/storage. The investigation commences by assessing the effects of middle wall thickness (2, 4, 6, and 8 mm) on the PCM's phase change characteristics, comparing liquid fraction and mean temperature with a straight middle plate. Subsequently, the influence of various sinusoidal wavelengths (250, 125, 50, and 25 mm) on both melting and solidification performances of the PCM is numerically examined to identify the optimum case. The research also delves into the effects of various sinusoidal amplitudes (2.5, 5.0, 7.5, and 10 mm) on the PCM's phase change process. In the final step, the capability of the wavy middle plate, with various phase shifts (0°, 90°, 180°, and 270°), in improving the PCM's phase change characteristics is analyzed. Numerical results highlight that, among the tested scenarios, the configuration with a 5 mm amplitude and a 25 mm wavelength (A5λ250) exhibits outstanding performance during both melting and solidification phases. A5λ250 showcases a 19.92 % reduction in melting time and a 2.44 % reduction in solidification time compared to other cases, coupled with a 22.55 % improvement in heat storage and a 3.48 % enhancement in heat release. However, introducing a phase shift in the melting process adversely affects system performance. Conversely, adjusting the phase shift of A5λ25 to 270° leads to enhancements in both solidification time and heat release rate. Specifically, solidification time improves by 0.86 %, and the rate of heat release increases by 0.66 W compared to A5λ25–0.

Unzipped multiwalled carbon nanotube oxide / PEG based phase change composite for latent heat energy storage

Polyethylene glycol (PEG) as a phase change material (PCM) is being explored for latent heat energy storage systems due to its high thermal storage capacity. In the current study, PCM composites were synthesized with different mass fractions of unzipped multiwalled carbon nanotube oxides (UMCNOs) in PEG by melt mixing method. The influence of UMCNOs loading on the thermal conductivity (TC), phase change properties such as temperatures and latent heats of melting and solidifying, thermal energy storage and release rates were investigated. At a loading of 6 mass% of UMCNOs, the TC of the prepared PCM composite increased by 2.1 times as compared to that of pure PEG (0.21 W/m-K). Differential scanning calorimetry analysis showed that as the concentration of UMCNOs increased, there was a slight decrease in the melting temperature. Additionally, the latent heats of melting were found to be reduced by 1.11–9.46 % with the addition of 0.5–6 mass% UMCNOs. Further, the thermal energy storage and release rates were improved with the addition of UMCNOs in PCM composites. In addition, there was negligible change in phase change properties after 100 melting and solidifying cycles of PCM composite, indicating the great prospects for the latent heat energy storage application.

Experimental studies on the enhancement in discharging characteristics of phase change material with steatite nanoparticles

Phase change materials are latent heat energy storage systems that can store huge quantities of thermal energy in a small volume. Latent heat energy storage systems are complicated to design due to the low thermal conductivity of phase change materials for discharging to enhance the heat capacity and latent heat storage. The objective of the study is to examine the discharging of phase change material in a latent heat energy storage system for maintaining the temperature of the water. Paraffin wax utilized as the phase change material due to its higher latent heat capacity. The experiments were performed with the flow of the hot water through a phase change material container by using a copper tube to enhance the discharging of phase change material during solidification to maintain the temperature of the water. Furthermore, the steatite nanoparticle has been dispersed with phase change material to enhance the discharging of characteristics. The steatite nanoparticle has been selected due to its low thermal conductivity, and the weight percentages nanoparticles were varied viz. 10 %, 20 %, 30 %, and 40 %. The increase in water temperature from 0.1 °C to 1 °C has been taken 7 h by enhancing the discharging of phase change material with various concentrations of the steatite nanoparticle. The work shows the significant discharging characteristics of phase change material with steatite nanoparticles. The nano-phase change material has the potential to maintain the temperature of water without any external energy for a particular duration, which shows cost-effectiveness.

Numerical investigation of the impact of toothed fins on the heat transfer performance of a shell-and-tube exchanger during phase change material melting process

The poor thermal conductivity of phase transition materials hampers the development of latent heat energy storage devices. There is much scholarly interest in enhancing heat transmission in these materials. Using a finned shell-and-tube exchanger is a traditional strategy for improving the effectiveness of latent thermal energy storage devices. However, the storage systems' actual working volume decreases when many fins are added. Numerous studies have shown that toothed fins are more efficient in transferring heat than regular fins. As a result, it is anticipated that toothed fin latent heat energy storage systems will produce better thermal effects. Unfortunately, the impact of toothed fins on the melting of phase transition materials has only been briefly discussed in published literature. To close this important knowledge gap, this paper thoroughly studies two regularly used fins, namely the annular fin and longitudinal fin with toothed apertures. The impact of different toothed-opening volumes and tooth spacing on the melting process of phase transition materials are examined using numerical simulations. The results show that toothed fins have a 20% lower fin volume than traditional circular and longitudinal fins, which has a marginally less positive impact on phase change material melting times of 1.09% and 0.98%, respectively. The recommended toothed-opening volume and tooth count for the annular fin are 10%–20% and 16 teeth, respectively, whereas the recommended toothed-opening volume and tooth spacing for the longitudinal fin are 10%–20% and 1 mm, respectively. Additionally, the tooth spacing affects heat transfer, in one investigation, decreasing the tooth spacing by 2.5 and 2 times led to reductions in the melting periods of phase change materials of 60 and 70 s, respectively.

Analysis of the discharging process of latent heat thermal energy storage units by means of normalized power parameters

Many efforts are being made to mitigate the main disadvantage of most phase change materials – their low thermal conductivities – in order to deliver latent heat energy storage systems (LHESS) with adequate performance. However, the effect of applied methods is difficult to compare as they are mostly tested for different storage types and sizes and/or different boundary and initial conditions, which hinders rapid progress in the optimization of these approaches. In this work, a previously developed method for comparing the performance of LHESS is applied to experimental results of different storage systems under different conditions and subsequently analyzed and further refined. The main idea of the method is to normalize the power with the volume and a reference temperature difference and compare its mean value plotted over the normalized mean capacity flow of the heat transfer fluid (HTF). This enables the presentation of the results in a compact and easily comparative way. Attention has to be paid when it comes to the choice of the reference temperature difference, the reference volume and the method for calculating the mean value. Two variants of calculating the mean value (time-weighted and energy-weighted) and two variants of reference temperatures for determining the temperature difference to the inlet temperature of the HTF (initial temperature and melting temperature) are applied and discussed in detail. While the method significantly increases the comparability of results, none of the options listed above are without drawbacks. Approaches are shown to reduce or eliminate these drawbacks in the future. The recommendation for comparing different LHESS under different conditions is to use the method described here and clearly state the chosen reference temperature, reference volume and method for calculating the mean value.

Numerical validation and assessment of vertical and horizontal latent heat energy storage system during a melting process

Passive enhancement techniques have been widely adopted in thermal energy storage applications such as the phase change material (PCM) based latent heat energy storage systems to improve the thermal performance of these systems with minimal complexities. Recent studies have shown high interest in investigating the effect of different system orientations as a passive technique to improve the performance of thermal energy storage systems. This paper, thus, seeks to fill the research void in developing a numerical model that can be applied to assess the thermal effectiveness of the vertical and horizontal LHESS as a heat exchanger in addition to the melting dynamics of the PCM. This paper discusses a detailed numerical investigation using Computational Fluid Dynamics (CFD) simulation that was developed based on an experimental study. This paper displayed the numerical validation of the temperature profiles and heat exchanger effectiveness of both vertical and horizontal LHESS with insight into behaviour of the phase change material within the systems. The simulation results displayed the trends of the temperature profile and effectiveness were well captured against the experimental study. The numerical model displayed that the horizontal LHESS was more thermally effective than the vertical LHESS which was attributed to its superior free convective heat transfer behaviour and transient supply temperature of the heat transfer fluid. The horizontal LHESS reduced the PCM melting duration by 23 %, 13.3 %, and 33.3 % in comparison to the vertical LHESS for the HTF flow rates of 1.4, 0.7, and 0.35 l/min, respectively. It was observed that at all HTF flow rates, the rate of melting at the horizontal LHESS slowed down after approximately 85 % of the PCM have been melted which was caused by the absence of natural convection, resulting in the remaining PCM to melt mainly by conduction.

Influence of different rotational speeds of inner and outer tubes on phase change heat storage: An optimization study

The implementation of the solar phase change heat storage evaporation heat pump system with a latent heat energy storage system has shown promising potential in enhancing solar heating and facilitating the efficient utilization of solar energy. Nevertheless, the utilization of a heat storage medium phase change material with low thermal conductivity in the latent heat energy storage system has hindered its broad-scale application. This present study focuses on a triplex-tube latent heat energy storage unit with N-eicosane serving as the phase change material. A subzone rotation strategy has been developed to improve the melting properties of the unit, and a numerical model of the energy storage unit has been constructed and authenticated. The Taguchi method has been utilized to examine the effect of inner tube speed, outer tube speed, and fin/wall material on melting properties, and the interaction between control variables has been scrutinized. The research findings indicate that the optimized structure, according to the Taguchi method, significantly shortens the melting time by 26.22%, and increases the average rate of temperature response and average heat storage rate by 22.98% and 32.39%, respectively. It should be noted, however, that there is a certain decrease in the total heat absorption during the melting period. By examining the internal dynamic temperature/velocity response, this study displays that the augmentation of the rotation speed in the zone improves the overall convective intensity and heat transfer performance in the unit.

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.

Solidification acceleration of phase change material in a horizontal latent heat thermal energy storage system by using spiral fins

One important solution for societies to overcome the energy crisis is to manage the production and storage of energy. In this regard, the latent heat energy storage systems have recently gained a remarkable attention. Hence, this work is devoted to enhance performance of a latent heat tube-shell storage system by using novel spiral fins with different geometrical characteristics. Different number of vanes have been employed on the fins with constant twisting pitch. The different cases studied include the cases with single-fin, double-fin, triple-fin and quadruple-fin. These fins have been employed to augment heat transfer from a low temperature fluid to the PCM inside the shell container during the solidification process. To model the phase change, the enthalpy-porosity technique has been adopted. Various parameters have been used to assess the functionality of the system including the Nusselt number, total solidification time, temperature, solid fraction evolution, solid fraction contours, temperature contours and etc. The results demonstrated that the triple-fin and double-fin cases took the advantage in heat transfer augmentation and discharging process while the case with single-fin showed the worst performance. The results indicated that fin number is not the only influencing factor and fin length also has a dominant role.

연소시스템 화석연료 사용량 저감을 위한 잠열에너지저장 기술동향 연구: Part II 상변화물질의 열전달 특성과 열교환기 설계유형, 실증사례

Following the publication of Part 1, Part 2 focuses on the development trends of key element technologies associated with heat transfer characteristics. Previous research focused on methods to overcome low thermal conductivity, and various heat exchanger design methods have been proposed to improve this using solid media such as fins or additives such as carbon particles. In addition, the operation method for optimal performance, when the latent heat energy storage system is connected to the main combustion system, is discussed. Finally, demonstration research cases, which are being conducted in Germany and Korea, are introduced to discuss the current status and future direction of this technological development in combined heat and power, and steam generation. In Korea, R&D for a latent heat energy storage system, through waste heat recovery, is an ongoing national project and is scheduled to be demonstrated in 2025. Projects involved in high-temperature latent heat energy storage technology to reduce carbon emissions, by reducing the direct use of fossil fuels, are currently ongoing.

Application and analysis of flip mechanism in the melting process of a triplex-tube latent heat energy storage unit

In order to improve the characteristics of uneven melting in the melting process of the horizontal latent heat energy storage system, the triplex-tube latent heat energy storage unit is taken as the research object, and the flip mechanism is applied to its melting process. Numerical simulation is used for the research, and the numerical model is verified by experimental data. The results show that under different dimensionless times, the melting performance of the unit can be significantly improved by a single flip. When the dimensionless time is 0.4576, it is found that the total melting time of the unit is reduced by 16.17 %, the average heat absorption rate is increased by 14.7 %, but the total heat energy absorption is reduced by 3.85 %. The results show that the addition of a flip can effectively shorten the melting time and increase the heat absorption rate, but it has a negative effect on the total heat absorption in one melting cycle. Moreover, through the comparison of dynamic flow rate, dynamic temperature response, and temperature interval, it is shown that the addition of flip effectively reduces the negative influence of the hard-to-melt zone on the melting performance of the unit during the melting process. The flip mechanism reduces the proportion of high-temperature phase change material in the melting process and makes the melting process more uniform.

Improved Performance of Latent Heat Energy Storage Systems in Response to Utilization of High Thermal Conductivity Fins

Analytical, computational and experimental investigations directed at improving the performance of latent heat thermal energy storage systems that utilize high thermal conductivity fins in direct contact with phase change materials are reviewed. Researchers have focused on waste heat recovery, thermal management of buildings/computing platforms/photovoltaics/satellites and energy storage for solar thermal applications. Aluminum (including various alloys), brass, bronze, copper, PVC, stainless steel and steel were the adopted fin materials. Capric-palmitic acid, chloride mixtures, dodecanoic acid, erythritol, fluorides, lauric acid, naphthalene, nitrite and nitrate mixtures, paraffins, potassium nitrate, salt hydrates, sodium hydrate, stearic acid, sulfur, water and xylitol have been the adopted fusible materials (melting or fusion temperature Tm range of −129.6 to 767 °C). Melting and solidification processes subject to different heat exchange operating conditions were investigated. Studies of thawing have highlighted the marked role of natural convection, exhibiting that realizing thermally unstable fluid layers promote mixing and expedited melting. Performance of the storage system in terms of the hastened charge/discharge time was strongly affected by the number of fins (or fin-pitch) and fin length, in comparison to fin thickness and fin orientation. Strength of natural convection, which is well-known to play an important role on thawing, is diminished by introduction of fins. Consequently, a designer must consider suppression of buoyancy and the extent of sacrificed PCM in selecting the optimum positions and orientation of the fins. Complex fin shapes featuring branching arrangements, crosses, Y-shapes, etc. are widely replacing simple planar fins, satisfying the challenge of forming short-distance conducting pathways linking the temperature extremes of the storage system.