<p> For the long-term strategy of gradual decarbonization of the world&rsquo;s energy supply, high penetration of PV electricity is critical in the future world energy landscape. In order to achieve this, solar electricity with competitive cost to fossil fuel energy is necessary. To be able to obtain high efficiency solar cells, many advanced cell architectures have been developed commercially by PV industry. However, the fabrication of these cells necessitates complex processing steps and high requirements on semiconductor materials, which make it not as cost-effective as the state-of-the-art conventional Al-BSF structure. In order to keep the cost of PV cell low and improve on the efficiency with fewer processing steps, this thesis work focuses on the understanding of the conventional Al-BSF solar cell structure. The research work therefore, focuses on the (i) design, and modeling of front metal electrodes including the use of multi-bus-bar capable of decreasing the gridline resistance, (ii) fine-line printing and (iii) metal contact co-firing using high belt speed that is not common to the solar industry to achieve ~20% efficient industrial Al-BSF silicon solar cells.</p><p> In order to achieve the objectives of this thesis work, firstly, the appropriate Al paste was investigated for lowest back surface recombination velocity (BSRV), which gives high open circuit voltage (V_oc). Secondly, the impact of emitter sheet resistance on solar cell performance was modeled to determine the optimal sheet resistance, and the uniformity of emitter was also investigated. Thirdly, modeling on the front metal electrodes was carried out to investigate the optimal number of busbars, and determine the optimum number of gridlines and gridline geometries that would result in low series resistance (R_s), high fill factor (FF) and hence high efficiency. Fourthly, the modeled results were experimentally validated through fine-line printing and optimized contact co-firing. By combining each layer to make solar cells, V_oc of ~642 mV, J_sc of ~38.5 mA/cm² and FF of ~80.4% led to average ~19.8% efficient cell. Based on the experimental results, other innovative front grid designs are proposed that can lead to >20% energy conversion efficiency.</p>

<p> Foam has been widely used in the petroleum industry. The use foam as a drilling fluid takes advantages of the foam's physical properties. Foam decays into liquid after a certain time. The decay process happens faster at an elevated temperature. The research on foam thermal stability has not been thorough. This paper presents experimental research about the stability of foam from three polymers with viscosity of 10cp, 20cp, and 30cp. The stabilities of foam were tested at an elevated temperature. The most thermal stable foam among the foams provided was determined. There are some unclear behaviors that need to be studied in future work.</p>

<p> Combined effects of socio-economic, environmental, technological and political factors impact fresh cooling water availability, which is among the most important elements of thermoelectric power plant site selection and evaluation criteria. With increased variability and changes in hydrologic statistical stationarity, one concern is the increased occurrence of extreme drought events that may be attributable to climatic changes. As hydrological systems are altered, operators of thermoelectric power plants need to ensure a reliable supply of water for cooling and generation requirements. The effects of climate change are expected to influence hydrological systems at multiple scales, possibly leading to reduced efficiency of thermoelectric power plants. This study models and analyzes drought characteristics from a thermoelectric systems operational and regulation perspective. A systematic approach to characterize a stream environment in relation to extreme drought occurrence, duration and deficit-volume is proposed and demonstrated. More specifically, the objective of this research is to propose a stochastic water supply risk analysis and projection methods from thermoelectric power systems operation and management perspectives. The study defines thermoelectric drought as a shortage of cooling water due to stressed supply or beyond operable water temperature limits for an extended period of time requiring power plants to reduce production or completely shut down. It presents a thermoelectric drought risk characterization framework that considers heat content and water quantity facets of adequate water availability for uninterrupted operation of such plants and safety of its surroundings. In addition, it outlines mechanisms to identify rate of occurrences of the said droughts and stochastically quantify subsequent potential losses to the sector. This mechanism is enabled through a model based on compound Nonhomogeneous Poisson Process. This study also demonstrates how the systematic approach can be used for better understanding of pertinent vulnerabilities by providing risk-based information to stakeholders in the power sector.</p><p> Vulnerabilities as well as our understanding of their extent and likelihood change over time. Keeping up with the changes and making informed decisions demands a time-dependent method that incorporates new evidence into risk assessment framework. This study presents a statistical time-dependent risk analysis approach, which allows for life cycle drought risk assessment of thermoelectric power systems. Also, a Bayesian Belief Network (BBN) extension to the proposed framework is developed. The BBN allows for incorporating new evidence, such as observing power curtailments due to extreme heat or lowflow situations, and updating our knowledge and understanding of the pertinent risk. In sum, the proposed approach can help improve adaptive capacity of the electric power infrastructure, thereby enhancing its resilience to events potentially threatening grid reliability and economic stability.</p><p> The proposed drought characterization methodology is applied on a daily streamflow series obtained from three United States Geological Survey (USGS) water gauges on the Tennessee River basin. The stochastic water supply risk assessment and projection methods are demonstrated for two power plants on the White River, Indiana: Frank E. Ratts and Petersburg, using water temperature and streamflow time series data obtained from a nearby USGS gauge. </p>

<p> Magnetic refrigeration is one of the alternative cooling technologies that is environmental friendly and has high theoretical coefficient of performance values. This thesis study focuses on magnetic field and heat transfer enhancement of a reciprocating-type magnetic refrigeration system. A set of NdFeB 52 MGOe permanent magnets were employed to form a Halbach magnet array. Gadolinium (Gd) was used as the magnetocaloric material. It was placed concentrically within the Halbach array aperture with the working fluid running through the gap in between the magnet assembly and Gd yielding annular flow. Three different annular flow geometries namely; circular, octagonal and hexagonal cross-sections were studied. Magnetization process was analyzed theoretically, numerically and experimentally for k = 4 configuration. Numerical analysis was done by Finite Element Method Magnetics (FEMM), theoretical analysis was conducted by a mathematical model, and experimental analysis was performed on a Halbach magnet array. Obtained magnetic field results were used to calculate corresponding entropy changes and heat flux values. These values were compared to numerical heat transfer results from ANSYS and a close agreement between results were observed.</p><p>

<p> Better understanding of phase change phenomena can be obtained through local measurements of the heat transfer process, which cannot be attained by traditional thermocouple point measurements. Infrared (IR) technology, which has been used by many researchers in the past, cannot be used under certain circumstances due to spectral transparency issues present in some materials. In the current study, the optical properties of fluorescing materials are proposed as a novel tool for heat transfer measurements. Two fluorescing materials were examined within the framework of the current dissertation: Namely Quantum dots and Ruthenium based temperature sensitive paint, which tend to fluoresce upon excitation by blue or Ultraviolet (UV) light. The light intensity emitted by those fluorescing materials tends to drop with temperature, which can be utilized to obtain the surface temperature distribution at a pixel resolution, for a given monochromic camera. Advantages of the fluorescing materials include feasibility, applicability to various surface geometries, and the ability to resolve submicron features. The main objective behind the current research work was to develop and assess the optical measurement technique of fluorescing materials, where phase change heat transfer applications, including ethanol drop evaporation and pool boiling, were used to quantify the advantages and limitations of the current temperature measurement technique. Furthermore, a thermofluid study was conducted in order to examine the mechanism of rapid vapor patch formation near critical heat flux (CHF) conditions. Results from the current research work show a correlation between the fluid velocity gradient near the wall and surface heat flux, where both tend to follow similar trend with surface super heat. Thus, it&rsquo;s believed that the incomplete wetting of previous vapor patches near CHF is associated with restricted capillary motion near the surface, where the wetting liquid fails to reach the dry areas with the increased bubble generation activity, due to the local heating caused by the mushroom bubble ebullition.</p><p>

<p> An experimental effort has been completed in which water injection was investigated as a means of enabling increases in engine output and high load efficiency. Water was injected into the intake port of a direct fuel injected, 4-cylinder, boosted engine with dual independent variable valve timing. The water was shown to increase volumetric efficiency and decrease the onset of knock which in turn enable more optimal combustion phasing. Both of these affects resulted increases in load of up to 5.5% at the same manifold pressure as the baseline case. The advancement of combustion phasing, combined with elimination of fuel enrichment resulted in an increase in full load thermal efficiency of up to 35%. Analysis is provided around these affects, as well as the phase transformation of water throughout the engine cycle.</p><p>

<p> In-cylinder heat transfer is one of the most critical physical behaviors which has a direct influence on engine out emission and thermal efficiency for IC engine. In-cylinder wall temperature has to be precisely controlled to achieve high efficiency and low emission. However, this cannot be done without knowing gas-to-wall heat flux. This study reports on the development of a technique suitable for engine in-cylinder surface temperature measurement, as the traditional method is &ldquo;hard to reach.&rdquo; A laser induced phosphorescence technique was used to study in-cylinder wall temperature effects on engine out unburned hydrocarbons during the engine transitional period (warm up). A linear correlation was found between the cylinder wall surface temperature and the unburned hydrocarbons at mediate and high charge densities. At low charge density, no clear correlation was observed because of miss-fire events. A new auto background correction infrared (IR) diagnostic was developed to measure the instantaneous in-cylinder surface temperature at 0.1 CAD resolution. A numerical mechanism was designed to suppress relatively low-frequency background noise and provide an accurate in-cylinder surface temperature measurements with an error of less than 1.4% inside the IC engine. In addition, a proposed optical coating reduced time delay errors by 50% compared to more conventional thermocouple techniques. A new cycle-averaged <span style="text-decoration:overline">Re_s</span> number was developed for an IC engine to capture the characteristics of engine flow. Comparison and scaling between different engine flow parameters are available by matching the averaged <span style="text-decoration:overline">Re_s</span> number. From experimental results, the engine flow motion was classified as intermittently turbulent, and it is different from the original fully developed turbulent assumption, which has previously been used in almost all engine simulations. The intermittent turbulence could have a great impact on engine heat transfer because of the transitional turbulence effect. Engine 3D CFD model further proves the existence of transitional turbulence flow. A new multi zone heat transfer model is proposed for IC engines only. The model includes pressure work effects and improved heat transfer prediction compared to the standard Law of the wall model.</p><p>

<p> In the interest of studying the propagation of shock waves, this work sets out to design, construct, and characterize a pneumatic accelerator that performs high-velocity flyer plate impact tests. A single stage gas gun with a dual diaphragm breach allows for a non-volatile, reliable experimental testing platform for shock phenomena. This remotely operated gas gun utilizes compressed nitrogen to launch projectiles down a 14 foot long, 2 inch diameter bore barrel, which subsequently impacts a target material of interest. A dual diaphragm firing mechanism allows the 4.5 liter breech to reach a total pressure differential of 10ksi before accelerating projectiles to velocities as high as 1,000 m/s (1570-2240 mph). The projectile&rsquo;s velocity is measured using a series of break pin circuits. The target response can be measured with Photon Doppler Velocimetry (PDV) and/or stress gauge system. A vacuum system eliminates the need for pressure relief in front of the projectile, while additionally allowing the system to remain closed over the entire firing cycle. Characterization of the system will allow for projectile speed to be estimated prior to launching based on initial breach pressure.</p><p>

Offshore wind energy technology is maturing in Europe and is poised to make a significant contribution to the U.S. energy production portfolio. Building on the knowledge the wind industry has gained to date, this dissertation investigates the influences of different site conditions on offshore wind farm micrositing—the layout of individual turbines within the boundaries of a wind farm. For offshore wind farms, these conditions include, among others, the wind and wave climates, water depths, and soil conditions at the site. An analysis tool has been developed that is capable of estimating the cost of energy (COE) from offshore wind farms. For this analysis, the COE has been divided into several modeled components: major costs (e.g. turbines, electrical interconnection, maintenance, etc.), energy production, and energy losses. By treating these component models as functions of site-dependent parameters, the analysis tool can investigate the influence of these parameters on the COE. Some parameters result in simultaneous increases of both energy and cost. In these cases, the analysis tool was used to determine the value of the parameter that yielded the lowest COE and, thus, the best balance of cost and energy. The models have been validated and generally compare favorably with existing offshore wind farm data. The analysis technique was then paired with optimization algorithms to form a tool with which to design offshore wind farm layouts for which the COE was minimized. Greedy heuristic and genetic optimization algorithms have been tuned and implemented. The use of these two algorithms in series has been shown to produce the best, most consistent solutions. The influences of site conditions on the COE have been studied further by applying the analysis and optimization tools to the initial design of a small offshore wind farm near the town of Hull, Massachusetts. The results of an initial full-site analysis and optimization were used to constrain the boundaries of the farm. A more thorough optimization highlighted the features of the area that would result in a minimized COE. The results showed reasonable layout designs and COE estimates that are consistent with existing offshore wind farms.

The concept of seasonal heat storage is based on storing sensible heat during the season of low heat demand to be used during the cold season, when the need for heating is higher. Combining this concept with solar thermal energy collection produces what is known as: Central Solar Heating Plant with Seasonal Storage (CSHPSS). Thermal energy is stored by injecting heat into the ground by circulating hot water through a matrix of U-tubes inserted 10 to 30 meters deep into the soil. While the CSHPSS technology is becoming increasingly attractive the heat transfer process of seasonal storage remains complex and only very few modeling tools are available. In an effort to properly design a CSHPSS system for the University of Massachusetts at Amherst, several comprehensive design and performance analyses were conducted. Thus, a complete and detailed CSHPSS system model using TRNSYS is presented in this dissertation. The U-tube seasonal storage is modeled based on a validated ground heat storage module, DST. The storage performance given by this model was compared with a finite element model and experimental results. The simulations yielded positive comparisons and a procedure for modeling U-tube storage system was established. The CSHPSS model developed in this work features a unique control strategy that operates on a seasonal basis. This control strategy is based on four modes of operation and is found to contribute to the simulation stability. This strategy can also provide greater solar contribution to the load as opposed to the conventional ON/OFF controllers. The heat collected by solar collectors is transferred to a storage or a building side through a shell and tube heat exchanger. A heat exchanger model that takes into account variations in the heat transfer coefficient and effectiveness caused by variable flow rates is developed to provide a realistic heat exchanger performance. A thermal analysis of the seasonal storage and the heat exchanger was performed from the first and second law analysis viewpoints. Meaningful interpretations of the heat transfer process in the CSHPSS system can be made from these analyses. Finally, recommendations for improving CSHPSS simulations and performance are discussed.