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Numerical investigation of air forced convection in channels with differently shaped transverse ribs

Numerical investigation of air forced convection in channels with differently shaped transverse ribs Purpose – The purpose of this paper is to investigate the flow and the heat transfer characteristics of a two‐dimensional rib‐roughned rectangular duct with the two principal walls subjected to uniform heat flux. In particular, the main goal is to generate friction and heat transfer data, for different values of p/e with square, rectangular, trapezoidal and triangular shape ribs for Reynolds numbers in the range between 20,000 and 60,000 and different heights and to describe the temperature and fluid‐dynamic fields around the ribs. Design/methodology/approach – The model is constituted by a two‐dimensional duct. On the duct wall square, rectangular, triangular and trapezoidal ribs are introduced by changing different geometry ratios. Governing equations are solved numerically by means of the finite‐volume method. Findings – Simulations show that maximum Nusselt numbers are detected in correspondence with dimensionless pitch equal to 12 and 10 for the square, trapezoidal and rectangular ribs, and triangular ones, respectively. Heat transfer rate is at most 2.45 times higher than the smooth duct, when dimensionless height is equal to 0.05, and 1.85 at a dimensionless height equal to 0.02; furthermore, the friction factor is the highest at a pitch ratio of ten for the rectangular, trapezoidal and square ribs while the triangular ones show the maximum values at a dimensionless pitch equal to 8. For Re>40,000 an asymptotic behavior is detected. Best thermal performances are provided by triangular ribs with w/e =2.0 while the rectangular ribs with w/e =2.0 present the lowest friction factor values. Local Nusselt number profiles reveal that the maximum values are detected from three to five times the rib height from the downstream turbulator. Finally, temperature fields and stream function contours are given in order to visualize the temperature distribution and flow pattern in presence of d‐type and k‐type roughness behavior also for triangular ribs. Originality/value – The paper investigates evaluation of temperature and velocity fields thermal and fluid‐dynamic behaviors (in terms of average and local Nusselt number profiles and friction factors ones) of roughned ducts with different shapes, heights and aspect ratios of ribs in turbulent regime. The thermo‐physical properties of fluid are assumed to be dependent on temperature. The paper is useful to thermal designers. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Numerical Methods for Heat and Fluid Flow Emerald Publishing

Numerical investigation of air forced convection in channels with differently shaped transverse ribs

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References (37)

Publisher
Emerald Publishing
Copyright
Copyright © 2011 Emerald Group Publishing Limited. All rights reserved.
ISSN
0961-5539
DOI
10.1108/09615531111135864
Publisher site
See Article on Publisher Site

Abstract

Purpose – The purpose of this paper is to investigate the flow and the heat transfer characteristics of a two‐dimensional rib‐roughned rectangular duct with the two principal walls subjected to uniform heat flux. In particular, the main goal is to generate friction and heat transfer data, for different values of p/e with square, rectangular, trapezoidal and triangular shape ribs for Reynolds numbers in the range between 20,000 and 60,000 and different heights and to describe the temperature and fluid‐dynamic fields around the ribs. Design/methodology/approach – The model is constituted by a two‐dimensional duct. On the duct wall square, rectangular, triangular and trapezoidal ribs are introduced by changing different geometry ratios. Governing equations are solved numerically by means of the finite‐volume method. Findings – Simulations show that maximum Nusselt numbers are detected in correspondence with dimensionless pitch equal to 12 and 10 for the square, trapezoidal and rectangular ribs, and triangular ones, respectively. Heat transfer rate is at most 2.45 times higher than the smooth duct, when dimensionless height is equal to 0.05, and 1.85 at a dimensionless height equal to 0.02; furthermore, the friction factor is the highest at a pitch ratio of ten for the rectangular, trapezoidal and square ribs while the triangular ones show the maximum values at a dimensionless pitch equal to 8. For Re>40,000 an asymptotic behavior is detected. Best thermal performances are provided by triangular ribs with w/e =2.0 while the rectangular ribs with w/e =2.0 present the lowest friction factor values. Local Nusselt number profiles reveal that the maximum values are detected from three to five times the rib height from the downstream turbulator. Finally, temperature fields and stream function contours are given in order to visualize the temperature distribution and flow pattern in presence of d‐type and k‐type roughness behavior also for triangular ribs. Originality/value – The paper investigates evaluation of temperature and velocity fields thermal and fluid‐dynamic behaviors (in terms of average and local Nusselt number profiles and friction factors ones) of roughned ducts with different shapes, heights and aspect ratios of ribs in turbulent regime. The thermo‐physical properties of fluid are assumed to be dependent on temperature. The paper is useful to thermal designers.

Journal

International Journal of Numerical Methods for Heat and Fluid FlowEmerald Publishing

Published: Jun 14, 2011

Keywords: Convection; Heat transfer; Thermodynamics; Fluid dynamics; Flow; Separation

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