Natural convection in a circular enclosure with an internal cylinder of regular polygon geometry

Yanping Wang,Jie Chen,Wei Zhang

doi:10.1063/1.5100892

Abstract

This work presents a numerical investigation on the natural convection heat transfer in a circular enclosure with an internal cylinder at Ra=103-106 in both conduction and convection dominant regimes. The cross-section of the cylinder is of regular polygon geometry with various numbers of edges, including circle, triangle, square, pentagon and hexagon. The polygon cylinders are positioned at two orientations, i.e., the corner-upward and edge-upward orientations where one of the sharp corners or flat edges faces upward. The simulations are performed using our in-house fourth-order finite difference code which is well validated. Our objective is to explore the effects of cylinder geometry and orientation on the thermal and flow characteristics. The results are presented and analysed by the total equivalent conductivity coefficient for the quantitative assessment of the contribution of fluid circulation, the streamlines and thermal fields for the flow pattern and qualitative evaluation of heat transfer performance, and the distributions of local heat transfer rate on the surfaces of cylinder and enclosure. We also perform the first synergy principle analysis on this physical model to identify how the fluid circulation contributes to the heat transfer and its spatial behaviours. Numerical results reveal that the corner-upward orientation generally exhibits better heat transfer performance by permitting the well development of flow above the cylinder and in the top region of the enclosure.

Highlights

Natural convection in an enclosure is one of the most fundamental and classical physical problems in the fields of fluid mechanics and heat transfer
For natural convection in an enclosure with internal entities, the overall heat transfer rate generally increases with the Rayleigh number because of the enhanced convective heat transfer arising from intensified fluid circulation
We use the mean equivalent conductivity coefficient to quantify the effect of fluid circulation in enhancing the heat transfer which is affected by the geometry and orientation of the polygon cylinder

Summary

Introduction

Natural convection in an enclosure is one of the most fundamental and classical physical problems in the fields of fluid mechanics and heat transfer. The enclosure can be heated and cooled on different walls or in different regions on the same wall, or keeps at a different temperature with respect to that of an internal entity. The physical problem is significant in researches and engineering in that the fluid flow and heat transfer processes are extensively integrated. The outer enclosure and internal cylinder are kept at low and high temperatures, respectively; the fluid is heated by the cylinder and moves upward till the top of the enclosure, cooled by the enclosure surface and circulates downward to the bottom of the enclosure

Objectives

Results

Conclusion