Browsing by Subject "Thermal Management"

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    Modeling, Design, and Fabrication of Spectrally-Selective Mirrors for Photovoltaic Thermal Management
    (2020-07) Slauch, Ian
    A typical c-Si photovoltaic module will operate 20-30K above ambient temperature due to waste heat generated as it converts incident sunlight into electrical power. As temperature increases, the conversion efficiency drops by ~0.4%/K, reducing overall power output. Reducing the total amount of waste heat generated during operation would both lower the module operating temperature and improve its efficiency and energy yield. Waste heat is generated in the module in part due to parasitic absorption of sub-bandgap light that does not have enough energy to be useful for power conversion. Sub-bandgap reflection offers a method of preventing parasitic absorption, cooling the module, and increasing its efficiency. In this thesis, a time-independent matrix model is introduced to calculate module energy yield and waste heat generation through parasitic absorption, recombination, and electronic losses. The model considers the spectral and angular dependence of the optical properties of the module including modification by photonic structures, and is used to characterize and optimize the design of aperiodic photonic mirrors which selectively reflect sub-bandgap light from the module and enhance its energy yield. Importantly, these mirrors are designed considering weather and irradiance conditions typical for outdoor fixed-tilt module installations. As a result, it is shown that these mirrors are omnidirectional, achieving the required spectral selectivity regardless of the angle of incidence of sunlight or the geographic location of installation. Low-complexity mirror designs which are simple to fabricate offer the most potential for reducing the cost of energy. These designs are primarily anti-reflection coatings, but also avoid a rise in operating temperature while increasing energy output. Two simple designs are fabricated, integrated into modules, and tested outdoors. The fabricated mirrors have the desired spectral selectivity, and reduce module operating temperature by over 1K. Alternative strategies to reject sub-bandgap light, including reflection from the cell surface or cell rear contact, and backscattering from near the cell are also modeled and compared to result for reflection from the glass. Designing for the glass interface in particular allows maximization of the dual benefit, optical and thermal, of the mirrors.
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    A New Realistic Approach To Convective Heat Transfer Modeling And Simulation In The Presence Of Swirling Flows
    (2017-12) Ilamparuthi, Santosh
    The thesis deals with internal fluid flows with heat transfer where swirl is a dominant component. The modeling of these flows is important due to their wide prevalence in industrial processes. The use of appropriate turbulence models for swirling flows and verification is performed in the chapter 2. Chapters 3 and 4 deals with applications with swirling flows. This includes the cooling and thermal management of a PCR machine and studying the thermal and flow behavior of fluid flows in large pipes under directly ducted fan flows. Fluid flow was visualized with both normalized and non-normalized vector plots while temperature contour plots and turbulence ratio contour plots were utilized to delineate the various thermal and fluid flow regimes which were encountered. The simulations were all carried out in ANSYS – CFX predominantly using versions 14 through 16. The results demonstrated the need for further adoption of the SST turbulence model especially in flows where swirl was a significant factor.