Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Comprehensive Calorimetry and Modeling of the Thermally-Induced Failure of a Lithium Ion Battery(2016) Liu, Xuan; Stoliarov, Stanislav I; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A lithium ion battery (LIB) subjected to external heat may fail irreversibly. Manifestation of this failure include venting of potentially combustible gases and aerosols followed by a rapid self-heating accompanied by ejection of the battery materials. Quantification and simulation of the dynamics and energetics of this process are important to ensure LIBs’ safety. Here we report on development of a new experimental technique for measuring the energetics of the thermally-induced failure of LIBs as well as a new thermo-kinetic model to predict battery failure behaviors. The newly developed experimental technique, Copper Slug Battery Calorimetry (CSBC), was employed to investigate a widely utilized form factor of LIB (i.e. 18650) with 3 different battery chemistries: lithium cobalt oxide (T-Energy ICR18650, LCO), lithium nickel manganese cobalt oxide (Panasonic CGR18650CG, NMC) and lithium iron phosphate (K2 18650E, LFP), at various states of charge (SOCs). This technique can yield time resolved data on the rate of heat production inside the failing battery. The heat capacity of these LIBs was evaluated to be 1.1±0.1 J g-1 K-1 for all three cathode types. It was shown that the total heat generated inside the batteries increases with increasing amount of electrical energy stored. The maximum total internal heat generated by fully-charged LIBs was found to be 37.3±3.3, 34.0±1.8 and 13.7±0.4 kJ/cell for LCO, NMC and LFP LIBs, respectively. Additionally, experiments were carried out in which the CSBC technique was combined with cone calorimetry to measure the heat produced in flaming combustion of vented battery materials. The released combustion heat did not show a clear dependence on the stored electrical energy; this heat varied between 35 and 63 kJ/cell for LCO LIBs, 27 and 81 kJ/cell for NMC LIBs, and 36 and 50 kJ/cell for LFP LIBs. Beyond the experimental work, detailed modeling of heat transfer in the CSBC experiments was carried out, by utilizing COMSOL Multiphysics software, to evaluate thermal conductivities of the LIBs and demonstrate the satisfactory accuracy of CSBC experimental analysis in the determination of the battery failure energetics for all examined battery types. Moreover, it is presented in this study a general methodology to develop a thermo-kinetic model of thermally-induced failure of lithium ion batteries (LIBs), using COMSOL and experimental data collected by CSBC. This methodology is demonstrated specifically on LCO LIBs (T-Energy ICR18650), but it can be easily extended to other battery types. The model was parameterized based on Arrhenius’ Law and via an iterative inverse modeling analysis of CSBC test results using COMSOL. These model parameters are dependent on the cells’ states of charge (SOCs) and they can effectively represent the tested cells’ heat production energetics during failure. The fully-parameterized thermo-kinetic model was then validated against CSBC tests that were not utilized in the model parameterization: CSBC tests on 100% SOC LIB cell with non-standard heating rates ranging from 40 W to 100 W; and CSBC tests on 75% SOC LIB cell with a standard heating rate of 20 W. The agreements between the experimentally measured and the simulated copper slug temperature histories in these tests were found within in 5% on average. Last but not least, this model was applied to predict the thermally-induced failure of LIB cells in a more complex scenario – cascading LIB failure of 6 LIB cells in a billiard battery pack. The simulated onset time of thermal runaway of each LIB cell in the battery pack were found of excellent agreements with experimental observations.Item Statistical Analysis of Online Eye and Face-Tracking Applications in Marketing(2015) Liu, Xuan; Wedel, Michel; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eye-tracking and face-tracking technology have been widely adopted to study viewers' attention and emotional response. In the dissertation, we apply these two technologies to investigate effective online contents that are designed to attract and direct attention and engage viewers emotional responses. In the first part of the dissertation, we conduct a series of experiments that use eye-tracking technology to explore how online models' facial cues affect users' attention on static e-commerce websites. The joint effects of two facial cues, gaze direction and facial expression on attention, are estimated by Bayesian ANOVA, allowing various distributional assumptions. We also consider the similarities and differences in the effects of facial cues among American and Chinese consumers. This study offers insights on how to attract and retain customers' attentions for advertisers that use static advertisement on various websites or ad networks. In the second part of the dissertation, we conduct a face-tracking study where we investigate the relation between experiment participants' emotional responseswhile watching comedy movie trailers and their watching intentions to the actual movies. Viewers' facial expressions are collected in real-time and converted to emo- tional responses with algorithms based on facial coding system. To analyze the data, we propose to use a joint modeling method that link viewers' longitudinal emotion measurements and their watching intentions. This research provides recommenda- tions to filmmakers on how to improve the effectiveness of movie trailers, and how to boost audiences' desire to watch the movies.Item Design and Analysis of New Gasification Apparatus based on the Standard Cone Calorimeter(2012) Liu, Xuan; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A simple, inexpensive, safe version of pyrolysis apparatus is developed base on the standard cone calorimeter (ASTM E 1354). A controllable oxygen concentration (0% to 21% by volume) environment in the vicinity of 80 mm by 80 mm square sample positioned under the cone radiant heater is achieved by means of "Controlled Atmosphere Pyrolysis Apparatus". Valid gasification mass loss rate measurements have been obtained for both poly(methyl methacrylate) (PMMA) and polypropylene (PP) samples under external heat fluxes of 35kW/m^2 and 50kW/m^2. Reasonable value of thermal conductivity for PMMA is measured. With the thermal conductivity and parameters defined by Differential Scanning Calorimeter (DSC) of PMMA, the gasification mass loss rate is well simulated using Thermo-Kinetic Model of Burning (ThermaKin).