Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations
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Thermosiphon
Copper oxide
Mass fraction
Suspension
Absorbance
Molar absorptivity
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Solar thermal collector
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Solar thermal collector
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ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2 (2009)
Solar energy utilization is very important in the background of global warming and reduction of carbon dioxide emission. Solar air/water collectors are convenient to convert solar energy into heat. Compared with regular solar collectors, direct absorption solar absorbers are not common. However, nanofluids can be used in direct solar absorbers to improve their performances. The objective of this paper is to evaluate the potential of application of nanofluids in direct solar absorbers. Spectral transmittances of nanofluids within the solar spectrum have been measured by a customized spectrophotometer. A direct solar absorber has been built to use nanofluids as the working fluid and its performance has been experimentally investigated. It is found that the radiative properties of nanofluids deviate significantly from that of the base fluid. A remarkable amount of visible light can pass through the SiO2 nanofluid while solar radiation can hardly transmit through the TiO2 nanofluid and ZrC nanofluid. The ZrC nanofluid shows the highest solar absorbance among the studied nanofluids. The temperature increase rate of the nanofluid is faster than that of water when the liquid stagnant in the absorber is illuminated by solar radiation. Furthermore, the temperature differences between the inlet and outlet of the TiO2 nanofluid and ZrC nanofluid are higher than that of the SiO2 nanofluid at the same flow rate. This work is beneficial for the exploration of nanofluids in direct solar absorbers.
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Nanofluids are the type of fluid suspensions that contains nano-sized particles. Their thermophysical properties have been studied to a great extent. Nanofluids have outstanding thermal as well as optical properties. Carbon-based materials are also being used nowadays as nanofluid additives for solar thermal collectors. The preparation of nanofluids is the most important step which may affect its thermal properties. Properties of both the individual components play role in determining the properties of the nanofluid. Thermal conductivity of a nanofluid is the most important property which certifies its heat transfer performance. Viscosity is one of the most crucial properties of nanofluids. The widespread use of solar energy for heating and cooling buildings is affected by the cost of the flat-plate collector. Flat-plate solar collectors are classified as a special class of heat exchangers. The efficiency of solar cells can be improved by using cooling solar cells. The solution to this problem is by using nanofluids.
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This chapter focuses on the application of the nanofluids in direct absorption solar collectors (DASCs) in which the working fluid is immediately exposed to the incident solar radiation. It investigates the influence of various thermophysical properties and optical properties as well as nanofluid properties on the performance of the low-flux and high-flux DASCs. The chapter discusses challenges and future perspectives of nanofluids. The mass and heat flow of nanofluids are affected by their viscosity. In other words, the pumping power and convective heat transfer have a significant relationship with the nanofluid viscosity. The transmittance of nanofluids, like other optical properties, depends on many elements such as nanoparticles type, base fluid type, path depth, particle size, and concentration. Despite of the growing interest with nanofluids applications in solar collectors, there are some weakness and difficulties that need to be addressed when optimising the application of the nanofluids in the DASCs.
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