illustrates a schematic diagram of experimental setup.
Nanofluid is pumped towards the solar collector and after the heating
process in the collector, the liquid passes a heat exchanger to cool
down. Three thermocouples with an accuracy of 0.1 °C are used to
measure the inlet and outlet temperatures of solar collector, as well as
the ambient temperature. Themass flow rate of nanofluid is determined
based on the measurement of time required to fill a small vessel with a
capacity of one liter. Experiments were conducted in sunny days for
volume concentrations of 0, 0.5%, 0.75%, and 1% and three mass flow
rates including 0.018, 0.032, and 0.045 kg/s. The solar collector surface
area was about 1.59 m2, and its inclination angle was 45°. The tests
were performed at Sun Air Research Institute, Ferdowsi University of
Mashhad, Iran. The performance characteristics of the collector were
determined based on ASHRAE Standard as described in Refs. [5–7].
The thermal efficiency of a flat plate solar collector (η) can be
calculated by the following relation [23]: