Mixed Convention in a Ventilated Concentric Horizontal Cylindrical Annulus for Aiding and Opposing Buoyancy Forces

Abstract

A numerical study of laminar mixed convective heat transfer of water in the vented annular region between the two concentric horizontal cylinders has been carried out. The diameter ratio of the outer and inner cylinders is 2.6. The forced flow conditions are imposed through the inlet opening (θinlet=30°) at the top of the outer cylinder around the upper symmetry plane. The smaller outlet vent (θoutlet=10°) compared to the inlet vent is at the bottom and is placed diametrically opposite from the inlet. The inner cylinder wall is considered at a constant temperature while the outer one is insulated except the inlet and outlet ports. This geometry is suitable as a heat exchanger for solar energy applications. The two-dimensional conservative form of continuity, Navier-Stokes and the energy equations are solved by using control volume based finite difference technique on a uniform staggered grid arrangement. The Boussinesq approximation is employed to implement the natural convection term in the momentum equations. The effect of main non-dimensional parameters governing the problem such as the Richardson number (RI) varying from 0 ≤ RI ≤ 2.0 and the Reynolds number (ReD) varying from 50 ≤ ReD ≤ 200 is considered. The nature and the basic characteristics of the aiding as well as opposing flows are numerically investigated. In the cases studied, the aiding flow is found to have a significant effect in the enhancement of average Nusselt number on the inner cylinder compared to the opposing flow. It has been also found that the average Nusselt number increases with the increase of the Reynolds number. Furthermore, it is predicted that after a certain value of the Richardson number the average Nusselt number remains practically unchanged for the both imposed flow conditions irrespective of the Reynolds number due to the insignificant effect of the buoyancy force. To get a visual understanding of the mixed convection phenomena in the vented annulus, streamlines and isotherms for various cases are also presented. Empirical correlations are developed for the average Nusselt number as a function of Richardson number and Reynolds number for the both aiding and opposing flow situations in the studied ranges..

Keywords

• Laminar Mixed Convection
• Numerical Study
• Aiding and Opposing Flow
• Vented Cavity
• and Horizontal Concentric Cylinders

How to cite

Latifa Begum, Tonny Tabassum, Mainul Hasan (2020). Mixed Convention in a Ventilated Concentric Horizontal Cylindrical Annulus for Aiding and Opposing Buoyancy Forces. Sonargaon University Journal, 3(I & II), 12–30.

@article{begum20202,
  title   = {Mixed Convention in a Ventilated Concentric Horizontal Cylindrical Annulus for Aiding and Opposing Buoyancy Forces},
  author  = {Latifa Begum and Tonny Tabassum and Mainul Hasan},
  journal = {Sonargaon University Journal},
  volume  = {3},
  number  = {I & II},
  pages   = {12--30},
  year    = {2020},
  issn    = {2518-3125},
  url     = {https://su.edu.bd/journal/volume-3/mixed-convention-in-a-ventilated-concentric-horizontal-cylindrical-annulus-for}
}