Frontiers in Heat and Mass Transfer (FHMT), 17, 19 (2021) DOI: 10.5098/hmt.17.19 Global Digital Central ISSN: 2151-8629 1 NATURAL CONVECTON IN SINUSOIDAL–CORRUGTED ENCLOSURE UTITIING SILVER/WATER NANOLUID WITH DIFFERENT SHAPES OF CONCENTRIC INNER CYLINDERS Emad D. Aboud 1 , Qusay Rasheed Al-Amir 2 , Hameed K. Hamzah 2 , Ammar Abdulkadhim 3 , Mustafa M. Gabir 3 , Salwan Obaid Waheed Khafaji 2 , Farooq H. Ali *, 2 1 College of Engineering, Al-Musayab-Autombile Engineering Department, University of Babylon, Babylon, Hilla, Iraq 2 College of Engineering-Mechanical Engineering Department - University of Babylon-Babylon City–Hilla– Iraq. 3 Air Conditioning and Refrigeration Techniques Engineering Department – Al-Mustaqbal University College-Babylon City– Iraq. ABSTRACT The natural convection of nanofluid flow, which occurs between a sinusoidal-corrugated enclosure and a concentric inner cylinder has been numerically investigated. The two horizontal walls of this enclosure are considered adiabatic and two vertical corrugated walls are held at a constant value of the cold temperature while the inner concentric cylinder is heated isothermally. Different cylinder geometries (i.e, circular, square, rhombus, and triangular) located inside the enclosure are examined to find the best shape for optimum heat transfer. The physical and geometrical parameters influencing heat transfer are Rayleigh number (Ra=10 3 -10 6 ), undulation numbers (N=0,1 and 2), aspect ratios (AR=5, 2.5 and 1.67) and two values for the volume fraction (φ=0 and 0.05). The numerical simulation was carried out using Comsol Multiphysics Software (5.3a). Galerkin approach along with the finite element method are used to solve equations of Navier-Stokes and energy with associated boundary conditions. In this study, validations of results between some available literatures and the present study found to be in an excellent agreement. Results indicate that the heat transfer and nanofluid flow characteristics in the sinusoidal-corrugated enclosure is significantly influenced by aspect ratio, undulation number, and Rayleigh number for all cylinder shapes. Thus, with the decrease in the aspect ratio, the intensity of streamlines becomes smaller, whereas, with rice in the Rayleigh number and undulation number, intensity increase is observed. Moreover, as the undulation number increases, the average value of the Nusselt number, including the hot surface of cylinders increases. At high Rayleigh numbers, the undulation number effect on the average value of the Nusselt number is more pronounced. Besides, the research showed that the circular cylinder shape inside the enclosure has the best heat transfer characteristics and flow than the others. Keywords: Natural convection, Inner cylinder shapes, Undulation number, Aspect ratio, Streamline and isotherm contours, Flow and heat transfer characteristics. 1. INTRODUCTION For several years owing to a wide range of practical applications like heat exchangers, electronic devices cooling, crude oil storage tanks, solar collectors and the nuclear reactor, the topic of the implanted solid body inside enclosures motivated the researchers among the world to deeply examine it (Joudi et al. (2004); Ostrach (1988); Baytos and Pop (1999); Bin et al. (2001), Chamkha et al. (2011)). It was obtained based upon the previous publications, that the solid inserted body within the enclosure improves the heat transfer thermal rate. From the other hand it will decrease the flow, therefore lowering heat transfer inside the enclosures. Also, the effects of three shapes of inner cylinders (circular, square, and triangular) on heat transfer by Hussein et al.(2019). House et al. (1990) conducted computationally the buoyancy thermal driven flow in a square cavity containing conductive square body under transient conditions. It was achieved that the convection mode would be more dominant than conduction at a higher Rayleigh number. Besides that, they compared * Corresponding Author. Email: eng.farooq.hassan@uobabylon.edu.iq with and without the inner body and they conclude that inner body affect the heat transfer characteristics. The vertical shift for the location of an internal cylinder of the circular shape located within an enclosure taken the square shape illustrated numerically by Humaira et al. (2002). Hussain and Al-Amir (2011) demonstrated the influence of inner body size located within a square enclosure on the rate of heat transfer. Shu et al., (2001) employed the DQ technique to illustrate the impact of the eccentric annulus between the inner circular cylinder positioned within the square enclosure. Hussain S.H. and Hussein A.K., (2010) examined the impact of the circular inner body movement vertically within a square enclosure. Immersed boundary element method had beeu utilized by Lee et al. (2010) and Kang et al. (2013) to study the natural phenomenon for the square enclosure within circular body. They changed the inner cylinder position horizontally and diagonally. Roslan et al., (2014) analyzed the buoyancy fluid flow between the inner solid polygon placed within the square enclosure using COMSOL numerically. Choi et al. (2014) demonstrated numerically the inner circular position located Frontiers in Heat and Mass Transfer Available at www.ThermalFluidsCentral.org