Mechanical Engineering
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Item Additive Manufacturing of Microfluidic Technologies via In Situ Direct Laser Writing(2021) Alsharhan, Abdullah; Sochol, Ryan; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Innovations in microfluidic technologies hold great promise for a wide range of chemical, biomedical, and soft robotic applications. Unfortunately, key drawbacks associated with soft lithography-based microfabrication processes hinder such progress. To address these challenges, we advance a novel submicron-scale additive manufacturing (AM) strategy, termed “in situ direct laser writing (isDLW)”. IsDLW is an approach that benefits from the architectural versatility and length scales inherent to two-photon polymerization (2PP), while simultaneously supporting the micro-to-macro interfaces required for its effective utilization in microfluidic applications. In this dissertation, we explore isDLW strategies that enable passive and active 3D microfluidic technologies capable of enhancing “on-chip” autonomy and sophistication. Initially, we use poly(dimethylsiloxane) (PDMS)-based isDLW to fabricate microfluidic diodes that enable unidirectional rectification of fluid flow. We introduce a novel cyclic olefin polymer (COP)-based isDLW strategy to address several limitations related to structural adhesion and compatibility of PDMS microchannels. We use this COP-based approach to print microfluidic transistors comprising flexible and free-floating components that enable both “normally open” (NO) and “normally closed” (NC) functionalities—i.e., source-to-drain fluid flow (QSD) through the transistor is either permitted (NC) or obstructed (NO) when a gate input (PG) is applied. As an exemplar, we employ COP-based isDLW to print an integrated microfluidic circuit (IMC) comprised of soft microgrippers downstream of NC microfluidic transistors with distinct PG thresholds. All of these microfluidic circuit elements are printed within microchannels ≤ 40 μm in height, representing the smallest such components (to our knowledge). Theoretical and experimental results illustrate on the operational efficacy of these components as well as characterize their performance at different input conditions, while IMC experimental results demonstrate sequential actuation of the microrobotic components to realize target gripper operations with a single PG input. Furthermore, to investigate the utility of this strategy for static microfluidic technologies, we fabricate: (i) interwoven bioinspired microvessels (inner diameters < 10 μm) capable of effective isolation of distinct microfluidic flow streams, and (ii) deterministic lateral displacement (DLD) microstructures that enable continuous sorting of submicron particles (860 nm). In combination, these results suggest that the developed AM strategies offer a promising pathway for advancing state-of-the-art microfluidic technologies for various biological and soft robotic applications.Item DESIGN AND PERFORMANCE CHARACTERIZATION OF AN ADDITIVELY-MANUFACTURED HEAT EXCHANGER FOR HIGH TEMPERATURE APPLICATIONS(2018) Zhang, Xiang; Ohadi, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In its early stages of development, additive manufacturing was used chiefly for prototyping, but over the last decade, its use has evolved to include mass production of certain products for numerous industries in general, and speciality industries such as biomedical and aerospace industries in particular. Additive manufacturing can be used to fabricate unconventional/complex designs that are difficult and time-consuming through conventional fabrication methods, but offer significant performance advantage over state of the art. One such example is high temperature heat exchangers with complex novel geometries that can help improve the heat transfer density and provide better flow distribution, resulting in more compact and efficient designs and thereby also reducing materials costs considering fabrication of these heat exchangers from the suitable super alloys with the conventional manufacturing techniques is very difficult and laborious. This dissertation presents the results of the first high-temperature gas-to-gas manifold-microchannel heat exchanger successfully fabricated using additive manufacturing. Although the application selected for this dissertation focuses on an aerospace pre-cooling heat exchanger application, the results of this study can still directly and indirectly benefit other industrial sectors as heat exchangers are key components of most power conversion systems. In this work, optimization and numerical modelling were performed to obtain the optimal design, which show 30% weight reduction compared to the design baseline. Thereafter, the heat exchanger was scaled down to 66 × 74 × 27 mm3 and fabricated as a single piece using direct metal laser sintering (DMLS). A minimum microchannel fin thickness of 165 μm was achieved. Next, the additively manufactured headers were welded to the heat exchanger core and the conventionally manufactured flanges. A high-temperature experimental loop was next built, and the additively manufactured heat exchanger was successfully tested at 600°C with ~ 450 kPa inlet pressure. A maximum heat duty of 2.78 kW and a heat transfer density close to 10 kW/kg were achieved with cold-side inlet temperature of 38°C during the experiments. A good agreement between the experimental and numerical results demonstrates the validity of the numerical models used for heat transfer and pressure drop predictions of the additively manufactured heat exchanger. Compared to conventional plate-fin heat exchangers, up to 25% improvement in heat transfer density was achieved. This work shows that additive manufacturing can be used to fabricate compact and lightweight high temperature heat exchangers, which benefit applications where space and weight are constrained.Item RECENT DEVELOPMENTS IN HIGH TEMPERATURE HEAT EXCHANGERS: A REVIEW(Global Digital Central, 2018) Zhang, Xiang; Keramati, Hadi; Arie, Martinus; Singer, Farah; Tiwari, Ratnesh; Shooshtari, Amir; Ohadi, MichaelHeat exchangers are key components of most power conversion systems, a few industrial sectors can particularly benefit from high temperature heat exchangers. Examples include conventional aerospace applications, advanced nuclear power generation systems, and high efficiency stationary and mobile modular fossil fuel to shaft power/electricity conversion systems. This paper provides a review of high temperature heat exchangers in terms of build materials, general design, manufacturing techniques, and operating parameters for the selected applications. Challenges associated with conventional and advanced fabrication technologies of high temperature heat exchangers are discussed. Finally, the paper outlines future research needs of high temperature heat exchangers.Item Investigation into the Influence of Build Parameters on Failure of 3D Printed Parts(2016) Fornasini, Giacomo; Schmidt, Linda C; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Additive manufacturing, including fused deposition modeling (FDM), is transforming the built world and engineering education. Deep understanding of parts created through FDM technology has lagged behind its adoption in home, work, and academic environments. Properties of parts created from bulk materials through traditional manufacturing are understood well enough to accurately predict their behavior through analytical models. Unfortunately, Additive Manufacturing (AM) process parameters create anisotropy on a scale that fundamentally affects the part properties. Understanding AM process parameters (implemented by program algorithms called slicers) is necessary to predict part behavior. Investigating algorithms controlling print parameters (slicers) revealed stark differences between the generation of part layers. In this work, tensile testing experiments, including a full factorial design, determined that three key factors, width, thickness, infill density, and their interactions, significantly affect the tensile properties of 3D printed test samples.