A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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Subject: search.filters.subject.Heat Exchangers

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    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, Michael
    Heat 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.
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    Determining the Air-Side Performance of Small-Diameter, Enhanced Tube-Fin Heat Exchangers through Numerical and Experimental Methods
    (2017) Nasuta, Dennis; Hwang, Yunho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    New correlations for the air-side pressure drop and heat transfer coefficient (HTC) of slit and louver fin heat exchangers with 3-5 mm outer diameter tubes were developed based on Computational Fluid Dynamics (CFD) simulations of small, symmetric fin sections using Design of Experiments (DOE) techniques. The prediction accuracy of these CFD-based correlations was validated by experimental testing of 16 unique 5 mm slit and louver fin heat exchangers under a range of air velocities. The experimental results indicate that the proposed CFD-based correlation with correction factors for air-side pressure drop can predict 100% of the experimental observations with 20% error or less. After a new data reduction procedure accounting for fin conduction was implemented and a single correction factor applied, the HTC correlations could predict 98% of accepted test data with 20% error or less regardless of fin type.
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    A particle erosion model of monocrystalline silicon for high heat flux microchannel heat exchangers
    (2017) Squiller, David; McCluskey, Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    As package-level heat generation pushes past 1 kW/cm3 in various military, aerospace, and commercial applications, new thermal management technologies are needed to maximize efficiency and permit advanced power electronic devices to operate closer to their inherent electrical limit. In an effort to align with the size, weight and performance optimization of high temperature electronics, cooling channels embedded directly into the backside of the chip or substrate significantly reduce thermal resistances by minimizing the number of thermal interfaces and distance the heat must travel. One implementation of embedded cooling considers microfluidic jets that directly cool the backside of the substrate. However, as fluid velocities exceed 20 m/s the potential for particle erosion becomes a significant reliability threat. While numerous particle erosion models exist, seldom are the velocities, particle sizes, materials and testing times in alignment with those present in embedded cooling systems. This research fills the above-stated gaps and culminates in a calibrated particle-based erosion model for single crystal silicon. In this type of model the mass of material removed due to a single impacting particle of known velocity and impact angle is calculated. Including this model in commercial computational fluid dynamics (CFD) codes, such as ANSYS FLUENT, can enable erosion predictions in a variety of different microfluidic geometries. First, a CFD model was constructed of a quarter-symmetry impinging jet. Lagrangian particle tracking was used to identify localized particle impact characteristics such as impact velocity, impact angle and the percentage of entrained particle that reach the surface. Next, a slurry erosion jet-impingement test apparatus was constructed to gain insight into the primary material removal mechanisms of silicon under slurry flow conditions. A series of 14 different experiments were performed to identify the effect of jet velocity, particle size, particulate concentration, fluid viscosity and time on maximum erosion depth and volume of material removed. Combining the experimental erosion efforts with the localized particle impact characteristics from the CFD model enabled the previously developed Huang et al. cutting erosion model to be extended to new parameter and application ranges. The model was validated by performing CFD erosion simulations that matched with the experimental test cases in order to compare one-dimensional erosion rates. An impact dampening coefficient was additionally proposed to account for slight deviations between the CFD erosion predictions and experimental erosion rates. The product of this research will ultimately enable high fidelity erosion predictions specifically in mission-critical military, commercial and aerospace applications.