Numerical Investigation on Heat Transfer Enhancement due to Assisting and Opposing Mixed Convection in an Open Ended Cavity Antonio Carozza, Oronzio Manca, and Sergio Nardini Abstract----Combined natural convection and forced convection gets a great attention for its importance in practical applications in various modern systems. Channels with an open cavity are of interest in electronic cooling, nuclear reactors, building management and solar energy systems. In these geometrical configurations, sometimes natural convection is insufficient for thermal management and control of such systems, so forced convection is required. Numerical investigation on mixed convection heat transfer in a two- dimensional channel with open cavity is investigated in this article. Forced flow assisting and opposing the motion generated by the natural convection inside the cavity is considered. A uniform temperature is considered to be associated alternatively on the left surface and on the right side of the cavity. The other surfaces are taken to be adiabatic. Governing equations are solved using the cell centered finite volume method commercial code Fluent. The simulation is carried out for a wide range of Reynolds numbers ( Re = 10– 1000 ) and Richardson numbers ( Ri = 0.1–1.7x10 4 ). Results are presented in the form of streamlines, average temperatures of the fluid, vertical velocities at mid-length of the channel and mean velocity fields. The conclusion is that the enhancement of heat transfer rate is generated principally by the increasing Re and the opposing configuration is thermally more efficient with respect to the assisting one. Keywords----Mixed convection, opposing, assisting, open cavity, heat transfer enhancement, Nusselt number. Nomenclature Re=HU 0 / Ȟ Reynolds number Gr=gβ(T-T 0 )D 3 / Ȟ 2 Grashoff number Ri=Gr/Re 2 Richardson number Nu=hD/k Nusselt number L length of the cavity D height of the cavity U i reference velocity U non dimensional velocity V non dimensional velocity u x velocity v y velocity X x coordinate Y y coordinate Pr = υ/α T h hot wall temperature T c cold wall temperature T w wall temperature Antonio Carozza, Fluid Dynamics Department, CIRA, Italian Aerospace Research Centre, Via Maiorise Oronzio Manca, and Sergio Nardini, Industrial and Information Engineering Department, DIII, Second University of Naples, Aversa, via Roma 29. Greek Symbols Ȟ cinematic viscosity ρ density ȝ dynamic viscosity θ non dimensional tempreature κ conductivity α thermal diffusivity Ф generic field variable Subscripts  free stream h hot c cold w wall o reference I. INTRODUCTION HE problem of mixed convection resulting from the flow over a cavity is of considerable theoretical and practical interest. Mixed convection in a heated cavity has many practical applications in various fields of engineering such as electronic components cooling, solar components or nuclear reactors. Nevertheless the only natural convection is not sufficient in some cases for the thermal control of such systems, so forced convection is used. Several studies are carried out on this matter, each one with a focus on a specific aspect of the possible variables to investigate: 1. Different cavities’ shapes 2. Lid driven cavity/channel cavity 3. Different CFD methodologies In the following table 1 a meaningful summary of the produced works on the matter is reported. Papanicolaou et al. [1] have conducted a computational analysis of mixed convection in turbulent regime in a channel with a cavity heated from one side . Two typical values of the Reynolds number are chosen, Re=10 2 and Re=2.0x10 3 , and turbulent results are obtained in the range Gr= 5x10 7 - 5x10 8 . For both values of Re ,the average Nusselt number over the surface of the source is found to vary with Gr in a fashion consistent with previous numerical and experimental results for closed cavities, while the effect of Re in the chosen range of values is small. A numerical interesting study on mixed convection heat transfer in a ventilated cavity is also carried out by Papanicolaou et al. [2]. They studied in unsteady manner an isolated constant source of heat input within the enclosure for various parameters like Reynolds and aspect ratios and considering conductive walls. Oscillatory results characterized by a single frequency T 2nd International Conference on Emerging Trends in Engineering and Technology (ICETET'2014), May 30-31, 2014 London (UK) http://dx.doi.org/10.15242/IIE.E0514555 85