In this study, for the first time, the nanoparticle (NP) of Fe₂O₃@glutamine (C₅H₁₀N₂O₃) was synthesized to improve the Fe₂O₃ properties in absorbing carbon dioxide (CO₂) using the base fluid of hydrous N-methyl-2-pyrrolidone (NMP) solution (50 wt%), as a physically powerful CO₂ absorbent. To do this, several nano-NMP solutions, in different weight percentages of NPs, were first prepared. Then, in a batch setup, the nano-NMP solutions were directly exposed to CO₂ gaseous (at the pressures of 20, 30, and 40 bar) to clarify the effects of the mass percentage of NPs and initial pressure on CO₂ absorption. Results clearly illustrated that Fe₂O₃ nanofluid was not stable more than 0.025 wt%. However, Fe₂O₃@glutamine nanofluid was stable approximately two times more than Fe₂O₃ nanofluid due to the presence of glutamine as a hydrophilic agent in the structure of Fe₂O₃@glutamine. Moreover, in comparison to the base fluid (NMP solution), although Fe₂O₃ increased CO₂ absorption up to 9.14%, Fe₂O₃@glutamine NPs caused the CO₂ absorption to increase up to 19.41%, which can be determined as the chemical reactions of two amino groups in the glutamine structure with CO₂ and also higher stability of Fe₂O₃@glutamine NPs compared to bare Fe₂O₃ NPs. To achieve accurate results, all the mentioned experiments were repeated 5 times. The performance of Fe₂O₃ and Fe₂O₃@glutamine NPs after the fifth trial reduced by less than 3.5%, which reveals that the synthesized NPs had almost stable efficiency throughout their applications.

Solar energy will assist in lowering the price of fossil fuels. The current research is based on a study of a solar dryer with thermal storage that uses water and waste engine oil as the working medium at flow rates of 0.035, 0.045, and 0.065 l/s. A parabolic trough collector was used to collect heat, which was then stored in a thermal energy storage device. The system consisted of rectangular boxes containing stearic acid phase change materials with 0.3vol % Al₂O₃ nanofluids, which stored heat for the waste engine oil medium is 0.33 times that of the water medium at a rate of flow of 0.035 l/s which was also higher than the flow rates of 0.045 and 0.065 l/s. The parabolic trough reflected solar radiation to the receiver, and the heat was collected in the storage medium before being forced into circulation and transferred to the solar dryer. At a flow rate of 0.035 l/s, the energy output of the solar dryer’s waste engine oil medium and water was determined to be roughly 12.4, 14, and 15.1, and 9.8, 10.5, and 11.5 times lower than the crops output of groundnut, ginger, and turmeric, respectively. The energy output in the storage tank and the drying of groundnut, ginger, and turmeric crops with water and waste engine oil medium at varied flow rates of 0.035, 0.045, and 0.065 l/s were studied. Finally, depending on the findings of the tests, this research could be useful in agriculture, notably in the drying of vegetables.

Solar still, as one of the important devices for generating water using renewable energy, has been widely used in arid as well as coastal areas where access to fresh water is limited. This paper uses CFD simulation to compare double-slope solar still, hemispherical solar still, and tubular solar still using nanofluid film cooling. Al₂O₃-water nanofluids with a concentration of 0.1% are used due to facilitate sunlight penetration into the absorber plate inside the solar desalination. It is assumed the flow is steady, laminar, and air is an ideal and incompressible gas. The simple algorithm is considered to calculate the relationship between pressure and velocity and to separate the transfer and pressure interpolation terms from the appropriate upstream designs. Also, the economic, exergoeconomic, and CO₂ mitigation parameters of various solar stills were investigated. The study revealed that the water productivity of double-slope solar desalination using nanofluids film cooling is improved by about 4.8% compared with tubular solar desalination with nanofluid film cooling. Also, the lowest CPL of 0.0362 $/L was obtained in the double-slope solar desalination using nanofluid film cooling. The net CO₂ mitigation of 14.08 tons, 13.72 tons, and 13.44 tons was obtained for double-slope solar desalination, hemispherical solar desalination, and tubular solar desalination, respectively.

Previous studies have shown insufficient dispersion and thermal stability of nanofluids for high-temperature carbon capture and storage applications. Compared to the other NPs, TiO₂ nanofluids exhibit superior stability due to their high zeta potential. In previous studies, TiO₂ nanofluids have shown superior performance in heat transfer and cooling applications along with importing the stability of other nanofluids like SiO₂ in form of nanocomposites. Therefore, in this study, a nanofluid formulation consisting of titania nanofluid in a base solution of ethylene glycol (EG) with different co-stabilizers such as surfactants was synthesized for better dispersion stability, enhanced electrical, and rheological properties especially for the use in high-temperature industrial applications which include carbon capture and storage along with enhanced oil recovery. The formulated nanofluid was investigated for stability using dynamic light scattering (DLS) study and electrical conductivity. Additionally, the formulated nanofluid was also examined for thermal stability at high temperatures using an electrical conductivity study followed by rheological measurements at 30 and 90 °C. At a high temperature, the shear-thinning behavior of EG was found highly affected by shear rate; however, this deformation was controlled using TiO₂ nanoparticles (NPs). Furthermore, the role of surfactant was also investigated on dispersion stability, electrical conductivity followed by viscosity results, and it was found that the nanofluid is superior in presence of anionic surfactant sodium dodecyl sulfate (SDS) as compared to nonionic surfactant Triton X-100 (TX-100). The inclusion of ionic surfactant provides a charged layer of micelles surrounding the core of a NP and it produced additional surface potential. Consequently, it increases the repulsive force between two adjacent NPs and renders a greater stability to nanofluid while nonionic surfactant allowed monomers to adsorb on the surface of NP via hydrophobic interaction and enhances the short-range interparticle repulsion, to stabilize nanofluid. This makes titania nanofluid suitable for widespread high-temperature applications where conventional nanofluids face limitations. Finally, the application of the synthesized titania nanofluids was explored for the capture and transport of CO₂ where the inclusion of the anionic surfactant was found to increase the CO₂ capturing ability of titania nanofluids by 140–220% (over the conventional nanofluid) while also showing superior retention at both investigated temperatures. Thus, the study promotes the role of novel surfactant-treated titania nanofluids for carbon removal and storage and recommends their applications involving carbonated fluid injection (CFI) to carbon utilization in oilfield applications.

The present work aims to investigate the effects of various additives on the stability of graphene nanoplatelet (GnP)–based nanofluid phase change material (NFPCM) for cold thermal energy storage (CTES). The NFPCMs are prepared by dispersing six different types of surfactants (anionic, cationic, and non-ionic types) in deionized (DI) water at a mass ratio of 1:0.5 GnP to surfactant. NFPCMs can be found to be stable with a suitable surfactant even after 30 days using zeta-potential distribution, UV–vis absorption, visual inspection, and sedimentation tests at low temperature. The maximum enhancement in thermal conductivity of 8.3% and 48.3% is recorded in both liquid and solid states for the NFPCM with gum arabic (GA) respectively. The viscosity was enhanced by the dispersion of non-ionic surfactants, where the anionic surfactant (sodium dodecylbenzene sulfonate (SDBS)) NFPCM had a 29.9% lower augmentation compared to DI water. Furthermore, differential scanning calorimetry (DSC) results demonstrate that the phase change properties of the NFPCM are significantly affected depending on the surfactant type. The maximum phase change enthalpy is lowered (10.6%) in the Tween 80 NFPCM as compared to the base PCM. The long-term stability with the highest thermal transport property of the NFPCM storage unit integrated with the chiller is capable of achieving environmental pollution remediation by minimising the time it takes to charge the PCM.

To provide the progressive global demand for energy, the use of renewable energies is being rapidly developed. Since solar radiation is available in most parts of the earth, the photovoltaic (PV) power plant is one of the worthwhile solutions. As a deficiency, temperature rise in photovoltaic cells leads to a drop in their electrical output power. In this experimental study, the circulation of carbon black nanofluid was investigated as a coolant of PV modules. Both water and ethylene glycol (EG) were used as the base fluids. It is found that all modified cases generate more output power than the conventional one. For instance, water + carbon nanofluid yields 54% more output power compared with the conventional one. To make a real assessment of using nanofluid as a coolant, the electrical consumption by pump and fan must be counted. Therefore, in this study, the net output power is calculated. In the cases of EG and EG + carbon, the net output powers get lower than the conventional module. So, they are not justifiable. In this paper, a modified formula is proposed to calculate the exergy efficiency, in order to achieve more accurate results. Accordingly, from an exergy viewpoint, 16.3% and 4.5% in electrical and thermal exergy efficiencies are achieved, when water + carbon nanofluid was used. Moreover, the values of entropy generation and lost exergy were reported for all considered cases.

This work aims to explore the optical and thermal conversion characteristics of activated carbon—solar glycol nanofluids with various volume fractions namely 0.2, 0.4, and 0.6%, respectively. Kigelia africana leaves were synthesized into porous activated carbon nanomaterials by using the high-temperature sintering process and the pyrolysis process in a muffle furnace. The experimental investigation was carried out with different nanofluid concentrations by using the solar simulator. Nanofluids were heated with the assistance of a solar simulator test system and the convection/conduction heat loss was decreased by using the glass as an insulating material around the test section. Prepared nanofluid with 0.6 vol% activated carbon augmented the thermal conductivity by 14.36% at 60°C. The maximum temperature difference of 10°C was attained at 0.6% volume concentrations of nanofluid as compared with base fluid (solar glycol). In addition, maximum receiver efficiency of 94.51% was attained at 0.6% volume fractions of activated carbon-based nanofluid compared with solar glycol thru a light radiation time of 600 s. Moreover, activated carbon–based nanofluid exhibited significantly higher absorption efficiency as the majority of the radiation was absorbed by the nanofluid. It is concluded that activated carbon-based nanofluids could be a suitable low-cost highly stable material for developing working fluid for direct absorbance solar collector–based applications.

The main objective of this study is to lower the greenhouse gases by developing and optimizing a solar flat plate collector. The rifled tube is integrated into the collector to increase the thermal heat transfer thereby improving its performance. Two flat plate collectors, one with in-housed longitudinal fins and another without fins of 0.5 m² collector area, have been intended and fabricated with provisions for K-type thermocouples to examine the temperature variations inside the collector for different working fluids. This current study reveals using CuO and Al₂O₃ nanoparticles in varying weight fractions in incremental order to study the effect of weight fractions on the efficiency of the collector. The simulation was done using computational fluid dynamics both for the finned and without finned tube collectors separately and the outcome of the results for the collector outlet temperatures is compared with the experimental one and results show a valuable outcome for the intended collectors. Initially, the test was conducted with pure distilled water as working fluid and further nanoparticles were opted and doped inside the collector side for varying weight fractions of 0.2% and 0.4% and their results are compared. The experimental results showed an improved heat transfer was pragmatic in the collector side for using nanoparticles. Mixing the nanofluids exhibited superior efficiency on the collector side. The results showed after successful trials of experimentation, doping of CuO nanoparticles by varying weight fractions of 0.2% and 0.4%, augmentation of the collector (unfinned) efficiency is 2.1% and 4.05%, and similarly for finned tube collector, it is 3.02% and 5.5% for same weight fractions. In order to improve the thermal efficiency of collector, CuO is replaced by Al₂O₃ nanoparticles; for dissimilar weight fractions, the efficiency is enhanced nearly by 3.7% and 6.54% for unfinned tube collector, and for the finned tube, the collector is 4.8% and 7.8% respectively, compared with the base working fluid (water). Experimentation of the collectors with finned tube type achieved a superior efficiency compared with that of unfinned tube collectors which is proved to be higher when used for nanofluids to that of the base working fluid water.

Solar still, which uses solar renewable energy sources, especially solar energy, to produce pure water, is a promising technology as it is abundantly available and eco-friendly. Researchers have innovated in internal and external designs to enhance distillate productivity in solar desalination systems. The present review paper discusses the major internal modifications done in history and recent past to enhance the distillate output. Six sub-sections have been developed concerning historic internal modifications that discuss types of basin liners, water depth, stones, dyes, phase change materials, and weirs. It has been found that among all the historic internal modifications, phase change materials were the most effective with distillate yield enhancement of up to 80%. The limitation in distillate yield made the researchers to perform further modifications to enhance the productivity, and hence, recent internal designs have also been discussed. Recent internal modifications have six sub-sections: fins, wicks, nanofluids, nanostructures, dynamic modifications, and natural materials. Among the recent, dynamic modifications were the most efficient with productivity enhancement of up to 300%, with a maximum cumulative yield of 8.78 kg/m²/day for the rotating wick solar still compared to CSS which gave only 2.21 kg/m²/day. Such a kind of review work has not been performed till date, which covers all the internal design modifications in one paper exhaustively. Furthermore, gaps have been identified, and future perspectives have been presented in the conclusion section. It has been observed that nanostructures, nanoparticles, and dynamic modifications are the most promising internal modifications in recent times that can boost distillate productivity to a greater degree.

The present research work aims to investigate the energy saving aspects in cool thermal energy storage system (CTES) by improving the thermophysical properties of deionized (DI) water. The influence of phase change enthalpy, specific heat, thermal conductivity, and cooling rate of the DI water for the dispersion of chemically functionalized multi-walled carbon nanotubes (f-MWCNT) is studied experimentally. The covalent functionalization method is used to modify the surface of the multi-walled carbon nanotubes (MWCNT) with the use of concentrated nitric acid. The nanofluid phase change materials (PCMs) in different mass concentrations (0.25%, 0.50%, and 0.75%) were prepared by dispersions of the f-MWCNT in DI water. The minimum reduction in enthalpy (4.01%) was recorded for the nano-PCM with 0.75% f-MWCNT as compared to the base PCM with 0.5% of sodium dodecyl benzene-sulfonate (10%). The thermal conductivity enhancement of 53.15% and 28.2% was recorded in both states for the nano-PCM (with 0.75%) at the temperature of − 10 °C and 5 °C respectively. Also, the enhancement of 30% and 23% in cooling rate is recorded for the dispersion of maximum concentration of f-MWCNT at the HTF temperatures of − 8 °C and − 6 °C, respectively. It is proven from the above findings that the dispersion of f-MWCNT reduces the subcooling and facilitates the running of the CTES system at a higher operating temperature.