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Characterizing, Correlating, and Evaluating Swirl Flow and Heat Transfer in Wavy Plate-Fin Channels with Novel Enhancement Attributes

Shi, Dantong
http://orcid.org/0000-0002-7751-6369
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613742268339123

Abstract Details

2020, PhD, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
The pressure drop and heat transfer performance for airflows (Pr ~ 0.71 and 50 = Re = 4000) in sinusoidal wavy plate-fin heat exchangers have been studied both experimentally and computationally. Compared with the widely used plain plate-fins, the heat transfer enhancement from wavy fin surfaces stems not only from their corrugated and enlarged surface areas, but more significantly, from swirl flow effects and early trigger of turbulence. To characterize and scale the surface-curvature-induced swirl or vortical recirculation, Swirl number (Sw) is introduced from balancing viscous, inertial, and centrifugal forces. The measured Fanning friction factor f and Colburn j factor from experiments show the onset of transition from laminar (Sw < 300) to turbulent regime (Sw > 800) occurs at approximately the same Sw for fin cores with different wavy corrugations and inter-fin spacings. After analyzing the effects of Sw and fin geometries on the local friction and convective heat transfer, a new set of generalized correlations are developed based on the fully developed behavior in plain plate-fin cores and a supposition of corrugation-induced-convection enhancement. The former can be scaled by fin cross-section aspect ratio (?) and Re, respectively, in the laminar and turbulent regime. The latter is shown to be described or scaled by the surface-area enlargement ratio (?) and swirl flow effects (Ff (or j)) as a function of Sw, corrugation aspect ratio (?), and inter-fin spacing (?). The new correlations predicted f and j factors, respectively, within ± 20% and ± 15% of the experimental data from this study and in the literature. Subsequently, the overall thermal-hydraulic performance is evaluated, and wavy plate-fin cores generally require larger frontal area but much smaller core volume and surface heat transfer area compared with plain plate-fins. To optimize the fin geometries and heat exchanger sizes, a systematic approach based on Genetic Algorithm (GA) is established to achieve minimum economic cost and/or minimum core volume of the wavy plate-fin heat exchanger. Shown by a case study to re-design an air-cooled condenser in a 500 MW steam power plant, the air-side core volume can be shrunk by 74% and the total annual cost is cut in half compared with the benchmark design. Moreover, the wavy plate-fins are modified by cutting slots on fin surfaces to further improve the performance. The tested slotted-wavy-fin core achieves similar convective heat transfer performance with a largely reduced pressure drop (~30% smaller) compared with the continuous wavy fin core. As indicated from numerical simulations, the slots can benefit the flow resistance when cut at positions with large form drag, which is induced by flow recirculation in the wave trough. The local variation of form drag has been analyzed so that the slot position and slot size, characterized respectively by phase angle (ß) and slot size ratio (d) are further modified to obtain better thermal-hydraulic performance. With the modified design, the performance at low flow rates is characteristically unusual, where enhancement in heat transfer is accompanied by a considerable reduction in pressure loss. Additionally, at high flow rates, though a slight decline in heat transfer is present, the pressure drop is nearly cut in half. Finally, the overall performance evaluation suggests 15% of heat transfer area reduction by cutting slots on wavy fin surfaces.
Milind Jog, Ph.D. (Committee Chair)
Je-Hyeong Bahk, Ph.D. (Committee Member)
Raj Manglik, Ph.D. (Committee Member)
Sarah Watzman, Ph.D. (Committee Member)
143 p.
Mechanical Engineering
wavy fin; swirl flow; plate-fin heat exchanger; heat transfer enhancement; slotted wavy fin; performance evaluation and optimization

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Citations

  • Shi, D. (2020). Characterizing, Correlating, and Evaluating Swirl Flow and Heat Transfer in Wavy Plate-Fin Channels with Novel Enhancement Attributes [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613742268339123

    APA Style (7th edition)

  • Shi, Dantong. Characterizing, Correlating, and Evaluating Swirl Flow and Heat Transfer in Wavy Plate-Fin Channels with Novel Enhancement Attributes. 2020. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613742268339123.

    MLA Style (8th edition)

  • Shi, Dantong. "Characterizing, Correlating, and Evaluating Swirl Flow and Heat Transfer in Wavy Plate-Fin Channels with Novel Enhancement Attributes." Doctoral dissertation, University of Cincinnati, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613742268339123

    Chicago Manual of Style (17th edition)

ucin1613742268339123
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This open access ETD is published by University of Cincinnati and OhioLINK.
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