The effect of pH value of nanofluids on the efficiency of a new
cylindrical solar collector with helical tube is investigated.
The experimental research is carried out using CuO–H2O and
Al2O3–H2O nanofluids as the working fluids. The results show that
the more differences between the pH of nanofluid and the pH of
isoelectric point causes the more increase in the thermal efficiency
of the solar collector. So that for CuO nanofluid (pHIEP = 9.5) at the
acidic condition (pH = 3), the increased efficiency obtained by
about 52% compared with the nanofluid at pH = 10.5. Also, for
Al2O3 nanofluid (pHIEP = 7.4) at the basic condition (pH = 10.5)
the efficiency of the collector is calculated by 64.5% greater than
that with the nanofluid at pH = 9.2. The efficiency of the solar collector
with Al2O3 nanofluid at the basic condition and far from isoelectric
point is higher than that with CuO nanofluid.