Mechanical Engineering

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    A 1D Reduced-Order Model (ROM) for a Novel Latent Thermal Energy Storage System
    (MDPI, 2022-07-14) Kailkhura, Gargi; Mandel, Raphael Kahat; Shooshtari, Amir; Ohadi, Michael
    Phase change material (PCM)-based thermal energy storage (TES) systems are widely used for repeated intermittent heating and cooling applications. However, such systems typically face some challenges due to the low thermal conductivity and expensive encapsulation process of PCMs. The present study overcomes these challenges by proposing a lightweight, low-cost, and low thermal resistance TES system that realizes a fluid-to-PCM additively manufactured metal-polymer composite heat exchanger (HX), based on our previously developed cross-media approach. A robust and simplified, analytical-based, 1D reduced-order model (ROM) was developed to compute the TES system performance, saving computational time compared to modeling the entire TES system using PCM-related transient CFD modeling. The TES model was reduced to a segment-level model comprising a single PCM-wire cylindrical domain based on the tube-bank geometry formed by the metal fin-wires. A detailed study on the geometric behavior of the cylindrical domain and the effect of overlapped areas, where the overlapped areas represent a deviation from 1D assumption on the TES performance, was conducted. An optimum geometric range of wire-spacings and size was identified. The 1D ROM assumes 1D radial conduction inside the PCM and analytically computes latent energy stored in the single PCM-wire cylindrical domain using thermal resistance and energy conservation principles. The latent energy is then time-integrated for the entire TES, making the 1D ROM computationally efficient. The 1D ROM neglects sensible thermal capacity and is thus applicable for the low Stefan number applications in the present study. The performance parameters of the 1D ROM were then validated with a 2D axisymmetric model, typically used in the literature, using commercially available CFD tools. For validation, a parametric study of a wide range of non-dimensionalized parameters, depending on applications ranging from pulsed-power cooling to peak-load shifting for building cooling application, is included in this paper. The 1D ROM appears to correlate well with the 2D axisymmetric model to within 10%, except at some extreme ranges of a few of the non-dimensional parameters, which lead to the condition of axial conduction inside the PCM, deviating from the 1D ROM.
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    Effect of Encapsulation on Electrolyte Leakage in Aluminum Electrolytic Capacitors Under Constant Thermal and Electrical Loading
    (2014) Parsa, Ehsan; Dasgupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study focuses on the influence of encapsulation (with silicone elastomer potting compound) on electrolyte leakage in aluminum electrolytic capacitors. Experiments were conducted on potted capacitors at constant elevated temperature and rated DC voltage, and results were compared to those from a control batch of unpotted capacitors. The weight, ESR and capacitance were periodically monitored. Encapsulation was found to decelerate electrolyte loss rate and ESR degradation. There was an increasingly discernible deceleration of capacitance degradation but the magnitude did not reach statistically significant thresholds within the test period. A simplified axisymmetric finite element model was constructed for theoretical understanding of the electrolyte loss process. The experimental measurements were used to guide the selection of the material properties in the model. The model addresses several possible sources of non-uniformities in the mass flux density in the test specimen: (i) radial nonuniformity of mass transport properties of the rubber seal; and (ii) delamination between the potting compound and the capacitor leads. This model was then used: (i) to conduct parametric investigation of the effect of mass transport properties of the potting compound; and (ii) in conjunction with the experimental results to estimate the electrolyte mass loss from the capacitor through the rubber seal.