Parametric Study on the Effect of Partial Charge on Water Infiltration Behavior in MFI Zeolites

This work analyzes the infiltration behavior of water into sub-nanometer MFI zeolite pores using molecular dynamics simulations. Infiltration simulations are run for a range of partial charge values on the zeolite atoms. Infiltration behavior is compared to partial charges to verify dependence and determine critical charge above which infiltration becomes severely inhibited even at high pressures. Attraction energy is calculated and correlated to the observed infiltration behavior. The critical partial charge of Si~1.8 occurs when the waterzeolite interaction energy becomes stronger than water-water attraction due to which water molecules get stuck and infiltration is significantly reduced. Topics: Wate

Comprehensive modeling of thin film evaporation in micropillar wicks

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, June, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 48-50).In the Information Age, society has become accustomed to continuous, rapid advances in electronics technology. As the power density of these devices increases, heat dissipation threatens to become the limiting factor for growth in the electronics industry. In order to sustain rapid growth, the development of advanced thermal management strategies to efficiently dissipate heat from electronics is imperative. Porous wicks are of great interest in thermal management because they are capable of passively supplying liquid for thin film evaporation, a promising method to reliably dissipate heat in high-performance electronics. While the maximum heat flux that can be reliably sustained (the dryout heat flux) has been well-characterized for many wick configurations, key design information is missing as many previous models cannot determine the distribution of evaporator surface temperature nor temperature at the evaporator's interface with electronic components.Temperature gradients are inherent to the passive capillary pumping mechanism since the shape of the liquid-vapor interface is a function of the local liquid pressure, causing spatial variation of permeability and the heat transfer coefficient (HTC). Accounting for the variation of the liquid-vapor interface to determine the resulting temperature gradients has been a significant modeling challenge. In this thesis, we present a comprehensive modeling framework for thin film evaporation in micropillar wicks that can predict dryout heat flux and local temperature simultaneously. Our numerical approach captures the effect of varying interfacial curvature across the micropillar evaporator to determine the spatial distributions of temperature and heat flux. Heat transfer and capillary flow in the wick are coupled in a computationally efficient manner via incorporation of parametric studies to relate geometry and interface shape to local permeability and HTC.While most previous models only consider uniform thermal loads, our model offers the flexibility to consider arbitrary (non-uniform) thermal loads, making it suitable to guide the design of porous wick evaporators for cooling realistic electronic devices. We present case studies from our model that underscore its capability to guide design with respect to temperature and dryout heat flux. This model predicts notable variations of the HTC (-30%) across the micropillar wick, highlighting the significant effects of interfacial curvature that have not been considered previously. We demonstrate the model's capability to simulate non-uniform thermal loads and show that wick configuration with respect to the input thermal distribution has a significant effect on performance due to the distribution of the HTC and capillary pressure. Further, we are able to quantify the tradeoff associated with enhancing either dryout heat flux or the HTC by optimizing geometry.We offer insights into optimization and further analyze the effects of micropillar geometry on the HTC. Finally, we integrate this model into a fast, compact thermal model (CTM) to make it suitable for thermal/electronics codesign of high-performance devices and demonstrate a thermal simulation of a realistic microprocessor using this CTM. We discuss further uses of our model and describe an experimental platform that could validate our predicted temperature distributions. Lastly, we propose a biporous, area-enhanced wick structure that could push thermal performance to new limits by overcoming the design challenge typically associated with porous wick evaporators.by Geoffrey Vaartstra.S.M.S.M. Massachusetts Institute of Technology, Department of Mechanical Engineerin

Kinetics of Heat and Mass Transfer Near the Liquid-Vapor Interface

Evaporation and condensation can be seen in our daily lives but also play a key role in technologies that drive our modern society, such as power generation, distillation, refrigeration, and thermal management for buildings and electronics. Over the past century, great advances have been made in improving the performance of evaporators and condensers; yet the risk of overall system performance being bottlenecked by these components remains. Recently, state-of-the-art materials and micro-nanofabrication techniques have been applied to develop high-performance prototypes to prevent such a bottleneck. These advances are pushing toward the fundamental limit of evaporation/condensation in which the kinetics of heat and mass transport at the liquid-vapor interface become rate-limiting. As we approach this regime, experimental validation of our fundamental understanding of these kinetics ensures the accuracy of computationally-efficient models suitable for engineering design. These efforts will aid further innovation of the thermofluid systems which are critical to our modern society. A century of research on the kinetics of liquid-vapor phase change has provided a plethora of knowledge on the topic, yet the literature contains many discrepancies in theoretical treatment and conflicting experimental results. In this thesis, we seek to bridge the gap between kinetic theory and practical thermofluid engineering using computational analysis, and then experimentally validate the application of the kinetic model to condensation heat transfer. We first apply theory and a high-accuracy numerical technique to evaluate computationally-efficient models for evaporation/condensation rates. We quantify the accuracy of the Schrage equation—an approximation commonly used to predict heat fluxes in thermofluid engineering—and identify an existing moment-based model that ought to be used instead. Next, we fabricate and test an ultrathin, freestanding, nanoporous membrane designed to achieve high experimental sensitivity to the properties of the liquid-vapor interface. As a supplement to that experiment, we use highly-accurate direct simulation Monte Carlo calculations to validate the dusty-gas model. We demonstrate that this model accurately and efficiently predicts gas transport in our experimental system and state-of-the-art membranes that could be used for high-selectivity membrane separation processes. Finally, we carefully design an experimental setup to observe high-rate dropwise condensation under a microscope with strict measures to prevent contamination. We achieve unprecedented sensitivity to kinetics near the interface and our results validate the kinetic theory for condensation. Further, these experiments show that the accommodation coefficient of water is at least 0.5 and likely quite close to 1, indicating nearly ideal behavior of the interface. This thesis advances our fundamental understanding of the kinetics of heat and mass transfer near the liquid-vapor interface and provides guidelines for using models that can ultimately lead to better-performing components in power generation, desalination, and thermal management systems.Ph.D

Effectiveness and Causal Mechanisms for a ‘Life after Sport’ Career Development Intervention with Collegiate Student-Athletes

This dissertation is comprised of two studies based on data collected from NCAA Division I student-athletes comparing treatment and intervention groups during a 9-week career development intervention. Study 1 examined intervention effectiveness comparing psychosocial and behavioral outcomes over time, and Study 2 investigated why the intervention was effective by examining psychosocial and contextual factors as potential mediators and/or moderators of the relationship between the intervention and behavioral outcomes. Repeated-measures analysis of variance results from Study 1 indicated that the career development intervention significantly enhanced career decision-making self-efficacy, positive emotions, identified regulation, integrated regulation, self-reported career development behaviors, and stage of change; and significantly decreased amotivation towards career development. Results from Study 2 indicated that career decision-making self-efficacy, identified regulation, and integrated regulation significantly mediated the relationship between the intervention and several of the targeted psychosocial and behavioral outcomes. Intervention engagement was found to be a significant moderator of the relationship between the intervention and several targeted behavioral outcomes. The discussion focuses on the impact of the career development intervention on student-athletes and identifying the psychosocial and contextual factors that are critical to the effectiveness of the intervention. Suggestions are made for maximizing the effectiveness career development interventions targeted towards student-athletes and potential directions for future research on student-athlete career development interventions.doctoral, Ph.D., Movement & Leisure Sciences -- University of Idaho - College of Graduate Studies, 201

Cognitive reactivity as a risk factor for non-suicidal self-injury

Non-suicidal self-injury (NSSI) risk in young adults is impacted by both affective and cognitive responses to stress. The current study examined individual differences in cognitive reactivity to stress and their relationship to NSSI. Participants completed a baseline questionnaire followed by a laboratory visit involving measures before and after a stress induction task. Analyses indicated that individuals who engage in NSSI reported more affective and cognitive reactivity to stress. Higher levels of affective and cognitive reactivity uniquely predicted NSSI. The combined model yielded mixed results, with higher levels of affective reactivity leading to lower levels of cognitive reactivity, while higher levels of cognitive reactivity predicted more NSSI