Background: Aqueous-alumina nanofluid was prepared using magnetic stirrer and ultrasonication
process. Then, the prepared nanofluid was subjected to flow through the unshielded receiver
of the parabolic trough solar collector to investigate the performance of the nanofluid and the effects of
the dimensionless parameter were determined.
Methods: The experimental work has been divided into two sections. First, the nanofluid was prepared
and tested for its morphology, dimensions, and sedimentation using X-Ray Diffraction and Raman shift
method. Then, the nanofluids of various concentrations from 0 to 4.0% are used as heat transfer fluid in
unshielded type collector. Finally, the effect of the dimensionless parameter on the performance was
Results: For the whole test period, depending upon the bulk mean temperature, the dimensionless parameters
such as Re and Nu varied from 1098 to 4552 & 19.30 to 46.40 for air and 2150 to 7551 & 11.11 to
48.54 for nanofluid. The enhancement of thermal efficiency found for 0% and 4.0% nanoparticle concentrations
was 32.84% for the mass flow rate of 0.02 kg/s and 13.26% for the mass flow rate of 0.06 kg/s.
Conclusion: Re and Nu of air depend on air velocity and ambient temperature. Re increased with the
mass flow rate and decreased with concentration. Heat loss occurred by convection mode of heat transfer.
Heat transfer coefficient and global efficiency increased with increased mass flow rate and volume
fraction. The thermal efficiency of both 0% and 4.0% concentrations became equal for increased mass
flow rate. It has been proven that at high mass flow rates, the time available to absorb the heat energy
from the receiver is insufficient.