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Research Papers: Heat Transfer Enhancement

Heat Transfer Enhancement of Air Flowing Across Grooved Channels: Joint Effects of Channel Height and Groove Depth

[+] Author and Article Information
El Hassan Ridouane

Department of Mechanical Engineering,  The University of Vermont, Burlington, VT 05405eridouan@cems.uvm.edu

Antonio Campo

Department of Mechanical Engineering,  The University of Vermont, Burlington, VT 05405

J. Heat Transfer 130(2), 021901 (Feb 04, 2008) (7 pages) doi:10.1115/1.2790022 History: Received November 30, 2006; Revised June 15, 2007; Published February 04, 2008

Abstract

A numerical study was conducted to investigate convective heat transfer and laminar fluid flow in the developing region of two-dimensional parallel-plate channels with arrays of transverse hemicircular grooves cut into the plates. Air with uniform velocity and temperature enters the channel whose plates are at a uniform temperature. The finite-volume method is used to perform the computational analysis accounting for the traditional second-order-accurate QUICK and SIMPLE schemes. Steady-state results are presented for parallel-plate channels with and without hemicircular grooves for comparison purposes. The study revolves around four controlling parameters: (1) the height of the channel, (2) the relative groove depth, (3) the number of grooves, and (4) the Reynolds number. A prototypical $120‐cm$-long channel contains two series of 3, 6, and 12 transverse grooves with four relative groove depths $δ∕D$ of 0.125, 0.25, 0.375, and 0.5. Three ratios of channel height to groove print diameter $H∕D$ of 0.5, 1, and 2 are employed. Computations are performed for Reynolds numbers based on the hydraulic diameter ranging from 1000 to 2500. It is found that the grooves enhance local heat transfer relative to a flat passage at locations near their downstream edge. The maximum heat transfer enhancement occurs at an optimal depth of the grooves. For purposes of engineering design, generalized correlation equations for the Nusselt number in terms of the pertinent Re, $δ∕D$, and the number of grooves $N$ were constructed using nonlinear regression theory.

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Figures

Figure 1

Schematic of the physical systems: (a) symmetric arrangement, (b) staggered arrangement, and (c) spacing between 6 and 12 cavities

Figure 2

Geometry of the hemicircular grooves

Figure 3

A portion of the computational grid showing the distribution of elements in a groove∕channel with δ∕D=0.25 on the lower plate of a channel with three grooves onto each plate

Figure 4

Velocity vectors and isotherms inside a shallow groove with half radius depth δ∕D=0.25: (a) Re=1000(u¯=0.198ms−1) and (b) Re=2500(u¯=0.496ms−1)

Figure 5

Local wall heat flux along the upper plate of the channel with 12 grooves at Re=2500(u¯=0.496ms−1)

Figure 6

Variations of the mean Nusselt number with Re for the two arrangements and different relative groove depths in a channel with three grooves

Figure 7

Variations of the mean Nusselt number of channel with 6 and 12 grooves with Re for different relative groove depths

Figure 8

Optimal groove depth that maximizes the heat transfer through the channel

Figure 9

Evolution of the mean wall heat flux with Reynolds parametrized by the channel height and groove arrangement. Three relative heights of the channel are considered, H∕D=0.5, 1, and 2.

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