Optical precursor is the sharp optical pulse front that does not show delay in absorptive media. In this thesis, optical precursor behavior in rubidium (Rb) vapor was investigated in the picoseconds regime. An amplified femtosecond laser was shaped to a 7-ps square pulse with sharp rising and trailing edges. This pulse was then sent into a hot rubidium vapor, and the center frequency of the laser pulse was absorbed. The output pulses were measured by a fast streak camera with 2-picosecond resolution. By varying the temperature of the Rb vapor, the measured pulse shapes showed the progression of formation of optical precursors. The measured pulses shapes showed good agreement with theory. On the other hand, a connection between optical precursors and femtosecond laser pumped 3-photon superradiance was investigated in this thesis. Maxwell-Bloch equations were numerically solved in two steps with commercial software Mathematica 8. A good agreement was found between simulation and experiment. It was confirmed that, at low excitation regime, superradiance generated from hot rubidium vapor, which were pumped by a femtosecond laser, can be understood as the formation of optical precursors.

Vapor compression cycles are the primary method by which refrigeration and air-conditioning systems operate, and thus constitute a significant portion of commercial and residential building energy consumption. This thesis presents a data-driven approach to find the optimal operating conditions of a multi-evaporator system in order to minimize the energy consumption while meeting operational requirements such as constant cooling or constant evaporator outlet temperature. The experimental system used for controller evaluation is a custom built small-scale water chiller with three evaporators; each evaporator services a separate body of water, referred to as a cooling zone. The three evaporators are connected to a single condenser and variable speed compressor, and feature variable water flow and electronic expansion valves. The control problem lies in development of a control architecture that will minimize the energy consumed by the system without prior information about the system in the form of performance maps, or complex mathematical models. The control architecture explored in this thesis relies on the data collected by sensors alone to formulate a function for the power consumption of the system in terms of controlled variables, namely, condenser and evaporator pressures, using recursive least squares estimation. This cost function is then minimized to attain optimal set points for the pressures which are fed to local controllers.

Federal regulation 49 CFR 193 and standard NFPA 59A require the use of validated consequence models to determine the vapor cloud dispersion exclusion zones for accidental liquefied natural gas (LNG) releases. For modeling purposes, the physical process of dispersion of LNG release can be simply divided into two stages: source term and atmospheric dispersion. The former stage occurs immediately following the release where the behavior of fluids (LNG and its vapor) is mainly controlled by release conditions. After this initial stage, the atmosphere would increasingly dominate the vapor dispersion behavior until it completely dissipates. In this work, these two stages are modeled separately by a source term model and a dispersion model due to the different parameters used to describe the physical process at each stage. The principal focus of the source term study was on LNG underwater release, since there has been far less research conducted in developing and testing models for the source of LNG release underwater compared to that for LNG release onto land or water. An underwater LNG release test was carried out to understand the phenomena that occur when LNG is released underwater and to determine the characteristics of pool formation and the vapor cloud generated by the vaporization of LNG underwater. A mathematical model was used and validated against test data to calculate the temperature of the vapor emanating from the water surface. This work used the ANSYS CFX, a general-purpose computational fluid dynamics (CFD) package, to model LNG vapor dispersion in the atmosphere. The main advantages of CFD codes are that they have the capability of defining flow physics and allowing for the representation of complex geometry and its effects on vapor dispersion. Discussed are important parameters that are essential inputs to the ANSYS CFX simulations, including the mesh size and shape, atmospheric conditions, turbulence from the source term, ground surface roughness height, and effects of obstacles. A sensitivity analysis was conducted to illustrate the impact of key parameters on the accuracy of simulation results. In addition, a series of medium-scale LNG spill tests have been performed at the Brayton Fire Training Field (BFTF), College Station, TX. The objectives of these tests were to study key parameters of modeling the physical process of LNG vapor dispersion and collect data for validating the ANSYS CFX prediction results. A comparison of test data with simulation results demonstrated that CFX described the physical behavior of LNG vapor dispersion well, and its prediction results of distances to the half lower flammable limit were in good agreement with the test data.

The statistics from the US Department of Energy show that about one-third of the total consumption of electricity in the households and industries is due to the Air Conditioning and Refrigeration (AC & R) systems. This wide usage has prompted many researchers to develop models for each of the components of the vapor compression systems. However, there has been very little information on developing simulation models that have been validated for the conditions of start-up/shutdown operations as well as vapor compression system faults. This thesis addresses these concerns and enhances the existing modeling library to capture the transients related to the above mentioned conditions. In this thesis, the various faults occurring in a vapor compressor cycle (VCC) have been identified along with the parameters affecting them. The transients of the refrigerant have also been studied with respect to the start-up/shutdown of a vapor compression system. All the simulations related to the faults and start-up/shutdown have been performed using the vapor compression system models developed in MATLAB/Simulink environment and validated against the 3-ton air conditioning unit present in the Thermo-Fluids Control Laboratory at Texas A & M University. The simulation and validation results presented in this thesis can be used to lay out certain rules of thumb to identify a particular fault depending on the unusual behavior of the system thus helping in creating certain fault diagnostic algorithms and emphasize the importance of the study of start-up/shutdown transient characteristics from the point of actual energy efficiency of the systems. Also, these results prove the capability and validity of the finite control volume models to describe VCC system faults and start-up/shutdown transients.

In development projects, designers should take into consideration the possibility of a vapor cloud explosion in the siting and design of a process plant from day one. The most important decisions pertinent to the location of different process areas, separation between different areas, location of occupied buildings and overall layout may be made at the conceptual stage of the project. During the detailed design engineering stage the final calculation of gas explosion loads is an important activity. However, decisions related to the layout and location of occupied buildings at this stage could be very costly. Therefore, at the conceptual phase of the development project for a hydrocarbon facility, it would be helpful to get a picture of possible vapor cloud explosion loads to be used in studying various options. This thesis presents the analytical parameters that are used in vapor cloud explosion risk analysis. It proposes a model structure for the analysis of vapor cloud explosion risks to buildings based on exceedance methodology. This methodology was developed in a computer program which is used to support this thesis. The proposed model considers all possible gas release scenarios through the use of the Monte Carlo simulation. The risk of vapor cloud explosions can be displayed using exceedance curves. The resulting model provides a predictive tool for vapor cloud explosion problems at the early stages of development projects, particularly in siting occupied buildings in onshore hydrocarbon facilities. It can also be used as a quick analytical tool for investigating various aspects of vapor cloud explosions. This model has been applied to a case study, a debutanizer process unit. The model was used to explore the different alternatives of locating a building near the facility. The results from the model were compared to the results of other existing software to determine the model validity. The results show that the model can effectively examine the risk of vapor cloud explosions.

Removal of water vapor from humid streams is an energy-intensive process used widely in industry. Effective dehumidification has the potential to significantly reduce energy consumption and the overall cost of a process stream. Membrane-based separations, particularly dehumidification, are an emerging technology that can change the landscape of global energy usage because they have a small footprint, they are easy to scale up, to implement and to operate. The focus of this thesis is to evaluate new directions for the development and use of materials for membrane-based dehumidification processes. It will show advances in the synthesis of new copolymers, a surprising boost in performance with the addition of 2-D materials, propose the use of polybenzimidazole for challenging dehumidification applications, and show how by tuning the nanostructure of a commercially available block copolymer (BCP) it is possible to increase the performance. The design of novel amphiphilic ternary copolymers comprising P(AN-r-PEGMA-r-DMAEMA) allowed selective removal of water vapors from gaseous streams; the effect of varying PEGMA chain length on membrane performance was studied. The membranes showed an excellent performance when the content of the PEGMA segment was 2.9 mol% with a chain length of 950Da. In the mixed-matrix approach, the inclusion of graphene oxide (GO) nanosheets in a different copolymer enhanced the membrane performance by creating selective tortuous pathways for inert gases. The well-distributed GO nanosheets in the defect-free composite membranes resulted in an 8 fold increase in water vapor/N2 selectivity compared to neat membranes. Thirdly, dense polybenzimidazole membranes showed good water vapor permeability, and the addition of TiO2-based fillers with varying chemistry and geometry enhanced the performance of PBI membranes. Lastly, the effect of tuning the morphology of commercially available BCP on dehumidification was demonstrated successfully. The self-assembled morphology formed with cylindrical hydrophobic cores, and the hydrophilic coronas, formed ion-rich highways for fast water vapor transport. Water vapor permeability improved up to 6-fold with the nanostructure modulation more than any membrane reported in the literature. In summary, the work reported in this dissertation has the potential to lay a framework towards tailor-made next-generation membranes aimed for water vapor removal in various dehumidification applications.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 270-273).

Thesis (Ph.D.)--Tufts University, 1996. / Adviser: Terry E. Haas. Submitted to the Dept. of Chemistry. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D.)--McMaster University (Canada), 1994. / Source: Dissertation Abstracts International, Volume: 56-08, Section: B, page: 4527. Adviser: G. C. Weatherly.

Thesis (M.S.)--Ohio University, November, 2001. / Title from PDF t.p.