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Flow and Thermal Transport at Porous Interfaces.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Flow and Thermal Transport at Porous Interfaces./
作者:	Vijay, Shilpa.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2023,
面頁冊數:	118 p.
附註:	Source: Dissertations Abstracts International, Volume: 85-06, Section: B.
Contained By:	Dissertations Abstracts International85-06B.
標題:	Mechanical engineering. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30817553
ISBN:	9798381168273

Flow and Thermal Transport at Porous Interfaces.
Vijay, Shilpa.

Flow and Thermal Transport at Porous Interfaces. - Ann Arbor : ProQuest Dissertations & Theses, 2023 - 118 p.

Source: Dissertations Abstracts International, Volume: 85-06, Section: B.

Thesis (Ph.D.)--University of Southern California, 2023.

This item must not be sold to any third party vendors.

This thesis aims to systematically investigate the impact of porous substrates on fluid flow and heat transfer with potential applications in mitigating drag and enhancing thermal transport. For porous and patterned surfaces, porosity and surface microstructure have been shown to modify the structure and dynamics of near-wall turbulence. It is important to understand how the microstructure of these surfaces influences momentum and scalar transport to facilitate the design of passive flow control strategies. In addition to leveraging additive manufacturing to design porous substrates that have the potential to enhance heat transfer or reduce drag in channel flow, this effort seeks to improve our understanding of how porous medium microstructure affects flow and thermal dispersion.The effects of permeability on turbulent heat transfer across a porous interface were experimentally investigated in a partially porous channel flow setup with commercially available aluminum foams. Temperature measurements at various locations in the channel were used to characterize heat exchanger performance for a range of bulk Reynolds numbers (Reb {acute}{89}{88} 800{acute}{88}{92}2500). Particle Image Velocimetry measurements at a subset of these Reynolds numbers were used to characterize the shear stress at the interface and gain insight into the flow structure. Increasing the permeability of the aluminum foams significantly alters the flow structure and dynamics, resulting in the emergence of large vortex structures associated with the Kelvin-Helmholtz (K-H) instability. These structures enhance interfacial thermal dispersion. However, this increase comes at the cost of increased pumping power requirements: an increase in permeability also leads to an increase in friction.Previous numerical simulations have demonstrated drag reduction over streamwise preferential substrates, which yield larger effective slip lengths for the streamwise mean flow compared to the turbulent cross-flows. A deterioration in performance is typically observed when the normalized wall normal permeability ({acute}{88}{9A}{A0}Kyy+) is higher than 0.4, likely due to the presence of large-scale motions associated with the K-H instability. To determine whether the trends observed in the numerical simulations are applicable to physically realizable materials, a family of anisotropic periodic lattices was created using 3D printing. This allowed rod size and spacing in different directions to achieve different ratios of streamwise, wall-normal, and spanwise bulk permeabilities (Kxx, Kyy, Kzz). We investigated the thermophysical properties of these 3D-printed materials to establish a connection between the microstructure and the saturated thermal conductivity and permeability. Our results show that empirical models for stochastic foams or isotropic lattices are inadequate for predicting the thermophysical properties of anisotropic porous lattices. To address this, we developed phenomenological models to predict the principal components of the permeability tensor and effective thermal conductivity. Comparisons between the predictions and results from experiments and ANSYS Fluent simulations show that small variations in rod spacing and size due to manufacturing tolerances can lead to significant discrepancies between measured and predicted thermophysical properties, highlighting the limitations of physically realizable materials.Finally, we experimentally investigated the effect of anisotropic permeability on the drag response for the 3D-printed porous substrates. The porous materials were mounted in a benchtop water channel. Pressure drop measurements were taken in the fully developed region of the flow to characterize drag as a function of bulk permeability for materials with Kxx/Kyy approx 0.1 - 10$. Results show that porous substrates with high streamwise permeability {acute}{88}{9A}{A0}Kxx+ lead to the lowest increase in drag compared to a reference smooth wall measurement. Drag increase is mainly governed by the wall-normal permeability {acute}{88}{9A}{A0}Kyy+, which is linked to the emergence of spanwise coherent rollers resembling K-H vortices. This evidence suggests that streamwise preferential porous materials could be a viable option for passive drag reduction or for heat transfer enhancement with minimal drag penalties. Manufacturing limitations precluded materials with a wall-normal permeability low enough to observe drag reduction as per previous numerical predictions. However, this study provides the first set of friction factor data over porous substrates with a wide range of anisotropy.

ISBN: 9798381168273Subjects--Topical Terms:

649730
Mechanical engineering.
Subjects--Index Terms:

Heat transfer

Flow and Thermal Transport at Porous Interfaces.
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100 1 $a Vijay, Shilpa. $3 3765109
245 1 0 $a Flow and Thermal Transport at Porous Interfaces.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2023
300 $a 118 p.
500 $a Source: Dissertations Abstracts International, Volume: 85-06, Section: B.
500 $a Advisor: Luhar, Mitul.
502 $a Thesis (Ph.D.)--University of Southern California, 2023.
506 $a This item must not be sold to any third party vendors.
520 $a This thesis aims to systematically investigate the impact of porous substrates on fluid flow and heat transfer with potential applications in mitigating drag and enhancing thermal transport. For porous and patterned surfaces, porosity and surface microstructure have been shown to modify the structure and dynamics of near-wall turbulence. It is important to understand how the microstructure of these surfaces influences momentum and scalar transport to facilitate the design of passive flow control strategies. In addition to leveraging additive manufacturing to design porous substrates that have the potential to enhance heat transfer or reduce drag in channel flow, this effort seeks to improve our understanding of how porous medium microstructure affects flow and thermal dispersion.The effects of permeability on turbulent heat transfer across a porous interface were experimentally investigated in a partially porous channel flow setup with commercially available aluminum foams. Temperature measurements at various locations in the channel were used to characterize heat exchanger performance for a range of bulk Reynolds numbers (Reb {acute}{89}{88} 800{acute}{88}{92}2500). Particle Image Velocimetry measurements at a subset of these Reynolds numbers were used to characterize the shear stress at the interface and gain insight into the flow structure. Increasing the permeability of the aluminum foams significantly alters the flow structure and dynamics, resulting in the emergence of large vortex structures associated with the Kelvin-Helmholtz (K-H) instability. These structures enhance interfacial thermal dispersion. However, this increase comes at the cost of increased pumping power requirements: an increase in permeability also leads to an increase in friction.Previous numerical simulations have demonstrated drag reduction over streamwise preferential substrates, which yield larger effective slip lengths for the streamwise mean flow compared to the turbulent cross-flows. A deterioration in performance is typically observed when the normalized wall normal permeability ({acute}{88}{9A}{A0}Kyy+) is higher than 0.4, likely due to the presence of large-scale motions associated with the K-H instability. To determine whether the trends observed in the numerical simulations are applicable to physically realizable materials, a family of anisotropic periodic lattices was created using 3D printing. This allowed rod size and spacing in different directions to achieve different ratios of streamwise, wall-normal, and spanwise bulk permeabilities (Kxx, Kyy, Kzz). We investigated the thermophysical properties of these 3D-printed materials to establish a connection between the microstructure and the saturated thermal conductivity and permeability. Our results show that empirical models for stochastic foams or isotropic lattices are inadequate for predicting the thermophysical properties of anisotropic porous lattices. To address this, we developed phenomenological models to predict the principal components of the permeability tensor and effective thermal conductivity. Comparisons between the predictions and results from experiments and ANSYS Fluent simulations show that small variations in rod spacing and size due to manufacturing tolerances can lead to significant discrepancies between measured and predicted thermophysical properties, highlighting the limitations of physically realizable materials.Finally, we experimentally investigated the effect of anisotropic permeability on the drag response for the 3D-printed porous substrates. The porous materials were mounted in a benchtop water channel. Pressure drop measurements were taken in the fully developed region of the flow to characterize drag as a function of bulk permeability for materials with Kxx/Kyy approx 0.1 - 10$. Results show that porous substrates with high streamwise permeability {acute}{88}{9A}{A0}Kxx+ lead to the lowest increase in drag compared to a reference smooth wall measurement. Drag increase is mainly governed by the wall-normal permeability {acute}{88}{9A}{A0}Kyy+, which is linked to the emergence of spanwise coherent rollers resembling K-H vortices. This evidence suggests that streamwise preferential porous materials could be a viable option for passive drag reduction or for heat transfer enhancement with minimal drag penalties. Manufacturing limitations precluded materials with a wall-normal permeability low enough to observe drag reduction as per previous numerical predictions. However, this study provides the first set of friction factor data over porous substrates with a wide range of anisotropy.
590 $a School code: 0208.
650 4 $a Mechanical engineering. $3 649730
650 4 $a Materials science. $3 543314
650 4 $a Applied physics. $3 3343996
650 4 $a Fluid mechanics. $3 528155
653 $a Heat transfer
653 $a Permeability
653 $a Porous media
653 $a Turbulence
653 $a Wall-bounded channel flows
690 $a 0548
690 $a 0794
690 $a 0204
690 $a 0215
710 2 $a University of Southern California. $b Mechanical Engineering. $3 1669217
773 0 $t Dissertations Abstracts International $g 85-06B.
790 $a 0208
791 $a Ph.D.
792 $a 2023
793 $a English
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30817553