Phase Change Materials Research Papers (original) (raw)

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- Computational Fluid Dynamics, Solidification, Applied Sciences, Phase Change Materials
- by dharam buddhi
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- Engineering, Environmental Science, Economics, Energy Conservation

This study presents the experimental results of concrete bricks based macroencapsulated phase change material (PCM) in different capsule designs (circular, square and rectangular cross-sections). Eight concrete bricks (including a reference brick without PCM) are fabricated, and their thermal performance is tested under hot summer conditions of Al Amarah city, Iraq. The study considered several indicators such as the interior maximum temperature reduction (MTR), decrement factor (DF) and time lag (TL) to compared among tested bricks in addition to the thermal behaviour during melting and solidification of PCM. Results indicated that all PCM based bricks are performed better than the reference brick in which the maximum interior temperature is shaved and shifted. Moreover, the best thermal performance is reported for bricks of large PCM capsules number. Amongst others, the brick-based square cross-section PCM capsules showed the best thermal contribution where the average MTR of 1.88 • C, average DF of 0.901 and average TL of 42.5 min were obtained compared with the reference brick. The study concluded that PCM capsules' heat transfer area is the main parameter that controls PCM's thermal behaviour as long as all PCM capsules have the same PCM quantity and position. Therefore, excessive encapsulation area might influence the thermal performance of concrete brick and should be specified for the efficient use of PCM storage capacity.

- by Qudama Al-Yasiri and +1
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- Thermal Engineering, Sustainable Building Design, Sustainable Building Materials, Energy Efficiency in Buildings

• Core-sheath CNT@PC with 3D network structure was synthesized. • The carbon sheath was conductive to the stability of network structure. • The CNTs provide heat transfer paths for ss-PCMs. • The hierarchical porous carbon sheath reduced interfacial thermal resistance. • The ss-PCMs exhibited excellent thermal storage capability (up to 99.9%). A B S T R A C T Energy storage capacity and heat transfer ability are two important indexes for shape-stabilized phase change materials (ss-PCMs). In this paper, a core-sheath CNT@PC was prepared via carbonation of CNT@ZIF-8, simultaneously 3D structural supports were obtained due to the porous carbon (PC) sheath stabilized the CNT@PC network structure. Porous carbon (PC), derived from carbonized metal organic frameworks (MOFs), exhibited high porosity and large specific surface area. PCMs, absorbed by capillary force of porous structure, was stabilized in the pores of PC sheath. Further, the interaction between PCMs and CNTs reduced the interfacial thermal resistance greatly. Carbon nanotubes (CNTs), acting as heat transfer pathways, provided continuous channels for phonons transfer and realized rapid heat transformation between ss-PCMs and external environment. The obtained SA/CNT@PC ss-PCMs exhibited excellent thermal conductivity (1.023 W/mK), large phase change enthepy (155.7 J g −1) and high thermal storage capabilities (99.9%). The thermal conductivity of SA/ CNT@PC was improved 222.6% and phase change enthalpy was increased 92.6% over SA/PC ss-PCM. SA/ CNT@PC with large energy storage density, flexible designation, simple operation and near-constant temperature properties during phase change process shows great potential in waste heat utilization.

- by Xiao Chen
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- Phase Change Materials, Thermal Conductivity, Carbon Materials

Using phase change materials (PCMs) for thermal energy storage is an effective technique of energy management to address the mismatch problems between energy supply and demand. Shape-stabilized composite PCMs could efficiently solve their leakage problem during the solid-liquid phase change process, which have been widely used and extensively reviewed in literature. However, those reviews mainly focused on microencapsulated PCMs and the broad properties and applications of composite PCMs but paid little attention to the nanoporous shape-stabilized composite PCMs. The nanoporous shape-stabilized composite PCMs do solve the leakage problem and show excellent chemical stability and thermal cycling stability, but most of their enthalpy values were much lower than that of the pure PCMs component. So in this review we have highlighted recent progress in the research of nanoporous shape-stabilized PCMs, such as the design concept of porous support, fabrication and characterization techniques, and especially the nanoconfinement effects of the porous support on the thermal properties of the PCMs confined in the nanopores. Finally, we have provided a brief outlook of the future challenges and potential prospects of nanoporous shape-stabilized composite PCMs. This review paper will help to explore and develop better nanoporous shape-stabilized composite PCMs for practical applications and offer basic understanding of nanoconfinement effects on thermal properties.

- by Xiao Chen
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- Phase Change Materials, Thermal Energy Storage
- by Ron Warzoha
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- Thermal Engineering, Heat Transfer, Solar Energy, Graphite
- by Christine Labrugère and +3
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- Inorganic Chemistry, Crystallography, Phase Transformations, Crystal Growth

Melamine formaldehyde microcapsules containing paraffin wax as phase change material (PCM) were synthesized. Free space was generated in-situ inside microcapsules. These were characterized by FTIR Spectrophotometer, Scanning electron microscope (SEM), Differential Scanning colorimeter (DSC), and optical microscope. It was confirmed that PCM was successfully encapsulated inside the shell material. Encapsulated PCM showed good phase change properties during heating and cooling. Enthalpy value of about 100 J/g was observed. The shape of the microcapsule, showing rough morphology is expected to help during processing and crystallization. It has been experimentally confirmed that no leakage occurs during the melting of PCM. Effectiveness in temperature control in a hot environment was also found to be satisfactory.

- by asit samui
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- Management, Microencapsulation, Phase Change Materials, Melamine Formaldehyde Resin

A combination of heat transfer augmentation techniques is highly necessary to enhance the performance of Thermal Energy Storage (TES) systems employed in a wide range of applications. The major issue is that many of the Phase Change Materials (PCMs) possess low thermal conductivity (k ≤ 0.2 W/m K), resulting in an inefficient melting process. Triplex Tube Heat Exchanger (TTHX) based TES system is both numerically and experimentally studied using Paraffin (RT82) with Alumina (Al 2 O 3) nanoparticles that has a charging temperature in the range of 78.15-82.15 ∘ C. The experimental findings indicate that the Paraffin is not completely melted within the required time of four hours for the inside heating method at 97 ∘ C. The Paraffin is successfully melted for both sides heating at 90 ∘ C in lesser time and average temperature than the outside heating. With different charging temperatures, the Paraffin melting was consumed a short time for the non steady state at the mass flow rate of 29.4 kg/min, compared with the 16.2 and 37.5 kg/min for inner and outer tubes. Other outcomes were that with the fins-nanoparticle combination, an improved performance for melting the Paraffin, compared with those that occurred without nanoparticle. Furthermore, in the numerical study, compared with the pure Paraffin case, the melting time was minimized for TTHX with longitudinal fins (12%) and TTHX with triangular fins (22%) for the PCM having 10% nanoparticle, respectively. Close agreement is found between the numerical and experimental findings.

- by Hakeem Niyas
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- Heat Exchanger, Phase Change Materials, Heat transfer enhancement

Fundamental principles of science are now increasingly employed for the manufacturing of innovative textile products. One such principle is 'Phase Change', the process of going from one physical state to another i.e. from a solid to a liquid. Substances that undergo the process of Phase Change are better known as Phase Change Materials (PCMs). These materials store, release or absorb heat as they oscillate between solid and liquid form. They give off heat as they change to a solid state and absorb as they return to a liquid state. The three fundamental phases of matter solid, liquid, and gas are known, but others are considered to exist, including crystalline, colloid, glassy, amorphous, and plasma phases. A study conducted by NASA identified more than hundred of these materials. Some of these PCMs change phases within a temperature range just above and below human skin temperature. Since the process of phase change is dynamic, the materials are constantly changing from a solid to a liquid and back depending upon level of physical activity of the body and outside temperature. It is important for persons to keep protected from the elements in a suddenly changing climatic condition such as flying high or climbing mountain peaks. Usual dressing with bulky layers of woolens and overheating of body, It has been found that layering with garments with auto thermal regulation can help lighten the load and increase human efficiency by keeping the temperature of the body constant.

- by GOPALAKRISHNAN DURAISAMY
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- Phase Change Materials
- by Ron Warzoha
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- Thermal Engineering, Nanofibers, Heat Transfer, Nanocomposites

This work aims to investigate the solidification behavior of de-ionized (DI) water as the base phase change material (PCM) dispersed with various mass fractions of sodium chloride and D-sorbitol in a spherical encapsulation. The DSC analysis of water illustrated that subcooling of DI water increases with respect to cooling rate due to inadequate time to complete the crystallization. The solidification experiments were carried out at a bath temperature of −7 °C and DI water undergoes a subcooling of −5.4 °C. However, the subcooling substantially reduced to −2.8 °C for DI water with 0.5 wt. % sodium chloride and 1 wt. % of D-sorbitol. Accelerated mode of charging prevails in all the PCM samples and the innermost 6% of volume got solidified in decelerated mode. The cooling rate is found to decrease with respect to increase in concentration of the dispersants in subcooling region, but at a particular concentration both dispersants provide the enhanced cooling rate for a given driving potential than DI water. It is concluded that reduction of subcooling and partial charging of water based PCMs would be helpful to enhance the energy efficiency of the cool thermal energy storage (CTES) system.

Latent heat storage (LHS) using phase change materials (PCMs) in the form of encapsulated capsules are recently used in steam accumulators for reducing the pressure drop during the discharge of steam. Due to high thermal resistance offered by the PCM in capsules with a larger diameter, more number of smaller diameter capsules need to be used for meeting the required storage capacity. In the present study, a novel heat-transfer enhancement technique consists of tube-in-tube LHS system with a very small inner tube is proposed for effective heat transfer in cylindrical LHS capsules. With this technique, less number of capsules can yield the similar or higher storage capacity in a comparatively lesser charging/discharging time. A numerical model is developed to study the performance characteristics of the proposed novel heat-transfer enhancement technique. For comparing the performance characteristics of the basic and the proposed novel heat-transfer enhancement technique , capsules having a LHS capacity of 0.5 MJ are considered. Sodium nitrate and SS304 are selected as the PCM and encapsulating material. In the numerical model, the effective heat capacity method is applied to consider the latent heat of the PCM and Boussinesq approximation is used to include the natural convection of the molten layer of the PCM. Numerically predicted melt fraction values during the charging process match well the experimental data reported in the literature. Various storage performance parameters such as charging/ discharging time, energy storage/discharge rate and melt fraction are evaluated for basic/novel capsule and a comparison is made between them. For the given operating conditions, basic/novel LHS capsule complete the charging and discharging processes around 64/33 min and 158/57 min, respectively. A commercial viability study is also done on the proposed novel concept and the results showed that the novel LHS capsule has promising features for commercialization.

- by Ron Warzoha
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- Thermal Engineering, Renewable Energy, Energy, Heat Transfer

The solid solutions of bismuth–vanadate were prepared by the conventional solid-state reaction. The sample characterization and the study of phase transition were done by using FT-IR, X-ray diffraction (XRD) and DSC measurements. AC impedance measurements proved that the oxide ion conductivity predominantly arises from the grain and grain boundary contributions as two well-defined semicircles are clearly seen along with an inclined spike. The electrical conductivity of Bi2O3–V2O5 has been studied at different temperatures for various molar ratios. The isothermal conductivity increases with an increase in the concentration of V2O5 due to the vacancy migration phenomenon. It has been found that the conductivity of different compositions of Bi2O3–V2O5 increases and shows a jump in the temperature range 230–260°C due to the phase transition of BiVO4 from monoclinic scheelite type to that of tetragonal scheelite type. The endothermic peak in DSC at around 260°C reveals the phase transition, which is also confirmed by the XRD and FT-IR analysis. The XRD patterns confirmed the monoclinic structure of BiVO4.

- by Niyazi Al-Areqi
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- Phase Change Materials, Electrical Conductivity, Oxides

In this paper, the effects of pure water, SiO2/water nanofluid, and a phase-change material (PCM) as coolants on the performance of a photovoltaic thermal (PVT) system are numerically investigated. The simulations are performed on two modules of PVT with PCM (PVT/PCM module) and without (PVT module). Parameters including PV surface temperature, thermal, and electrical efficiencies of the systems are studied and compared with each other. Moreover, the results of nanofluid as a working fluid is compared with those obtained using pure water. The results show that in the water-based PVT/PCM, the average PV cell temperature is decreased by 16 °C compared to that of the PVT system. This results in an increase of 8% in the electrical efficiency and 25% in the thermal efficiency. In addition, using nanofluid (SiO2 with 1 and 3 mass% mass fraction) as a coolant in the PVT/PCM system increases the thermal efficiency by 3.51% and 10.40%, for 1 and 3 mass%, respectively, compared to that of the PVT/PCM with pure water as a coolant. This study shows that increasing the melting temperature of the phase-change material leads to an increase in the thermal efficiency of the PVT/PCM system.

- by Amin Farzanehnia and +1
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- Photovoltaics, Renewable Energy, Energy efficiency, Nanofluids

A latent heat storage system for concentrated solar plants (CSP) is numerically examined by means of CFD
simulations. This study aims at identifying the convective flows produced within the melted phase by
temperature gradients and gravity. Simulations were carried out on experimental devices for applications
to high temperature concentrated solar power plants. A shell-and-tube geometry composed by a vertical
cylindrical tank, filled by a Phase Change Material (PCM) and an inner steel tube, in which the heat trans-
fer fluid (HTF) flows, from the top to the bottom, is considered. The conjugate heat transfer process is
examined by solving the unsteady Navier–Stokes equations for HTF and PCM and conduction for the tube.
In order to take into account the buoyancy effects in the PCM tank the Boussinesq approximation is
adopted. The results show that the enhanced heat flux, due to natural convective flow, reduce of about
30% the time needed to charge the heat storage. A detailed description of the convective motion in the
melted phase and the heat flux distribution between the HTF and PCM are reported. The effect of the
mushy zone constant is also investigated.

- by Francesco Fornarelli and +4
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- Shell and tube heat exchanger design, Phase Change Materials, Thermal Energy Storage, Concentrated Solar Power

The energy industry needs to take action against climate change by improving efficiency and increasing the share of renewable sources in the energy mix. On top of that, refrigeration, air-conditioning, and heat pump equipment account for 25–30% of the global electricity consumption and will increase dramatically in the next decades. However, some waste cold energy sources have not been fully used. These challenges triggered an interest in developing the concept of cold thermal energy storage, which can be used to recover the waste cold energy, enhance the performance of refrigeration systems, and improve renewable energy integration. This paper comprehensively reviews the research activities about cold thermal energy storage technologies at sub-zero temperatures (from around −270 °C to below 0 °C). A wide range of existing and potential storage materials are tabulated with their properties. Numerical and experimental work conducted for different storage types is systematically summarized. Current and potential applications of cold thermal energy storage are analyzed with their suitable materials and compatible storage types. Selection criteria of materials and storage types are also presented. This review aims to provide a quick reference for researchers and industry experts in designing cold thermal energy systems. Moreover, by identifying the research gaps where further efforts are needed, the review also outlines the progress and potential development directions of cold thermal energy storage technologies.

In this study, the performance of six Phase Change Material (PCM) gypsum wallboards was evaluated in an office room. Several EnergyPlus simulations were performed after validating the model using real measured data in the office. Using simulation results, it was analyzed how PCM wallboards should be incorporated in an office. Four different parameters were considered: PCM melting temperature, wallboard location, PCM quantity and night ventilation (office air renewal). It was concluded that for an office in Lisbon or in Faro, a PCM that melts at around 26 ºC should be selected and the wallboards must be installed as internal mass. For an office in Bragança, PCM wallboards should be incorporated as a layer of external walls. Night ventilation should promote at least 11 air changes per hour to take full advantage of PCM. In Lisbon, incorporating PCM wallboards correctly reduces annual heating and cooling needs in 15.1%. Experimental results showed that PCM wallboards suspended in the ceiling can reduce the maximum interior air temperatures in almost 1 ºC. Considering the actual cost (40 €/m2) of the wallboards, very large payback periods were obtained for all cities, showing that incorporating PCM wallboards under these conditions is economically not viable.

- by Engineer Ali H Almaily
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- Phase Change Materials

This paper presents a review of thermal storage media and system design options suitable for solar cooling applications. The review covers solar cooling applications with heat input in the range of 60– 250 1C. Special attention is given to high temperature (4 100 1C) high efficiency cooling applications that have been largely ignored in existing reviews. Sensible and latent heat storage materials have been tabulated according to their suitability for double effect and triple effect chillers. A summary of system designs for water storage (sensible heat), and phase change material storage (latent heat) has been provided. The article summarizes literature related to solar thermal airconditioning systems from a material level as well as plant level considerations. This includes evaluating various control strategies for managing the thermal store, that aid in optimal functioning of a solar air conditioning plant. Modeling approaches are reviewed for sizing the solar thermal store, highlighting the large difference seen in specific storage size when applied in different applications.

A latent heat storage system for concentrated solar plants (CSP) is numerically examined by means of CFD simulations. This study aims at identifying the convective flows produced within the melted phase by temperature gradients and gravity. Simulations were carried out on experimental devices for applications to high temperature concentrated solar power plants. A shell-and-tube geometry composed by a vertical cylindrical tank, filled by a Phase Change Material (PCM) and an inner steel tube, in which the heat transfer fluid (HTF) flows, from the top to the bottom, is considered. The conjugate heat transfer process is examined by solving the unsteady Navier–Stokes equations for HTF and PCM and conduction for the tube. In order to take into account the buoyancy effects in the PCM tank the Boussinesq approximation is adopted. The results show that the enhanced heat flux, due to natural convective flow, reduce of about 30% the time needed to charge the heat storage. A detailed description of the convective motion in the melted phase and the heat flux distribution between the HTF and PCM are reported. The effect of the mushy zone constant is also investigated.

- by Marco Torresi
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- Engineering, Materials Science, Economics, Shell and tube heat exchanger design

Self-cleaning properties have received significant attention for the importance of their potential. Coatings at Nano-scales offer possibilities of using materials for self-cleaning surfaces. Recent efforts have begun to focus on the kinds of materials including metals, semiconductors and polymers. Such materials can have enormous potential in only a few applications. Moreover, the production of these materials requires high costs with low photo activity. In this regard, TiO 2 and its derived materials have shown acceptable and effective suggestions for this application. Moreover, the mechanism of self-cleaning has been explained by the effect of hydrophilic and hydrophobic. Hydrophilic and hydrophobic can have many applications in different areas like water purification, microfluidics and photovoltaic. In this review, the application of self-cleaning in solar cells and environment as well as TiO 2 derived materials and their applications in water management have been briefly illustrated. In addition, it has been explained that a huge number of self-cleaning materials, applications and improvement in utilities have been essential. In short, we have conducted a comprehensive review of the new approach and to mention numerous materials with hydrophobic and hydrophilic properties would be promising for most environmental concerns. Bio-inspired surface respond in nature through hydrophobic (Cicada Wing, Butterfly Wing, Lotus Leaf, Rice Leaf) and hydrophilic (Fish Scale, Snail Shell, Shark Skin) properties was divided in 4 and 3 respectively. Anti reflective coatings with self-cleaning properties have drowned considerable attention for both their basic appearances and vast applied usages. Antireflective coatings with self-cleaning properties have been considered because of their fascinating features and vast diversity of empirical uses.

A significant amount of heat is wasted in electricity general, manufacturing, chemical and industrial process. Recovery and reuse of this energy through storage can be useful in conservation of energy and meeting the peak demands of power. A shell and spiral type heat exchanger has been designed and fabricated for low temperature industrial waste heat recovery using phase change material. Paraffin wax (Melting Point 54 o C) was used as storage media due to its low cost and large-scale availability in Indian market. Experiments were performed for different mass flow rates and inlet temperature of heat transfer fluid for recovery and use of waste heat. The effect of mass flow rate on the performance of the system was studied. Calculations for overall heat transfer during charging (melting of PCM) and discharging (solidification of PCM) and heat discharging efficiency were also made.

- by GRD JOURNALS
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- Phase Change Materials, Paraffin Wax, Charging, Discharging
- by Yvan Dutil
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- Phase Change Materials

Globally there is profuse literature on the continuous developments of solar based thermal storage system. The performance characteristics of a solar based thermal storage system can be effectively improved by using circulating fluid in different types and content. Abundantly available solar energy utilization for domestic and industrial applications is hindered because of its intermittent nature. The thermal energy storage (TES) system using both sensible and latent heat has many advantages like large heat storage capacity in a unit volume and its isothermal behavior during the charging and discharging processes. In the present literature the efforts have been made to focus on diverse development of solar energy based thermal storage till now. The rural and urban population, depend mainly, on non-commercial fuels to meet their energy needs. Solar cooking is one possible solution but its acceptance has been limited partially due to some barriers. Solar cooker cannot cook the food in late evening. That drawback can be solved by the storage unit associated with in a solar cooker. So that food can be cook at late evening. Therefore, in this paper, an attempt has been taken to summarize the investigation of the solar cooking system incorporating with phase change materials (PCMs). Thermal energy storage system plays a critical role in developing an efficient solar energy device. Many research works is being carried out to determine the suitability of thermal energy storage system to integrate with solar thermal gadgets. This review paper summarizes all the research and development work carried out in the field of solar cooker in particular the storage type solar cookers. A novel concept of PCM-based storage type solar cooker is also presented which is under experimental investigation.

- by RAME Publishers
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- Phase Change Materials, Solar Collector, Solar cooker, Thermal Storage System

The study presents an experimental investigation of a thermal energy storage vessel for load-shifting purposes. The new heat storage vessel is a plate-type heat exchanger unit with water as the working fluid and a phase change material (PCM) as the energy storage medium. The thermal characteristics of the heat exchanger such as heat transfer coefficient, effectiveness, efficiency, water exit temperature, heat storage rate, total energy storage capacity and storage time were experimentally evaluated as a function of various inlet conditions. The compact parallel plate design showed an enhanced the performance compared to conventional storage systems with an effectiveness up to 83.1% even when a PCM of low thermal conductivity is used. The proposed phase change energy storage system not only can deliver substantial benefits as a thermal energy storage medium, but also provides cost savings in infrastructure, equipment, and maintenance/operations compared to conventional systems.

- by Rami M Saeed and +1
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- Heat Exchanger, Small Modular Nuclear Reactors, Designing of Heat Exchangers, Phase Change Materials

The main disadvantage of phase change materials (PCM) is related to their low thermal conductivities. In this study, the melting and solidification of a PCM within three various horizontal annulus configurations including two circular cylinders, one elliptical cylinder in a circular cylinder and one finned cylinder in a circular cylinder are investigated numerically in terms of the aspect ratio and the orientation of the ellipse and the number of fins. Different volume fractions of the copper nanoparticles are added to the base PCM to examine the effect of nano-particles on the heat transfer rate. Results indicate natural con-vection plays important roles in the melting process where the melting rate at the bottom section of the annulus is lower than that at the top section. By using the vertical-oriented tube instead of the circular one the melting rate increases. Adding nanoparticles to the base PCM enhances the melting and solidifi-cation rate as well. However, it does not eliminate the stable heat transfer at the bottom section of the annulus. Inserting fins leads to the significant enhancement of the melting and solidification rate. It is more efficient during the solidification process due to the suppression of the natural convection effect during the melting process.

- by Mahmoud Jourabian
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- Phase Change Materials

Moisture content in biomass is one of the major reasons for drop in power generation efficiency in biomass based power plants. Removal of this moisture is a major challenge especially during monsoon and winter. A design is proposed to achieve moisture reduction in minimum time by using waste heat recovery approach. A fluid bed (which can store heat) is continuously heated by exhaust flue gas from the biomass plant. This warm bed is used as a moisture removal system. Analysis of this system with various fluids will be carried out to obtain optimal results using COMSOL software. A special arrangement of a high resistance fluid packet with a static cylinder is used in the flow path of flue gas to study flow pattern and gas penetration which will help us estimate the work potential of exhaust flue gas from the system and corroborate with thermodynamically obtained analytical values.

- by Amrit Om Nayak
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- Thermal Engineering, Computational Fluid Dynamics, Renewable Energy, Biomass
- by D. Yogi Y Goswami
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- Phase Change Materials, Thermal Energy Storage
- by Amrit Om Nayak
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- Phase Change Materials

Finding a solution to store industrial wasted heat for later use in order to reduce energy usage has been on the rise in recent years. This paper investigates the capability of latent heat TES (Thermal Energy Storage) system using PCM (Phase Change Material) to store/release a large amount of energy in a small volume compared to sensible heat TES system. In this work, the issue of the low conductivity of PCMs has been addressed by using an embedded finned water-charged heat pipes into the PCM bulk. Both heat pipes and the PCM tank used in this investigation were made of 316 L stainless steel. The PCM used in this work was PLUSICE S89, which has a melting temperature of 89 C and crystallization point of 77 C. The evaporator section of the heat pipe was heated by condensing a steam flow. The heat that was absorbed in the evaporator section was then discharged to the PCMs by the heat pipe multi-legged finned condenser. Tests were conducted for both charging (melting) and discharging (crystallization) of PLUSICE S89. It was observed that the thermal resistance posed by PCM during the discharging stage was higher compared to that during the charging process.

- by Hussam Jouhara
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- Heat Pipes, Phase Change Materials, Steam Condenser

Solid-solid phase change materials (SS-PCMs) for thermal energy storage have received increasing interest because of their high energy-storage density and inherent advantages over solid-liquid counterparts (e.g., leakage free, no need for encapsulation, less phase segregation and smaller volume variation). Four main SS-PCMs for thermal energy storage are reviewed, with a focus on their thermal properties and the relationship between molecular structure, processes involved during phase transition, and thermal properties. This review aims to provide guidance for selecting appropriate SS-PCMs for various applications and tailoring the synthesis of SS-PCMs with desired thermal, physical and mechanical properties. Challenges and opportunities to use of SS-PCMs for thermal storage and other applications are also discussed.

- by Sergio Granados
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- Phase Change Materials, Thermal Energy Storage

This paper presents the performance tests carried out on a lab-scale latent heat storage (LHS) prototype during charging and discharging processes. The storage unit is a shell-and-tube type heat exchanger with embedded finned tubes, designed for an LHS capacity of 10 MJ. A ternary mixture comprising of potassium nitrate, sodium nitrate and sodium nitrite in the weight proportion of 53:7:40 is used as the phase change material (PCM). Hi-Tech Therm 60 is used as the heat transfer fluid (HTF). Performance parameters viz., melt fraction, charging/discharging time and energy storage/discharge rate were evaluated at different operating conditions. The effects of HTF inlet temperature and flow rate on the storage characteristics of LHS prototype were analyzed. It is observed that the temperature variation in the angular direction of the prototype during charging process is significant. This is due to the natural convection heat transfer that occurred around the molten layer of PCM while melting. During the discharging process, the angular temperature variation is negligible as the solidification phenomenon is controlled mainly by the conduction heat transfer. It took about 124 min/131 min for charging/discharging of the LHS prototype.

- by Hakeem Niyas and +1
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- Solar thermal, Phase Change Materials, Thermal Energy Storage, Heat transfer enhancement
- by Nizar Ben salah and +2
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- Engineering, Numerical Analysis, Sustainable Energy, Power System Economics

A latent thermal energy storage system, which consists of sodium nitrate filled spherical capsules in a cylindrical tank, is analyzed for concentrating solar power plant applications. The high temperature synthetic oil, Therminol 66, is used as heat transfer fluid. A numerical model is developed to investigate the behavior of the system. The developed model is validated using the reported experimental and numerical data. The influence of capsule size and the flow rate of heat transfer fluid (HTF) on the temperature distribution, fluid flow, melting and solidification of the system is studied. The natural convection effect present in the liquid region during melting is resolved by the effective thermal conductivity, which is calculated by enthalpy formulation method. The results indicated that the heat transfer rate is increased and eventually the charging/discharging time is decreased when the capsule size is decreased, or the HTF flow rate is increased.

- by D. Yogi Y Goswami
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- Phase Change Materials, Thermal Energy Storage
- by Suman Jha
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- Renewable Energy, Heat Transfer, Solar Energy, Differential scanning calorimetry

This study designed, tested, and evaluated an experimental energy storage system that uses a horizontal triplex tube heat exchanger (TTHX) with internal longitudinal fins incorporating phase-change material (PCM), with melting point in the range of 78.15–82.15 °C. The PCM did not entirely melt within the charge time (4 h) for the inside heating at 97 °C. The PCM melting for both-sides heating was successfully accomplished at 90 °C in lesser time than the outside heating method. The changes in the mass flow rates of 16.2, 29.4, and 37.4 min/kg on the PCM average temperature in the axial direction were investigated. The mass flow rate for the non-steady state at 29.4 kg/min consumed a short time to achieve PCM melting , compared with the 16.2 and 37.5 kg/min with different charging temperatures. However, two-types of extended surfaces, namely the longitudinal and triangular fins, were studied numerically. A significant enhancement was achieved using internal, internal-external, and external triangular fins at 11%, 12%, and 15% respectively, compared with the cases with longitudinal fins. Therefore, the external triangular finned tube has been considered the most efficient for the brief melting of PCM (193 min). The total energy stored capacities for the PCM with longitudinal and triangular fins were compared. The simulation agreed well with the experimental results.

- by Ammar M. Abdulateef
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- Thermal Engineering, Solar Energy, Phase Change Materials

Phase Change Materials (PCMs) have a high heat of fusion, which allows them to store and release large amounts of heat at a specific temperature. The inclusion of PCMs in buildings has attracted much interest worldwide due to their ability to reduce building energy consumption and increase comfort. This paper presents the results of an experimental investigation on the use of phase change materials (PCMs) in a concrete tile system. Concrete tiles, enhanced with microencapsulated PCM, were cast for use in a passive solar house developed for the Solar Decathlon China competition (Solatrium, Datong 2013). The concrete mix design and experimental results on the concrete’s strength and thermal properties are presented. It was found that the addition of the PCM reduces the overall compressive and flexural strength properties of the concrete. A more than 25% decrease in compressive strength was observed with the addition of 20% PCM, by volume of concrete. The most important benefit of adding PCM to concrete is the improved capacity to store latent heat. It was determined that a 3.8 cm thick concrete tile with 13.5% of PCM per volume of concrete has a thermal storage capacity equivalent to 10 cm of regular concrete. Results indicate that the use of PCM in concrete flooring tiles can significantly improve the thermal behavior of a lightweight building, while also keeping the concrete’s strength loss within an acceptable range.

This paper presents a new encryption scheme called Compact Coding that encodes information in time, phase, and intensity domains, simultaneously. While these approaches have previously been used one at a time, the proposed scheme brings to bear for the first time their strengths simultaneously leading to an increase in the secure information transfer rate. The proposed scheme is applicable to both optical fibers and free space optics, and can be considered as an alternative to polarization coding. This paper applies the proposed compact coding scheme to multi-photon tolerant quantum protocols in order to produce quantum-level security during information transfer. We present the structure of the proposed coding scheme in a multi-photon environment and address its operation.

A series of binary mixtures of Methyl Palmitate (MP) and Lauric Acid (LA) were prepared and investigated, aiming for potential phase change material (PCM) for thermal energy storage systems. The thermal analysis of the PCM binary mixtures was investigated by means of Differential Scanning Calorimetry (DSC). A theoretical and experimental determination of the eutectic mixture was established. The results indicated that the eutectic binary mixture of 60%MP and 40%LA has desirable properties of phase transition temperatures within the comfort temperature range (T m = 25.6 C, T f = 20.2 C) and high latent heat capacity (DH m = 205.4 J/g, DH f = 205.8 J/g). The paper experimentally studied the other important thermo-physical properties required for modelling and stimulating the PCM in any storage systems such as thermal conductivity, enthalpy curve, phase diagram, specific heat, thermal diffusivity, and density. The thermal stability test indicated that the eutectic mixture had reliable thermal performance upon thermal cycling. Based on all these results, the MP-LA eutectic mixture is a promising material for thermal energy storage.

- by Rami M Saeed and +1
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- Energy, Phase Change Heat Transfer, Phase Change Material, Phase Change Materials

In the current study, numerical analysis of the charging and discharging characteristics of a lab-scale latent heat storage (LHS) prototype is presented. A mathematical model is developed to analyze the performance characteristics of the LHS prototype of shell and tube heat exchanger configuration. Effective heat capacity (EHC) method is implemented to consider the latent heat of the phase change material (PCM) and Boussinesq approximation is used to incorporate the buoyancy effect of the molten layer of the PCM in the model. For proper modeling of velocities in the PCM, Darcy law's source term is added. The governing equations involved in the model are solved using a finite element based software product, COMSOL Multiphysics 4.3a. The number of embedded tubes and fins on the embedded tubes are optimized based on the discharging time of the model. Various performance parameters such as charging/dis-charging time, energy storage/discharge rate and melt fraction are evaluated. Numerically predicted temperature variations of the model during charging and discharging processes were compared with the experimental data extracted from the lab-scale LHS prototype and a good agreement was found between them.

- by Hakeem Niyas and +1
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- Comsol Multi Physics, Solar Energy, Phase Change Materials, Thermal Energy Storage

The article offers an analysis of the use of nanotechnological insulation materials (NIMs) for energy upgrading of buildings, illustrating the possibility of their integration into the building envelope and the benefits achievable in terms of architectural quality, comfort and energy saving, within the new framework of European legislation aimed at achieving
Zero energy buildings. Particular reference is given to Fibre Reinforced Aerogel Blankets for the building envelope, especially interesting for their wide possible applications even combined with phase change materials.

- by Marco Casini
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- Nanomaterials, Nanotechnology, Energy Efficient Retrofitting, Phase Change Materials

Phase change materials (PCMs) are classified according to their phase change process, temperature, and composition. The utilization of PCMs lies mainly in the field of solar energy and building applications as well as in industrial processes. The main advantage of such materials is the use of latent heat, which allows the storage of a large amount of thermal energy with small temperature variation, improving the energy efficiency of the system. The study of PCMs using computational fluid dynamics (CFD) is widespread and has been documented in several papers, following the tendency that CFD nowadays tends to become increasingly widespread. Numerical studies of solidification and melting processes use a combination of formulations to describe the physical phenomena related to such processes, these being mainly the latent heat and the velocity transition between the liquid and the solid phases. The methods used to describe the latent heat are divided into three main groups: source term methods (E-STM), enthalpy methods (E-EM), and temperature-transforming models (E-TTM). The description of the velocity transition is, in turn, divided into three main groups: switch-off methods (SOM), source term methods (STM), and variable viscosity methods (VVM). Since a full numerical model uses a combination of at least one of the methods for each phenomenon, several combinations are possible. The main objective of the present paper was to review the numerical approaches used to describe solidification and melting processes in fixed grid models. In the first part of the present review, we focus on the PCM classification and applications, as well as analyze the main features of solidification and melting processes in different container shapes and boundary conditions. Regarding numerical models adopted in phase-change processes, the review is focused on the fixed grid methods used to describe both latent heat and velocity transition between the phases. Additionally, we discuss the most common simplifications and boundary conditions used when studying solidification and melting processes, as well as the impact of such simplifications on computational cost. Afterwards, we compare the combinations of formulations used in numerical studies of solidification and melting processes, concluding that "enthalpy-porosity" is the most widespread numerical model used in PCM studies. Moreover, several combinations of formulations are barely explored. Regarding the simulation performance, we also show a new basic method that can be employed to evaluate the computing performance in transient numerical simulations.

- by Massimo Garai and +1
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- Computational Fluid Dynamics, Phase Change Materials, Phase Change Materials (PCM), melting and solidification processes

Inclusion of paraffin wax reduces the base temperature of heat sink. An enhancement ratio of 2.64 at w = 1.00 is achieved for a SPT of 60 °C at 3.174 kW/m 2 for 2 mm thick pin-fin heat sink. At heat input of 1.98 kW/m 2 , it took 145 min and 229 min to reach SPTs of 60 °C and 70 °C respectively. 3 mm Pin-fin thick heat sink outperform the 2 mm pin-fin thick heat sink for volume fractions of w = 0.33 and w = 0.66. An enhancement of 4.30 is achieved against heat flux of 3.174 kW/m 2 for 2 mm thick pin-fin heat sink. a b s t r a c t The present experimental investigation focuses on the passive cooling of electronic devices by using phase change material (PCM) based pin-fin heat sinks to increase reliability, to ensure sufficiently lower temperature, to stretch the operating duration and to improve the functionality of installed features. Paraffin wax is used as a PCM and filled in heat sinks made of aluminum. As the thermal conductivity of PCM is very low, aluminum square fins are used as thermal conductivity enhancer (TCE). A volume fraction of TCE is kept constant at 9% and the uniform heat flux is applied to finned and un-finned heat sinks. An un-finned heat sink is used for base line comparison. Fin thicknesses of TCE of 1 mm, 2 mm, and 3 mm with square cross sectional area are investigated with a constant height of 20 mm. Volume fractions of PCM are varied as 0.00, 0.33, 0.66 and 1.00 for each heat sink to determine the thermal performance. The present study reports thermal performance at various heat fluxes to enhance the operating time for different set point temperatures (SPTs) and to compare the latent heat phase duration for various heat sinks tested. The results reveal that maximum thermal performance in operating time is achieved for 2 mm thick pin-fin heat sink filled with PCM volumetric fraction of 1.00.

- by Hafiz Muhammad Ali
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- Electronics, Heat Transfer, Electronics Cooling, Phase Change Materials
- by Ron Warzoha
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- Thermal Engineering, Nanofibers, Heat Transfer, Composite Materials