Mechanical Engineering Dept., University of Technology-Iraq, Alsina’a street, 10066 Baghdad, Iraq.


Experimental and numerical investigations are carried out on water injection in a humidification process of air traveling steadily through the curved part with a constant cross-section. A principal aim is to study the flow behavior through the curved duct and the generation of secondary flow. The effect of bend angle on the development of secondary flow and flow structure intensities and enhancement of the heat and mass transfer downstream the curved duct. Moreover, the influence of the mixing process between liquid and gas in an air humidification process was examined. Experiments were performed with an average air velocity range from (2.5 to 5 m/s) while keeping the water injection rate of (19 kg/h) through (50) cm square wind tunnel includes three bend angles of (45º, 90ºand 135º) along with three sets of nozzle tilt angles of (-45º, 0º and 45º) to the axial flow direction. The study also implies a numerical analysis using ANSYS FLUENT 2019 R3 with the turbulent model of RNG using (k-ε). Experimental results showed that the optimum operating condition (greater extent of cooling and humiliation) was obtained with a bend angle of 135º at axial water injection, i.e., 0º nozzle tilt angle at the lowest air velocity of 2.5 m/s. This could be attributed to the strong identical vortices developed and better droplet distribution across the duct, and more time available for heat exchange between water droplets and the air stream. The maximum reduction in treated air temperature was 28 %, with 219% in the relative humidity of the air stream. This condition gave corresponding cooling effectiveness of 58%.      


  • Curved portion in inlet duct of gas turbine generators is a power boosting expedient.
  • Secondary flow generated enhances the phase mixing due to momentum exchange.
  • Wider bend angle promotes mass and heat transfer rates within four cell vortices.
  • Mixing process is greatly sensitive to flow within the inner half of a curved duct. 


Main Subjects

[1] M. Boutabaa, L. Helin, G. Mompean, and L. Thais, Numerical study of Dean vortices in developing Newtonian and viscoelastic flows through a curved duct of square cross-section C. R. Mec. 337, 40, (2009).
[2] A. S. J. Mohammed1 and S. G. Abed-Alfathel the Effect of Curvature Ratio on Flow Structure and Fluids Mixing in 90o bent square duct, Journal of the University of Babylon For Engineering Sciences, Vol. (28), no. (2): 2020.
[3] P. Dutta and N. Nandi, Numerical Study on Turbulent Separation Reattachment Flow in Pipe bends with Different Small Curvature Ratio, J. Inst. Eng. India Ser. C, Howrah 711103, (2018).
[4] S. Mondol, Md. I. Hossain, and Md. T. Islam, Characteristics of Gas Flow through Bend Pipes of Different Angles IOSR Journal of Mathematics (IOSR-JM) e-ISSN: 2278-5728, p-ISSN: 2319-765X. 14 (2018)  85-93
[5] M. Anwer, R. M. C. So, and Y. G. Lai, Perturbation by and recovery from bend curvature of a fully developed turbulent pipe flow, Phys. Fluids (1989) 1387–1397, 1989.
[6] Y. D.Tridimas, and Woolley, N. H., A study of turbulent flows in pipe bends, Proceedings of the Institution of | Mechanical Engineers. Part C. Mechanical engineering science, 204(6), 399–408, (1990).
[7] P. Dutta and N. Nandi, Effect of Reynolds number and curvature ratio on single-phase turbulent flow in pipe bends, Mech. Eng., 19 (2015) 5–16.
[8] K. Wei Development of secondary flow field under 4 rotating conditions in a straight channel with square 5 cross-section Chinese Society of Aeronautics and Astronautics & Beihang University Chinese Journal of Aeronautics. CJA 1079 .23 June (2018).
[9] B. W. Morton, DRI-S. Corporation, Humidification Hand Book, Third Edition, United States of America, (2015).
[10] S. K. Wang, Handbook of Air Conditioning and Refrigeration, Second Edition, the McGraw-Hill Companies, (2001).
[11] R. Maurya, N. Shrivastava and V. Shrivastava, Performance and Analysis of an Evaporative cooling System: A Review, Int J Sci Eng Res, 5 (10) (2014) 1064-1071.
[12] S. T. Ahmed, A.J. Mohammed and H.H. M., The Effect of Atomizer Position in a Curved Duct on the Humidification Process of Steadily Flowing Air, Eng. & Tech. Journal, 31 (2013) A.
[13] J. Mohammed, and H. A. Nasser-allah, The Effect of Turbulences Flow on a Gas-Liquid Mixing Process Downstream of a Curved Duct, Journal of University of Babylon, Engineering Sciences, 26(2018) 147-157.
[14] A. S. J. Mohammed1 and S. G. Abed-AlfathelThe Effect of Curvature Ratio on Flow Structure and Fluids Mixing in 90o bent square duct, Journal of the University of Babylon for Engineering Sciences, 28(2020).
[15] ASHRAE, HVAC Systems and Equipment, Handbook, ASHRAE Inc., Atlanta; (2000).
[16] B. ABRAMZON and W. SIRIGNANO, Droplet vaporization model for spray combustion calculations, Int. j. Heat Mass Transfer. 32 (1988) 1605–1618.
[17] A. Collin, P. Boulet, G. Parent, and D. Lacroix, Numerical simulation of a water spray—Radiation attenuation related to spray dynamics, Int. J. Therm. Sci., 46 (2007) 856–868.
[18] T. Mon Soe and S. Yu Khaing, Comparison of Turbulence Models for Computational Fluid Dynamics Simulation of Wind Flow on Cluster of Buildings in Mandalay, Int. J. Sci. Res. Publ., 7 (2017) 337–350.
[19] M. Cable, An Evaluation of Turbulence Models for the Numerical Study of Forced and Natural Convective Flow in Atria, MS.C. Thesis, Queen's University, (2009).
[20] N. Nivedita, P. Ligrani, and I. Papautsky, Flow Dynamics in Low-Aspect Ratio Spiral Microchannels, Sci. Rep. 7, 44072; doi: 10.1038/srep44072 (2017).