Experimental analysis and exergetic assessment of the solar air collector with delta winglet vortex generators and baffl
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Experimental analysis and exergetic assessment of the solar air collector with delta winglet vortex generators and baffles Ali Sari1 · Meisam Sadi1 · Ghobad Shafiei Sabet1 · Mohammad Mohammadiun1 · Hamid Mohammadiun1 Received: 1 June 2020 / Accepted: 22 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract To increase the efficiency of solar air collectors (SACs), the combined effects of baffles and delta winglet vortex generator (DWLVG) on the performance of SAC have been investigated. An experimental setup has been made, and numerical simulation is carried out in Ansys Fluent. The numerical investigation is validated by the experimental study and focused on the number of baffles as well as the number and the height of DWLVG. The results show that the SAC with no baffles and DWLVG has the lowest efficiency with the maximum value of 13%, while for SAC with six baffles and three pairs of DWLVG, the efficiency reaches up to 20%. The exergy analysis of three cases, SAC without baffles and DWLVG, SAC with six baffles without DWLVG, and SAC with six baffles and three pairs of DWLVG, shows that the maximum exergy efficiency of the SAC is 30.44% and occurs when the height ratio and the number of DWLVG pairs are 0.5 and 3. The results show that for SAC with six baffles and three pairs of DWLVG, the energy and exergy efficiency improve 7.4% and 12% on an average basis compared to the typical flat plate SAC, respectively. This improvement in thermal and exergy efficiency is due to the implementation of DWLVG which produces more turbulence and eliminates the vortices generated at the corners of SAC. Keywords Solar air collector · Delta winglet vortex generators · Thermal and exergy efficiency · Heat transfer enhancement · Experimental investigation · Numerical analysis List of symbols Ac Aperture area of the collector (m2) C1 Constant function C2 Constant C1𝜖 Constant C3𝜖 Degree to which 𝜖 is affected by the buoyancy C𝜇 Constant Cp Specific heat capacity of top glass cover (J kg−1 K−1) Cpair Specific heat capacity of air (J kg−1 K−1) Ė Energy rate (W) ̇ Exergy rate (W) Ex ̇ dest Rate of irreversibility or exergy destruction Ex (W) Gk Generation of turbulence kinetic energy Gb Generation of turbulence kinetic energy due to buoyancy gi Component of the gravitational vector
* Meisam Sadi m.sadi@iau‑shahrood.ac.ir 1
I Effective solar irradiation over the surface of the collector (W m−2) k Turbulent kinetic energy ṁ air Mass flow rate of air M Mass (kg) P Fluid pressure (N m−2) Prt Turbulent Prandtl number for energy qout,k Energy flux leaving the surface qin,k Energy flux incident on the surface from the surroundings Q̇ s Useful heat rate (W) R Universal gas constant (J kg−1 K−1) Re Reynolds number s Entropy (J kg−1 K−1) S Modulus of the mean rate-of-strain tensor Sk User-defined source terms S𝜖 User-defined source terms T Periphery temperature u Velocity component in corresponding direction (m s−1) x Characteristic of length (m) YM Contribution of the fluctuating dilatatio
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