Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: www.elsevier.com/locate/ijts Mixed convection characteristics in rectangular enclosure containing heated elliptical block: Effect of direction of moving wall Krunal M. Gangawane *,1 , Siddharth Gupta Department of Chemical Engineering, School of Engineering, University of Petroleum and Energy Studies, Dehradun-248007, Uttrakhand, India ARTICLE INFO Keywords: Elliptical block Mixed convection Reynolds number Nusselt number Grashof number Rectangular enclosure ABSTRACT The present research numerically explores the hydrodynamic and thermal characteristics due to mixed con- vection in the rectangular enclosure with one of the vertical wall moving and containing centrally placed heated elliptical block for steady state condition. In particular, the influence of different flow pertaining parameters, such as, the direction of moving vertical wall (either in positive –y or negative –y coordinate directions), aspect ratio of an elliptical cylinder (E r = 0.5, 1 and 2) are studied for the broad range of dimensionless parameters (Reynolds number: 1 ≤ Re ≤ 5000; Prandtl number: 1 ≤ Pr ≤ 100 and Grashof number: 0 ≤ Gr ≤ 10 5 ) by using finite volume method (FVM) and SIMPLE numerical approach. The analysis of physical insights of an enclosure is accomplished by systematic evaluation of the streamlines as well as isotherms profiles. In order to compare mean heat transfer from an elliptical cylinder with that of circular shape, normalized Nusselt number (Nu N ) is esti- mated. Heat transfer characteristics are more predominantly affected due to the direction of moving lid than the aspect ratio of the elliptical cylinder. Also, the enclosure with moving wall along positive –y direction tends to enhance heat transfer rate. Rather than a pure circular shape, the enclosure with heated elliptical block (Er≠1) shows a higher rate of convective heat transfer. 1. Introduction Convective heat transfer from cylinders of an elliptical cross section has received huge consideration in recent years because of its numerous engineering applications as well as pragmatic relevance. The develop- ment of high-performance heat exchanger devices for making effective use of energy is a very crucial and pressing problem nowadays. For an instance, the process heat transfer equipment, such as heat exchangers made of tubes of circular cross-section are widely used in many che- mical/process, automobile or like industries (probes and sensors, hot wire anemometry, RTM process of producing fiber composites, filters of aerosol, screens of filtration process, etc.). The flow circulation over such tubes, however, is not necessarily normal to the tube axis which makes the tube cross-section in the direction of flow to have an ellip- tical shape. In general, the elliptical geometry can represent the circular cylinder as well as very thin plate depending on the value of the axis ratio [1,2]. The heat transfer characteristics from an elliptical tube/ block depend on its geometry (i.e. aspect ratio, surface roughness, etc.), fluid properties, flow approaching condition, and the block/tube sur- face temperature variation. Moreover, the study of heat transfer from an elliptical body inside a channel/enclosure is of great theoretical significance as elliptical shape can be considered as a prototype for modeling heat transfer from a broad range of bluff bodies (as it can used to the elaborate the influence of both angle of attack and thickness). The different modes of convective heat transfer modes may significantly take place ranging from forced convection dominated regime to natural convection one inside above mentioned systems. The mixed convection (combined free and forced) heat transfer occurs when both inertial and buoyancy forces are of comparable magnitude. The basic parameters which govern the forced and natural convection are Reynolds number (Re) and Grashof number (Gr), respectively [1–3]. On the account of fundamental and pragmatic implication, the ex- perimental and numerical investigations within square/rectangular enclosures have been extensively studied and very well documented. The reason for the overwhelming popularity of such constellations is due to the simple domain with the ability to explore the broad varieties of fluid flow and heat transfer fundamentals (multiplicity of steady solutions, boundary layer, vortex size and location, circulation of fluid, etc.). Typical examples which can be idealized as an enclosure are cooling systems of electronic gadgets, high performance building in- sulation, multi-shed structures, furnace, food processing (heating of various foodstuffs like beans, carrot and potato chips, etc.), lubrication https://doi.org/10.1016/j.ijthermalsci.2018.04.010 Received 22 November 2016; Received in revised form 15 January 2018; Accepted 9 April 2018 * Corresponding author. 1 Current address: Department of Chemical Engineering, National Institute of Technology Rourkela, Rourkela 769008, Orissa, India. E-mail addresses: krunalgangawane@gmail.com, gangawanek@nitrkl.ac.in (K.M. Gangawane). International Journal of Thermal Sciences 130 (2018) 100–115 1290-0729/ © 2018 Elsevier Masson SAS. All rights reserved. T