Master of Science / Department of Mechanical and Nuclear Engineering / Steven Eckels / The current research presents the experimental investigation of heat transfer and flow characteristics of sonic multiphase flow in a converging-diverging nozzle. R134a and R123 are used in this study. Four different nozzle assemblies with two different throat sizes (2.43mm and 1.5 mm with 1° growth angle with the centerline of the nozzle in the diverging section) and two different heater lengths (200 mm and 125 mm) were tested. Each test section was an assembly of aluminum nozzle sections. The experimental facility design allowed controlling three variables: throat velocity, inlet temperature, back pressure saturation temperature. The analysis used to find the average heat transfer of the fluid to each nozzle section. This was achieved by measuring the nozzle wall temperature and fluid pressure in a steady state condition. Two methods for finding the average heat flux in sonic nozzle were included in the data analysis: infinite contact resistance and zero contact resistance between nozzle sections. The input variables ranges were 25 °C and 30 °C for inlet temperature and back pressure saturation temperatures, 1100-60,000 kg/m[superscript]2s for mass flux, and 1.4-700 kW/m[superscript]2 heat flux. The effect of the mass flux and heat flux on the average two-phase heat transfer coefficients was investigated. The flow quality, Mach number(M), and Nusselt number ratio ([phi]) were also calculated for each section of the nozzle. As the fluid flowed through the nozzle, the pressure of the liquid dropped below the inlet saturation pressure of the liquid due to sonic expansion in the nozzle. This temperature drop was significantly lower in the case of R134a than R123. The results showed that the two-phase heat transfer coefficients were above of 30000 W/m^2 K in the first 75 mm of the nozzle, and they decreased along the nozzle. The Mach number profile appeared similar to the temperature profile, and the fluid was in the sonic region as long as temperature of the fluid dropped in the nozzle. Nusselt number ratios were compared with the Mach numbers and showed that the Nusselt number ratio were increased in the sonic region. The results showed that the length of the sonic region was larger for R123 than for R134a, and the Mach numbers were higher for R123. The Nusselt ratios of R123 were low compared to the R134a cases, and the trend in the Nusselt ratios was notably different as well.

Master of Science / Department of Mechanical and Nuclear Engineering / Gurpreet Singh / Graphene because of its unique electrical (electron mobility = 2 x 10[superscript]5 cm[superscript]2 V[superscript]-1 s[superscript]-1), mechanical (E = 1 TPa), optical, thermal and chemical properties has generated a lot of interest among the research community in recent years. One of the most notable methods of synthesizing large area pristine graphene sheets, which are several 100 micrometers wide, is through thermal chemical vapor deposition (CVD). But very little has been known about the effects of heating and cooling rate of the substrate on the quality of graphene produced. Hence we varied various growth parameters to understand the process of graphene growth on Cu and Ni substrates when subjected to fast heating and quenching. This allowed optimization of the CVD process to achieve large-area graphene films consistently and repeatedly. This work provides new insights on synthesis of graphene at atmospheric pressures and the effect of (a) fast heating and fast cooling of substrates, (b) catalyst type and (c) gas flow rates on quality of the graphene produced. A carbon nanotube CVD furnace was restored and modified to accommodate graphene synthesis. We started with synthesis of graphene on Cu substrate following procedures already available in the literature (heating rate ~ 15 °C/min and cooling rate ~ 5 °C/min; total processing time 7 hours). This provided a good reference point for the particular furnace and the test setup. The best results were obtained for 15 minutes of growth at a CH4:H2 ratio of 1:30 at 950 °C. SEM images showed full coverage of the substrate by few layer graphene (FLG), which was indicated by the relatively high I[subscript]2D/I[subscript]G ratio of 0.44. The furnace was further modified to facilitate fast cooling (~4 °C/sec) of substrate while still being in inert atmosphere (Argon). The effect of growth time and concentration of CH[subscript]4 was studied for this modified procedure (at H[subscript]2 flow rate of 300 SCCM). SEM images showed full coverage for a CH[subscript]4 flow rate of 10 SCCM in as little as 6 minutes of growth time. This coupled with the fast cooling cycle effectively reduced the overall time of graphene synthesis by 7 times. The I[subscript]2D/I[subscript]G ratio in Raman spectrum was 0.4 indicating that the quality of graphene synthesized was similar to that obtained in conventional CVD. This modification also facilitated introduction of catalyst substrate after the furnace has reached growth temperature (fast heating ~8 °C/sec). Hence, the overall time required for graphene synthesis was reduced to ~6 % (30 minutes) when compared to the traditional procedure. SEM images showed formation of high concentration few layer graphene islands. This was attributed to the impurities on the catalyst surface, which in the traditional procedure would have been etched away during the long heating period. The optimum process parameters were 30 minutes of growth with 20 SCCM of CH[subscript]4 and 300 SCCM of H[subscript]2 at 950 °C. The Raman spectrum for this condition showed a relatively high I[subscript]2D/I[subscript]G ratio of 0.66. We also studied the effect of Ni as a catalyst. Similar to Cu, for Ni also, traditional procedure found in the literature was used to optimize the graphene growth for this particular furnace. Best results were obtained for 10 minutes of growth time with 120 SCCM of CH[subscript]4 in 300 SCCM of H[subscript]2 at 950 °C. SEM images showed large grain growth (~50 μm) with full coverage. The Raman spectrum showed formation of bi-layer graphene with a I[subscript]2D/I[subscript]G ratio of 1.03. Later the effect of growth time and concentration of the hydrocarbon precursor for Ni substrate subjected to fast heating (~ 8 °C/sec) was studied. It was found that because the process of graphene synthesis on Ni is by segregation, growth period or gas flow rate had little effect on the quality and size of the graphene sheets because of the presence of impurities on the substrate. This procedure yielded multilayer graphite instead of graphene under all conditions. Future work will involve study of changing several other parameters like type of hydrocarbon precursor and pressure in the chamber for graphene synthesis. Also various other substrates like Cu or Ni based alloys will be studied to identify the behavior of graphene growth using this novel procedure.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / B. Terry Beck / The current experimental method to determine the transfer length in prestressed concrete members consists of measuring concrete surface strains before and after de-tensioning with a mechanical strain gage. The method is prone to significant human errors and inaccuracies. In addition, since it is a time-consuming and tedious process, transfer lengths are seldom if ever measured on a production basis. A rapid, non-contact method for determining transfer lengths in prestressed concrete members has been developed. The new method utilizes laser-speckle patterns that are generated and digitally recorded at various points along the prestressed concrete member. User-friendly software incorporating robust and fast digital image processing algorithms was developed by the author to extract the surface strain information from the captured speckle patterns. Based on the laser speckle measurement technique, four (4) successively improved generations of designs have been made. A prototype was fabricated for each design either on an optical breadboard for concept validation, or in a portable self-contained unit for field testing. For each design, improvements were made based on the knowledge learned through the testing of the previous version prototype. The most recent generation prototype, incorporating a unique modular design concept and self-calibration function, has several preferable features. These include flexible adjustment of the gauge length, easy expansion to two-axis strain measurement, robustness and higher accuracy. Extensive testing has been conducted in the laboratory environment for validation of the sensor’s capability in concrete surface strain measurement. The experimental results from the laboratory testing have shown that the measurement precision of this new laser speckle strain measurement technique can easily achieve 20 microstrain. Comparison of the new sensor measurement results with those obtained using traditional strain gauges (Whittemore gauge and the electrical resistance strain gauge) showed excellent agreement. Furthermore, the laser speckle strain sensor was applied to transfer length measurement of typical prestressed concrete beams for both short term and long term monitoring. The measurement of transfer length by the sensor was unprecedented since it appears that it was the first time that laser speckle technique was applied to prestressed concrete inspection, and particularly for use in transfer length measurement. In the subsequent field application of the laser speckle strain sensor in a CXT railroad cross-tie plant, the technique reached 50 microstrain resolution, comparable to what could be obtained using mechanical gauge technology. It was also demonstrated that the technique was able to withstand extremely harsh manufacturing environments, making possible transfer length measurement on a production basis for the first time.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Kevin B. Lease / The overall goal of this study was to assess the effects of surface chemistry on adhesion of polymeric systems underwater. The adhesion is quantified by the thermodynamic work of adhesion (W) when two surfaces are approached and the energy release rate (G) when the surfaces are separated. For some polymeric systems there is a difference between W and G, referred to as adhesion hysteresis. For this study an experimental approach based upon Johnson-Kendall-Roberts (JKR) theory of contact mechanics was utilized to evaluate how surface chemistry affects the adhesion behavior (both W and adhesion hysteresis) in the presence of water. The interfacial interactions were also studied in air and contrasted to those obtained underwater. To accomplish the overall goal of this research, this study was divided into two phases where smooth model surfaces with disparate surface chemistries were used. The model surfaces in the first part included poly(dimethysiloxane) (PDMS), glass surfaces chemically functionalized to display hydrophilic to medium to hydrophobic characteristics, and thin films of wood-based biopolymers. The functionalities used to modify glass surfaces included polyethylene oxide (PEO) with hydrophilic nature; amine, carbomethoxy, and mercapto (thiol) with intermediate characteristics; cyclohexyl, fluorocarbon, and methyl with hydrophobic behavior. In addition to these surfaces, flat PDMS and clean glass surfaces were also used for means of comparison. The wood-derived polymers included two different cellulose types (natural cellulose and regenerated cellulose) as well as one lignin surface (from hardwood milled lignin). These surfaces were probed with native PDMS hemispheres, which are hydrophobic. The results showed that in air the value of W for all model surfaces was independent of the surface chemistry, except fluorocarbon which was lower. Underwater W was significantly affected by the surface hydrophilicity/ hydrophobicity. The adhesion hysteresis both in air and underwater was significantly dependent on the structure of the probed surface. For the second phase PDMS hemispheres were chemically modified with amine functionality to probe model surfaces with hydrophilic and intermediate behavior. These surfaces included glass surfaces functionalized with PEO and amine as well as PDMS sheets that were functionalized with amine. Native PDMS flat surfaces were also used for means of comparison. The results showed that for the selected surfaces both W and hysteresis were affected by the surface chemistry in both media.

Master of Science / Department of Mechanical and Nuclear Engineering / Kevin B. Lease / Xiao J. Xin / The study of buckling behavior of tubular and cellular structures has been an intriguing area of research in the field of solid mechanics. Unlike the global Euler buckling of slender structures under compressive loads, tubular and cellular structures deform with their walls buckling as individual supported plates. The aspect ratio and the dimensional characteristics of the tube define the buckling behavior of any tube structure. In this thesis, a thorough study on the buckling of polygon tubular structures with different cross sections is discussed. In the first study, the theoretical buckling formulation of a square tube using the energy method is reviewed from existing solutions in literature. The elastic critical load of a square tube derived from the theoretical solution is then compared with results of finite element elastic buckling simulations. The formation of lobes along the height of the walls at different aspect ratios of the tube is investigated and compared to theory. Also, the buckling behavior of multi-wall structures is studied and the relationship between these structures and a rectangular simply supported plate is established. A brief study on the buckling behavior of rhombic tubes is also performed. The results of the simulation match closely with the theoretical predictions. The study is then extended to quadrilateral tubes with cross-sections in the shape of square, rectangle, rhombus and parallelogram. The theory of buckling of these tubes is explicitly defined using classical plate mechanics based on the previous works presented in literature. Also, the possibility of global Euler buckling in the tubular structures after a certain critical height is discussed. The prediction from the theory is validated using extensive finite element elastic buckling simulations and experimental tests on square and rhombic tube specimens. The results of the simulations and experiments are observed to be consistent with the theory. Using the formulation of plate buckling under different boundary conditions, the buckling behavior of triangular tubes is also determined. A theoretical formulation for calculating the critical load of triangular tubes is derived. The theoretical critical loads for a range of aspect ratios are compared with corresponding finite element simulation results. The comparisons reveal high degree of similarity of the theoretical predictions with the simulations.

Master of Science / Department of Mechanical and Nuclear Engineering / Kevin B. Lease / This research was intended to measure the interfacial shear strength between fiber/ matrix systems and to investigate the relation between structure-mechanical properties and performance of fiber/matrix systems. This work conducted a systematic study on model fiber/matrix systems to enhance the fundamental understanding on how variation of polymeric compositions (and hence, different structures), different curing conditions, and fiber surface treatments influence the interactions between the fiber and matrix. In order to measure the interfacial shear strength of fiber/matrix systems, the microdroplet technique was used. In this technique a polymer droplet was deposited on a fiber in the liquid state. Once the droplet was cured a shear force was applied to the droplet in order to detach the droplet from the fiber. The amount of the force needed to de-bond the droplet was directly related to the strength of the bonds formed between the fiber and matrix during the curing process. In addition, the micro-droplet technique was used to evaluate effects of different crosslinker ratio of fiber/ matrix system and also to see if different curing conditions affect the interfacial shear strength of fiber/ matrix system. Surface treatment was also conducted to evaluate its effects on the interfacial shear strength of the fiber/ matrix system using microdroplet technique. The interfacial shear strength of fiber/ matrix system increased along with the increase of crosslinker ratio to a limiting value, and it decreased as long as the crosslinker ratio increased. Curing condition also caused the interfacial shear strength of fiber/ matrix system to increase when it was cured at higher temperature. Fiber surface treatment exhibited a significant effect to the interfacial shear strength as well as the fiber/ matrix contact angle measurement.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / M. H. Hosni / B. W. Jones / This dissertation focuses on airflow distribution in the longitudinal direction of a wide-body mockup aircraft cabin, turbulence energy and dissipation rates, and the effect of thermal plumes, generated by passengers, on airflow distribution within the cabin. The mockup cabin utilized for this study mimics a Boeing 767 passenger cabin and includes 11 rows in the longitudinal direction with each row consisting of seven seats. Each seat is occupied by an inflatable manikin which is instrumented with a 10 meters long wire heater generating approximately 100 Watts of distributed sensible heat, representing heat load from a sedentary human being. In order to investigate the fluid dynamics characteristics of the airflow within the cabin, different experimental techniques were implemented. Smoke visualization was used to qualitatively visualize the general airflow pattern inside the cabin. A tracer gas composed mainly of carbon dioxide was used to track the airflow distribution inside the cabin. The tracer gas was released in several locations and then sampled at various locations throughout the mockup cabin. The release and sampling of the tracer gas allowed tracing the airflow inside the cabin using non dispersive infrared sensors. Combining results from different release-sampling scenarios gave better understanding of the chaotic and three-dimensional nature of the airflow behavior inside the cabin. Air speed and turbulence parameters were evaluated using omni-directional probes. Finally, the effect of the heat generated by the thermal manikins on the airflow behavior was investigated. The results from the airflow visualization and the tracer gas were complementary and showed that there were multiple air circulations along the length of the cabin. The dimension of the circulations were controlled by the minimum physical distance inside the cabin. The identified-isotropic turbulence were spread over the full width of the cabin in the front and middle sections of the cabin, whereas, multiple-smaller circulations were identified in the rear section. Cabin sections identified with high speed fluctuations were associated with higher turbulence kinetic energy levels and lower local dissipation rates. These sections served as driving forces to create the circulations identified in the tracer gas experiments. Furthermore, the heat generated by the thermal manikins was shown to significantly impact the behavior of the gaseous flow inside the cabin, the turbulence parameters, and speed fluctuations. Detailed uncertainty analysis was conducted to estimate the uncertainty limits for the measurements taken. The uncertainty estimates obtained for the tracer gas results ranged from ±14% for the test cases with the heated manikins to ±17% with the corresponding unheated manikins cases. The data uncertainty limits for the turbulence parameters were of higher levels due to limitations associated with the omni-directional probes used to measure the speed. With flow repeatability phenomena in same locations inside the mockup cabin during different days reaching up to ±10%, the uncertainty estimates were considered acceptable for these chaotic and highly random airflow conditions within the cabin.

Master of Science / Department of Mechanical and Nuclear Engineering / Steven J. Eckels / NanoActiveTM metal oxide particles have the ability to destructively adsorb organophosphorus compounds and chlorocarbons. These nanomaterials with unique surface morphologies are subjected to separate, low concentrations of gaseous ammonia in air. NanoActiveTM materials based on magnesium oxide have large specific surface areas and defective sites that enhance surface reactivity and consequently improved adsorptivity. In gas contaminant removal by adsorption, presence of vast specific surface area is essential for effective gas-solid interaction to take place. This is also the case in many industrial and chemical applications such as purification of gases, separation and recovery of gases, catalysis etc,. Typically carbonaceous compounds are utilized and engineered in toxic gas control systems. The purpose of this study was to compare NanoActiveTM materials with carbon based compounds in the effectivity of toxic gas adsorption at low concentrations. A test facility was designed to investigate the adsorption properties of novel materials such as adorption capacity and adsorption rate. Adsorption capacity along with adsorption kinetics is a function of properties of the adsorbent and the adsorbate as well as experimental conditions. Nanomaterials were placed on a silica matrix and tested with increasing flow rates. Electrochemical sensing devices were placed at inlet and outlet of the facility to monitor real time continuous concentration profiles. Breakthrough curves were obtained from the packed bed column experiments and saturation limits of adsorbents were measured. Adsorption rates were obtained from the breakthrough curves using modified Wheeler-Jonas equation. The NanoActiveTM materials adsorbed ammonia though to a lesser extent than the Norit® compounds. This study also included measurement of pressure drop in packed beds. This information is useful in estimating energy losses in packed bed reactors. Brauner Emmet Teller tests were carried out for the calculation of surface area, pore volume and pore size of materials. These calculations suggest surface area alone had no notable influence on adsorption capacity and adsorption rates. This lead to the conclusion that adsorption was insignificant cause of absence of functional groups with affinity towards ammonia. In brief, adsorption of ammonia is possible on NanoActiveTM materials. However functional groups such as oxy-flouro compounds should be doped with novel materials to enhance the surface interactions.

Master of Science / Department of Mechanical & Nuclear Engineering / Gurpreet Singh / Carbon nanotubes (CNT) and polymer-derived ceramics (PDC) have gained considerable research attention due to their unique structure and physical properties. Carbon nanotubes are known for their exceptional mechanical (Young’s modulus= 1 TPa) and thermal properties (thermal conductivity = 4000 W/m.K). However, CNTs tend to lose their unique -sp2 carbon structure and cylindrical geometry at temperatures close 400°C in air. PDC, which are obtained by the controlled degradation of certain organosilicon polymers however exhibit high temperature stability (upto approx. 1400 °C). To this end, a hybrid composite material consisting of PDC functionalized CNT is of interest as it can combine the unique physical properties of the two materials for applications requiring operation under harsh conditions. Here, we report synthesis and chemical characterization of an Al-modified polysilazane polymer, which was later utilized to functionalize the outer surfaces of four commercially available CNTs. This polymer-CNT composite upon heating in nitrogen environment resulted in Si(Al)CN-CNT ceramic composite. The composite was characterized using a variety of spectroscopic methods such Raman, FTIR and electron microscopy. The thermal stability of the ceramic composite was studied by use of Thermogravimetric analysis (TGA) that showed an improvement in the thermal stability compared to bare nanotubes. Further, we also demonstrate that a stable dispersion of the composite in organic solvents such as toluene can be spray coated on a variety of substrates such as copper disks and foils. Such coatings have application in high energy laser power meters. This research opens new avenues for future applications of this novel material as coatings on surfaces that require both good thermal properties and protection against degradation in high temperature environments. We also suggest the future use of this material as an electrode material in high electrochemical capacity rechargeable batteries.

Master of Science / Department of Mechanical and Nuclear Engineering / Steven Eckels / Both cavitating and flashing flows are important phenomena in fluid flow. Cavitating flow, a common consideration in valves, orifices, and metering devices, is also a concern in loss of coolant accidents for liquid water in power plants when saturation pressures are below atmospheric pressure. Flashing flow is a common consideration for devices such as relief and expansion valves and fluid injectors as well as for loss of coolant accidents in which the coolant’s saturation pressure is above atmospheric. Of the two phenomena, flashing flow has received greater interest due to its applicability to safety concerns, though cavitating flow is perhaps of greater interest in terms of energy efficiency. It is possible for cavitating and flashing flow to actually become sonic. That is, the local velocity of a fluid can exceed the local speed of sound due to the unique properties of two-phase mixtures. When a flow becomes sonic, it is possible for the flow to accelerate and impose additional energy losses that would not otherwise occur. Models of this aspect of two-phase flow are not well developed, typically only being presented for the case of constant area ducts. In this paper two models for cavitating sonic flow are developed and described by applying the integral forms of the mass, momentum, and energy equations to a control volume of variable cross-sectional area. These models, based on the homogeneous equilibrium model (HEM) and separated flow model, are then applied to experimental data taken by the author with R-134a as the fluid of interest. Experimental data were taken with four instrumented converging-diverging nozzles of various geometries using a custom testing rig that allowed for precise control and measurement of flow parameters such as mass flow, temperature, and pressure. The resultant data from the models are then examined, focusing on the resultant velocities, Mach numbers, quality, and shear stresses.