High Specific Power Electrical Machines: A System Perspective

There has been a growing need for high specific power electrical machines for a wide range of applications. These include hybrid/electric traction applications, aerospace applications and Oil and Gas applications. A lot of work has been done to accomplish significantly higher specific power electrical machines especially for aerospace applications. Several machine topologies as well as thermal management schemes have been proposed. Even though there has been a few publications that provided an overview of high-speed and high specific power electrical machines [1-3], the goal of this paper is to provide a more comprehensive review of high specific power electrical machines with special focus on machines that have been built and tested and are considered the leading candidates defining the state-of-the art. Another key objective of this paper is to highlight the key “system-level” tradeoffs involved in pushing electrical machines to higher specific power. Focusing solely on the machine specific power can lead to a sub-optimal solution at the system-level

Modelling the Inhomogeneities of the extragalactic background light

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. August 2015.This work investigates the impact of the extragalactic background light fluctuations on very high energy !-ray spectra from distant blazars. We calculate the extragalactic background light spectral energy distribution using a model that extends those proposed by Razzaque et al. (2009ApJ.697.483R) and Finke et al. (2010ApJ.712.238F). We introduce a model for fluctuations in the extragalactic background light based on fluctuations in the star formation rate density, since these two fluctuations can reasonably be expected to be correlated. Fluctuations in the star formation rate are estimated from the semi-analytical galaxy catalogue of Guo et al. (2013MNRAS.428.1351G), we use his model to derive the resulting opacities for !-rays from distant sources. We determine the mean, lower and upper limits for the scatter of the star formation rate density, which then allow us to compute corresponding limits on the extragalactic background light spectrum. We then calculate the impact of these fluctuations limits on the !-ray optical depth. This appears to be the first detailed analytical model that aims to account for the impact of extragalactic background light fluctuations on the !-ray opacity. The model predicts relatively high variations ( 15%) on the opacity in the energy range less than 100 GeV for nearby sources. The impact is found to be smaller (⇠ 5%) for very high energy !-rays from distant sources

METSIM Modelling of Selenium Recovery on Lignin Using Bio-sorption

Selenium is an important mineral for plants and living organisms; trace amounts are needed for our everyday function. However, when large amounts are consumed, it becomes really dangerous with adverse health effects; as a result of this, its removal has been the focus of many studies over the past decades. Selenium is found in most sulfide ores since they both share similar chemical attrib-utes, such as atomic radius. The mining and refining industries release the most amounts of selenium which are present in their wastewater in most cases. Current conventional methods of recycling selenium include pyrometal-lurgical and hydrometallurgical processes, which are often costly, environmentally unfriendly and potentially hazardous. Therefore, researchers have turned towards the study of biomass-based ad-sorbents, also known as biosorbents, for applications in selenium recovery and recycling. Biosorp-tion was the process of choice for reasons such as its operating cost, its recovery rates and reusa-bility In the research presented in the thesis herein, lignin which is a major component in plants was used to adsorb selenium from selenium monochloride (Se2Cl2) using METSIM as the simulation soft-ware of choice due to its versatility and flexibility to control numerous parameters, add new com-ponents and perform mass and heat balances. Lignin was the only component that was added, and the thermodynamic data was found via some research articles where it was plotted in excel and en-tered in METSIM. Further data analysis revealed that the adsorption rate of selenium (Se) on lignin progressed via the pseudo-second order rate model. Adsorption isotherm model studies indicate that the adsorption of Se by lignin followed the Freundlich adsorption isotherm. Calculated energy levels of activation by Se suggest that adsorption progresses due to chemisorption in nature. Thermodynamic studies re-veal that lignin adsorption of Se is exothermic in nature and that the increasing temperature reduces the efficiency of the adsorption process. A recovery rate of 99.4% was achieved for Se2Cl2 at 25 °C temperature and 0.39M HCl. To fur-ther prove that this model is functional, the two other known chloride forms of selenium, SeCl2 and SeCl4 were tested; selenium recovery rate from SeCl2 and SeCl4 was 45% and 40%, respectively

Characterization and Assessment of Tensile Behavior of Carbon Nanofibers Enhanced Ultra-High Performance Concrete

Second only to water, concrete is the world’s most consumed material, not surprisingly, concrete contributes to around 8% of global carbon emissions (Gagg, 2014). This motivates researchers to advance in cementitious material and explore possible breakthroughs in an attempt to further improve and optimize the limited available resources. One recent breakthrough in cementitious materials is Ultra High-Performance Concrete (UHPC). UHPC is an advanced class of concrete and cementitious materials that exhibits high mechanical and durability performance. These properties are achievable using packing density theory which optimizes the gradation of granular materials. In other words, UHPC depends on enhanced microstructure, accompanied by a low water/cement ratio and fiber reinforcement to achieve superior overall performance and durability. UHPC typically consists of cement, silica fume, sand, and a fine supplementary material including -but not limited to- fly ash or slag cement. The robustness and popularity of UHPC in different fields has pushed the interest of stakeholders to explore the UHPC tensile capabilities and behaviors. Evidently, there has been a growth in UHPC tensile research. The literature lacks any set of extensive data with variable fiber dosage.In this study, extensive data is examined and commented on. This study is examining a commercial material named CeEntek which consists of sand, cement, water, carbon nanofiber, and superplasticizer. This study’s comprehensive goal is to assess and characterize the tensile behavior of a nanofiber enhanced UHPC. Another goal of the study is to document the post-cracking tensile behavior of the material. It dictates the future usage of the material as there are two anticipated failure behaviors: failure after gradual strain hardening or failure after crack localization. The first behavior would provide warnings at peak loads which is favorable in general concrete elements design. With the variable fiber percentage in the experimental program, extensive data is generated helping in a better understanding of the tensile behavior of UHPC. To achieve the mentioned goals, an experimental program was set. The experimental investigation consisted of tests on prims, cylinders, and dog-bone-shaped specimens with varying steel fiber content. Four-point bending, direct tension, and compression tests were carried out according to ASTM specifications and extensive data on their compressive, tensile, and flexural behavior were recorded and analyzed