3. RESULTS AND DISCUSSION
Fig. 4 demonstrates temperature contours for the basic system without
the turbulator at Re=5000 filled with hybrid nanofluid. Effects of solar
radiation on heat transfer fluid (HTF) from inlet to outlet of absorber
tube and formation of the thermal boundary layer are clearly seen in
this figure. Also at a certain cross section, detailed temperature
contours inside absorber tube (HTF and thickness of absorber tube) and
the annulus between absorber tube and glass cover. Fig. 5 shows
temperature contours for basic and novel systems at Re=5000 filled with
hybrid nanofluid (Effects of using the turbulators on temperature
distribution in absorber tube). It is found that usage of the
turbulators leads to more thermal diffusion because of destroying the
laminar sub-layer and increasing heat transfer surface and also
convection heat transfer coefficient.
Fig. 6 illustrates the effects of different the turbulators angles on
thermal-hydraulic characteristics of novel parabolic through solar
collector filled with hybrid nanofluid. As it is seen in this figure,
usage of the turbulators has a significant effect on thermal-hydraulic
characteristics of studied parabolic through the solar collector. It is
seen in Fig. 6a that for model \(\theta=180\) the maximum values of
Nuave are achieved during all studied range of Reynolds
numbers, which is followed with models \(\theta=90\) and\(\theta=0\), respectively. Usage of the turbulators destroys the
laminar sub layers and consequently leads to more HTC which increases
the Nuave. It is seen in Fig. 6b that for model\(\theta=180\) the maximum values of pressure drop are achieved during
all studied range of Reynolds numbers, which is followed with models\(\theta=90\) and \(\theta=0\), respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more vortexes which increase the pressure drop penalty.
It is seen in Fig. 6c that for model \(\theta=180\) the maximum values
of friction factor are achieved during all studied range of Reynolds
numbers, which is followed with models \(\theta=90\) and\(\theta=0\), respectively. Usage of the turbulators destroys the
laminar sub layers and consequently leads to more vortexes which
increase the average friction factor. It is seen in Fig. 6d that for
model \(\theta=90\) the maximum values of PEC are achieved during all
studied range of Reynolds numbers, which is followed with models\(\theta=0\) and \(\theta=180\), respectively. It is found that the
model with \(\theta=90\) has not the maximum average Nusselt values
but it has lower pressure drop than model \(\theta=180\).
Fig. 7 illustrates the effects of different the turbulators heights on
thermal-hydraulic characteristics of novel parabolic through solar
collector filled with hybrid nanofluid. It is seen in Fig. 7a that for
model \(HO=15\)mm the maximum values of Nuave are
achieved during all studied range of Reynolds numbers, which is followed
with models \(HO=10\)mm and \(HO=5\)mm, respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more HTC which increases the Nuave. It is seen in Fig.
7b that for model \(HO=15\)mm the maximum values of pressure drop are
achieved during all studied range of Reynolds numbers, which is followed
with models \(HO=10\)mm and \(HO=5\)mm, respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more vortexes which increase the pressure drop penalty. It is seen in
Fig. 7c that for model \(HO=15\)mm the maximum values of friction
factor are achieved during all studied range of Reynolds numbers, which
is followed with models \(HO=10\)mm and \(HO=5\)mm, respectively.
Usage of the turbulators destroys the laminar sub layers and
consequently leads to more vortexes which increase the average friction
factor. It is seen in Fig. 7d that for model \(HO=5\)mm the maximum
values of PEC are achieved during all studied range of Reynolds numbers,
which is followed with models \(HO=10\)mm and \(HO=15\)mm,
respectively. It is found that the model with \(HO=5\)mm has not the
maximum average Nusselt values but it has lower pressure drop than model\(HO=15\)mm.
Fig. 8 illustrates the effects of different the turbulators positions on
thermal-hydraulic characteristics of novel parabolic through solar
collector filled with hybrid nanofluid. It is seen in Fig. 8a that for
model \(BO=1000\)mm the maximum values of Nuave are
achieved during all studied range of Reynolds numbers, which is followed
with \(BO=800\)mm and smooth channel, respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more HTC which increases the Nuave. It is seen in Fig.
8b that for models \(BO=1000\)mm and \(BO=800\)mm the maximum values
of pressure drop are achieved during all studied range of Reynolds
numbers, which are followed with smooth channel, respectively. Usage of
the turbulators destroys the laminar sub layers and consequently leads
to more vortexes which increase the pressure drop penalty. It is seen in
Fig. 8c that for models \(BO=1000\)mm and \(BO=800\)mm the maximum
values of friction factor are achieved during all studied range of
Reynolds numbers, which are followed with smooth channel, respectively.
Usage of the turbulators destroys the laminar sub layers and
consequently leads to more vortexes which increase the average friction
factor. It is seen in Fig. 8d that for model \(BO=1000\)mm the maximum
values of PEC are achieved during all studied range of Reynolds numbers,
which is followed with models smooth channel and \(BO=1000\)mm,
respectively. It is found that the model \(BO=800\)mm mm has lower
thermal-hydraulic performance than smooth channel.
Fig. 9 illustrates the effects of different turbulators slops on
thermal-hydraulic characteristics of novel parabolic through solar
collector filled with hybrid nanofluid. It is seen in Fig. 9a that for
model \(\delta=60\) the maximum values of Nuave are
achieved during all studied range of Reynolds numbers, which is followed
with \(\delta=40\) and \(\delta=20\), respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more HTC which increases the Nuave. It is seen in Fig.
9b that for model \(\delta=60\) the maximum values of pressure drop
are achieved during all studied range of Reynolds numbers, which is
followed with \(\delta=40\) and \(\delta=20\), respectively. Usage
of the turbulators destroys the laminar sub layers and consequently
leads to more vortexes which increase the pressure drop penalty. It is
seen in Fig. 9c that for model \(\delta=60\) the maximum values of
friction factor are achieved during all studied range of Reynolds
numbers, which is followed with \(\delta=40\) and \(\delta=20\),
respectively. Usage of the turbulators destroys the laminar sub layers
and consequently leads to more vortexes which increase the average
friction factor. It is seen in Fig. 9d that for model \(\delta=40\)the maximum values of PEC are achieved during all studied range of
Reynolds numbers, which is followed with models smooth channel and\(\delta=20\) and \(\delta=60\), respectively.
Fig. 10 illustrates the effects of different turbulators distances on
thermal-hydraulic characteristics of novel parabolic through solar
collector filled with hybrid nanofluid. It is seen in Fig. 10a that for
model \(bO=20\)mm the maximum values of Nuave are
achieved during all studied range of Reynolds numbers, which is followed
with \(bO=15\)mm and \(bO=8\)mm, respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more HTC which increases the Nuave. It is seen in Fig.
10b that for model \(bO=20\)mm the maximum values of pressure drop are
achieved during all studied range of Reynolds numbers, which is followed
with \(bO=15\)mm and \(bO=8\)mm, respectively. Usage of the
turbulators destroys the laminar sub layers and consequently leads to
more vortexes which increase the pressure drop penalty. It is seen in
Fig. 10c that for model \(bO=20\)mm the maximum values of friction
factor are achieved during all studied range of Reynolds numbers, which
is followed with \(bO=15\)mm and \(bO=8\)mm, respectively. Usage of
the turbulators destroys the laminar sub layers and consequently leads
to more vortexes which increase the average friction factor. It is seen
in Fig. 10d that for model \(bO=20\)mm the maximum values of PEC are
achieved during all studied range of Reynolds numbers, which is followed
with models smooth channel and \(bO=15\)mm and \(s=8\)mm,
respectively.
Finally, the parabolic through solar collector model with\(\theta=180\), \(HO=15\), \(BO=1000\)mm, \(\delta=40\) and\(bO=20\)mm filled with hybrid nanofluid suggested as the optimum
model in present investigation.