Nanofluids in solar collectors

Nanofluid-based direct solar collectors are solar thermal collectors where nanoparticles in a liquid medium can scatter and absorb solar radiation. They have recently received interest to efficiently distribute solar energy. Nanofluid-based solar collector have the potential to harness solar radiant energy more efficiently compared to conventional solar collectors.Nanofluids have recently found relevance in applications requiring quick and effective heat transfer such as industrial applications, cooling of microchips, microscopic fluidic applications, etc. Moreover, in contrast to conventional heat transfer (for solar thermal applications) like water, ethylene glycol, and molten salts, nanofluids are not transparent to solar radiant energy; instead, they absorb and scatter significantly the solar irradiance passing through them.Typical solar collectors use a black-surface absorber to collect the sun's heat energy which is then transferred to a fluid running in tubes embedded within. Various limitations have been discovered with these configuration and alternative concepts have been addressed. Among these, the use of nanoparticles suspended in a liquid is the subject of research. Nanoparticle materials including aluminium, copper, carbon nanotubes and carbon-nanohorns have been added to different base fluids and characterized in terms of their performance for improving heat transfer efficiency. Nanofluid-based direct solar collectors are solar thermal collectors where nanoparticles in a liquid medium can scatter and absorb solar radiation. They have recently received interest to efficiently distribute solar energy. Nanofluid-based solar collector have the potential to harness solar radiant energy more efficiently compared to conventional solar collectors.Nanofluids have recently found relevance in applications requiring quick and effective heat transfer such as industrial applications, cooling of microchips, microscopic fluidic applications, etc. Moreover, in contrast to conventional heat transfer (for solar thermal applications) like water, ethylene glycol, and molten salts, nanofluids are not transparent to solar radiant energy; instead, they absorb and scatter significantly the solar irradiance passing through them.Typical solar collectors use a black-surface absorber to collect the sun's heat energy which is then transferred to a fluid running in tubes embedded within. Various limitations have been discovered with these configuration and alternative concepts have been addressed. Among these, the use of nanoparticles suspended in a liquid is the subject of research. Nanoparticle materials including aluminium, copper, carbon nanotubes and carbon-nanohorns have been added to different base fluids and characterized in terms of their performance for improving heat transfer efficiency. Dispersing trace amounts of nanoparticles into common base fluids has a significant impact on the optical as well as thermo physical properties of base fluid. This characteristic can be used to effectively capture and transport solar radiation. Enhancement of the solar irradiance absorption capacity leads to a higher heat transfer resulting in more efficient heat transfer as shown in figure 2.The efficiency of a solar thermal system is reliant on several energy conversion steps, which are in turn governed by the effectiveness of the heat transfer processes. While higher conversion efficiency of solar to thermal energy is possible, the key components that need to be improved are the solar collector. An ideal solar collector will absorb the concentrated solar radiation, convert that incident solar radiation into heat and transfer the heat to the heat transfer fluid. Higher the heat transfer to fluid, higher is the outlet temperature and higher temp lead to improved conversion efficiency in the power cycle.nanoparticles have several orders of magnitude higher heat transfer coefficient when transferring heat immediately to the surrounding fluid. This is simply due to the small size of nanoparticle. We know that thermal conductivity of solids is greater than liquids. Commonly used fluids in heat transfer applications such as water, ethylene glycol and engine oil have low thermal conductivity when compared to thermal conductivity of solids, especially metals. So, addition of solid particles in a fluid can increase the conductivity of liquids .But we cannot add large solid particles due to main problems: Due to these drawbacks, usage of solid particles have not become practically feasible.Recent improvements in nanotechnology made it possible to introduce small solid particles with diameter smaller than 10 nm. Liquids, thus obtained have higher thermal conductivity and are known as Nanofluids. As can be clearly seen from figure 4 that carbon nanotubes have highest thermal conductivity as compared to other materials.