Heat transfer enhancement in solar air heater with turbulent natural convection by two flapping elastic winglets


Department of Mechanical Engineering, School of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran



The positive effect of self-sustained passive oscillations of two flexible vortex generators (VGs) in the naturally air flow of a solar air heater (SAH) is examined in this paper. Two VGs are attached on opposite walls of 2-D channel of the heater, where the turbulent air flows because of the buoyancy effect. The set of continuity, momentum and energy equations for free convection flow and also the equation of motion for elastic solid structure considering a two-way strongly-coupled fluid-solid interaction (FSI) are solved in transient condition by the finite element method (FEM).  Numerical result shows higher performance for SAH with two VGs in comparison with a single winglet and also with clean SAH. Although, the airflow rate decreases about 16% in SAH with two VGs because of the blockage effect of winglets, but 35% improvement in bulk temperature increase along the SAH is seen in comparison to the single VG solar heater. The applied numerical simulation has been validated against experimental and theoretical results of literature and good agreement was found.


[1] Hosseini SS, Ramiar A, Ranjbar AA. Numerical investigation of natural convection solar air heater with different fins shape. Renewable Energy 2018: 117: 488–500.
[2] Singh AP, Akshayveer, Kumar A, Singh OP., Designs for high flow natural convection solar air heater, Sol. Energy 2019: 193: 724-737.
[3] Singh AP, Singh OP, Thermo-hydraulic performance enhancement of convex-concave natural convection solar air heaters, Sol. Energy. 2019: 183: 146–161.
[4] Singh S, Experimental and numerical investigations of a single and double pass porous serpentine wavy wiremesh packed bed solar air heater, Renew. Energy. 2020:145: 1361–1387.
[5] Nemś M, Kasperski J, Experimental investigation of concentrated solar air-heater with internal multiple-fin array, Renew. Energy. 2016: 97: 722–730.
[6] Singh S, Performance evaluation of a novel solar air heater with arched absorber plate, Renew. Energy. 2017: 114: 879–886.
[7] Bensaci CE, Moummi A, Sanchez de la Flor FJ, Rodriguez Jara EA, Rincon-Casado A, Ruiz-Pardo A, Numerical and experimental study of the heat transfer and hydraulic performance of solar air heaters with different baffle positions, Renew. Energy. 2020: 155: 1231–1244.
[8]  Priyam A, Chand P, Effect of wavelength and amplitude on the performance of wavy finned absorber solar air heater, Renew. Energy. 2018:119: 690–702.
[9] Jin D, Quan S, Zuo J,  Xu S, Numerical investigation of heat transfer enhancement in a solar air heater roughened by multiple V-shaped ribs, Renew. Energy. 2019: 134: 78–88.
[10] Sivakandhan C, Arjunan TV, Matheswaran MM, Thermohydraulic performance enhancement of a new hybrid duct solar air heater with inclined rib roughness, Renew. Energy. 2020: 147: 2345–2357.
[11] Singh S, Chaurasiya SK, Negi BS, Chander S, Nemś M, Negi S, Utilizing circular jet enhancement to enhance thermal performance of solar air heater, Renew. Energy. 2020: 154: 1327-1345.
[12] Foruzan Nia M, Gandjalikhan Nassab SA, Ansari AB.  Numerical simulation of flow and thermal behavior of radiating gas flow in plane solar heaters, ASME, Journal of thermal sciences and engineering application, 2020: 12: 031008-1.
[13] Dehghani A, Gandjalikhan Nassab SA. Effects of gas radiation on thermal performance of single and double flow plane solar heaters, IJE Transaction C: Aspects 2020: 33(6): 1156-1166
[14] Jacobi AM, Shah RK. Heat transfer surface enhancement through the use of longitudinal vortices, a review of recent progress, Exp. Therm. Fluid Sci. 1995: 11: 295-309.
[15] Leu JS, Wu YH, Jang JY. Heat transfer and fluid flow analysis in plate-fin and tube heat exchangers with a pair of block shape vortex generators. International Journal of Heat and Mass Transfer 2004: 47: 4327-4338.
[16] Srinil N. Multimode interactions in vortex-induced vibrations of flexible curved/straight structures with geometric nonlinearities. J. Fluid Structure 2010: 26: 1098-1122
[17] Srinil N, Zanganeh H. Modeling of coupled cross flow/in-line vortex-induced vibrations using double Duffering and Van der Pol oscillators. Ocean Eng. 2012: 53(10): 83-97.
[18] Shi J. Hu J. Schafer SR. Chen CL. Numerical study of heat transfer enhancement of channel via vortex-induced vibration. Applied Thermal Engineering 2014: 70: 838- 845.
[19] Ali S. Menanteau S. Habch C. Lemenand T. Harion JL. Heat transfer and mixing enhancement by using multiple freely oscillating flexible vortex generators. Applied Thermal Engineering 2016: 105: 270- 289.
[20] A. K. Soti, R. Bhardwaj, J. Sheridan, Flow-induced deformation of a flexible thin structure as man- ifestation of heat transfer enhancement, International Journal of Heat and Mass Transfer. 2015: 84: 1070-1081.
[21] S. Ali et al., Three-dimensional numerical study of heat transfer and mixing enhancement in a circular pipe using self-sustained oscillating flexible vorticity generators, Chem. Eng. Sci. J. 2017: 162: 152–174.
[22] Zheng L. Xu X. Li K. Chen Y. Huang G. Chen CL. A flapping vortex generator for heat transfer enhancement in a rectangular airside fin. International Journal of Heat and Mass Transfer .2018: 118: 1340- 1356.
[23] Choi SK, Kim SO. Turbulence modeling of natural convection in enclosures: A review, Journal of Mechanical Science and Technology 2012: 26(1): 283-297.
[24] Heindel TJ, Ramadhyani SR, Incropera FP. Assessment of turbulences models for natural convection in enclosure, Numerical Heat Transfer Part B. 1994: 26: 147-172.
[25] Duffie J, Beckman W, Worek M. Solar Engineering Thermal Processes, Second edition 1994: 116.
[26] Cheng X. Müller U. Turbulent natural convection coupled with thermal radiation in large vertical channels with asymmetric heating, Int. J. Heat Mass Transfer. 1998: 41: 1681–1692.