Synthesis of organic phase change materials (PCM) for energy storage applications: A review

Nano-Structures & Nano-Objects 20 (2019) 100399

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Synthesis of organic phase change materials (PCM) for energy storage applications: A review ∗

Suhanyaa S. Magendran a , Fahad Saleem Ahmed Khan a , N.M. Mubarak a , , Mahesh Vaka b , ∗ ∗ Rashmi Walvekar b , Mohammad Khalid c , , E.C. Abdullah d , , Sabzoi Nizamuddin e , Rama f Rao Karri a

Department of Chemical Engineering, Faculty of Engineering and Science, Curtin University, 98009 Sarawak, Malaysia Sustainable Energy and Green Technology Group, School of Engineering, Taylor’s University Lakeside Campus, Subang Jaya, 47500 Selangor, Malaysia c Graphene & Advanced 2D Materials Research Group (GAMRG), School of Science and Technology, Sunway University, No. 5, Jalan Universiti, Bandar Sunway, 47500 Subang Jaya, Selangor, Malaysia d Department of Chemical Process Engineering, Malaysia–Japan International Institute of Technology (MJIIT) Universiti Teknologi Malaysia (UTM), Jalan Sultan Yahya Petra, 5410 Kuala Lumpur, Malaysia e School of Engineering, RMIT University, Melbourne, 3000, Australia f Petroleum and Chemical Engineering, Universiti Teknologi Brunei, Brunei Darussalam b

article

info

Article history: Received 20 February 2019 Received in revised form 19 September 2019 Accepted 4 October 2019 Keywords: Thermal energy storage Phase change materials Organic phase change Thermal conductivity

a b s t r a c t The present energy generation from renewable resources does not meet the current global demand for energy supply, and there is a need to come up with more innovative technologies that could bridge the gap between the energy supply and demand. Phase change materials (PCM) are one of the most effective and on-going fields of research in terms of energy storage. Especially, organic phase change materials (OPCM) has grabbed a lot of attention due to its excellent properties that can be combined with thermal energy storage systems to preserve renewable energy. However, the practical application of OPCM is restricted to thermal energy storage due to their low thermal conductivity and leakage during the phase change. Entrapping OPCM in a shell using different encapsulation techniques is the best solution to eradicate the leakage and boost the storage capacity of the material. This review mainly highlights the thermal energy storage and thermal properties associated with it. Moreover, we emphasise the selection of materials based on different properties and different encapsulation processes from macro to nanoscale level. Finally, the use of PCMs in various applications challenges faced, and future directions are also discussed. © 2019 Elsevier B.V. All rights reserved.

Contents 1. 2. 3. 4.

5. 6.

7.

Introduction......................................................................................................................................................................................................................... Thermal energy storage ..................................................................................................................................................................................................... Latent heat storage materials ........................................................................................................................................................................................... Phase change materials ..................................................................................................................................................................................................... 4.1. Definition ................................................................................................................................................................................................................ 4.2. Classification of PCMs ........................................................................................................................................................................................... Material selection measures.............................................................................................................................................................................................. Organics PCMs .................................................................................................................................................................................................................... 6.1. Paraffin .................................................................................................................................................................................................................... 6.2. Non-paraffins.......................................................................................................................................................................................................... Factors affecting PCM energy storage capacity .............................................................................................................................................................. 7.1. Encapsulation techniques for PCM ...................................................................................................................................................................... 7.2. Classification...........................................................................................................................................................................................................

∗ Corresponding authors. E-mail addresses: [email protected] (F.S.A. Khan), [email protected], [email protected] (N.M. Mubarak), [email protected] (M. Khalid), [email protected], [email protected] (E.C. Abdullah). https://doi.org/10.1016/j.nanoso.2019.100399 2352-507X/© 2019 Elsevier B.V. All rights reserved.

2 3 3 4 4 4 5 6 6 6 6 8 9

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8. 9.

10.

Inclusion of carbon nanoscale........................................................................................................................................................................................... Application of PCMs ........................................................................................................................................................................................................... 9.1. Solar energy storage systems ............................................................................................................................................................................... 9.2. Solar water heater ................................................................................................................................................................................................. 9.3. Solar cooking .......................................................................................................................................................................................................... 9.4. Solar green-house .................................................................................................................................................................................................. 9.5. Building applications ............................................................................................................................................................................................. 9.5.1. PCM Trombe wall................................................................................................................................................................................... 9.5.2. PCM wallboards ...................................................................................................................................................................................... Conclusion ........................................................................................................................................................................................................................... Declaration of competing interest.................................................................................................................................................................................... Acknowledgements ............................................................................................................................................................................................................ References ...........................................................................................................................................................................................................................

1. Introduction Energy is the critical component to review the progress of society in different aspects such as technological development, environmental safety and economic advancement all around the world. Continuous depletion of non-renewable resources leads to critical global warming issues, which strongly encourage the researchers to switch to safer and cleaner energy usage like sustainable energy resources [1]. This opens a new window to investigate more on renewable energy resources to fulfil the thermal, electrical and storage demands. Currently, renewable energy resources are the primary source of energy consumption and meeting more than 18% of energy consumption globally. Although, the current renewable energy sources such as solar and wind are available all over the year, however, there is a huge fluctuation in their supply due to the natural and climatic conditions. Therefore, there is a need to develop new materials and technology to successfully utilise/store the energy harvested from renewable sources during their absence. Development of hybrid energy systems composed of different technologies are combined to cut down the energy demand during peak times need to be employed in the present situation [2]. Phase change materials (PCMs) acts as a connecting bridge between energy supply and demand for a long time because of their properties. PCMs are the most advanced materials, which can store in the form of latent heat and release the energy depending on the temperature differences. During a sudden drop in temperature/climatic change, favours the material by switching its phase from solid to liquid to release the stored energy meeting the demand [3,4]. Moreover, these PCMs grabbed a lot of attention and can be used effectively after the integration with TES system. However, the major issues that restrict the potential viability of PCMs in terms of applications and commercialisation point of view. This might be due to low thermal conductivity, poor stability, corrosiveness, supercooling, leakage of PCMs that leads to system failure [5–7]. Most of the scientists are concentrating on enhancing the thermo-physical properties of PCMs, but still different techniques and strategies need to be implemented to utilise the PCMs capability in full range as TES material. To overcome, the low thermal conductivity and supercooling problem, the most efficient technique is addition of various additives [8– 10]. The most effective method to prevent PCM leakage into the system is encapsulating PCMs using other supporting materials are highlighted in the next following sections [10–12]. PCMs are categorised into two different sorts known as organic PCMs and inorganic PCMs. Inorganic PCMs such as salt hydrates, or also known as Glauber’s salt, were few of the research that has studied in the early stages for the development of latent TES materials [13]. They are also well known for their few appealing characteristics such as high thermal conductivity, increase in latent heat values, non-flammable and lower in cost compared

10 11 12 12 12 14 14 14 14 14 15 15 15

with other organic compounds [14]. This fact has led the researchers to investigate organic PCMs extensively. Organic PCMs are widely used in a number of applications, and comparatively effective than inorganic PCMs due to its remarkable qualities such as non-corrosive, re-useable, low initial-cost, possess limited or zero super-cooling, significant latent heat and soften consistently [15]. One of the drawbacks of organic PCMs is the installation cost which is higher than inorganic PCMs [16]. Various investigations have concentrated on organic PCMs. With their better thermal stability, freezing without super-cooling characteristics, capacity to consistently melt, non-segregation, and toxicless made to provide better considerable measures based on their favourable circumstances. Paraffin and fatty acids are commonly used organic PCM compared to other types of organic PCMs because of high latent heat. Moreover, organic PCM can be grouped into few different sorts, for example, polyalcohol and polyethylene, that experiences solid–solid phase transformation by absorbing and discharging at a fixed temperature of extensive quantity of the latent heat, have been focused as a favourable PCMs [17]. Encapsulation of PCMs, impregnation of PCMs into polyurethane (PU) froth, and a balanced form by introducing PCMs as a cross-section of other material are examples of frameworks has been done earlier. There were two different types of encapsulation techniques that have been discovered and studied during this research study. The main strategy is by considering the encapsulation of PCMs. The encapsulation techniques are classified into micro, macro and nanoencapsulation. Microencapsulation can be compressed as assurance of unstable, sensitive materials from the surroundings, better managing of the process by enhancing solubility and dispensability of core and shell materials, time-span by preventing degradative responses and evaporation and, protected and appropriate handling of core materials [16]. Meanwhile, the second containment method is macro encapsulation method, that owing to the advantage like its sensitiveness towards both liquid and air for heat transfer fluid and the demand towards ships and handles were less [18]. Micro and micro-encapsulation method can be prepared by using three different types of methods such as physico-mechanical method, chemical or physico-chemical method based on organic PCMs with physico-chemical applications [19–21]. Several researchers have proposed addition of different nanoparticles to PCMs with improve the thermal performance and reported the usage of graphene oxide [22], CuO [23], Al2 O3 [24], Fe3 O4 [15] and other nanoparticles [25]. Among all the nanoparticles, carbon nanotubes have become one of the most significant material because of its properties such as higher thermal conductivity, low density and high thermal performance. CNTs cannot only work to build thermal conductivity of PCMs, yet it helps to decrease the level of cooling under specific temperature and enhance on the PCM’s stability range. CNTs demonstrates

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huge potential with included substances to enhance better and efficient thermal conductivity for latent heat TES. [26] reported that the increase in thermal conductivity of phase change material by 11.4% after the addition of 3% of CNT into stearic acid. This paper critically reviews different properties, types and key parameters for the selection of PCM. We also highlighted the factors affecting the PCMs and different encapsulation methods from macro to nanoscale level. To best of the author’s knowledge, no study underscored the effect of CNTs on PCMs to improve thermal performance. Finally, this paper offers an overview of organic PCMs in different applications are highlighted. 2. Thermal energy storage Fossil fuel as of now supply the most significant part of the world’s energy needs, and however inadmissible of their longterm outcomes, the provisions are probably going to stay satisfied for the following couple of ages [27–34]. Researchers and approach producers must influence on the utilisation of this time of grace to assess replacement sources of energy and figure out on the logical conceivable, environmentally adequate and technologically encouraging [19]. Sustainable energy, known as renewable energy, has to be created to meet the needs of energy and to wellfounded on vitality provided in order to diminish on the reliance of fossil fuel [35] has agreed that wind turbines cannot work when the breeze is not sufficiently forceful or excessively forceful. Photovoltaic (PV) boards cannot produce power during night or on days with thick overcast cover. To guarantee the power to organise advancements, discontinuity of the source of power can be overwhelmed by charged stockpiling gadgets, for instance, power devices throughout maximum hours to store vitality to be utilised later [36]. Thermal energy produced from the Sun can be utilised to stockpile heat [37]. There are again classified into two that can be arranged such as compound stockpiling and physical stockpiling [19]. Compound stockpiling includes breaking and development of synthetic, for instance, chemical term, utilising a reversible synthetic response by an extensive enthalpy change. The heat from the Sun or any other thermal sources shows responses towards a high shape energy item that carries the response on charging the system, and the response continues with storing, and then on the opposite direction on discharging the heat during the release [13]. Fig. 1 shown an illustration of a simple storage cycle, where three processes in a general TES system. For cold storage, heat Q1 is invading, and it has positive in value. During discharging, the heat will be released to the environment and the Q1 will be negative [13]. Meanwhile, the physical stockpiling uses properties of thermal-based on TES substances on supplying heat and also the focal point of this study. Two classifications can be contemplated with the need for physical TES which is sensible heat storage (SHS) and latent heat of storage (LHS) [19]. Increasing the temperature of a solid or fluid would be a platform to store thermal energy via heat capacities based on sensible heat of storage. The temperature changes towards the charging and releasing process is the adjustment where an SHS system manipulates with the capacities of the heat. Amount of heat needed relies upon the form of the heat, changes in temperature and measurement relative to the capacity of the material [38]. A diagram of sorts and significant strategies of thermal energy storage is shown in Fig. 1. Sensible heat storage material compromises of holding heat via heat limitations. As long as a provided material can store an amount of heat, Q, it then relies upon the temperature range between each other when the substance is heated and mass of the material, m. The higher is the heat capacity, the better the sensible heat storage materials. In this regard, water is known for

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Table 1 PCM characteristics. Characteristics of PCM Capacity Power Efficiency Charge and discharge time Cycling stability Non-flammable Not corrosive

their primary SHS material, with a specific heat capacity of 4.2 J K−1 g−1 [19]. Water is also known for its inexpensive and highly sensible heat characteristics [38]. A higher range of temperature prompts higher heat stored depending on the amount of heat identified. Furthermore, latent heat of storage is known for their best sensible heat storage materials upon a lower range of temperature. These materials depend on the absorption of heat or heat discharge. The input of energy based on phase change materials (PCMs) at a certain transition temperature; it is known as transition enthalpy change or called as latent heat [19]. Thermal energy storage or known as TES is a system that requires thermal energy storage for future utilisation of systems. In these applications, [39] has discovered that TES is an innovation that stocks thermal energy by warming and cooling process so that it can be used later for power generation. TES frameworks applications are utilised mainly in buildings and industrial processes in this era. A solid PCMs slowly changes into liquid phase at a constant temperature when thermal energy being absorbed into the material [36]. Solar energy is taken as an example of this type of system during the day as a significant part using the Sun’s energy [40]. To have a better understanding of this kind of applications, concentrating solar power (CSP) plant is introduced whereby solar heat can be utilising for electricity during there is no existence of sunlight during the night [41]. Applications such as solar system framework in PCMs have a higher ability on increasing density of the energy and reduction in solar storage volume. The characteristics involved in an energy storage framework is presented in Table 1: Capacity, power and time of discharge are those known for their independent values. Capacity and power are known for their dependable to each other in the storage framework [39], has discovered on parameters for TES systems based on PCMs on familiarising few crucial parameters. As an example, PCMs has a capacity between 50 to 150 kWh/t, power between 0.001 to 1.0 MW, efficiency of 75 to 90% and price range between $10 to $50/kWh. Fig. 2 shows an example of a solar power plant to have a clear understanding of thermal energy storage. The generalised execution measurements are connected to the particle TES concepts in a CSP thermal system design. (See Fig. 3.) 3. Latent heat storage materials Latent heat storage is a storage material that undergoes a phase transition of absorption or releasing of heat. They are known as phase change materials (PCMs) [38]. The phase changes from solid to liquid or vice versa indirectly contributes to the process of energy interchange. This ultimate rural change is widely known as the state, or ‘‘Phase’’. When a material faces a situation to exchange the energy to the environment or atoms loses vital, that is the time solidification reaction takes place. It is known for its reverse reaction. This can be clearly understood in Fig. 4. This leads them to transform into their solid phase. The melting– solidification cycles took place when the substances face solid to liquid phase transitions. These cycles exist in between the range

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Fig. 1. Three processes in a TES system.

Fig. 2. Thermal energy storage for solar power plant.

of temperature of selected applications by thermal energy [36]. There will be zero phase change will take place if the temperature is not at the condition of the operating range. The solid–liquid PCMs are considered to be giving better efficient because of their increase in temperature when they consume more heat than liquid–vapour and solid–solid transition. Meanwhile, PCMs retains and discharge heat at a consistent range of temperature during the sensible storage of materials take place [38]. During the melting process, there is an increment in energy when phase transitions from a solid phase to liquid phase has taken place meanwhile there is a reduction in energy when it changes from liquid to solid state during the solidifying process. 4. Phase change materials 4.1. Definition Numerous methods of TES have been discovered, but phase change materials (PCMs) has always accepted as a favourable option because of their characteristics where they can hold and release higher latent heat amount during the phase process. The transition process can be function by constructing energy conservation, heat recovery waste, solar energy utilisation and some other fields [43,44]. PCMs are also known as materials with solid– liquid transition phases which can be utilised for both storage applications [45].

4.2. Classification of PCMs There are different types of PCMs, and they are classified according to different kinds of criteria. Based on substances, PCMs has been divided into four known as solid–solid PCMs, solid– liquid PCMs, solid–gas PCMs, and liquid–gas PCMs [46]. Moreover, based on underlying chemical nature, solid–liquid PCMs can be classified into organic PCMs, inorganic PCMs and eutectic PCM [40] as shown in Fig. 5. At this era, solid–liquid PCMs are utilised as one of the most common types of PCMs. This is because they consist of increase in latent heat of capacity and smaller changes in volume during the transition of phase change compared to others [46]. The PCMs at first acts almost same to sensible of heat storage materials, whereby the temperature of PCMs is higher while it assimilates energy, until the temperature transformed at a point [47]. It initially ingests a higher heat amount to convey the changes from solid phase to liquid phase [48]. The solid–liquid PCMs then break down into examples of classifications of each type [16]. Broad research is carried out for the past four decades, in identifying of different types of PCMs in a wide variety of temperature transition at different phases and latent heat of fusion which compromises with classifications of PCMs (see Table 2) as shown in Fig. 6 [49].

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Table 2 PCM’s impact. PCMs

Impacts

Remarks

Paraffin wax

Discharges harmful toxins when burnt, non-biodegradable, combustible carcinogenic (Commercial Grade Wax)

[42]

Fatty acids

Variable toxicity

[42]

Vegetable oils

Eco-friendly, high flammable, no carbon release, safe when consumed, food-grade, renewable.

[42]

Fig. 3. Types of thermal energy storage.

5. Material selection measures

Fig. 4. Melting and solidification process.

There is numerous material selection contemplation which is ordinary to applications of PCMs. As a matter of first importance, the melting point is one of the primary reflections while choosing a material. One of the essential elements is that the melting point of the PCMs has to be smaller than the temperature of heat and higher than the surrounding temperature when the material is exposed to the environment. Likewise, considering every one of the contraries in temperature parameters to which the gadget will be subjected [36]. Based on frameworks that are planned especially for thermal management consisting of maintenance of a particular point, the ideal guidance is to select a phase change material with the most noteworthy melting point which is beneath the ideal thermal controlling sector. This action helps in consuming longer time consumption for melting and gives higher effectiveness in thermal management before the PCMs is liquefied [50]. Finally, few other criteria that can be looked through while selecting the best phase change material. The material should consist of better stability, chemically and physically replicating thermal cycling. The similarity of the chosen material is the packaging and materials with different ought to likewise be considered since few PCMs are corrosive [51]. (See Fig. 7.)

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• Thermal Properties For specific applications by choosing a PCM, the operating temperature of both processes should be coordinated based on a different temperature of the PCM. The latent heat is higher as reasonably, mainly based on the volume basis [40]. This helps to reduce the magnitude of the latent heat. The absorbing and releasing of energy storage would be improved with high thermal conductivity [38].

• Physical Properties During freezing melting process, phase strength will help in settling heat stockpiling and with high density. This will help to permit a limitation of smaller size compartment with its attractive characteristics [40]. On decreasing the regulation issues, changes on a small volume of phase transition and lower vapour pressure conditions. An excellent physical properties consist of characteristics in such beneficial phase equilibrium, higher density, lower in vapour pressure and decrease in volume change [38].

• Kinetics Properties Meanwhile, one of the most troublesome parts of PCM has always been the supercooling process, especially for salt hydrates. Excessive of a couple of degrees in supercooling will gives an interfering problem with proper heat extraction, but about 5–10 ◦ C of supercooling process that can counteract it overall. The best kinetic properties for PCM involves no supercooling process and adequate rate of crystallisation [38].

• Chemical Properties PCM experiences from corruption such as mortification with water loss for hydration, chemical decay or contradictory with construction materials [40]. For safety purpose, PCM should be acknowledged with characteristics such as non-poisonous, nonflammable and not explosive. Less fire hazard and non-toxicity would be those preferences for selection [38].

• Economics PCM has a vital role in the economics aspect under latent heat storage materials. Additionally, low in price and expansive scale accessibility of phase change materials is critical enough. According to earlier studies [38], it stated that PCM should experience profuse in large quantity and has cost-effectiveness as important characteristics. (See Table 3.) 6. Organics PCMs Organic material is known as natural materials. They are described and classified into two known as paraffin and nonparaffin [6]. Organic materials incorporate compatible melting where melt and freeze more than once isolation and ensuing mortification of latent heat of fusion, self-nucleation implies them to solidify with almost or negative supercooling and also less corrosiveness [38]. (See Table 4.) 6.1. Paraffin Paraffin has been utilised for storage of energy because of significant characteristics which consist of high heat of fusion [54], fluctuated stage change temperature, zero super cooling characteristics, vapour pressure is lower, and chemically inert and has constant conductivity. TES materials are lower in cost than PCM due to their storage density which is higher lower operating temperatures [55]. These PCMs are economically accessible at lower cost which makes only technical grade paraffin is used in latent heat of storage systems [38], biologically safe and also, non-toxic [56]. Paraffin is effectively accessible from numerous manufacturers. The most promising candidates would be from the alkane (paraffin) family which is the Cn H2n+2 [36]. These are from

the family of alkanes CH3 –(CH2 )–CH3 [57]. The most common type of paraffin used in commercial organic heat storage for PCM is the paraffin wax. They are known for their chemically inert and stable below the temperature of 500 ◦ C [38]. Many researchers have been developing new experiments to observe and analysis on the paraffin type of organic phase change for the industrial applications as they consist of characteristics in betterment in such applications and many other considerations. Table 5 shows the previous work done based on the paraffin study to indicate a better understanding of the motive of the experiment carried out. Meanwhile, Table 6 indicates on the physical properties of well-known paraffin based on their respective carbon atom 6.2. Non-paraffins Fatty Acids Phase change parameters such as temperature and latent heat are known as the two critical parameters that have been analysed and investigated in PCM. Based on previous studies [65], it has stated that researchers have tested on these two properties by using many types of organic materials mainly by using fatty acids as PCMs. Besides paraffin, fatty acid is included in the subgroups of organic phase change materials known as non-paraffin. They are known in a small group of renewable PCMs since fatty acids are classified and produced by animals and plants. These are known as an animal and plant-based which is classified as hydrolysis to obtain a mixture of fatty acids which has been purified and separated from each other producing fats and oils. Compare to paraffin waxes in PCM applications, and fatty acids are among the rare renewable feedstock which has the same properties. Few of their properties such as density, specific heat, latent heat and thermal conductivity of fatty acids as PCM has been discovered and analysed. Fatty acids have higher-ranking parameters and production in chemical and thermal properties, zero toxicity, melting compatibility, has been suitable for melting temperature range for few heat storage applications and biodegradability compare to other phase change materials which have been discussed and experimented. Without thermal degradation, they have the capability of having melting and freezing cycles that accumulates many sorts. On the meantime, eutectic mixture of fatty acid has been recently signified as one of the PCMs with promising energy-storing composites. Few applications such as solar energy systems and for buildings are examples of the use of fatty acids. They are chosen because they comprise with excellent thermal and physical properties and their easy saturation into compound structures. Furthermore, all the fatty acids have been commercialised widely in many applications, since few of the industries already start producing fatty acids in more massive amounts such as plastics, textiles and cosmetics applications. Many research reviews have reported on experimenting fatty acids for PCM applications in Table 7. Moreover, Table 8 indicates the advantages and disadvantages faced by both paraffin and fatty acids under the circumstances of organic materials. 7. Factors affecting PCM energy storage capacity PCMs oxidation results in harmful compounds growth like ketones, aldehydes and carboxylic acid that can dissolve in uncontaminated PCM forming PCM solution. Consequently, PCM oxidation leads to a fall in energy storage capability, lessen in phase change temperature and expand transition temperature

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Fig. 5. Classification of PCMs.

Fig. 6. Classifications of PCMs with their respective examples.

Fig. 7. Flow chart of desirable properties of latent heat storage materials.

range. Therefore, it might be determined that coating materials are needed to avoid oxygen diffusion. Furthermost, water-soluble organic PCMs are generally hygroscopic substances; subsequently they could absorb moisture

conveniently developing greater hydrates in reduction in energy storage capability at its phase transition temperature. Lately, PCMs encapsulation has been established to resolve the problem stated above.

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Table 3 Properties eligibility of the materials to categorised as PCM. Physical

Chemical

Thermal

Kinetic

Remarks

Minor vapour pressure

Chemically stable after a numerous number of free thaw phase.

Significant thermal, latent capacity and specific heat value

Non-super-cooling and sub-cooling

[42]

Limited phase transition volume change

Not corrosive, toxicity and flammability

The melting point in the preferred operating temperature range

No phase Isolation

[52]

Significant density

Well-matched with container material

Remarkable nucleating strength

[53]

Table 4 Merits and demerits of organic PCMs [42].

Organics PCMs Paraffin wax, fatty acids and vegetable oil

Merits

Demerits

■ Lower or non-supercooling effects.

■ Decreases in enthalpy of phase changes

■ Non-corrosive

■ Lower in thermal conductivity, density and melting point

■ Chemically and thermally stable ■ Encounter good thermal behaviour

■ Flammability

■ Available in the large temperature range

■ Higher volatile

■ No segregation

■ Cost is unaffordable and expensive

■ Recyclable

■ Changes in volume during phase change

■ Has better nucleation rate ■ Transition zone can be adjustable.

Table 5 Previous work done based on paraffin study. Paraffin considered

The objective of the research

References

Microencapsulated n-heptadecane

Melting point and latent heat of fusion before and after 5000 cycles that varies at different temperature range.

[58]

Paraffin

The small scale of difference in melting point and latent heat of fusion of paraffin

[49,59]

Three different hydrocarbon

C22.2 H44.1 shows steady behaviour with small change in melting point and latent heat.

[60]

Three paraffin waxes

Degradation in transition temperature and enthalpies of respective three samples and one was chosen as a good PCM based on LHS system

[57]

Commercial grade paraffin

Observed and made an analysis on the differences in melting temperature, latent heat and specific heat

[61]

Same PCM with different 1500 cycles

Slight different changes in melting point and latent heat

[57,62].

Three different hydrocarbons

C23.2 H40.4 proposed as an efficient material for LHS system with shoddy price and higher enthalpy characteristics

[16]

Table 6 Physical properties of well-known paraffin. Paraffin with carbon atoms

Oil content (%)

Freezing point (◦ C)

Heat of fusion (kJ/kg)

Density at 20 ◦ C

Specific heat at 100 ◦ C(kJ/kg K)

Thermal conductivity at solid phase (W/M K)

References

C13 -C24 C18 C16 -C28 C20 -C33 C22 -C45 C23 -C45 C21 -C50

20 0 5

22–24 28 42–44 48–50 58–60 62–64 66–68

189 244 189 189 189 189 189

0.900 0.814 0.910 0.912 0.920 0.915 0.930

2.1 2.16 2.10 2.1 2.1 2.1 2.1

0.21 0.15 0.21 0.21 0.21 0.21 0.21

[63] [64] [64] [63] [57] [63] [57]

< 0.5 4

< 0.5 3

7.1. Encapsulation techniques for PCM

or incorporated in a matrix, forming a capsule shape. The capsule can be of spherical, tubular, oval or irregular shape. To accommo-

It is a procedure of offering a support structure to PCM to inhibit its interaction with the surrounding; moreover, it also provided the increase in heat transfer area, limit leakage issues and guarantee compatibility among the PCM and the environment. It is a process where a particle is surrounded by material

date the changes in volume at the time of phase transformation, sometimes an air pocket is introduced. The shell must be capable of resisting the stresses that are produced due to volumetric changes at the time of PCMs phase change process. The core

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Table 7 Previous research studies on fatty acids. Fatty acids considered

The objective of the research

References

Fatty acid

Research on physical and thermal properties in energy-storing materials Thermal behaviour and solubility of fatty acid esters and glycerides

[16]

Capric, lauric, palmitic and stearic acid

Thermal properties of a few types of fatty acid and their binary mixture

[67]

Fatty acids

Fatty acids act as PCM and their thermal stabilities

[68]; [69]

Stearic acid and palmitic acid

Thermal properties of stearic acid and palmitic acid

[70,71]

Myristic acid

Thermal performance of myristic acid

[60]

Palmitic, stearic and oleic acid

The melting temperature and the heat of fusion measurement data of a few types of fatty acid and respective binary and ternary mixtures

[72]

Tridecanoic acid to tricosanoic acid

Thermal properties as well as the crystal structure of odd numbered fatty acids known as [C12 H25 COOH to C22 H45 COOH]

[73]

Fatty acids

Review of thermal properties of fatty acids

[74]

Capric and lauric acid

Mixture of capric and lauric acids for low temperature storage

[75]

Lauric acid and palmitic acid

Solid–liquid phase transitions and binary system at different temperatures

[76]

Oleic, lauric, myristic, palmitic acid

Thermal properties of the binary mixtures

[77]

Fatty acid esters and glycerides

[66]

Table 8 Comparison of types of organic PCMs. Organic PCM

Paraffins

Advantages

■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■

Disadvantages

■ Has insoluble characteristics in water ■ Water resistance ■ No side reactions with chemical reagents ■ Can produce flame easily (burn) ■ Phase change enthalpy is low ■ Smaller in amount for phase change enthalpy, thermal conductivity, density and melting point ■ Flammability ■ High changes in volume between solid and liquid state ■ Have undefined melting temperature [57]

could be solid or dissolved into a carrier fluid, in which scenario the material is known as MPCS (Microencapsulated Phase Change Material Slurry) [81]. This process widely used to solve problems related to PCM such as low conductivity, super-cooling and thermal instability, that followed to lower the system rate of heat release as well as thermal efficiency [80,82]. The PCMs encapsulation technique offers a way to increase the surface area, shielding the PCM from environmental factors, increasing PCM compatibility and lessening corrosion [83]. Based on the encapsulation approach, PCMs are categorised into physico-mechanical, physicochemical and chemical [84]. A brief description of encapsulation approaches of different PCMs (organic) are illustrated in Fig. 8 [85,86] Encapsulation Approaches of Different PCMs. (See Table 9.) 7.2. Classification Encapsulation approach categorised into three kinds based on the capsules final diameter:

• Microencapsulation

Fatty acids

Having a bigger scale of temperature in phase change Thermal storage densities are moderate Chemically inert and stable mainly in closed containers Strong and stable Better storage density (respect to mass) Good similarities with metals Fewer constraints on safety-wise Zero effect based on supercooling process Available at a rational cost/operating cost Higher heat of fusion Safe and non-reactive [42,78]

■ Has good range of melting point of temperature ■ High capacity for heat transfer ■ There is no or either little supercooling during transitions of phase change ■ Lower vapour pressure ■ No toxic ■ Chemical and thermal stability is lower ■ Slight differences in volume ■ Freezing cycle period has better stability ■ The heat of fusion is higher ■ Easily receive from vegetables and animal oils [79] ■ Lower phase change in enthalpy ■ Smaller effect on thermal conductivity, density and melting point ■ Flammability ■ Triple the cost than paraffin [42,80]

A method of producing capsule in micrometre size through coating the PCM materials with a thin material coating of polymer. The purpose of this procedure is to take care of issues such as outflow, volumetric changes at the time of melt–freeze phase and reactivity to the surrounding. It also capable of improving the heat transfer surface area. Furthermore, microencapsulation procedure is divided into chemical and physical. Both processes are extensively used in industries, but chemical methods are comparatively preferable than physical. However, physical microencapsulation procedures are economical as well as conveniently scaled up but come with drawbacks such as non-uniform sizes and unacceptable properties. On the other hand, chemical techniques offer required properties and sizes [103]. The only disadvantage of chemical method is high cost and complex process.

• Microencapsulation In this technique, the PCM holds in pouches, thin plates, tubes and shell etc. The inclusion of PCM in the building is convenient, offer volume control as well as safeguard against environmental degradation. Microencapsulation techniques are preferable compared to macro encapsulation as it comes with a number of

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Fig. 8. Encapsulation approaches of different PCMs.

drawbacks such as leakage issues, low heat transfer properties and thermal stratification [42].

• Nanoencapsulation Recently a new technique for PCMs to encapsulate is Nanoencapsulation, to safeguard leakage, enhancement of thermal physical strength, heat transfer improvement and upgrade in the reliability, i.e. charging/ discharging cycle phase. In general, nanoencapsulation as the technology of nanoparticles packaging, sometimes referred to as core or active, along a secondary material, called as matrix/ shell to obtain nanocapsules. The core consists of active ingredient, whereas, shell isolates and safeguards the core from environment. This shelter can be temporary or permanent, in such case the core is commonly released by diffusion or in retort to a trigger (pH, shear etc.) thus allowing their measured and timely delivery to a directed site. However, for nanomaterials development, the technique uses whether top-down or bottom-up method. – Top-Down Approach This approach includes the usage of specific tools which let size reduction as well as shaping for required nanomaterials applications. Emulsification and emulsification solvent evaporation are the techniques used in this approach [104]. – Bottom-Up Approach In this approach, materials are produced by molecules selfassembly that were influenced by factors such as pH, concentration, temperature and ionic properties. Techniques such as coacervation, nanoprecipitation and inclusion complexation fall under this approach [91]. (See Table 10.) 8. Inclusion of carbon nanoscale Organic Phase Change (PCM) constituents referred as an essential latent heat energy storage resource and also an applicable candidate in a variety of fields such as thermal protection, thermal energy storage and heat transfer fluid [82,114]. Due to its low thermal conductivity, its uses are restricted. However, various procedures have been suggested to improved PCM low thermal conductivity but still more efforts required. It has been reported that Single-Walled Carbon Nanotubes (SWNTs) and Multi-Walled Carbon Nanotubes possess ultra-high thermal conductivity of ∼6600 W/mK and ∼3000 W/mK [115,116], respectively. The CNTs significant thermal conductivity has made them a suitable material to be used as a thermally conductive

filler [117]. The inclusion of carbon nanoscale materials within PCM shows promising results due to carbon nanomaterials remarkable properties. The success of considering carbon-based nanomaterials lies in interpretation how the heat is transferred within themselves but among nanoparticles when valued in a composite [36]. Several types of research testified the enhancement of PCM’s thermal properties when incorporated with carbon nanomaterials, particularly SWNTs, MWNTs and Graphite Nanofibers (GNF) [118,119]. Hence, the availability of nanoparticles helps the material thermal conductivity to different degrees. In the past, a researcher studied the MWNTs (100 nm diameter, 20 µm length) effect when incorporated into paraffin PCM (67 ◦ C Melting Temp., (1–4) wt. %) [120]. The results quantified the increase in thermal conductivity that was greater than 35%, from just less 0.25 W m−1 K−1 for the base paraffin to 0.33 W m−1 K−1 at 4 wt.%. With the loading level, the upsurge in conductivity rise was linear. As mentioned above, many kinds of research were conducted where PCM/nanoparticles composites thermal cycling behaviour was examined. These researches focus on the PCM impact when combined with GNF (100 nm diameter, length 100 µm length) on solidification and melting cycle [119,121]. The composite was prepared using herringbone style fibres. At the time of the heating cycle, GNF significant loading level was shown to decrease the temperature flows within the material as it heat rises to melt temperature because of GNF significant thermal conductivity [119]. Nevertheless, once reached the melting point, the considerable loading levels blocked the natural convection inside the PCM, much as the slight porosity foams did. Moreover, thermal performance improvement was shown during solidification that was mainly because of the prominent conduction nature of the solidification procedure [36]. In actual, GNF (10 wt. %) directed to 61% drop in complete solidification duration. For application that required fast PCM recharge for the upcoming transient pulse, it can be extensively valuable. Based on the literature, it clearly shows that carbon nanomaterial-based PCM composites, i.e. SWNTs, MWCNTs and GNF are capable of enhancing the thermal strength. Among these GNF based composites display more promising performance because of remarkable phonon transport and interface contacts lower number when applied in a matrix. Since GNF composites have not gone through thermal cycle, therefore, the melt phase impact is not visible. Apart from this, these materials seem to offer substantial advantages, but before implementation extensive development work is required. (See Table 11.)

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Table 9 Different PCMs Encapsulation Techniques Merits and Demerits. Encapsulation

Approaches

Advantages

Physicomechanical

Spray drying

• Convenient, reproducible and • The process may change

Centrifugal extrusion

Vibrational nozzle

Disadvantages

high yield technology. • Comparatively lower production cost. • Significant encapsulation efficiency. • Energy saving technology. • Ideal for temperature-sensitive materials

significantly from one to another drier. • Difficult to maintain the particle size. • Small batches production is adequate. • Because of the higher air velocities, it has insignificant uniformity. • Insignificant loading efficiency of the drugs.

• Particles forms via this

• Appropriate for liquid/

process range from 400–2000 µm in diameter. • High production rate, i.e. 22.5 kg per nozzle per hour. • Moderately low temperature entrapping process. • Any extra core is cleaned from the exterior.

slurries. • Capsules should be detached from a dried and liquid bath.

Applications

Remarks

Food, pharmaceutics and chemical industries.

[87–91]

Heat labile substances, such as vitamin C

[91,92]

• Capable for the production of • Partial use of liquids that droplets from 20–10 000 µm. displays significant viscosity. • Process installed in industries

[93]

can produce 1– 20 000 kg/hr at 20–1500 ◦ C temperature. Solvent evaporation

Chemical

Suspension polymerisation

Delivery of peptide and vaccines.

[90,94,95]

• Extremely complex process.

For the production of resins, for instance, PVC and polystyrene.

[90,96]

Paints, adhesives, coating varnishes, plastics, drug delivery

[97]; [98]

• Ease of use • Higher yield. • Limited residual solvent.

• Difficult to select the

• Economical wall materials • Production equipment is

encapsulation materials. • Insignificant efficiency of encapsulation of moderately water-soluble and water-soluble compounds. • Energy consumption is higher

simple.

Physicochemical

Miniemulsion polymerisation

• Spray machine technology

• Not appropriate for large

was introduced via this technique. • Able to produced narrow sized micro-nanocapsules.

scale production. • Expensive technique. • Encapsulation efficiency is low. • Capsule formation control is problematic.

Coacervation

• It is one of the oldest

• Low mechanical strength and Pharmaceuticals, food industry,

technologies. • Excellent Physicochemical strength and functional attributes. • Capable of maintaining mechanical stress and sustained release. • Simple, fast and offers microparticles production in aqueous surrounding.

high microparticles permeability. • The further procedure required such as thermal treatment for stabilisation. • Used harmful chemical agents. • On the surface of capsules, solvents and coacervating agents left. • Complex coacervates are extremely unstable. • Complex and expensive process.

agro-industrial and medical fields.

• It uses minor conditions as

• Used restricted to labs. • Capsules produced holds

Biomedical and food sector.

Ionic gelation

well as restricts harmful organic solvents. • pH and temperature are avoided by organic solvents and extreme conditions.

9. Application of PCMs

PCMs have a vast number of applications for passive as well as active heating/ cooling as a combined part of the cascaded thermal energy system (TES) [85,125]. There is significant number

[99]; [100]; [101]; [91]

[91,102]

high porosity that promotes intensive burst.

of PCMs applications that are in the stage of research and development, for instance compact TES system and smart thermal grid. The inclusion of PCMs concept in smart thermal grid system is mainly studied by applications with large thermal inertia integrating the inconsistent renewable resources supply wanting the heat to be deposited and delivered upon as per request [126].

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Table 10 Encapsulation techniques merits and demerits. Encapsulation techniques

Merits

Demerits

Applications

Remarks

Microencapsulation (1 µm to 1 mm)

■ During the phase change, it maintains reasonable volume control ■ Inclusion into conventional building materials with ease ■ Extensive enhancement of thermal reliability. ■ Act as a barrier and prevent leakage of PCM ■ Enhanced chemical strength.

■ Material strength may affect. ■ Direct to supercooling properties. ■ Expensive encapsulation technique. ■ Natural convention is disturbed disturbing solidification occurrences.

■ Food Industry: Incorporate at any time during the process and stays unaltered. ■ Extend the food product life. ■ Beverage production. ■ Transport drugs to the target site in the body. ■ Widely used in agricultural and environmental regions. ■ Textile Industry: Imparting finishes.

[105,106]

Macroencapsulation (1mm to >1 cm)

■ Enriched material compatibility with the environment. ■ Exterior volume changes properties are moderated. ■ Handling of PCM also improved during manufacturing. ■ May act as heat exchangers ■ Preventing alterations of its composition via exposed with the surrounding. ■ Lower production cost process. ■ Mechanical strength of PCM increased due to the shells usage.

■ Low thermal conductivity or heat transfer features. ■ Solidification at the boundaries.

■ Building envelope: Lower the building energy consumption and enhance thermal comfort.

[107]; [42,108–110]

Nanoencapsulation (<1 µm)

■ API protection from degradation ■ Targeted drug transport with exterior coating. ■ Modification to external charge can offer cell entry. ■ Luminous identifying for imaging.

■ Production cost is higher. ■ Further treatment required for purification.

■ Delivered drug delivery to the desired location as required. ■ Products stability and life span extended, such as vitamin. ■ Incorporated fragrances for aromatic clothing.

[111–113]

Table 11 Major process for PCM heat transfer improvement. PCM Paraffin wax

Materials added

Influence on PCM thermal conductivity

Remarks

Graphite matrix CENG Carbon nanofillers Carbon fibre

20 ∼ 130 times higher than pristine PCM More significant than 6.1 times than pristine PCM 1.7 times higher than pristine PCM 18 ∼ 57 times higher than pristine PCM

[122] [123] [124] [108]

Furthermore, PCMs can also be used in constructing energy storage systems, smart textile materials, thermal management of the batteries, applications related to space as well as terrestrial thermal energy storage and microelectronic temperature management [127–129]. In this paper, PCMs applications are briefly discussed for better understanding and also show the previous work done based on these applications. (See Fig. 9.)

9.1. Solar energy storage systems The discontinuous of solar oriented irradiance and the ability to use solar energy frameworks in a consistent and static load made the utilisation of capacity frameworks necessary in a large portion. In the meantime, the usage of phase change material based on TES in these applications can broaden the use of technology which benefits even when there is low or no direct insolation. The use of PCMs can be seen in solar water heater, solar cooking, solar air heater, and solar greenhouse.

9.2. Solar water heater Solar water heaters are known for their admiration because of their inexpensive and simplicity to fabricate [130,131]. Moreover, [132]also have discovered and analysed on a built-in-storage type of water heater at the bottom that consists of a layer of PCM as shown in Fig. 10. Heat exchange to PCM underneath happens when the water gets warmed during the day hours. The PCM then undergoes melting and gathers energy as latent heat. When there is no light or sun hour, the temperature of the water cools down and starts gaining energy from the PCM which leads to discharged by PCM. These phenomena occur during the transition state from liquid to solid phase. Since there is poor heat transfer between PCMs and water, then this sort of framework may not be compelling. Few research studies have been identified based on the solar water heater applications as shown in Table 12. 9.3. Solar cooking Cooking based on solar are utilised for households such as cooking rice, vegetables, meat and many other utensils. [64] have designed, tested, made hypothesis and use the box-type of solar

S.S. Magendran, F.S.A. Khan, N.M. Mubarak et al. / Nano-Structures & Nano-Objects 20 (2019) 100399

Fig. 9. PCMs applications.

Fig. 10. Built-in heater with PCM layer [133]. Table 12 Previous research studies on solar water heater. The objective of the research

Outcomes of the research

Research studies

Cylindrical systems for domestic hot water

A theoretical model was developed by using paraffin wax and stearic acids as PCM

[134]

Conducted the properties of PCM storage for a water heater by including water flow

Hot water with (temperature 15–20 ◦ C is more prominent than ambient air temperature) can remain throughout the whole day

[135]

System for domestic hot water using Na2SO4.10H20 as a PCM and a simulation model was compared

The optimum flow rate was optimised with the supply of inlet water required to maintain the temperature of water at the outlet

[136]

To measure the suitable PCM for storage framework

Concluded that paraffin wax can be used as a storage system for solar water heating.

[137]

13

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9.5.1. PCM Trombe wall PCM scan has been recommended that can be utilised as a part of partitions, vertical walls, ceilings and floors for controlling temperature. Masonry in a Trombe wall is supplanted by PCM. This PCM is exceptionally helpful to be utilised in building applications. There were experiments that have been carried out to examine the efficiency and productivity of PCMs used as a part of the Trombe wall [143]. Compared to water, a phase change unit consists of lower density and requires fewer spaces contrast with walls of water for a predetermined measure of heat storage. Hydrocarbons are mainly used in building applications. Generally, conductivity is then expanded by including metallic additives, and in this way, it made it more efficient and productive. Previous research work done was made based on PCM Trombe wall to measure on the applications of PCM in buildings as shown in Table 14.

Fig. 11. Solar cabinet crop dryer with PCM.

cookers. Usage of solar cookers is restricted because they have insufficient storage mainly during regular days or late evening. Moreover, during the daytime, PCMs can be utilised for solar heat by stockpiling for latent heat meanwhile during evening, stored heat can be used days [130,138,139]. Previous research studies have been discussed based on solar cooking, and it is shown in Table 13. 9.4. Solar green-house The environment is being maintained with the aid of greenhouse walled in the area which is appropriate for growth and development of plants. PCMs have also been used for two purposes which are drying and curing in greenhouse sector. As an instance, aerosol cans were investigated on the energy storage capabilities of both inside and outside energy in a tail-coated fibreglass type of greenhouse. It was proven that energy was stored in the can during the daytime meanwhile energy was discharged at night by switching airflow. Greenhouse oriented in solar agriculture have been broadly utilised as a part of two decades to expand quality of the plant and efficiency together with decrease utilisation of non-renewable energy sources for heating and cooling. PCM that frequently used for these applications are CaC12 ·6H2 O, Na2 SO4 ·10H2 O, PEG, and paraffin [142]. (See Fig. 11.) This framework is appropriate for use as a solar cabinet crop dryer for fragrant herbs, restorative plants and different yields, which do not demand coordinate presentation to daylight. 9.5. Building applications Thermal energy storage for PCMs has been taken into considerations for the application in buildings since 1980. The materials used in these applications have been actualised at different spots like Trombe wall, shutters, wallboards and few others in heating and cooling applications. The models of PCM were created, developed and analysed to improvise on the capacity of heat storage as stated in literature and researchers. The heat energy which is involved in these applications is absorbed in PCM during daytime and then gradually discharges the heat energy at night [107]. PCM can be encapsulated in concrete, gypsum wallboard, and others can be stored by lowering the internal temperature variance and conserving optimum or desired temperature [109].

9.5.2. PCM wallboards The new way of using PCMs into building structures is to fuse the PCM into concrete or either cement. It is known as thermocrete. PCM wallboards are easier to encapsulate and have been used in various applications. PCM has been consolidated into plasterboard by different procedures. Various research applications consisting in such [148,149] has detailed that the concrete adjustments and PCM consolidation procedures give an influenced on the capacity of thermal energy storage upon thermal performance of PCMs in various sorts of concrete blocks. [150] has conducted an investigation based on a full scale on the utilisation of PCM in internal partition wall in a lightweight building. Based on the experiment, they discovered that the change in surrounding temperature in the room is diminished due to the overheating period. Tests were directly carried out during few seasons for utilisation of PCM copolymer composite wallboard and reasoned that surrounding temperature was increases or decreases to 4.2 ◦ C. Meanwhile [151] contemplated another inventive cement with PCM based on thermal properties to build up an item which would not give an effect on the mechanical strength of concrete divider. 10. Conclusion The research background and analysis that is being drafted out in these proves on the importance of organic phase change materials in the fast-developing nanotechnology field. The applications which compromise on the organic phase change materials have been utilised and will be used for future development in these areas. The selection of Organic PCM is based on different parameters such as chemical, thermal, physical and kinetic properties besides latent heat, thermal conductivity, sensible heat and melting. Although organic phase change materials are known for their expensive operating cost, synthesising on the materials will reduce the cost and increases the productivity in industrial use. The synthesis of organic phase change has been widely done to improve with the aid of latest and greatest methods of CNTs. From the research and literature review, the properties that have been identified will be tested on the organic phase change materials together with the raw materials known as CNTs. These covers explicitly on the multi-walled CNTs, is because of their higher concentration carbon purity for more than 95% compared to the single-walled CNTs. Identifying on the optimal level of purity would be crucial in yielding the highest attainable percentage of carbon purity. Based on the reviews made with various organic phase change (paraffin, non-paraffin, fatty acids, etc.), paraffin type of organic phase change materials has been considered to be more suitable for a higher thermal conductivity in energy applications. Paraffin

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Table 13 Previous research on solar cooking for PCM. Research objective

Research outcomes

Research studies

Investigation on the likelihood by cooking during hours without non-sunshine using PCM.

The overall productivity of the cooker to be 3–4 times greater, used for indoor cooking Rate of heat transfer towards cooking pot is slow, so more time consumption during cooking.

[140]

Designing a cylindrical PCM storage unit for a box-type solar cooker to cook the food.

Acetamide as a latent heat storage material will make the second batch of food to be cooked based on a time frame.

[139]

Used a box type solar cooker with three reflectors as a latent heat storage unit.

To ensure reflected solar irradiance on the absorber surface to improve on the solar radiation based on the exposure of the Sun.

[138]

The flat-plate solar cooker was designed with focusing plane mirrors using energy storage materials.

Overall energy conversion efficiency was to 28.4%, and use of PCM has obtained longer period of cooking.

[141]

Table 14 Previous research on PCM Trombe Wall. Research objective

Research outcomes

Research studies

Carried an investigation to use PCM wallboard that possible to maintain room temperature.

Reported that it took longer periods upon heating or cooling system when it was switched off.

[144]

Conducted an investigation of PCM with their respective thermal performance on the gypsum board in the solar building by impregnating with PCM.

Reported that the room temperature can be reduced during the daytime.

[145]

Infuse fatty acid and paraffin waxes into the gypsum wallboard and examined the thermal dynamics with different room temperature parameters

Energy storage takes place and decreases if the phase change transition happens at a range of temperature when it is closer to the melting temperature of PCM.

[146]

Built a room by using PCM gypsum wallboard in the northeast of China

PCM wallboards could attenuate indoor air fluctuation, reduces heat transfer and functions to keep warm.

[147]

acts as a better thermal storage density and has higher scale of temperature in phase change compared to the other organic phase change. Organic phase change materials by using carbon nanofillers (metallic/oxide nanoparticles, metallic nanowires, carbon nanofibers, carbon nanotubes, and the emerging graphene/graphite nanoplatelets) on the thermal conductivity in energy storage applications, CNTs have been considered and preferred because they possess extremely high thermal conductivity and relatively low density. More noteworthy changes can only be visualised when the materials were permitted to permeate, even though the advantage will be most elevated in solidification as the permeating nanostructures in the fluid stage will be smother. All these materials discussed to offer remarkable benefits, yet facilitate improvement work are fundamental before the usage in industry such as fillers or any other applications. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors gratefully acknowledge the support from Curtin University Malaysia. The authors would like to acknowledge Taylor’s University, Malaysia Flagship grant (TUFR/2017/001/01) for this project. References [1] J.P. Da Cunha, P. Eames, Thermal energy storage for low and medium temperature applications using phase change materials–a review, Appl. Energy 177 (2016) 227–238. [2] X. Huang, J. Guo, J. He, Y. Gong, D. Wang, Z. Song, Novel phase change materials based on fatty acid eutectics and triallyl isocyanurate composites for thermal energy storage, J. Appl. Polym. Sci. 134 (2017) 44866.

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