The first two flow rates were
in the laminar flow region, and the third one was in the
transient flow region. The results indicated that the collector’s
efficiency improved at all flow rates, but the least
improvement was observed at the highest flow rate
(Figs. 14–16). From this research, it can be concluded that
the enhancement in the efficiency of the collector resulting
from the use of the TiO2 nanofluid was less than that of
MWCNT. Also, the attempt to increase the stability in heat
transfer applications by using surfactants was unsuccessful
because the formation of foam had a severe adverse effect on collector’s efficiency. Therefore, other methods for
increasing the stability of the nanofluid should be studied
further. Also, it can be concluded that the nanoparticles
had a more significant and beneficial effect in the laminar
flow region.