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The research and development effort for the next generation of nuclear power stations is being coordinated by the Generation IV International Forum (GIF). The supercritical water reactor (SCWR) is one of the six reactor technologies currently being pursued by the GIF. The unique nature of supercritical water necessitates further examination of its heat transfer regimes. The GIF SCWR blind computational benchmark exercise is focused on furthering the understanding of the heat transfer to supercritical water as well as its prediction. A methodology for computational fluid dynamics (CFD) simulations using STAR-CCM+ 9.02.005 has been developed for submission to the GIF SCWR computational benchmark exercise. The experiments of the GIF SCWR computational benchmark exercise were those conducted by the Japan Atomic Energy Agency (JAEA). They are of supercritical water flowing upward in a 7 rod bundle. Of the three experimental cases there are (i) an isothermal case, (ii) a low enthalpy, low heat flux case and (iii) a high enthalpy, high heat flux case. A separate effects study has been undertaken and the SST turbulence model has been chosen to model each of the three experiments. A near wall treatment that ensures a y+<0.09 has been used for both of the heated cases and a near wall treatment that ensures a y+<0.53 has been used for the isothermal case. This computational approach was determined to be the optimal choice which balances solution accuracy with computation time. Final simulation results are presented in advance of the release of the experimental results in June 2014. / Thesis / Master of Applied Science (MASc)

<p> The progress of technology in the electronic components industry has been rapidly growing. The evolution of various techniques has made it possible for this industry to grow and diversify with the market demand. Thus, the development of electronic component products over a short span of time requires having highly efficient tools for design and manufacturing. Advances in commercial Computational Fluid Dynamics (CFD) softwares and computational power have enabled modeling to a high level of architectural details. Nowadays, computer aided design becomes an essential design tool in the engineering environment. Computer analysis reduces both the time development cycle and the prototyping costs in the early to intermediate design phases. The accuracy of the computational prediction of heat transfer rates depends mostly on the correct choice of turbulent model. Although many turbulent models, rather than a universal turbulent model, have been developed during the last two decades, there is usually one model that performs better than others for certain flow conditions. </p> <p> In the present research, a turbulence model is selected from amongst a few candidates, namely standard k- 8, RNG k- 8, shear stress transport (SST), and Reynolds Stress Model (RSM), based on comparisons with experimental data and direct numerical simulation (DNS) results from previous work. The SST turbulence model shows excellent agreement with the DNS results and, hence, is considered an appropriate turbulence model for thermal analysis of electronic packages with elements that have almost the same heights. Moreover, the average Nusselt number of array of obstacles is obtained numerically using commercial code ANSYS-CFX 1 0.0. The effects upon the mean Nusselt number arising from parameteric changes in Reynolds number, element height, element width, and element-to-element distance are compared and discussed. Finally, the parametric study has offered a set of correlations for the mean Nusselt number of arrays of mounted obstacles in the channel flow. </p> / Thesis / Master of Applied Science (MASc)

Focused Ion Beam (FIB) technology is a versatile tool that can be applied in many fields to great effect, including semiconductor device prototyping, Transmission Electron Microscopy (TEM) sample preparation, and nanoscale tomography. Developments in FIB technology, including the availability of alternative ion sources and improvements in automation capacity, make FIB an increasingly attractive option for many tasks. In this thesis, FIB systems are applied to photonic device fabrication and modification, semiconductor reverse engineering, and the production of structures for the study of nanoscale radiative heat transfer. Optical facets on silicon nitride waveguides were produced with plasma FIB (PFIB) and showed an improvement of 3 ± 0.9 dB over reactive ion etched (RIE) facets. This process was then automated and is capable of producing a facet every 30 seconds with minimal oversight. PFIB was then employed to develop a method for achieving local backside circuit access for circuit editing, creating local trenches with flat bases of 200 x 200 μm. Gas assisted etching using xenon difluoride was then used in order to accelerate the etch process. Finally, several varieties of nanogap structure were fabricated on devices capable of sustaining temperature gradients, achieving a minimum gap size with PFIB of 60 nm. / Thesis / Master of Applied Science (MASc)

Additive friction stir deposition (AFSD) is an emerging solid-state additive manufacturing process that leverages the friction stir principle to deposit porosity-free material. The unique flow of material that allows for the transformation of bar stock into a near-net shape part is driven by the non-linear heat generation mechanisms of plastic deformation and sliding frictional heat generation. The magnitude of these mechanisms, and hence the total applied thermal power, implicitly depend on the thermal state of the system, forcing power input to become a dependent variable. This is not the case in other 3D printing methods; thermal power can be controlled independently. In this work, the heat generation in AFSD is explored, and its transfer is quantified. In particular, the time-dependent ratio between the amount of conduction into the AFSD tool versus into the substrate is quantified. It was found for the conditions tested with a single-piece AFSD tool, conduction up the tool was on the order of the conduction into the stir. For a more modern three-piece tool, the ratio between the tool and the substrate varied between 0.3-0.1. It was also found that traversing faster resulted in more heat flux into the substrate as would be expected by moving heat source modeling. The total heat generated was also quantified as being equal to between 60% and 80% of the mechanical spindle power depending on the tool type and the exact process conditions. That ratio was found to be time-invariant. At the same time, this changing heat flux ratio was shown to dramatically alter thermocouple measurements in the tool, showing the uncertainty of that method of process control. The contact state between the stir and the tool was treated as a thin conductive layer and a contact heat transfer coefficient was calculated on the order of 20 frac{kW}{m^2K}. The limitations of this treatment were found to occur when a significant amount of the heat generation came from frictional heating rather than plastic deformation. This implies that any measurement conducted in the tool is related to the stir by a complex function driven by the state of the stir; showcasing the need for more well-understood in-situ monitoring. Finally, some of the ideas about thermal control are applied to a case study on the repair of corroded through holes using AFSD to restore fatigue life. It was found that modifying the thermal boundary conditions and applying active cooling at the end of the repair could improve the fatigue life drastically. This was due to less time spent in a thermally active region leading to less heterogeneous nucleation and less grain boundary nucleation. This more preferred microstructure morphology led to a change in the fracture mode and increased the number of cycles to crack initiation and the number of cycles after crack initiation. / Doctor of Philosophy / Metal 3D printing of industrially relevant aluminum alloys is plagued with problems. Additive friction stir deposition seems well posed to overcome some of the problems associated with aluminum printing. Being able to 3D print these alloys with properties that are as good as traditional manufacturing offers a large potential cost and time savings over traditional manufacturing for the aerospace industry (e.g. Boeing, Lockheed Martin, U.S. Navy). For these components to be part of a plane, the manufacturer must prove the components were made the same way print-to-print regardless of the actual shape of the component being made. This dissertation focuses on the key metallurgical variable of temperature and explores how thermal energy is generated and where that energy goes in to the system. The key takeaway is, that without precise knowledge of the total heat generated and the entire thermal system, assurances about processing temperature cannot be made. An exploration of heat generation and metrics about its dispersion are presented. This is followed by a study on repairing structural components while changing the thermal system to understand its effects.

The unsteady interaction of shock waves emerging from the trailing edge of modern turbine nozzle guide vanes and impinging on downstream rotor blades is modeled in a linear cascade. The Reynolds number based on blade chord and exit conditions (5*10^6) and the exit Mach number (1.2) are representative of modern engine operating conditions. The relative motion of shocks and blades is simulated by sending a shock wave along the leading edges of the linear cascade instead of moving the blades through an array of stationary shock waves. The blade geometry is a generic version of a modern high turning rotor blade with transonic exit conditions. The blade is equipped with a showerhead film cooling scheme. Heat flux, surface pressure and surface temperature are measured at six locations on the suction side of the central blade. Pressure measurements are taken with Kulite XCQ-062-50a high frequency pressure transducers. Heat flux data is obtained with Vatell HFM-7/L high speed heat flux sensors. High speed heat flux and pressure data are recorded during the time of the shock impact with and without film cooling. The data is analyzed in detail to find the relative magnitudes of the shock effect on the heat transfer coefficient and the recovery temperature or adiabatic wall temperature (in the presence of film cooling). It is shown that the variations of the heat transfer coefficient and the film effectiveness are less significant than the variations of recovery temperature. The effect of the shock is found to be similar in the cases with and without film cooling. In both cases the variation of recovery temperature induced by the shock is shown to be the main contribution to the overall unsteady heat flux. The unsteady heat flux is compared to results from different prediction models published in the literature. The best agreement of data and prediction is found for a model that assumes a constant heat transfer coefficient and a temperature difference calculated from the unsteady surface pressure assuming an isentropic compression. / Ph. D.

Standard methods for fire resistance testing require large-scale assemblies and are typically conducted on specialized furnaces at considerable cost. This research focused on developing a scaling methodology for a reduced-scale fire resistance test that reduces the size of the test article while maintaining the same thermal and structural response exhibited in the large-scale test. The developed scaling methodology incorporates uniform geometric scaling, Fourier number time scaling, and furnace boundary condition matching. The scaling laws were experimentally validated with fire exposure tests on gypsum wallboard samples at three scales (full-scale, 1/2-scale, and 1/6-scale). Next, these scaling laws were demonstrated for wood with combined thermo-structural loading. Dimensional lumber boards at ½-scale and ¼-scale were subjected to combined bending and thermal loading. Samples were placed in static three-point bending with the loading scaled to have structural similitude, while simultaneously, the bottom surface was exposed to a scaled fire exposure. Analytical modeling of wood pyrolysis demonstrated that, due to char kinetics as the heating rate is increased in the tests, equivalently less char is formed in the reduced-scale tests. Therefore, we developed a char timescale correction factor, calculated from both model predictions and measured charring rates, which modified the previous Fourier number time scaling laws. Finally, we investigated the effect of multi-orientation materials with a similar set of combined thermo-structural three-point bending tests on plywood samples. The stacking sequence of laminated wood significantly impacts the composite mechanical behavior of the material, especially when scaling down thermo-mechanical tests on plywood. A consequence of the different stacking sequences is that the data from the reduced-scale test cannot be directly scaled to predict the behavior of the larger-scale tests. Thus, modeling becomes essential to extrapolating the data from the reduced-scale test to predict the behavior of the larger-scale test. Reduced cross-sectional area models incorporating classical lamination theory were used to predict the mechanical response of the composite samples as the char front increased. / Doctor of Philosophy / How do we know that a structure will be safe during a fire? The response of structures to fire is typically evaluated using large-scale tests with combined thermo-structural loading: one side of the test sample is exposed to a furnace at standard gas temperatures, while at the same time the sample is loaded with a structural load. Fire resistance testing is essential to evaluating if building components can maintain structural integrity and allow people to egress a building safely during a fire. Standard methods for fire resistance testing require large-scale test samples and are typically conducted on specialized furnaces at national testing facilities at considerable cost. In order to support research and development efforts to design new fire-resistant structures, reduced-scale tests are more desirable because they are cost-effective. However, no reduced-scale test exists to evaluate fire resistance. This research focused on developing a methodology for reducing the size of a test with combined thermo-structural loading. The goal is to have a reduced-scale test that provides insight into the thermal and structural behavior of a similar sample in the large-scale test. The test scaling laws were demonstrated with both experiments and modeling. We developed a small-scale furnace setup to conduct combined thermo-structural tests on samples of different scales. To investigate material type, we tested samples made from gypsum wallboard, dimensional lumber, and plywood. This work will ultimately allow manufacturers to replace costly standard fire resistance tests with reduced-scale versions of these tests during the material screening phase.

Energy conservation, efficiency, and environmental responsibility are priorities for modern energy technologies. The ever increasing demands for lower pollutants and higher performance have driven the development of low-emission gas turbine engines, operating at lean equivalence ratios and at increasingly higher turbine inlet temperatures. This has placed new constraints on gas turbine combustor design, particularly in regards to the cooling technologies available for the combustor liner walls. To optimize combustor thermal management, and in turn optimize overall engine performance, detailed measurements of the flame side heat transfer are required. However, given the challenging environment at which gas turbine combustors operate, there are currently only limited studies that quantify flame side combustor heat transfer; in particular at reacting conditions. The objective of the present work was to develop methodologies to measure heat transfer within a reacting gas turbine combustor. To accomplish this, an optically accessible research combustor system was designed and constructed at Virginia Tech, capable of operating at 650 K inlet temperature, maximum air mass flow rates of 1.3 kg/s, and flame temperatures over 1800 K. Flow and heat transfer measurements at non-reacting and reacting conditions were carried out for Reynolds numbers (Re) with respect to the combustor diameter ranging from ~11 500 to ~140 000 (depending on the condition). Particle Image Velocimetry (PIV) was used to measure the non-reacting flow field within the burner, leading to the identification of coherent structures in the flow that accounted for over 30% of the flow fluctuation kinetic energy along the swirling jet shear layers. The capability of infrared (IR) thermography to image surface temperatures through a fused silica (quartz) glass was demonstrated at non-reacting conditions. IR thermography was then used to measure the non-reacting steady state heat transfer along the combustor liner. A peak in heat transfer was identified at ~1 nozzle diameter downstream of the combustor dome plate. The peak Nusselt number along the liner was over 18 times higher than that predicted from fully developed turbulent pipe flow correlations, which have traditionally been used to estimate flame side combustor heat transfer. For the reacting measurements, a novel time-dependent heat transfer methodology was developed that allowed for the investigation of transient heat loads, including those occurring during engine ignition and shutdown. The methodology was validated at non-reacting conditions, by comparing results from an experiment with changing flow temperature, to the results obtained at steady state. The difference between the time-dependent and the steady state measurements were between 3% and 17.3% for different mass flow conditions. The time-dependent methodology was applied to reacting conditions for combustor Reynolds numbers of ~12 000 and ~24 000. At an equivalence ratio of ~0.5 and a combustor Reynolds number of ~12 000, the peak heat load location in reaction was shifted downstream by 0.2 nozzle diameters compared to the non-reacting cases. At higher equivalence ratios, and more visibly at a Reynolds number of ~24 000, the heat transfer distribution along the combustor liner exhibited two peaks, upstream and downstream of the impingement location (X/DN=0.8-1.0 and X/DN=2.5). Reacting PIV was performed at Re=12 000 showing the presence of a strong corner recirculation, which could potentially convect reactants upstream of the impingement point, leading to the double peak structure observed. The methodologies developed have provided insight into heat transfer within gas turbine combustors. The methods can be used to explore additional conditions and expand the dataset beyond what is presented, to fully characterize reacting combustor heat transfer. / Ph. D.

This work is an experimental study of the effect of impinging distance on the heat transfer from a cylinder to turbulent isothermal and non-isothermal jets. The isothermal jet is discharged horizontally at the same temperature as the ambient air while the non-isothermal jet is discharged vertically upwards and vertically downwards at a temperature colder than the ambient air. Temperature measurements are made on a heated cylinder using an infrared (IR) camera at five equal impinging distances ranging from Z/d =4 to Z/d=20 and the distributions of the local Frossling numbers are determined. The overall decrease in the average Frossling numbers of the cylinder impinged by the isothermal jet and the cold jets was 25 % and 40% respectively. The peak values of average Frossling number for the isothermal and the cold jets occurred at Z/d=8 and Z/d=4 respectively. The Stagnation Frossling number and the normalized jet centerline velocity for the isothermal and the cold jets were found to be very close to each other at all impinging distances indicating that the effect of buoyancy is negligible in the range of jet temperatures and distances used in the experiment. / Master of Science

In a gas turbine engine, turbine blades are exposed to temperatures above their melting point. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines a novel cooling technique called a microcircuit, which combines internal convection and pressure side injection on a turbine blade tip. Holes on the tip called dirt purge holes expel dirt from the blade, so other holes are not clogged. Wind tunnel tests are used to observe how effectively dirt purge and microcircuit designs cool the tip. Tip gap size and blowing ratio are varied for different tip cooling configurations. Results show that the dirt purge holes provide significant film cooling on the leading edge with a small tip gap. Coolant injected from these holes impacts the shroud and floods the tip gap reducing tip leakage flow. With the addition of a microcircuit, coolant is delivered to a larger area of the tip. In all cases, cooling levels are higher for a small tip gap than a large tip gap. Increased blowing ratio does not have a dramatic effect on microcircuit film-cooling at the midchord but does improve internal cooling from the microcircuit. While the combined dirt purge holes and microcircuit cool the leading edge and midchord areas, there remains a small portion of the trailing edge that is not cooled. Also, results suggest that blowing from the microcircuit diminishes the tip leakage vortex. Overall, the microcircuit appears to be a feasible method for prolonging blade life. / Master of Science