Browsing by Author "Wang, Jue"

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    Grinding Behaviors of Components in Heterogeneous Breakage of Coals of Different Ash Contents in a Ball-and-Race Mill
    Duan, Jin; Lu, Qichang; Zhao, Zhenyang; Wang, Xin; Zhang, Yuxin; Wang, Jue; Li, Biao; Xie, Weining; Sun, Xiaolu; Zhu, Xiangnan (MDPI, 2020-03-03)
    Coals used for power plants normally have different ash contents, and the breakage of coals by the ball-and-race mill or roller mill is an energy-intensive process. Grinding phenomena in mill of power plants is complex, and it is also not the same with ideal grinding tests in labs. The interaction among various coals would result in changes of grinding behaviors and energy consumption characterization if compared with those of single breakage. In this study, anthracite and bituminous coal of different ash contents were selected to be heterogeneously ground. Quantitation of components in products was realized using the relation between sulfur content of the mixture and mass yield of one component in the mixture. Product fineness t10 of the component was determined, and split energy was calculated on the premise of specific energy balance and energy-size reduction model by a genetic algorithm. Experimental results indicate that breakage rate and product fineness t10 of the mixture decrease with the increase of hard anthracite content in the mixture. Unlike the single breakage, t10 of anthracite in heterogeneous grinding is improved dramatically, and bituminous coal shows the opposite trend. The interaction between components results in the decrease of the specific energy of the mixture if compared with the mass average one of components in single breakage. Breakage resistance of hard anthracite decreases due to the addition of soft bituminous coal, and grinding energy efficiency of anthracite is also improved compared with that of single grinding.
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    Impacts of process-induced porosity on material properties of copper made by binder jetting additive manufacturing
    Kumar, Ashwath Yegyan; Wang, Jue; Bai, Yun; Huxtable, Scott T.; Williams, Christopher B. (Elsevier, 2019-07-03)
    Binder Jetting (BJ) is an efficient, economical, and scalable Additive Manufacturing (AM) technology that can be used in fabricating parts made of reflective and conductivematerials like copper, which have applications in advanced thermal and electrical components. The primary challenge of BJ is in producing fully dense, homogeneous partswithout infiltration. To this end, copper parts of porosities ranging from2.7% to 16.4%were fabricated via BJ, by varying powder morphology, post-process sintering, and Hot Isostatic Pressing conditions. The aim of this study is to characterize and quantify the effects of porosity on the material properties of Binder Jet pure copper parts. Copper parts with the lowest porosity of 2.7% demonstrated a tensile strength of 176 MPa (80.2% of wrought strength), a thermal conductivity of 327.9 W/m·K (84.5% that ofwrought copper), and an electrical conductivity of 5.6 × 107 S/m (96.6% IACS). The porosity-property relationship in these parts was compared against theoretical and empiricalmodels in the literature for similar structures. These studies contribute towards developing a scientific understanding of the process-property-performance relationship in BJ of copper and other printed metals, which can help in tailoring materials and processing conditions to achieve desired properties.
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    System Design, Fabrication, and Characterization of Thermoelectric and Thermal Interface Materials for Thermoelectric Devices
    Wang, Jue (Virginia Tech, 2018-06-13)
    Thermoelectric devices are useful for a variety of applications due to their ability to either convert heat directly into electricity, or to generate a temperature gradient from an electric current. These devices offer several attractive features including compact size, no moving parts, limited maintenance requirements, and high reliability. Thus thermoelectric devices are used for temperature-control, cooling, or power generation in various industrial systems such as automobiles, avionics, refrigerators, chillers, laser diodes, dehumidifiers, and a variety of sensors. In order to improve the efficiency of thermoelectric devices, many endeavors have been made to design and fabricate materials with a higher dimensionless thermoelectric figure of merit (ZT), as well as to optimize the device structure and packaging to manage heat more effectively. When evaluating candidate thermoelectric materials, one must accurately characterize the electrical conductivity, thermal conductivity, and the Seebeck coefficient over the temperature range of potential use. However, despite considerable research on thermoelectric materials for decades, there is still significant scatter and disagreement in the literature regarding accurate characterization of these properties due to inherent difficulties in the measurements such as requirements for precise control of temperature, simultaneous evaluation of voltage and temperature, etc. Thus, a well-designed and well-calibrated thermoelectric measurement system that can meet the requirements needed for multiple kinds of thermoelectric materials is an essential tool for the development of advanced thermoelectric devices. In this dissertation, I discuss the design, fabrication, and validation of a measurement system that can rapidly and accurately evaluate the Seebeck coefficient and electrical resistivity of thermoelectric materials of various shapes and sizes from room temperature up to 600 K. The methodology for the Seebeck coefficient and electrical resistivity measurements is examined along with the optimization and application of both in the measurement system. The calibration process is completed by a standard thermoelectric material and several other materials, which demonstrates the accuracy and reliability of the system. While a great deal of prior research has focused on low temperature thermoelectric materials for cooling, such as Bi2Te3, high temperature thermoelectric materials are receiving increasing attention for power generation. With the addition of commercial systems for the Seebeck coefficient, electrical resistivity, and thermal conductivity measurements to expand the temperature range for evaluation, a wide range of materials can be studied and characterized. Chapter Two of this dissertation describes the physical properties characterization of a variety of thermoelectric materials, including room temperature materials such as Bi0.5Sb1.5Te3, medium temperature level materials such as skutterudites, and materials for high temperature applications such as half-Heusler alloys. In addition, I discuss the characterization of unique oxide thermoelectric materials, which are Al doped ZnO and Ca-Co-O systems for high temperature applications. Chapter Four of this dissertation addresses the use of GaSn alloys as a thermal interface material (TIM), to improve thermal transport between thermoelectric devices and heat sinks for power generation applications at high temperature. I discuss the mechanical and thermal behavior of GaSn as an interface material between electrically insulating AlN and Inconel heat exchangers at temperatures up to 600 °C. Additionally, a theoretical model for the experimental thermal performances of the GaSn interface layer is also examined.