[en] Highlights: • Nanoparticles are more suited and adapt to enhance the performance of solar systems. • Extinction coefficient and refractive index of nanofluids are found higher. • Optimum range of volume fraction for which enhancement in heat transfer coefficient is maximum. • Overall response of specific heat capacity of nanofluids is highly anomalous. - Abstract: In recent times solar energy has attracted the attention of scientists to a great deal. On the surface, there are two reasons for it: primarily, the scientists are interested in it with the intent to innovating new devices and secondly, developing new methods to harness it. Miniaturization of devices and energy efficiency are the major focal domains around which new materials are being worked on. The design of solar system may get some basic changes, if the new materials get applied successfully. Albeit, the nanofluids are a comparatively recent innovation which exhibit enhanced heat absorbing and heat transport ability. This paper intends to reinforce the working of nanofluids applied on solar system in the light of works done earlier; it further also explores the variable performance of the solar-system with and without application of nano-fluids. This work has been segmented into two parts: the first part focuses on presenting the experimental and numerical results for the thermal conductivity, viscosity, specific heat and the heat transfer coefficient reported by several authors. The second part deals with the application of nanofluids on different types of solar systems: solar collectors, photovoltaic systems, and solar thermoelectric and energy storage system. A study of the works earlier done seems to be suggesting that the nanofluids have great potential to enhance the functioning of various thermal systems. The recent results of the application of nanofluids in PV/T systems too have been consolidating. It can be safely assumed further that it might enhance the overall performance of the solar energy conversion process

[en] Highlights: • Solar collectors are special kind of heat exchangers. • Particle concentration is important parameter for thermal conductivity of nanofluid. • Rise of Bejan number indicates systems qualitative response. • Multi walled carbon nanotube is best performing. - Abstract: The present analysis focuses on a wide variety of nanofluids for evaluating performance of flat plate solar collector in terms of various parameters as well as in respect of energy and exergy efficiency. Also, based on our experimental findings on varying mass flow rate, the present investigation has been conducted with optimum particle volume concentration. Experiments indicate that for ∼0.75% particle volume concentration at a mass flow rate of 0.025 kg/s, exergy efficiency for Multi walled carbon nanotube/water nanofluid is enhanced by 29.32% followed by 21.46%, 16.67%, 10.86%, 6.97% and 5.74%, respectively for Graphene/water, Copper Oxide water, Aluminum Oxide/water, Titanium oxide/water, and Silicon Oxide/water respectively instead of water as the base fluid. Entropy generation, which is a drawback, is also minimum in Multiwalled carbon nanotube/water nanofluids. Under the same thermophysical parameters, the maximum drop in entropy generation can be observed in Multiwalled carbon nanotube/water, which is 65.55%, followed by 57.89%, 48.32%, 36.84%, 24.49% and 10.04%, respectively for graphene/water, copper oxide/water, Aluminum/water, Titanium Oxide /water, and Silicon oxide /water instead of water as the base fluid. Rise of Bejan number towards unity emphasizes improved system performance in terms of efficient conversion of the available energy into useful functions. The highest rise in energy efficiency of a collector has been recorded in Multiwalled carbon nanotube/water, which is 23.47%, followed by 16.97%, 12.64%, 8.28%, 5.09% and 4.08%, respectively for graphene/water, Copper oxide/water, Aluminum oxide/water, Titanium oxide /water, and Silicon oxide/water instead of water as the base fluid.

[en] Highlights: • Use of nanofluid improves the performance of solar collector. • Thermo-physical properties of the nanofluid have been discussed. • Optimum particle concentrations are found to exist. • Bejan number reaches closer to unity. - Abstract: In present work, testing of solar collector has been performed for MgO/water working fluid having particle size ∼40 nm and particle volume concentration at 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5% at 0.5, 1.0, 1.5, 2.0, 2.5 lpm respectively. Performance analysis of solar collector is based on first law of energy balance and qualitative nature of energy flow based on second law analysis. Parameters of performance analysis are chosen in order to examine both quantitative and qualitative characteristics of system performance. These parameters are thermal efficiency, energetic efficiency, pumping power, entropy generation; Bejan number and reduction in surface area. Experimental observation establishes thermal efficiency enhancement 9.34% for 0.75% particle volume concentration at flow rate 1.5 lpm. Exergetic efficiency enhancement observed 32.23% for same concentration and flow rate. Bejan number also reaches closer to unity (0.97) which throws light on systems qualitative response in terms of decline in entropy generation contribution due to internal irreversibilities and frictional heat loss. Entropy generation is 0.0611 W/K for 0.75% particle concentration compare to 0.1394 W/K for same flow rate and 0.071 W/K for 1.5% particle volume concentration. In this endeavor some penalty in form of rise in pumping power loss also incurred. 6.84% enhancement in pumping power loss observed for optimum flow rate and particle volume concentration which has not as much pronounced effect as enhancement in thermal efficiency and exergetic efficiency.

[en] Sustainable development of second most populated country of world, India depends on the planning and utilization of conventional and non-conventional energy sources. Presently energy safety has top most prime concerned for sustainable development. Energy barriers/bottleneck, prospect of solar energy with consideration of cost, hot spot of solar energy, government policies, training and education of solar sector and data of solar radiation analyze in this article. Key aspect that helpful in barrier reduction and growth of solar sector suggested through paper. By this study it has been found that sustainable growth of India depend of utilization of solar energy. Full concentration by country over solar sector necessary for satisfying future demand of energy for country growth and development. (paper)

[en] Highlights: • An experimental test loop has been constructed to study the PHE thermal characteristics. • For a given heat duty, the nanofluid volumetric flow rate required is lower than that of water. • For a given pumping power, more heat could be removed by the nanofluids. • Nanofluids may be a good choice for heat transfer fluid because of higher exergy efficiency. - Abstract: The present experimental investigation focuses on the effect of symmetric (β ∼ 30°/30° and 60°/60°) and mixed (β ∼ 30°/60°) chevron angles in PHE on comparative energetic and exergetic performance for nanofluid-water. The particle volume concentration of selected ZnO/water nanofluid being used as coolant lies in range 0.5–2.0%. The experimental findings elucidates the detailed observations of the effect of different chevron angles in PHE on heat transfer rate ratio, heat transfer coefficient ratio, overall heat transfer coefficient ratio, pumping power ratio, performance index ratio, exergy loss, non-dimensional exergy loss, qualitative response of system by exergetic efficiency, total entropy generation and contribution of irreversible heat transfer arises due to frictional losses by Bejan number. Experimental observation confirm that optimum enhancement in heat transfer rate ratio, heat transfer coefficient ratio and optimum reduction in exergy loss are obtained at β ∼ 60°/60° for 1.0% particle volume concentration of ZnO/water nanofluid. Total entropy generation also minimized for this configuration, which is 41.78% and 26.94% for β ∼ 60°/60° as compared to β ∼ 30°/30° and β ∼ 30°/60° in PHE respectively. Bejan number is the highest for β ∼ 60°/60° in PHE indicates reduction in irreversible heat transfer due to frictional losses, thus improving the qualitative response of the system.

[en] Highlights: • Use of nanofluid improves the heat transfer performance of plate heat exchanger. • Thermo-physical properties of the nanofluid have been discussed. • Optimum particle concentrations for maximum heat transfer is found to exist. - Abstract: Writing, or even making an attempt to write anything on or about Plate Heat Exchangers (Henceforth, PHE) would be no more than a futile effort to reassert and glorify an already stronghold state of PHEs, as is evident with the kind of multilayered and multi-tasked functions it performs, obviously in different forms, in various domains of work & walks of life, since a good long time. Nonetheless, in a bid to bring about a certain makeshift in the way the PHE has been functioning and sustaining, there was a need to revisit the structural pattern and the fluids that contribute to the performance of PHE. Summarily, this brings the researcher and designers to shift the focus not only from the conventional design but also to introduce a new substance which could further contribute to enhance the performance of the PHE. That is why, in recent times, the miniaturization of PHE and energy efficiency have become focal point of attention, discourse and research. While exploring for better alternates, the nanofluids have surfaced as probable (replaceable) substitutes. The Nanofluid is a relatively recent (in contrast with the PHEs) finding that promises, pronouncedly, greater heat absorbing and heat transport ability. The review article attempts to take a sneak peak into some of the important published articles that deal with the function and performance of PHEs using nanofluids. The first section of the paper presents observations by several authors on experimental and numerical results regarding thermal conductivity, viscosity, specific heat and heat transfer coefficients. The second section talks of application of nanofluids in plate heat exchangers. It has also examined the utility of nanofluids, particularly in PHEs, based on experiments and numerical studies. A review of previous works featuring experimental and numerical investigations seems to be suggesting, to the level of establishing, that nanofluids have great potential in increasing the overall performance of the plate heat exchangers. There is a further vital scope to work on the performance and utility of nanofluids and work on the equative proportions of its application, in the direction, the paper has made an attempt of.

[en] This paper highlights an investigation on the comparative analyses of exergetic performance with optimum volume concentration of hybrid nanofluids in a plate heat exchanger (PHE). Different types of hybrid nanofluids (Al₂O₃ + MWCNT/water, TiO₂ + MWCNT/water, ZnO + MWCNT/water, and CeO₂ + MWCNT/water) as coolant have been tested. Proportion of 0.75% of nanofluid has been found to be the optimum volume concentration. The requisite thermal and physical properties of the hybrid nanofluids were measured at 35 °C. Various exergetic performance parameters have been examined for comparing different hybrid nanofluids. The highest reduction in exergy loss of CeO₂ + MWCNT/water hybrid nanofluid has been obtained at a concentration of about 24.75%. Entropy generation decreased with the increase in volume concentration. The results established that CeO₂ + MWCNT/water hybrid nanofluid can be a promising coolant for exergetic performances in a PHE. (paper)

[en] In the past decade, nanotechnology’s rapid developments have created quite a lot of prospects for researchers and engineers to check up on. And nanofluids are important consequences of this progression. Nanofluids are created by suspending nanoparticles with average diameters below 100 nm in conventional heat transfer carriers such as water, oil, ethylene glycol, etc. Nanofluids are considered to offer substantial advantages over usual heat transfer fluids. When dispersed in a uniform way and suspended stably in the base fluids, a minimal amount of nanoparticles can significantly improve the thermal properties of host fluids. Present work attempts to address this challenge considering state-of-the-art advances in understanding, discussing, and mitigating problems about nanofluids’ stability. Stable and highly conductive nanofluids are produced by generally, one-step and two-step production methods. Both approaches suffer from problems with the nanoparticles’ agglomeration to be an important one. Thus, numerous numerical models and the principal physical phenomena affecting the stability (fundamental physical principles that govern the interparticle interactions, clustering and deposition kinetics, and colloidal stability theories) have been analyzed. Concerning the particles’ dynamic motion, the significance of different forces in nanofluid in particulate flows such as drag, lift (Magnus and Saffman), Brownian, thermophoretic, Van der Waals, electrostatic double-layer forces are investigated.

d1e12380^>Furthermore, an overview of nanofluids’ thermophysical properties, physical models, and heat transfer models is​included in this work. In order to realize the unexpected discoveries and overcome classical models’ limitations, several researchers have suggested new physical concepts and mechanisms, and they have created new models to enhance the transport properties. This review study includes numerous aspects of the nanofluids’ science by investigating applications, thermal properties and giving critical chronological milestones about the nanofluids’ evolution. Also, the present review discusses in detail various modeling and slip mechanisms for the heat transfer of nanofluids. Potential novel 2D materials as nanofluids have also been discussed and reported. A brief overview of the potential applications utilizing nanofluids has been reviewed, and future research gaps have been reported. Furthermore, recommendations were extracted regarding current scientific gaps and future research directions to cover the physical phenomenon, stability, thermophysical properties, overview of some applications, and the limitations hindering these nanofluids’ deployment. The review is presumed to be valuable for scholars and researchers working in the area of numerical simulations of nanofluids and experimental aspects and help them understand the fundamental physical phenomena taking place during these numerical simulations and experiments and explore the potential of nanofluids both in academia and industry.