Natural Convection in a Horizontal Cylinder with Partial Heating: Energy Efficiency Analysis
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https://doi.org/10.1007/s11630-020-1238-x
Article ID: 1003-2169(2019)00-0000-00
Natural Convection in a Horizontal Cylinder with Partial Heating: Energy Efficiency Analysis MAZGAR Akram1*, JARRAY Khouloud2, HAJJI Fadhila2, BEN NEJMA Fayçal2 1.The Higher Institute of Applied Sciences and Technology of Sousse, University of Sousse, Tunisia - Ibn Khaldun Street, Taffala City, 4003 Sousse Tunisia 2.The Preparatory Institute for Engineering Studies of Monastir, University of Monastir, Tunisia - Rue Ibn El Jazzar, 5019 Monastir, Tunisia © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: The current study reports a numerical analysis of free convection of air in an isothermal horizontal cylinder, cooled and heated at different wall locations. Three heater sizes are discussed in this study. The first heated zone is spread across one-quarter of the sidewall; the second is uniformly distributed over the half of the wall and the third active wall covers three-quarters of the cylinder. Five various locations are considered and examined for each active zone of the sidewall. The computation is carried out for Rayleigh number ranging from 102 to 106. Numerical results characterizing heat transfer and flow features are achieved using an iterative model developed in COMSOL Multiphysics. The effect of Rayleigh number on heat transfer and fluid flow characteristics within the cavity are investigated. Particular attention is paid to the influence of heater location and heater size on energy efficiency. It is found that the mean Nusselt number and dimensionless velocity increase when increasing the Rayleigh number. Moreover, the optimal level of energy efficiency is achieved if the heating zone is centered at the upper part of the cylinder, regardless of the heater size. It is also shown that the optimal configuration providing higher energy efficiency is obtained when three-quarters of the sidewall are locally heated, and more precisely, if the active zone is centered at the top of the cylinder.
Keywords: natural convection, cylinder, partial heating, energy efficiency, Rayleigh number
1. Introduction Fluid flow and heat transfer generated by free heat convection in enclosures [1–6] is a field of intense research due to its wide variety of engineering applications, which include thermal insulating systems, building heat transfer, heat exchangers design, boilers, burners, industrial furnaces, combustion chambers, thermal behavior of nuclear reactor, crystal growth reactors, etc. In the majority of investigations dealing Received: Apr 21, 2019
AE: LI Guiqiang
with free convection in enclosures, walls are kept adiabatic, isothermal, or exposed to a constant heating. Nevertheless, in several industrial applications like solar collectors and cooling electronic circuits, heat generation is induced through a narrow segment of walls, where the buoyant flow rising close to walls is generated by temperature gradients along boundaries. In such systems, it is
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