Investigation of micro gas turbine system configurations for compact lightweight applications based on reversible bladeless Tesla machinery

Globally, the demand for low-emission, cost-effective, low-noise, lightweight and compact devices is rapidly increasing. In order to meet such market demands on a small scale, microgas turbines (MGTs) could play a crucial role. However, there are many challenges with MGT compatibility with internal combustion engines (e.g., low efficiency, fuel flexibility, light weight-compactness). As part of this study, the focus is on the component basis, where the study examines the Tesla or bladeless turbomachinery in both a compressor and expander configuration. Since little data is available on Tesla compressors/pumps, this study focuses primarily on the bladeless compressor, which is also analyzed as an expander due to its reversibility. The activity started from a 3-kW air Tesla expander prototype available at the University of Genoa. It is examined in compressor mode using a 3D CFD approach and its results are compared to experimental results. The CFD and experiments show good agreement for the pressure, with an error of less than 3% at zero flow condition. Despite the CFD analysis predicting a static efficiency of around 42% (without losses), the experiment did not meet that prediction due to significant leakage flows and other losses. Moreover, using LMS Test Lab software, the acoustic behavior of the Tesla compressor has been analyzed at different speeds and distances, and several aspects are compared with conventional or bladed technologies (same tip speed, same mass flow rate, and same pressure). It has been demonstrated that Tesla technologies are substantially quieter than bladed technologies. To improve Tesla compressor performance, a 3D numerical analysis has been carried out for the rotor only and coupled rotor-stator and volute configurations. The disk gap is optimized by relying on Ekman and Reynolds numbers. Based on the numerical analysis, the disk gap should be 3 times the thickness of the boundary layer with the best Reynolds number 9-11 and Ekman number 1.5-1.65. Moreover, numerical analysis has been performed for 2, 2.5, 3 and 4 diameter ratios in order to optimize the rotor diameter ratio. Higher diameter ratios indicate better performance than lower diameter ratios. Based on a CFD analysis, it has been predicted that at low mass flow rates, greater than 95 % efficiency can be achieved with the optimal disk gap and diameter ratio. In this case, the outlet flow angle would be around 89.9 degree, however, in practice, maintaining almost a tangential flow angle is difficult. In order to improve the performance of Tesla compressors, several stators have been studied. The stator outlet and inlet ratio between 2 and 4 is optimal for stator/diffuser performance. With an optimal rotor and eight stators, CFD analysis predicts a total stator efficiency of >53%; however, with a low number of stators, this efficiency will be somewhat improved. As part of an effort to enhance the performance of the Tesla compressor, a (stator-less) volute design has also been numerically analyzed, which shows better performance in terms of pressure ratio and efficiency than the stator configuration. Compared to a stator configuration, the total to static efficiency is estimated to increase by 3 to 5%. A new reversible Tesla prototype model has been developed using an optimized rotor (optimal disk gap and diameter ratio) and volute configuration for 22 krpm. CFD predicted total to static efficiency of 58% in compressor mode and 66% in expander mode without consideration of system losses. For this new reversible machine, leakage and end wall losses are also analyzed under a variety of conditions, including different end wall gaps and different exit radial clearances (with and without sealing systems). The implementation of the sealing system has resulted in a reduction in leakage, but the amount varies in accordance with the clearance of the radial exit. The end wall power loss varies with end wall gap, but usually ranges between 50 W-60 W for 22 krpm design speed, while power is around 600 W. During this dissertation writing, experimental work on a reversible bladeless machine is in progress. Preliminary results show the pressure ratio is 1.24 and the isentropic efficiency is 31%. Comparing these results with CFD simulations at closed valve conditions shows good agreement in terms of pressure ratio with < 3% error. It is observed that leakage occurs during the first test which passes through the narrow radial clearance of 0.3 mm. As a result of this preliminary investigation, some modifications have been made to the test-rig in order to ensure that good results are achieved with the least amount of leakage. An in-depth study of the reversible Tesla machine (compressor and expander) has shown that such technologies possess several attractive features (reversibility, low noise level, cost effective and operate with any kind of fluid), but are difficult to implement as Tesla envisioned (higher efficiency). Under ideal design conditions, however, such technologies could potentially achieve > 50% efficiency. The use of such technologies can be beneficial in areas where conventional technologies are not practical or less efficient

Determinants of Mobile Payments: An Empirical Analysis

Success of mobile commerce hinges on the availability of methods of payment that are secure, ubiquitously available, globally accepted, and easy-to-use. Mobile payment (mPayment) entails making payments using mobile devices such as wireless handsets, personal digital assistants, and other radio frequency (RF) and near field communication (NFC) devices. While mPayment is still in its infancy, its acceptance is likely to increase considerably in the coming years. In the United States, the acceptance of mPayment lags behind that of Europe and Asia. In the U.S, many experts believe that the next step in mPayment evolution is the development of a single-device and ubiquitous mPayment solution that offers consumers speed and convenience in both online and point-of-sale transactions. This paper identifies factors that influence consumer mPayment adoption in the United States using data gathered from 299 consumers. Further, the paper examines the relationships between adoption enabling factors and users’ demographic and digital lifestyle traits

A Study of the Relationship Between Internet Diffusion and Culture

The unevenness in the diffusion rates of the Internet across nations is commonly referred to as the digital divide. Technological, economic and political factors are often mentioned as the primary contributing factors to this digital gap. However, there is sufficient evidence in support of the proposition that a nation\u27s culture also plays a role in how citizens adopt and use technology innovations. This paper examines the relationship between the cultural dimensions proposed by Hofstede and the Internet adoption rate of nations. Data from sixty-two countries are used to establish a regression model and the empirical results show that cultural traits such as uncertainty avoidance and masculinity index of a nation are significantly related to the nation\u27s Internet dijfusion rate. These findings suggest that policy makers must also consider these national culture traits along with technological, economical, and political factors in setting national policies to promote Internet-related innovations

An examination of the relationship between digital divide and economic freedom: An international perspective

Due to various economic, political and social reasons, the Internet usage remains relatively Iom\u3e in many countries around the world. The difference in access to new information technologies and the Internet among countries, is known as the digital divide. This is a significant economic phenomenon that warrants the attention of analysts and policy makers. Furthermore, since information technologies and the Internet have proven to be key drivers for economic growth and global trade, many nations are in danger of being marginalized. This paper examines the relationship between economic freedom as indicated by the Economic Freedom Index (EFI), proposed by Beach and O\u27Driscoll (2003) and the digital divide. By analyzing data from sixty-two countries that include variables such as the cost of Internet access, number of personal computers and phones, personal income level, and innovation capability, it is shown that EFI is significantly related to the diffusion rate of the Internet. Therefore, countries need to examine and implement economic policies that are conducive to narrowing the digital gap

Mutually Supportive or Trade-Offs: An Analysis of Competitive Priorities in the Emerging Economy of India

To refine the theories of operations strategy, we need research from all different situational contexts, including different countries—both developing and developed. There have been many studies, including some replications, done in various parts of the world to further the debate on whether competitive priorities are mutually supportive or if they present potential trade-offs, but hardly any from a rapidly growing economy, such as India. This study is a significant attempt in that direction. After a thorough review of the literature, a set of hypotheses is introduced to test whether Indian manufacturers view competitive priorities as mutually supportive or trade-offs. The data from over 150 high-ranking individuals from over 75 manufacturers in India is used to test the hypotheses by way of cluster analysis and ANOVA. The resultant taxonomy reveals patterns that uniquely represent Indian manufacturers\u27 view of the competitive priorities, namely quality, flexibility, delivery and price. The study findings have significant managerial implications, both for India and other developing as well as developed economies. The taxonomy will serve to gauge India\u27s manufacturers\u27 role in the world. From a researcher\u27s perspective, this study makes a significant contribution to theory development, furthers our understanding of the strategic role of operations, moves forward the ongoing debate on the topic of trade-offs or complementarity, and paves the way for future studies in this topical area

Long Term Factors of Internet Diffusion in Sub-Saharan Africa: A Panel Co- Integration Analysis

Identifying factors that influence the diffusion of the Internet is paramount for researchers as well as policy makers in articulating strategies to improve the availability and subsequent use of the Internet. Most existing empirical studies have focused on this problem by analyzing diffusion data for countries for one fixed year and identified variables affecting the Internet diffusion. These variables, generally, come from the economic, technological, policy, culture, and human capital realms. These results have provided a good “snapshot” of what factors are important towards the diffusion of the Internet and the results tend to vary for studies conducted in different time frames. This paper also addresses, the phenomenon of cross-country dependence – the economic, political, and technological environment of one country affecting other countries- into account in their analyses. This paper, for the first time in the literature, empirically identifies long-term determinants of the Internet diffusion in sub-Saharan African (SSA) countries by considering data for the period 1997-2013. It employs a recently-developed technique named “panel co-integration analysis” to model the diffusion of the internet among the SSA countries. The analysis reveals that in SSA countries, the number of telephones, the level of per capita real gross product and the extent of ruralization (conversely, the degree of urbanization) are the key long-term drivers of the diffusion of the Internet. Finally, the paper concludes with a discussion of policy implications

太陽光発電システムと系統連系に関する研究 -モデリング、制御器設計、最適化-

九州工業大学博士学位論文（要旨）学位記番号：生工博甲第278号 学位授与年月日：平成29年3月24

The Evolutionary Construction of Sleep

To understand the biological basis of sleep we need to understand its neuronal and genetic regulation. In this thesis, I explore how individual behaviors serve as building blocks to construct the sleep state where a block is defined as a set of measurable behaviors. These behavioral blocks are shaped by evolutionary forces. From one animal to the next, blocks may remain or change. If a block remains across all the sleep states in the metazoan lineage then it must have an important and conserved role in sleep regulation. For example, reduced locomotion is a behavior that is often observed during sleep. There are two possible explanations for the changing of a block: either the block was vestigial or the block was easily replaceable with another block that fulfills the same function. Consider sleep duration: some animals may require five hours of sleep, while others only require one hour. The changing of a block is one way that the sleep state could evolve. Blocks may also be added during the evolution of the sleep state, increasing the dimensions and number of tasks that are accomplished during sleep. Here, I discuss the origin of sleep, as well as its conserved neuronal and genetic regulation. I report the following: the discovery of sleep in jellyfish which are among the first animals to evolve neurons and the identification of novel sleep regulators in the roundworm Nematode Caenorhabiditis elegans (C. elegans). The sleep regulators discovered in C. elegans may have conserved functions in vertebrates. These studies show that some sleep behaviors and various sleep molecules change or remain homologous across metazoans. The studies are united by our simple block hypothesis of sleep construction.</p