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Gas Turbines: Microturbines and Small Turbomachinery

A Study of Heat Transfer Augmentation for Recuperative Heat Exchangers: Comparison Between Three Dimple Geometries

[+] Author and Article Information
Michelle I. Valentino

University of Central Florida, Orlando, FL 32816MValentino@knights.ucf.edu

Lucky V. Tran

University of Central Florida, Orlando, FL 32816Lucky.V.Tran@gmail.com

Mark Ricklick

University of Central Florida, Orlando, FL 32816Mark.Ricklick@ucf.edu

J. S. Kapat

University of Central Florida, Orlando, FL 32816Jayanta.Kapat@ucf.edu

J. Eng. Gas Turbines Power 134(7), 072303 (May 23, 2012) (9 pages) doi:10.1115/1.4005990 History: Received October 12, 2011; Revised November 30, 2011; Published May 23, 2012

This study presents an investigation of the heat transfer augmentation for the purpose of obtaining high effectiveness recuperative heat exchangers for waste heat recovery. The focus of the present work is in the fully developed portion of a 2:1 aspect ratio rectangular channel characterized by dimples applied to one wall at channel Reynolds numbers of 10,000, 18,000, 28,000, and 36,000. The dimples are applied in a staggered-row, racetrack configuration. In this study, a segmented copper test section was embedded with insulated dimples in order to isolate the heat transfer within the dimpled feature. The insulated material used to create a dimpled geometry isolates the heat transfer within the dimple cavity from the heat transfer augmentation on the surrounding smooth walls promoted by the flow disturbances induced by the dimple. Results for three different geometries are presented, a small dimple feature, a large dimple, and a double dimple. The results of this study indicate that there is significant heat transfer augmentation even on the nonfeatured portion of the channel wall resulting from the secondary flows created by the features. Overall heat transfer augmentations for the small dimples are between 13–27%, large dimples between 33–54%, and double dimples between 22–39%, with the highest heat transfer augmentation at the lowest Reynolds number for all three dimple geometries tested. Heat transfer within the dimple was shown to be less than that of the surrounding flat regions at low Reynolds numbers. Results for each dimple geometry show that dimples are capable of promoting heat transfer over the entire bottom wall surface as well as the side walls; thus the effects are not confined to within the dimple cavity.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Dimple-protrusion surface for counter flow compact HX

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Figure 2

Flow structures in an (a) SD (b) DD

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Figure 3

Current experimental setup

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Figure 4

Cross-section of channel

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Figure 5

Description of geometric parameters

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Figure 6

Featured copper block: (a) Rohacell double dimple, (b) full copper double dimple, (c) Rohacell small dimple, (d) full copper small dimple, (e) Rohacell large dimple, (f) full copper large dimple

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Figure 7

Surface area (a) Bottom-A full-copper blocks and (b) Bottom-B copper with Rohacell inserts

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Figure 8

Local Nusselt number for SD channel (a) 10,000 Re, (b) 18,000 Re, (c) 28,000 Re, and (d) 36,000 Re

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