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ABSTRACT
This study aims to improve the thermal and hydraulic performance of the solar air collector through rectangular baffles perpendicular to the air inside the channel (duct). In the latter, four cases were examined for the number and position of baffles (6 b, 10 b, 14 b, 18 b) with a fixed inclination angle of 135° in the Reynolds range from Re = 5038 to Re = 10635 using Computational Fluid Dynamic (CFD) (Ansys Fluent 18.1). The turbulence model RNG k-ε was chosen because it gave closer results to the standard correlations of Dittus-Boelter and Modified Blasius, compared to the rest of the models. The validity of the CFD simulation was confirmed based on the experimental investigation. The study -of these cases shows that the increase in the number of baffles increases the average Nusselt number as well as the friction coefficient, where the highest value of Nusselt was recorded in the case of 18 baffles Nu = 49.40 at Re = 10257. The relationship between the positioning of the baffles and the local heat transfer coefficient was also concluded. The last three cases (10 b, 14 b, 18 b) gave a very close thermal-hydraulic performance factor (THPF), while the first case (6 b) is significantly greater than theirs by a significant percentage, where the highest value recorded THPF = 0.557 at Re = 5368. Throughout this work, the effect of baffles on the heat transfer from the absorber plate to the air was understood through the local heat transfer coefficient along the channel and the velocity fields and their rays. This said heat transfer was also perceived by adding this form of baffles in the four cases and their impact on the hydraulic and thermal performance of the collector.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Nomenclature
| A | = | Cross section area, m2 |
| Cp | = | Specific heat of air, J/kgK |
| DH | = | Hydraulic diameter, m, |
| H | = | Heat transfer coefficient,W/m2K |
| I | = | Turbulence intensity, % |
| K | = | Turbulent kinetic energy, m2/s2 |
| L | = | Length of the air duct, m |
| = | ||
| P | = | Witted perimeter, m |
| ΔP | = | Pressure drop, Pa |
| Q | = | Useful heat gain, W/m2 |
| S | = | Absorber plate area, m2 |
| U | = | Velocity, m/s |
| Dimensionless parameters: | = | |
| f | = | Friction factor |
| Nu | = | Nusselt number |
| Pr | = | Prandtl number |
| Re | = | Reynolds number |
| Y+ | = | Dimensionless wall distance |
| Greek symbols: | = | |
| λ | = | Thermal conductivity, W/m2K |
| ρ | = | Density, Kg/m3 |
| = | Kinematic viscosity, m2/s | |
| Subscripts: | = | |
| 0 | = | Smooth |
| b | = | Bulk |
| in | = | Inlet |
| out | = | Outlet |
| CFD | = | Computational Fluid Dynamic |
| THPF | = | Thermo-Hydraulic Performance Factor |
| w | = | Wall |