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Research Papers: Heat Exchangers

# High Performance Recuperator With Oblique Wavy Walls

[+] Author and Article Information
Kenichi Morimoto1

Department of Mechanical Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japankmrmt@se.ritsumei.ac.jp

Yuji Suzuki

Department of Mechanical Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japanysuzuki@thtlab.t.u-tokyo.ac.jp

Nobuhide Kasagi

Department of Mechanical Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japankasagi@thtlab.t.u-tokyo.ac.jp

1

Present address: Department of Micro System Technology, Faculty of Science and Engineering, Ritsumeikan University, Shiga 525-8577, Japan.

J. Heat Transfer 130(10), 101801 (Aug 07, 2008) (10 pages) doi:10.1115/1.2884187 History: Received September 27, 2006; Revised July 22, 2007; Published August 07, 2008

## Abstract

A series of numerical simulation of the flow and heat transfer in modeled counterflow heat exchangers with oblique wavy walls has been made toward optimal shape design of recuperators. The effects of oblique angles and amplitudes of the wavy walls are systematically evaluated, and the heat transfer and pressure loss characteristics are investigated. It is found that counter-rotating streamwise vortices are induced by the wavy walls, and the flow field has been drastically modified due to the intense secondary flow. By using the optimum set of oblique angle and wave amplitude, significant heat transfer enhancement has been achieved at the cost of relatively small pressure loss, and the $j∕f$ factor becomes much larger than that of straight square duct or conventional compact recuperators. When thermal coupling of hot and cold fluid passages is considered, the heat transfer is found to be strongly dependent on the arrangement of counterflow passages. The total heat transfer surface area required for a given pumping power and heat transfer rate can be reduced by more than 60% if compared to the straight square duct.

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## Figures

Figure 1

Surface geometry of the passage with oblique wavy walls and computational grids with boundary-fitted coordinate system

Figure 2

Configurations of modeled counterflow heat exchangers: (a) Case 1 and (b) Case 2

Figure 3

Pressure loss and friction drag versus the oblique angle for Reδ=200 and A∕δ=0.25

Figure 4

Averaged Nusselt numbers versus the oblique angle for Reδ=200 and A∕δ=0.25

Figure 5

j∕f factor versus the oblique angle for Reδ=200 and A∕δ=0.25

Figure 6

Pressure loss and friction drag versus the wave amplitude for γ=50deg and 60deg(Reδ=200)

Figure 7

Effect of wave amplitudes on the heat transfer in Case 2 (Reδ=200): (a) averaged Nusselt number and (b) j∕f factor

Figure 8

Wall shear stress vectors on the bottom wall projected onto the x-z plane (Reδ=200 and A∕δ=0.25). The vector corresponds to (∂u∕∂n,∂w∕∂n), nondimensionalized by Ub and δ: (a) γ=60deg and (b) γ=45deg

Figure 9

Velocity vectors and isocontours of the streamwise velocity in the y-z planes (Reδ=200 with A∕δ=0.25 and 60deg): (a) x∕δ=0.43 and (b) x∕δ=3.0. The contour increment is 0.2Ub. Refer to Fig. 1 for the streamwise positions.

Figure 10

Isosurfaces of the second invariant of the deformation tensor (Π<−5.0) for Reδ=200 with A∕δ=0.25 and γ=60deg: black, streamwise vorticity ωx<0; gray, ωx>0

Figure 11

Distribution of the streamwise wall shear stress for Reδ=200 with A∕δ=0.25 and γ=60deg

Figure 12

Velocity vectors and isocontours of temperature under thermal coupling condition in the y-z plane at x∕δ=3.0 for Reδ=200 with A∕δ=0.25 and γ=60deg: (a) Case 1 and (b) Case 2. The contour increment is 0.1×(∣Tb,I∣H−∣Tb,I∣C)

Figure 13

Distribution of the heat flux on the bottom wall under each thermal boundary condition for Reδ=200 with A∕δ=0.25 and γ=60deg: (a) isothermal heated condition, (b) coupling condition (Case 1), and (c) coupling condition (Case 2)

Figure 14

Effect of Reynolds numbers on the Nusselt number and j∕f factor with A∕δ=0.25 and γ=60deg. Reference data for conventional compact heat exchangers are plotted from the correlations provided in Refs. 14,21.

Figure 15

Effect of Reynolds numbers on the total amount of heat flux of the bottom and top walls (BT) and the sidewalls (LR) with A∕δ=0.25 and γ=60deg.

Figure 16

Isocontours of velocity and thermal fields in the y-z plane at x∕δ=3.0 for Reδ=400 (A∕δ=0.25 and γ=60deg): (a) streamwise velocity, (b) temperature in Case 1, and (c) temperature in Case 2. Velocity and temperature are scaled by Ub and ∣Tb,I∣H−∣Tb,I∣C, respectively.

Figure 17

Contour plot of heat transfer surface area required for constant heat-exchanger performances for Reδ=200. Each symbol is marked with the indices representing the oblique angle of the wavy wall.

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