The fundamental physics governing wildland fire spread are still largely misunderstood. This thesis was motivated by the need to better understand the role of radiative and convective heat transfer in the ignition and spread of wildland fires. The focus of this work incorporated the use of infrared thermographic imaging techniques to investigate fuel particle response from three different heating sources: convective dominated heating from an air torch, radiative dominated heating from a crib fire, and an advancing flame front in a laboratory wind tunnel test. The series of experiments demonstrated the uniqueness and valuable characteristics of infrared thermography to reveal the hidden nature of heat transfer and combustion aspects which are taking place in the condensed phase of wildland fuelbeds. In addition, infrared thermal image-based temperature history and ignition behavior of engineered cardboard fuel elements subjected to convective and radiative heating supported experimental findings that millimeter diameter pine needles cannot be ignited by radiation alone even under long duration fire generated radiant heating. Finally, fuel characterization using infrared thermography provided a better understanding of the condensed phase fuel pyrolysis and heat transfer mechanisms governing the response of wildland fuel particles to an advancing flame front.

The problem of calculating iso-surface statistics in turbulent flows is interesting for a number of reasons, some of them being combustion modeling, entrainment through turbulent/non-turbulent interfaces, calculating mass flux through iso-scalar surfaces and mapping of scalar fields. A fundamental effect of fuid turbulence is to wrinkle scalar iso-surfaces. A review of the literature shows that iso-surface calculations have primarily been done with geometric methods, which have challenges when used to calculate surfaces that have high complexity, such as in turbulent flows. In this thesis, we propose an alternative integral method and test it against analytical solutions. We present a parallelized algorithm and code to enable in-simulation calculation of isosurface area. We then use this code to calculate area statistics for data obtained from Direct Numerical Simulations and make predictions about the variation of the iso-scalar surface area with Taylor Peclet numbers between 9.8 and 4429 and Taylor Reynolds numbers between 98 and 633.

With the automotive industry ever striving to push the limits of fuel efficiency, the Shell EcoMarathon offers a glimpse into this energy conserving mindset by challenging engineering students around the world to design and build ultra-efficient vehicles to compete regionally. This requires synchronization of engineering fields to ensure that the vehicle and powertrain system work in parallel to achieve similar goals. The goal for Cal Poly – San Luis Obispo’s EcoMarathon vehicle for the 2015 competition is to analyze the unique operating mode that the powertrain undergoes during competition and improve their current package to increase fuel efficiency. In this study, fuel delivery, ignition timing and engine temperature are experimentally varied to observe trends in steady state fuel consumption. A developmental simulation is then implemented with these trends to analyze potential differences in transient and steady state tuning targets. The engine is then tuned to finalized tuning targets and performance compared with benchmark values.

Spacecraft testing includes acoustics, vibrations, and thermal vacuum. Cal Poly’s Space Environments Lab is equipped with multiple vacuum chambers, but no thermal vacuum chamber. The purpose of this thesis is to incorporate an ATS Chiller system with the HVEC vacuum chamber so students are able to experiment with a thermal vacuum chamber. The ATS Chiller had leaky pipes that needed to be refurbished and a shroud was implemented to improve thermal capabilities of the system. The full system was able to reach temperatures as low as -38ºC and as high as 58ºC at a pressure of 10-6 Torr. The ATS Chiller was able to absorb up to 500W of heat dissipation from a component mounted to the platen inside of the vacuum chamber. Thermal modeling of the apparatus was performed in Thermal Desktop. The model was incorporated with the test data to extract interface resistance information between connected surfaces. Another model is used to analyze a theoretical component inside the apparatus to evaluate mounting methods and determine theoretical temperatures of the component. The model adjusts for material properties, including thermal conductivity and emissivity to accurately simulate testing conditions within +/- 3ºC. Platen and shroud adjustments were able to accommodate a peak bake out temperature of 130±2.2℃ of any component without damage to the system. Three temperature cycles were performed by the thermal vacuum chamber to reach extreme temperatures of 58℃ and -38. A 300 Watt heater was used to simulate component heat dissipation for the duration of the test. Furthermore, this thesis lays out further possibilities for thermal testing using the HVEC Vacuum chamber and ATS chiller as a thermal vacuum chamber.

Current insulation solutions across multiple industries, especially the commercial sector, can be bulky and ineffective when considering their volume. Aerogels are excellent insulators, exhibiting low thermal conductivities and low densities with a porosity of around 95%. Such characteristics make aerogels effective in decreasing conductive heat transfer within a solid. These requirements are crucial for aerospace and spaceflight applications, where sensitive components exist among extreme temperature environments. When implemented into insulation applications, aerogel can perform better than existing technology while using less material, which limits the amount of volume allocated for insulation. The application of these materials into composites can result in enhancing a material's thermal and mechanical properties when exposed to mechanical testing. The main objective of this study was to perform theoretical and experimental analysis on a corrugated composite sandwich structure integrated with aerogel insulation by studying its effective thermal conductivity. The aerogel material used was Pyrogel XT-E, a silica aerogel-based fiberglass insulation manufactured by Aspen Aerogels. Theoretical models of the corrugated composite sandwich structure were constructed in ANSYS Workbench based on geometry from a previous study. The main goal of the theoretical models was to analytically and computationally study the effective thermal conductivity of this sample; the conditions of these simulations were modeled after the experimental setup. Additionally, two insulation studies were performed using the thermal models. The first study was performed on a flat plate structure to determine the optimal thickness of Pyrogel XT-E in a flat plate orientation. The second study compared multiple types of common insulation materials to Pyrogel XT-E when integrated into the corrugated composite sandwich structure model. As expected, aerogel particles and Pyrogel XT-E outperformed all insulation materials and had the lowest effective thermal conductivity. Experimental data was obtained using a test enclosure and a heating element source with an integrated temperature control circuit that was designed and built for this study. This experimental data was compared to the theoretical data obtained from the thermal model simulations. The corrugated composite sandwich structure did not perform as well as expected due to thermal bridging along the composite corrugation. Its effective thermal conductivity was much higher than that of the flat plate structure, even though the effective Pyrogel XT-E layer in the corrugated composite sandwich structure was more than twice as thick as the layer in the flat plate structure. Despite thermal bridging, the corrugated composite sandwich structure exhibits superb thermal resistance, which adds to its impressive strength. Thermal conductivity results from this study can be used to design efficient materials for high structural and thermal stress applications.

The significant increase in energy requirements across the world, provides several opportunities for innovative methods to be developed to facilitate the storage and utilization of energy. The major energy demand is in the form of electrical energy for domestic as well as industrial sectors, a large part of which are the heating and cooling requirements. Appropriate utilization of thermal energy storage can effectively aid in reducing the electrical demand by storage and release of this thermal energy during peak hours. Thermal Energy Storage using Phase Change Materials (PCMs) is an attractive method of energy storage, with a wide variety of potential applications. Several configurations have been tested by researchers to develop energy storage devices with PCMs. The cycling of melting and solidification of PCMs results in storage and release of heat at a relatively small temperature difference. Design and deployment of these storage systems have certain challenges and considerations associated to them for instance, when used in buildings, PCMs should be non-toxic, non-corrosive, and others. In this thesis, we aim to provide models for designing Latent Thermal Energy Storage (LTES) devices with PCMs, based on their operating conditions, thermophysical properties of materials, and geometric parameters. The models are developed considering fluid dynamics and heat transfer involved in melting and solidification of PCMs. Parameters like inlet temperature and velocity, and volume of storage container are varied to determine the time taken for melting or solidification. For sizing and predicting performance of the storage devices we aim at presenting an analytical correlation, with time taken for melting as the variable defining the ‘charging/discharging time’ of storage device. Along with this, a transient model is developed to predict amount of PCM melted/solidified, along with rate of latent energy storage in defined time period intervals.

Buildings in USA consume close to 40% of overall energy used and fenestration products (e.g. windows, doors, glazed-wall etc.) are the largest components of energy loss from buildings. Accurate evaluation of thermal performances of fenestration systems is critical in predicting the overall building energy use, and improving the product performance. Typically, two-dimensional (2-D) heat transfer analysis is used to evaluate their thermal performance as the 3-D analysis is highly complex process requiring significantly more time, effort, and cost compared to 2-D analysis. Another method of evaluation e.g. physical test in a hotbox is not possible for each product as they are too expensive. Heat transfer in fenestration products is a 3-D process and their effects on overall heat transfer need to be investigated. This thesis investigated 3-D heat transfer effects in fenestration systems in comparison to the 2-D results. No significant work has been done previously in terms of 3-D modeling of windows, which included all the three forms of heat transfer e.g. conduction, convection and radiation. Detailed 2-D and 3-D results were obtained for broad range of fenestration products in the market with a range of frame materials, spacers, insulated glass units (IGU), and sizes. All 2-D results were obtained with Therm5/Window5 (e.g. currently standard method of evaluating thermal performance) and GAMBIT/FLUENT while all 3-D results were obtained with GAMBIT/FLUENT. All the three modes of heat transfer mechanism were incorporated in the heat transfer modeling. The study showed that the overall 3-D heat transfer effects are relatively small (less than 3%) for present day framing and glazing systems. Though at individual component level (e.g. sill, head, Jamb) 3-D effects were quite significant (~10%) but they are cancelled by their opposite sign of variation when overall fenestration system effect is calculated. These 3-D heat transfer effects are higher for low conducting or more energy efficient glazing and framing systems and for smaller size products. The spacer systems did not have much impact on the 3-D effects on heat transfer. As the market transforms towards more insulating and higher performance fenestration products, 3-D effects on heat transfer would be an important factor to consider which it may require correlations to be applied to 2-D models, or may necessitate the development of dedicated 3-D fenestration heat transfer computer programs.

Analyses of heat and mass transfer between different materials and phases are essential in numerous fundamental scientific problems and practical engineering applications, such as thermal and chemical transport in porous media, design of heat exchangers, dendritic growth during solidification, and thermal/mechanical analysis of additive manufacturing processes. In the numerical simulation, interface treatment can be further divided into sharp interface schemes and diffuse interface schemes according to the morphological features of the interface. This work focuses on the following subjects through computational studies: (1) critical evaluation of the various sharp interface schemes in the literature for conjugate heat and mass transfer modeling with the lattice Boltzmann method (LBM), (2) development of a novel sharp interface scheme in the LBM for conjugate heat and mass transfer between materials/phases with very high transport property ratios, and (3) development of a new diffuse-interface phase-field-lattice Boltzmann method (PFM/LBM) for dendritic growth and solidification modeling. For comparison of the previous sharp interface schemes in the LBM, the numerical accuracy and convergence orders are scrutinized with representative test cases involving both straight and curved geometries. The proposed novel sharp interface scheme in the LBM is validated with both published results in the literature as well as in-house experimental measurements for the effective thermal conductivity (ETC) of porous lattice structures. Furthermore, analytical correlations for the normalized ETC are proposed for various material pairs and over the entire range of porosity based on the detailed LBM simulations. In addition, we provide a modified correlation based on the SS420-air and SS316L-air metal pairs and the high porosity range for specific application. The present PFM/LBM model has several improved features compared to those in the literature and is capable of modeling dendritic growth with fully coupled melt flow and thermosolutal convection-diffusion. The applicability and accuracy of the PFM/LBM model is verified with numerical tests including isothermal, iso-solutal and thermosolutal convection-diffusion problems in both 2D and 3D. Furthermore, the effects of natural convection on the growth of multiple crystals are numerically investigated.

Defrosting in the refrigeration industry is used to remove the frost layer accumulated on the evaporators after a period of running time. It is one way to improve the energy efficiency of refrigeration systems. There are many studies about the defrosting process but none of them use computational fluid dynamics (CFD) simulation. The purpose of this thesis is (1) to develop a defrost model using the commercial CFD solver FLUENT to simulate numerically the melting of frost coupled with the heat and mass transfer taking place during defrosting, and (2) to investigate the thermal response of the evaporator and the defrost time for different hot gas temperatures and frost densities. A 3D geometry of a finned tube evaporator is developed and meshed using Gambit 2.4.6, while numerical computations were conducted using FLUENT 12.1. The solidification and melting model is used to simulate the melting of frost and the Volume of Fluid (VOF) model is used to render the surface between the frost and melted frost during defrosting. A user-defined-function in C programming language was written to model the frost evaporation and sublimation taking place on the free surface between frost and air. The model was run under different hot gas temperatures and frost densities and the results were analyzed to show the effects of these parameters on defrosting time, input energy and stored energy in the metal mass of the evaporator. The analyses demonstrate that an optimal hot gas temperature can be identified so that the defrosting process takes place at the shortest possible melting time and with the lowest possible input energy.

Performance characterization was undertaken for an air augmented rocket mixing duct with annular cavity configurations intended to produce thrust augmentation. Three mixing duct geometries and a fully annular cavity at the exit of the nozzle were tested to enable thrust comparisons. The rocket engine used liquid ethanol and gaseous oxygen, and was instrumented with sensors to output total thrust, mixing duct thrust, combustion chamber pressure, and propellant differential pressures across Venturi flow measurement tubes. The rocket engine was tested to thrust maximum, with three different mixing ducts, three major combustion pressure sets, and a nozzle exit plane annular cavity (a grooved ring). The combustion pressures tested were , , and allowing for a nozzle pressure ratio range of relative to ambient pressure. The mixture ratio was fuel rich throughout all tests. The engine operated very consistently throughout all the tests performed; however, pressure losses in the feed system prevented higher combustion pressures from being tested. Three mixing ducts of the same outer diameter were tested. The short and diverging ducts were the same length and the long duct was long. The short and long ducts created positive mixing duct thrust and the diverging duct created negative mixing duct thrust. The long duct case did show better performance than the no duct case when the total thrust was divided by combustion pressure and nozzle throat area. The long duct always created several times more mixing duct thrust than either the short or diverging ducts, but none of the mixing ducts created positive overall thrust augmentation in the over expanded cases tested. The mixing duct thrusts ranged between and . As the combustion pressures were increased, getting closer the nozzle’s optimal expansion, the mixing duct thrusts started converging indicating a difference between nozzle operation at over expanded and under expanded. The annular cavity had a noticeable effect on the thrust of the engine and the appearance of the plume. The total thrust of the system was decreased by a maximum of and the plume was more sharply defined when the annular cavity was attached. Better mixing between the primary (engine exhaust) flow and the secondary (ambient air) flow was promoted by the annular cavity because it increased the shear layer’s turbulence and the increased turbulence reduced thrust. The greater mixing also allowed for secondary combustion which made the plumes more sharply defined. The annular cavity was also seen to enhance the mixing duct thrusts for all three mixing ducts.