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Experimental and Computational Study of Novel Plate-Fin-Surfaces for Enhancing Forced Convection Heat Transfer in Compact Heat Exchangers

Lin, Kuan-Ting
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1623166309984355

Abstract Details

2021, PhD, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
Compact heat exchangers are widely used in applications such as power plant condensers, automobile radiators, electronic cooling devices, and heating, ventilating and air conditioning (HVAC) systems. In this thesis, flow and heat transfer in various fin channels including plain fin, offset strip fin, and novel slotted and hybrid converging-diverging trapezoidal fin channels is characterized using experiments and computational analysis. New generalized correlations for predicting the average Fanning friction factor f and average Nusselt number Nu for laminar flow in plain plate-fin compact cores of rectangular cross-section are presented. The results indicate that while the fully developed forced convection scales only with the inter-fin channel cross-sectional ratio a (fin spacing by fin height), the entrance region hydrodynamic and thermal performance is additionally a function of the fin-core length L, flow Reynolds number Re, and fluid Prandtl number Pr. The predictions from these correlations are found to be within ±15% of all available experimental data. The development of rationalized correlations for predicting average f and j factors for airflow in rectangular offset-strip-fin cores is also presented in the study. The offset arrangement of the fins disrupts the fully-developed condition prevalent in plain plate-fin to promote boundary layer interruption and heat transfer enhancement, and this effect is found to be fundamentally scaled by offset length ratio (fin offset length by channel hydraulic diameter). Furthermore, form drag and wake effect are integral parts to the convection performance, and the influence is found to be characterized by the thickness ratio as well as the flow cross-section aspect ratio. Generalized correlations of f and j are developed by asymptotic matching, in which the fully laminar and turbulent flow behaviors are the asymptotic limits, and predict the extended experimental data set to within ±20%. To reflect the overall thermal performance of the pre-selected fin cores, the overall volume reduction is employed to achieve a more specific design of the outer dimensions of the fin core, for which both the flow length and the frontal width can be simultaneously optimized. This idea is also incorporated into the genetic algorithm for an overall optimization based on the design objective such that both outer dimensions and fin geometric features are considered at once. A case study is demonstrated to show the optimization process and outcomes by substituting the offset-strip-fin core for plain plate-fin core. Moreover, multi-objective optimization (overall volume and total annual cost) is revealed by plotting the Pareto front so that the trade-off between the two objectives can be visualized. Flow characterization and heat transfer behavior of continuous, slotted, and the proposed hybrid trapezoidal converging-diverging channels are investigated in this study, of which the last two can be only made by additive manufacturing. The unique flow behavior, due to the existence of slots, interrupts the boundary layer, diminishes the stagnation and recirculation zones, and facilitates the cold mainstream fluid flowing towards the heated surface, apart from accelerating and decelerating the flow. The proposed hybrid channel not only provides an extremely effective heat transfer surface area but also deflects the flow that inhibits the recirculation at the trough. For the hybrid channel, it requires only 25% to 33% of the heat transfer surface area of plain plate-fin under constant pressure drop condition in the laminar regime.
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)
220 p.
Mechanical Engineering

Recommended Citations

Citations

  • Lin, K.-T. (2021). Experimental and Computational Study of Novel Plate-Fin-Surfaces for Enhancing Forced Convection Heat Transfer in Compact Heat Exchangers [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1623166309984355

    APA Style (7th edition)

  • Lin, Kuan-Ting. Experimental and Computational Study of Novel Plate-Fin-Surfaces for Enhancing Forced Convection Heat Transfer in Compact Heat Exchangers. 2021. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1623166309984355.

    MLA Style (8th edition)

  • Lin, Kuan-Ting. "Experimental and Computational Study of Novel Plate-Fin-Surfaces for Enhancing Forced Convection Heat Transfer in Compact Heat Exchangers." Doctoral dissertation, University of Cincinnati, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1623166309984355

    Chicago Manual of Style (17th edition)

ucin1623166309984355
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This open access ETD is published by University of Cincinnati and OhioLINK.