Eutectic Phase Change Materials Research Articles

Study of eutectic organic phase change materials with enhanced thermal properties

Power shortage is a multifaceted problem of the developing nations. Due to the energy crisis, India, one of the Asia’s key economies is experiencing power shortages. During the recent years, electricity demand has gone up while there is a crunch in coal inventory at the thermal power plants. Therefore augmenting resources from solar energy to nuclear and fossil fuels helps to meet the energy demand. Thermal energy storage [TES] is an enabling technology which improves reliability, integrate generation sources and also help reduce environmental impacts. Phase change materials (PCMs) have been favourable in accumulation of energy in the form of latent heat. Latent heat thermal energy storage (LHTES) is preferred over sensible heat thermal energy storage (SHTES) due to thermal stability and higher storage density. This paper impart cognizance on methods to enhance thermal properties by introducing organic eutectic phase change materials (EO-PCMs) and nano-enhanced PCMs. Outcome of differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FT-IR), thermal reliability and thermal conductivity tests for various eutectic mixtures have been examined. Though practical application of PCMs is limited due to formidable challenges such as discharge during phase transformation and low thermal conductivity, eutectic PCMs & nano-enhanced PCMs address the aforementioned challenges due to congruent melting, stability under thermal cycling and significant sorption capacity. Finally, it deliberates some emerging research topics and challenges involved in developing EO-PCMs and nano-enhanced PCMs.

Performance Improvement of Lauric Acid-1-Hexadecanol Eutectic Phase Change Material with Bio-Sourced Seashell Powder Addition for Thermal Energy Storage in Buildings

Performance Improvement of Lauric Acid-1-Hexadecanol Eutectic Phase Change Material with Bio-Sourced Seashell Powder Addition for Thermal Energy Storage in Buildings

A comprehensive review on phase change materials for heat storage applications: Development, characterization, thermal and chemical stability

Phase change materials (PCMs) utilized for thermal energy storage applications are verified to be a promising technology due to their larger benefits over other heat storage techniques. Apart from the advantageous thermophysical properties of PCM, the effective utilization of PCM depends on its life span. Moreover, PCMs which are utilized for different solar thermal energy storage applications are required longer thermal and chemical stability for the extended performance of a system. This review shows the in-depth details on thermal stability and reliability of different PCMs such as organic, inorganic, eutectics, and composites materials for heat storage applications. Different methods for measuring the thermophysical properties along with the classification of PCMs based on applications and temperature ranges have been discussed. This paper also covers the selection criteria and commercial viability of PCMs for different domestic and industrial applications. In addition to this, the effect of thermal cycle testing on the properties of different organic, inorganic, eutectic, and composite PCMs has been summarized. The present article can be highly useful for researchers and practice engineers in the areas related to thermal energy storage applications.

Thermal properties and reliabilities of myristic acid-paraffin wax binary eutectic mixture as a phase change material for solar energy storage.

In this work, a myristic acid (MA)–paraffin wax (PW) binary eutectic phase change material (PCM) was prepared by a melt-solution blending method. The eutectic point of the MA–PW binary system was determined to be 62 wt% MA–38 wt% PW using a cooling curve. In addition, the phase transition properties and thermal stability of MA–PW binary eutectic PCM were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG) analysis. The melting temperature and latent heat as well as starting temperature of decomposition for MA–PW binary eutectic PCM were 41.99 °C, 171.43 J g−1 and 137.86 °C, respectively. Besides, analysis of the chemical and crystal structures of MA, PW and MA–PW revealed no chemical reaction between MA and PW to produce a new molecular structure and no change in the crystal structure. Finally, MA–PW binary eutectic PCM still has good thermal properties and chemical stability after 500 cold–hot cycles.

Experimental investigations on the phase change and thermal properties of nano enhanced binary eutectic phase change material of palmitic acid‐stearic acid / CuO nanoparticles for thermal energy storage

A novel nano enhanced binary eutectic phase change material (PCM) of Palmitic acid (64 wt%) and stearic acid (36 wt%) as base PCM and copper oxide nanomaterial in varying mass fractions (0.3%, 0.8%, 1.5% and 3%) as thermal conductive enhancer was prepared using two step method and its heat transfer properties were investigated. Thermal characteristics using DSC technique shows the significant stability with the inclusion of nano particles. The melting latent heat of nano embedded eutectic PCM decreases between 21.6% and 0.74% while no significant change is observed in phase transition temperature. The FTIR and XRD analysis confirm that no chemical reaction occurs but only physical interaction takes place between the eutectic PCM and nanoparticles. The TGA analysis shows that the CuO NPs in the nano enhanced PCM act as supporting material and reveals excellent thermal stability. Thermal conductivity of PA-SA eutectic PCM increases gradually by 19%, 34.23%, 55.24%, and 118.87% for the nano particle mass fraction of 0.3%, 0.8%, 1.5% and 3% respectively. The thermal cycling test after 1000 cycles reveals that the nano enhanced PA-SA eutectic mixture perceives excellent thermal and chemical stability. The findings of experimental study concluded that the prepared nano enhanced PA-SA mixture finds to be the suitable material for moderate temperature energy storage applications.

Characterization and Reliability of Caprylic Acid-Stearyl Alcohol Binary Mixture as Phase Change Material for a Cold Energy Storage System.

This study reports the in-depth investigation of the thermophysical properties and thermal reliability of caprylic acid-stearyl alcohol (CA-SA) eutectic phase change material (PCM) for cooling applications. The phase diagram of CA-SA showed a eutectic point at a 90:10 molar ratio. The onset melting/freezing temperature and latent heat of fusion of caprylic acid-stearyl alcohol from the differential scanning calorimetry (DSC) were 11.4 °C/11.8 °C and 154.4/150.5 J/g, respectively. The thermal conductivity for the prepared eutectic PCM in the solid phase was 0.267 W/m.K (0 °C), whereas, in the liquid phase, it was 0.165 W/m.K (20 °C). In addition, the maximum relative percentage difference (RPD) marked at the end of 200 thermal cycles was 5.2% for onset melting temperature and 18.9% for phase change enthalpy. The Fourier transform infrared spectroscopy (FT-IR) result shows that the eutectic PCM holds good chemical stability. Corrosion tests showed that caprylic acid-stearyl alcohol could be a potential candidate for cold thermal energy storage applications.

Constructing nanocarbon-loaded precisely phase transition-tuned energy composite eutectics with enhanced thermal conductivity: Nanocarbon’s crystallinity-dependent thermal transport

In this study, a eutectic composition consisting of myristic and stearic acid (MS) are developed to establish a cooling system with suitable operational temperature and enhanced thermal transport by adding a class of carbon nanoadditives (few-layer graphene platelets (FGP), nitrogen-doped tubular carbon (NTC) and deoxygenated graphene oxide (DGO)). Nanoadditives are added to phase transition-tuned eutectic phase change materials to derive at figure-of-merit (FOM) in enhancing thermal transport. MS-FGP exhibited significant thermal conductivity improvement as compared to MS-NTC and MS-DGO for 1 wt% loading. After ascertaining FOM, a system with variable FGP is developed, and it exhibited an increase in thermal conductivity of 128%, 420% and 597% for 1, 3 and 5 wt%, respectively. This study shed light on elucidation of underlying mechanism for nanocarbon’s structutural degree dependent thermal transport. This systematic approach could lay a step forward for controlling extreme operational temperature for thermal safety of an efficient high-powered Li-ion battery system to achieve prolonged life and energy density using phase change materials.

Enhanced thermal conductivity and shape stabilized LiNO3‐NaCl eutectic/exfoliated graphite composite for thermal energy storage applications

AbstractLiNO3 and NaCl salt mixtures are explored as phase change material (PCM) for thermal energy storage. We developed a process for synthesizing LiNO3 and NaCl eutectic mixture at room temperature and found that eutectic mixture consists of 88.8 wt% LiNO3 and 11.2 wt% NaCl salts. The latent heat and melting point of PCM are ~230°C and 302 kJ kg−1. Thermal conductivity of eutectic composition is measured with transient plane source (TPS) technique and value is 0.8 W m−1 K−1. We used thermochemically exfoliated graphite (ExG) in 5, 10, 15, and 20 wt% ratio with the developed eutectic to prepare PCM‐ExG composites to enhance thermal conductivity of pristine eutectic PCM. The maximum thermal conductivity of these PCM‐ExG composite PCMs is ~13.8 W m−1 K−1 for 20 wt% ExG and ~1400 kg m−3 density, ~16.5 times of pristine eutectic PCM. We observed that PCM‐ExG composite containing ExG ≥ 15 wt% retains liquid PCM inside the ExG pores, useful to reduce leakage problem of thermal energy storage vessel. The high thermal conductivity, high latent heat of fusion and suitable melting point of LiNO3‐NaCl eutectic PCM‐ExG composite PCM make it suitable for solar thermal energy storage and industrial waste heat recovery applications.

Performance evaluation of double slope solar still augmented with binary eutectic phase change material and steel wool fibre

Solar still integrated with phase change material (PCM) as latent heat storage material proves to be the prominent solution for obtaining potable water from brackish water. However, none of the individual organic PCM possesses all the required favourable characteristics such as specific melting temperature, latent heat of fusion etc to operate the solar still in any environmental conditions. Therefore, development of binary eutectic PCM by mixing two or more different types of organic PCMs, enhances the thermo physical properties of PCM. In this experimental work, an effort was made to fabricate and compare the energetic and exergetic performances of traditional and modified double slope solar still. Two techniques were used to augment the yield of traditional solar still. First, binary eutectic PCM (mixture of palmitic acid and stearic acid) have been stored in copper tubes and copper cylinder. Second, Steel wool fibre (SWF) is embedded in solar still basin with PCM. Additionaly the effect of variation of basin water depth on still performance has also been studied. Hence, four different cases namely MDSSS-1 (PCM with 4 cm water depth), MDSSS-2 (PCM with 3 cm water depth), MDSSS-3 (PCM with 2 cm water depth) and MDSSS-4 (PCM + SWF with 2 cm water depth) have been compared with TDSSS (traditional still with 4 cm water depth) in the environmental condition of Bhopal city, Madhya Pradesh, India. The result reveals that total cumulative yields for TDSSS, MDSSS-1, MDSSS-2, MDSSS-3 and MDSSS-4 are approximately 1.82, 2.46, 2.78, 3.26, and 3.40 kg/m2, respectively. The average energy efficiency of MDSSS-4 is 41%, which was higher than TDSSS (22.21%), MDSSS-1 (30.42%), MDSSS-2 (33.88%) and MDSSS-3 (38.14%).Meanwhile, the daily average exergy efficiencies for TDSSS, MDSSS-1, MDSSS-2, MDSSS-3 and MDSSS-4 are found to be 3.1855, 5.47, 9.13, 10.1 and 11.8% respectively. Hourly variation of heat transfer coefficient and exergy fraction has also studied for different cases and it shows that mean value of coefficients of evaporation, convection and radiation heat transfer for MDSSS-4 is higher than TDSSS by 45.9, 36.2, and 35 % respectively.

Long-term assessment of the thermal stability of sodium nitrate-urea eutectic phase change material

The eutectic mixture formed by urea and sodium nitrate can be an interesting candidate for use as a phase change material for thermal energy storage in space heating and domestic hot water applications. It shows a melting point of 85 °C, a melting enthalpy of 172 J/g and a price around 0.9 €/kg. However, the thermal stability of the mixture is a great concern for this application. A preliminary evaluation of the thermal stability was performed and previously reported by the authors. It consisted of an accelerated thermal cycling test with 210 thermal cycles and the material showed a stable behavior. Nevertheless, the long-term stability of urea in the liquid state at temperatures below 100 °C is uncertain and requires a specific study. The main objective of the present work is to evaluate the long-term thermal stability of the mixture when it is exposed to long periods of use under conditions representative of actual applications, by means of analyzing the thermal and compositional behavior of samples remaining at 100 °C for several periods up to one year. A methodology is proposed, which intends to isolate the thermal degradation phenomenon from others, such as phase segregation, supercooling, and polymorphism, that can be introduced by thermal-cycling. It also aims to be more representative of the actual application than the accelerated thermal cycling approach. • Long-term degradation study of the urea-sodium nitrate eutectic mixture as a phase change material. • Experimental tests representative of actual use conditions. • Urea mainly degrades to biuret and cyanuric acid. • Degradation levels stabilize after an initial significant decrease. • Tightness is a key parameter and greatly influences degradation.

Development of low-temperature eutectic phase change material with expanded graphite for vaccine cold chain logistics

This research aims to explore a novel PCM that can satisfy the needs of vaccine cold chain logistics temperature zone (2–8 °C), with decyl alcohol (DA) and lauric acid (LA) chose to be eutectic. Considering the thermal conductivity and leakage of materials, DA-LA/EG composite phase change material (CPCM) with a mass ratio of 12:1 is prepared by the vacuum adsorption method. The thermal properties of DA-LA/EG CPCM are analyzed by DSC, cooling curve, Hot Disk, SEM etc. From the DSC graphs of DA-LA eutectic phase change material (EPCM), it is found that there is difference between the melting temperature and solidification temperature, which is defined as phase change hysteresis. The results indicate that the phase transition temperature of DA-LA/EG CPCM is 2.08 °C, with high latent heat and thermal conductivity of 188.71 J g−1 and 1.7527 W m−1 K−1, respectively. Due to the unique porous structure of EG, the thermal conductivity is 13.75 times higher than that without EG, which leads to the phase transition time shortened by 79.47%. Furthermore, DA-LA/EG CPCM shows excellent cyclic stability and chemical stability after 500 high-low temperature alternating tests. From TGA, the decomposition temperature of DA-LA/EG CPCM is 186.55 °C, higher than the working temperature range. The applicability is demonstrated by using the CPCM into an incubator. Overall, DA-LA/EG CPCM has good application prospects in vaccine cold chain logistics.

Electromagnetic self-encapsulation strategy to develop Al-matrix composite phase change material for thermal energy storage

How to break through the corrosion rupture limit of eutectic Al-Si phase change material (PCM) in iron-based encapsulation container has been a major challenge for realizing the high temperature waste heat recovery in metallurgical industry. Herein, we proposed a self-encapsulation strategy of eutectic Al-Si PCM with no need of container via constructing the 3D-honeycomb-SiC reinforced Al matrix composite with Si-rich◎Si-poor cladding structure ([SiC&Si-rich]◎EAl-Si), which can fundamentally address the corrosion issue. Strikingly, such a structure feature delivers the excellent structural stability and superior energy storage capacity with a high thermal conductivity of 96 ~ 62 W·m−1·°C−1 at 75 ~ 550 °C (increased by ~ 10% after 1000 cycles), and giant discharge energy density of 490 J·g−1 (with the capacity retention of over 98.9% after 1000 cycles). Compared with the Al-Si@Al2O3 microcapsule with core–shell architecture, the discharge energy density of the [SiC&Si-rich]◎EAl-Si was enhanced by 19.3%~105.7%. In comparison with conventional iron-based container encapsulation, the [SiC&Si-rich]◎EAl-Si demonstrates a 10.7% and 16.2% improvement in efficiency of charge and discharge process. More importantly, this self-encapsulation strategy of eutectic Al-Si PCM can be further constructed continuously by the electromagnetic continuous separation technology, which can potentially pave the way to achieve the large scale production of the [SiC&Si-rich]◎EAl-Si, thus providing technological support for accelerating the application process of eutectic Al-Si PCM in metallurgical industry.

Macro-encapsulated 3D phase change material: Na2S2O3·5H2O-NaOAc·3H2O/carbonized Melamine sponge composite as core and SiC modified polyurethane thin-layer as shell

Micro-encapsulated phase change materials (PCMs) which constructed by PCMs as core and polymer as shell had been confirmed a good way to store and release latent heat, but its complex and expensive manufacturing process as well as poor mechanical strength impede its industrialization. Herein, based on the concept of micro-encapsulated PCM with core-shell structure, we conveniently prepared a 3D macro-encapsulated PCM with improved heat conductivity and mechanical performance. The optimized eutectic PCM with 72 wt%Na2S2O3·5H2O-28 wt%NaOAc·3H2O was impregnated into lightweight marco-porous carbonized Melamine sponge (CMS) carrier to prepare PCM@CMS composite as core, with pretty small enthalpy reduction within 1.23 %. Subsequently, SiC modified polyurethane thin-layer (PUSiC) was employed as shell to macro-encapsulate PCM@CMS, which solved leakage problem, improved thermal conductivity and guaranteed the steady function of PCM. The crystalline structure, composition and the morphology of PCM@CMS were analyzed in detail. Mechanical performance test revealed that PUSiC thin-layer possessed increased compression strength, tensile modulus and reduced fracture tensile strain, enabling the stable operation of PCM@CMS@PUSiC in high-intensity workplaces. Heat transfer experiment demonstrated that heat transfer of PCM@CMS@PUSiC was enhanced from the inside out. Thermal stability tests manifested the brilliant encapsulation effect of PUSiC thin-layer, by which PCM functioned steadily at 60 °C without leakage or dehydration. Furthermore, its thermal properties difference before and after 200 thermal cycles was small, showing a potential of long-time use.

Surface evolution of eutectic MgCl2·6H2O-Mg(NO3)2·6H2O phase change materials for thermal energy storage monitored by scanning probe microscopy

Surface evolution of eutectic salt hydrate phase change materials (PCMs) plays an important role in progressive degradation, and its tracking and control are crucial to the cycle stability in latent heat storage. In this study, we combined Peak Force quantitative nanomechanics with differential scanning calorimetry to monitor the topography evolution, nanomechanical performances, and corresponding thermal properties of the eutectic MgCl2·6H2O-Mg(NO3)2·6H2O PCM (EPCM). Topography of the EPCM was highly similar to those of the corresponding single crystallohydrates, accounting for its congruent melting and solidifying behavior. Surface evolution-induced initial phase separation at the nanoscale level was directly imaged. This deterioration is rooted in adsorption/evaporation of the surface water molecules, and can be restored accurately. Based on this, a universal strategy to eradicate phase segregation was proposed, with no significant degradation after 1500 thermal cycles. Moreover, evolution of the EPCM containing thickener hydroxyethyl cellulose and its effects on local supercooling due to the formed crosslinking networks were explored, and stable supercooling inhibition (≤0.6 °C) was achieved. This study provides a better understanding of the evolution mechanism and its effects on the thermal behavior, and can be used as an effective guide for improving the long-term stability of low-cost salt hydrate-based latent heat storage materials.

Applicability assessment of stearic acid/palmitic acid binary eutectic phase change material in cooling pavement

Phase change materials are functional materials that have the potential to cool asphalt pavement. This study focuses on the design of a stearic acid/palmitic acid binary eutectic phase change material (SA/PA-PCM) and its utilization in asphalt binder by conducting a series of tests. The results show that the dislocation density, micro-strain, and crystallinity of SA/PA-PCM increase by approximately 432%, 140%, 6%, respectively, which means that it can have a more stable crystal structure. Therefore, the SA/PA-PCM has a higher phase transition enthalpy (226.9 J/g) and a better phase transition temperature (54.8 °C) than traditional materials. Moreover, no chemical reaction is detected in the eutectic and modified asphalt binder processes. Crystalline SA/PA-PCM has the potential to increase the anti-deforming capability of the binder, whereas liquid SA/PA-PCM suppresses the rheological behaviors. The decomposition temperature of SA/PA-PCM (approximately 200 °C) is higher than that of two kinds of individual fatty acids. Meanwhile, it is still above the traditional hot-mix asphalt pavement construction temperatures. Thus, we concluded that SA/PA-PCM has exceptional phase change characteristics and is applicable for use in cooling asphalt binder. Nevertheless, encapsulating technologies must be adopted to prevent the deleterious impact of the liquefiable phase change materials on the binder.

Thermal buffering performance evaluation of fatty acids blend/fatty alcohol based eutectic phase change material and simulation

Eutectic PCM was prepared by mixing a unique proportion of commercial fatty acids blend, OM-21 and fatty alcohol, 1-dodecanol (DD) adopting blending-ultrasonication technique. The unique composition was found out based on thermal properties of series of samples made by mixing 0 -100 wt. % of DD with 100-0 wt. % of OM-21 keeping overall wt. % fixed at 100. Despite the presence of two PCMs, only one crystallization peak at 0.68°C (differential scanning calorimetry, DSC) was noted with 60:40 wt. % of OM-21: DD (denoted as OD-64) and the peak temperature was lower than either of the PCM, indicating eutectic behavior. FTIR-ATR spectra of OD-64 confirmed possibility of no chemical reaction in eutectic PCM. Enthalpies of phase transformation observed from DSC analysis were 140.6 kJ kg−1 (melting) and 139.1 kJ kg−1 (crystallization) while melting peaks were at 7.38°C / 12.21°C. Thermal stability was estimated from TGA (thermo gravimetric analysis) measurement. The duration of charging(-18°C) and discharging(40°C) for 180 g OD-64 in TCP box were estimated to be 65 min and 48 min respectively. 390 min of thermal buffering (between -17°C – 25°C) can be achieved for 240 g chocolate placed inside TCP box with ambient temperature of 27°C. Additionally, a three dimensional TCP box model was made using COMSOL Multiphysics 5.5 and unsteady state energy balance equations along with its boundary conditions were used to define experimental conditions. The model equation was validated with experimental data obtained at two extreme ambient temperatures i.e. 27°C and 40°C. The validated model equation was found to be closely (<±9.0%) matching with experiment performed at 30°C ambient conditions. Thus, eutectic OD-64 with good enthalpy would be effective for low temperature thermal buffering applications.

A techno-economic assessment on the adoption of latent heat thermal energy storage systems for district cooling optimal dispatch & operations

The adoption of high-density phase change materials as cold thermal energy storage media have been considered as potential alternatives to water and ice. In this paper, the implementation of these media has been investigated in the context of district cooling in mixed-used building micro-grids whereby the cold thermal energy storage is retrofitted into an existing eco-building cluster. The techno-economic feasibility of implementing phase change materials, which includes eutectic salt, polyethylene glycol and paraffin as cold thermal energy storage media for district cooling, have been evaluated by computing the economic dispatch of a cooling bus network using mixed-integer quadratic programming. Furthermore, the impact of high-density storage media with a reduced footprint on the integration and design of cold thermal energy storage systems in district cooling has been included in the analysis. The capital expenditure of cold thermal energy storage systems, the land rental price for required occupancy and operating expenditure are used to determine the net present value after 20 years. Through peak shaving, optimally sized cold thermal energy storage has shown a better alternative substituting one of the two chillers. The smaller chiller (1200 kWc) is no longer required in the plant, giving significant savings in capital expenditure. The cost-benefit analysis also showed that only eutectic salt phase change materials are competitive with ice, with a net present value approaching 200,000 $ after 20 years. When phase change materials are adopted, especially if compared with water, the building operations and related costs are significantly less affected by large fluctuations in land rental price given its smaller footprint, thus posing significantly lower financial risks.

Studies on microstructural and thermo-physico properties of microencapsulated eutectic phase change material incorporated pure cement system

Application of different MPCM dosage i.e. 5, 10 and 15% has been tested on the cement paste specimens in order to elucidate its role in deciphering the thermal comfort. Effective thermo-physico parameters like compressive strength, bulk density, porosity, water absorption, thermal conductivity and specific heat capacities were investigated and results obtained revealed significant changes in these properties with the incorporation of MPCM. Incorporation of MPCM causes decrement in compressive strength, bulk density, thermal conductivity while increment in porosity, water absorption and specific heat capacity. Moreover, instrumental analysis revealed that the incorporation of MPCM leads to loosening of dense microstructure in cement paste matrix and alters the rate of cement hydration to large extent as the formation of hydrated products like C-S-H and C-H decreases with the increase in the dosage of MPCM. Based on the findings, the developed MPCM may be used in the cement paste for better thermal comfort.

Energy and exergy analyses of a solar-based multi-generation energy plant integrated with heat recovery and thermal energy storage systems

By the depletion of natural resources, the utilization of solar energy to provide the required needs of societies attracted many researchers across the globe. An innovative multigeneration energy system driven by solar energy is proposed in this paper. The proposed system utilizes a pressurized cavity-based solar power tower and latent thermal energy storage (TES) to continuously harness the solar energy. Considering the high-temperature nature of solar tower technology, a four-step Copper-Chlorine (Cu-Cl) thermochemical cycle is used to produce hydrogen, oxygen, and steam. Using an unfired gas turbine unit, air is used as the heat transfer fluid of the solar tower unit, instead of molten salt, to supply the required heat for the thermolysis and hydrolysis reactions of the Cu-Cl cycle. Therefore, the deficiencies of molten salts are eliminated. Moreover, recovering heat within the integrated system improves the performance of the system significantly. Also, By utilization of a high-temperature ternary eutectic phase change material (PCM), a dynamic model is developed to deal with the intermittency of solar energy. Using energy and exergy approaches, the proposed system is investigated to assess exergy destruction rates and the overall system performance. A parametric study is performed to investigate the influence of design parameters such as the number of heliostats, pressure ratio of GT, and temperatures of reactions on the system performance. The results show that the system produces electricity, steam, hydrogen, and oxygen at a rate of 41.9 MW, 12.6 kg/s, 0.19 kg/s, and 0.76 kg/s, respectively. Energy and exergy efficiencies of the integrated system are found to be 49.9%, and 44.9%, respectively. The proposed system is compared with other alternative systems available in the literature and shows the best performance among others.

Thermal performance enhancement of eutectic PCM laden with functionalised graphene nanoplatelets for an efficient solar absorption cooling storage system

The present work investigates the thermal enhancement of a binary eutectic phase change material (PCM) (150–200 °C), laden with different concentrations of COOH-functionalized Graphene nanoplatelets (f-GNP) for a multi-effect solar cooling thermal storage system. The novel nano-composite is prepared by varying the weight concentration of f-GNP from 1% to 5% in a pristine eutectic salt of LiNO3-KCl (50:50) using the standard nano synthesis protocol. The microstructure, dispersion uniformity are evaluated using scanning electron microscope (SEM) and thermophysical properties of the nano-composite are characterized using dynamic Differential scanning calorimetry (DSC). The thermal conductivity enhancement due to the doping of f-GNP is studied through a series of experimental trials conducted with Laser flash analysis (LFA). The obtained data is plotted and compared with a more robust theoretical thermal conductivity model. It is found that thermal conductivity rises by 104% with f-GNP dispersions, which reflects the improved thermal performance of the storage system. The specific heats of the solid and liquid phase show an increase of 80% & 38% respectively at f-GNP concentration of 5%. Finally, the effect of doping f-GNP on the conjugate heat transfer inside the PCM and fluid flow of HTF is investigated in a vertical shell and tube type storage system, suitable for the double effect solar cooling system. The f-GNP dispersions accelerate the heat storage process with a maximum decrease of 17.3% in the total melt duration. In addition, the role of increased viscosity on the natural convection is simultaneously studied with the increased thermal conduction due to nanoplatelets dispersions.