4. CONCLUSION
Present work investigates thermal-hydraulic performances of turbulent
forced hybrid nanofluid flow and heat transfer inside a parabolic
through solar collector equipped with the turbulators. The main aim of
present work is to simulate the geometry using ANSYS-Fluent-Software and
also investigate the effects of different Reynolds numbers and
geometrical parameters on thermal and hydraulic characteristics of the
studied parabolic through solar collector to achieve the maximum PEC
value. The length of the collector is 860 mm and the absorber diameter
and glass cover diameter are 50 mm and 80 mm, respectively. Also the
inlet length of 600 mm and outlet length of 100 mm are determined
because it is important that the inlet flow is fully developed and there
be not any flow comeback at exit section of the channel. The absorber
system is made of stainless steel 304 with 2mm thickness and the glass
cover is made of normal glass with the thickness of 5mm. Also three
different Reynolds numbers, Re=2000, 5000 and 8000. For all studied
models initial nanofluid temperature is Tinitial= 450K and the solar irradiation of I = 900W/m2is adopted. The heat transfer fluid is water-based
MWCNT-Al2O3 (80%:20%) hybrid nanofluid
which makes a Newtonian nanofluid. Due to achieving the most efficient
Newtonian nanofluid in present study, solid nanoparticles of MWCNT and
Al2O3 are added to the base fluid in
volume concentration of 0.01 with diameters of 24 nm. A
three-dimensional computational fluid dynamic procedure has been
established in present investigation to study the turbulent hybrid
nanofluid flow and heat transfer performances in the absorber tube and
the annulus between absorber tube and glass cover. The RANS equations
with the shear-stress (SST) \(k\omega\) turbulence model have been
employed for modeling the turbulence regime. The most important results
are as follow:
- Usage of the turbulators leads to more thermal diffusion because of
destroying the laminar sub layer and increasing of heat transfer
surface and also convection heat transfer coefficient.
- Usage of the turbulators has a significant effect on thermal-hydraulic
characteristics of studied parabolic through the solar collector.
- For model \(\theta=180\) the maximum values of Nuaveare 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.
- Usage of the turbulators destroys the laminar sub layers and
consequently leads to more vortexes which increase the pressure drop
penalty.
- The model with \(\theta=90\) has not the maximum average Nusselt
values but it has lower pressure drop than model \(\theta=180\).
- For model \(HO=15\)mm the maximum values of Nuaveare achieved during all studied range of Reynolds numbers, which is
followed with models \(HO=10\)mm and \(HO=5\)mm, respectively.
- 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.
- The model with \(HO=5\)mm has not the maximum average Nusselt values
but it has lower pressure drop than model \(HO=15\)mm.
- For model \(BO=1000\)mm the maximum values of Nuaveare achieved during all studied range of Reynolds numbers, which is
followed with \(BO=800\)mm and smooth channel, respectively.
- 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.
- The model \(BO=800\)mm mm has lower thermal-hydraulic performance
than the smooth channel.
- For model \(\delta=60\) the maximum values of Nuaveare achieved during all studied range of Reynolds numbers, which is
followed with \(\delta=40\) and \(\delta=20\), respectively.
- For model \(\delta=40\) the maximum values of PEC are achieved
during all studied range of Reynolds numbers, which is followed by
models smooth channel and \(\delta=20\) and \(\delta=60\),
respectively.
- For model \(bO=20\)mm, the maximum values of Nuaveare achieved during all studied range of Reynolds numbers, which is
followed by \(bO=15\)mm and \(bO=8\)mm, respectively.
- 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 \(bO=8\)mm, respectively.
- 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.