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.