In the past decade, many researchers have evaluated the role of
nanofluids in heat transfer enhancement of thermal engineering
equipments (for instance see Refs. [1–4]). Among various
applications of nanofluids, the utilization of nanofluids in renewable
energy systems has attracted special interest. Nanofluids have a
lower heat capacity compared to common fluids; therefore, the use
of nanofluids in solar collectors as the main group of solar energy
devices leads to increases in outlet temperature of the collector. A
higher outlet temperature is significant for applications such as
building heating. There are no many studies on solar collectors
where the working fluid is a nanofluid. Here, a brief literature review
of nanofluid based solar collectors is performed.
Yousefi et al. [5] studied the effects of adding a surfactant to
Al2O3/water nanofluids on the thermal efficiency of a flat plate
solar collector. They found that the nanofluid with a weight fraction
of 0.2% provides a higher thermal efficiency than that of the weight
fraction of 0.4%. They also concluded that adding surfactant increases
the efficiency up to 15%. Next, Yousefi et al. [6] examined the
potential of multi walled carbon nanotubes/water nanofluids (with
weight fractions of 0.2% and 0.4%) on the efficiency of a flat plate
solar collector. Their results indicated that the thermal efficiency
increases with the increase of weight fraction. Later, Yousefi et al.
[7] experimentally determined the optimum pH of multi walled carbon
nanotubes/water nanofluids to maximize the efficiency of a flat
plate solar collector.