Adding nanoparticle to pure water can increase the thermal
conductivity of water. The heat transfer performance is changed.
The efficiency of CueH2O nanofluids with different mass fraction as
the working fluid in the flat-plate solar collectors were investigated.
The experimental results show that their collecting efficiencys
are all superior to that of water. The efficiency of CueH2O
nanofluids (Cu:25 nm, 0.1 wt%) is increase up to 23.83%. when the
mass fraction gets to 0.2 wt%, the efficiency of CueH2O nanofluids is
less than that of CueH2O nanofluids (0.1 wt%). It illustrates that the
nanoparticle concentration can not be too much. Nanoparticle size
also has a major effect on the efficiency of flat-plate solar collectors
with nanofluids. In allusion to the temperature and heat gain of
water in the water tank, the highest temperature and highest heat
gain of water in the nanofluid (25 nm, 0.1 wt%) tank can increased
up to 12.24% and 24.52% compared with that of water tank,
respectively. On the other hand, the frictional resistance coefficient
of nanofluids has a slight increase compared to water. In the
compatibility aspect, nanofluids has no corrosion on stainless steel
and silicone rubber but has a little corrosion on brass [31]. The
corrosion problem can be solved by adding some corrosion inhibitor.
In conclusion, the solar energy absorbing experiments show
that CueH2O nanofluids have good absorption ability for solar
energy, and can effectively enhance the efficiency of flat-plate solar
collectors. Thus, CueH2O nanofluids can be hopeful to apply in
solar thermal energy system.