Bc. COVRIGHIN Sergiu. Bulk forming technology of cases. Diploma thesis in fifth class of master studies, academic year 2009/2010, study group 5M/68, FME UT in Brno, Institute of Manufacturing Technology, Department of Metal Forming, May 2010, pages 46 , 18 fig., 7 tab., 4 annexes. In diploma thesis is introduced a technological proposal regarding production of cases by bulk forming from cemented steel 14 220.3. Despite the estimated number of parts which is 70000 a year, quality and product accuracy, 2 options of technological procedures concerning cold bulk forming wth combination of backward and forward extrusion are being considered. For chosen option are elaborated technological calculations. As for the suggested technology, crank press, force 8000 kN and made by company KRUPP was chosen. Material for extruder is steel 19 569 and material for extrusion die is steel 19 655.

This thesis deals with a proposal of a technology for manufacturing a carrier pin made of corrosion resistant chrome steel 17 021.3. Having studied the information about cold bulk-metal forming in the available literature, I have suggested two variants of manufacturing processes. The suggested manufacturing variants consist of four forming operations which combine upsetting and extrusion. As far as the chosen variant is concerned, there have been made technological and strength calculations for the individual operations. As regards the designed technology, I have opted for the automatic multistation forming machine TPZK 25, produced by the company ŠMERAL Brno.

This study investigated different underground bulk air heat exchanger (>100 m3/s) design criteria. It was found that no single document exist covering these heat exchangers and therefore the need was identified to generate a guideline with decision analyser steps to arrive at a technical specification. The study investigated the factors influencing the heat exchanger designs (spray chambers, towers and indirect-contact heat exchangers) and the technical requirements for each. The decision analysers can be used to generate optimised user-friendly fit-for-purpose bulk air heat exchanger (air cooler and heat rejection) designs. The study was tested against a constructed air cooler and heat rejection unit at a copper mine. It was concluded that the decision analysers were used successfully. It is recommended design engineers use these decision analysers to effectively design other heat exchangers. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Mining Engineering / unrestricted

Bulk modulus of hydraulic oil represents the resistance of hydraulic oil to compression and is the reciprocal of compressibility. The bulk modulus is a basic thermodynamic property of hydraulic oil that has a very important influence on work efficiency and dynamic characteristics of hydraulic systems, especially for the hydraulic systems at ultra-high pressure or ultra-high temperature. In this study, a bulk modulus experimental equipment for hydraulic oil was designed and manufactured, two types of hydraulic oil were selected and its isothermal secant bulk modulus were measured at pressures to 140MPa and temperatures of 20~180°C. Compared the experimental results with the calculated results from the prediction equations of liquid bulk modulus that proposed by Klaus, Hayward, and Song, it is found that the experimental results are not completely identical with the calculated results.

This paper describes an investigation into the effects of fluid bulk modulus and traction coefficient properties on piston pump flow losses and radial pison motor torque losses through experimentation, modelling and simulation. Synthetic ester, high bulk modulus, multi-grade, and single grade mineral oils were evaluated. The high bulk modulus fluid exhibited 20% lower pump case and compensator flow losses than a conventional mineral oil of the same viscosity grade. Low traction coefficient fluids reduced the lowspeed torque losses of the radial piston motor by 50%. Physical models for pump case flow and motor torque losses were derived from the experimental data. Field data was collected from a hydraulically propelled agricultural machine. This data was used to model fluid performance in the machine. The simulation results predict that at an operating temperature of 80⁰C, optimizing the bulk modulus and traction coefficients of the fluid could reduce flow losses by 18% and torque losses by 5%. These findings demonstrate the potential of combining comprehensive fluid analysis with modeling and simulation to optimize fluids for the efficient transmission of power.

The increasing price of oil, global warming and rapid industrial growth has drawn much attention to renewable energy technologies over the last few decades. The total energy consumption is estimated to increase 1.4% per year globally. About 90% of this energy supply is generated through fossil fuel combustion with a typical efficiency of 30-40%. The remaining 60-70% of the energy is lost to the environment via automotive exhaust or industrial processes. It is highly desired to retrieve wasted heat to improve the overall efficiency of the energy conversion. Developing thermoelectric materials and devices is a potential solution to utilize waste heat as an energy source. Skutterudites are known to be promising thermoelectric materials in the temperature range 600K to 900K. Novel nanoengineering approaches and filling of skutterudites structure can further improve the transport properties of the material. In this work, Cobalt Antimonide (Co4Sb12) based skutterudites were fabricated via mechanical milling and alloying. Rear earth material Ytterbium and Cerium are used as fillers to substitute the cages in the crystal lattice of these materials. Base material is synthesized via thermochemical reduction of the precursors under hydrogen. Further processing of the material is performed with ball milling and Spark Plasma Sintering (SPS). Ball milling parameters were optimized for nanostructuring of Co4Sb12. Grain size was significantly reduced after SPS compaction. Finally, Thermoelectric transport properties of the material is evaluated over the temperature range 300K to 900K for five different composition of the skutterudites materials. Significant reduction in materials thermal conductivity was achieved through nanostructuring.

A statistical investigation of the relationship between Lorentz force and Bursty Bulk Flow event (BBF) spatial location in the magnetotail is undertaken. Data is obtained in situ by the ESA Cluster II mission during the period July to October 2004. Firstly, a short introduction to BBFs and the Cluster mission is presented. Secondly, the curlometer method for determining Current densities in the Inner Central Plasma Sheet and its approximations are discussed. The curlometer method uses magnetic field density data from the Fluxgate Magnetometer (FGM) instrument and plasma velocities are obtained by the Hot Ion Analyzer (HIA) instrument. The satellite separation at the time of the measurement in the year 2004 was on the order of 1000 km. Results of the investigation are inconclusive. A few possible sources of error and reference material are mentioned.

Philosophiae Doctor - PhD / This thesis aimed at contributing knowledge on how the widespread changes in land use/cover resulting from increasing human population and their associated activities, are influencing hydrological responses in a sub-humid catchment. The study therefore hypothesised that reduced forest cover over time in favour of agricultural activities is altering hydrological processes of the catchment which is affecting the flow characteristics in a sub-humid catchment. The sub-humid catchment selected to investigate these issues is the Nyangores River Catchment in Kenya.

Many modern technologies are enabled by the use of thin films and/or nanostructured composite materials. For example, many thermoelectric devices, solar cells, power electronics, thermal barrier coatings, and hard disk drives contain nanostructured materials where the thermal conductivity of the material is a critical parameter for the device performance. At the nanoscale, the mean free path and wavelength of heat carriers may become comparable to or smaller than the size of a nanostructured material and/or device. For nanostructured materials made from semiconductors and insulators, the additional phonon scattering mechanisms associated with the high density of interfaces and boundaries introduces additional resistances that can significantly change the thermal conductivity of the material as compared to a macroscale counterpart. Thus, better understanding and control of nanoscale heat conduction in solids is important scientifically and for the engineering applications mentioned above. In this dissertation, I discuss my work in two areas dealing with nanoscale thermal transport: (1) I describe my development and advancement of important thermal characterization tools for measurements of thermal and thermoelectric properties of a variety of materials from thin films to nanostructured bulk systems, and (2) I discuss my measurements on several materials systems done with these characterization tools. First, I describe the development, assembly, and modification of a time-domain thermoreflectance (TDTR) system that we use to measure the thermal conductivity and the interface thermal conductance of a variety of samples including nanocrystalline alloys of Ni-Fe and Co-P, bulk metallic glasses, and other thin films. Next, a unique thermoelectric measurement system was designed and assembled for measurements of electrical resistivity and thermopower of thermoelectric materials in the temperature range of 20 to 350 °C. Finally, a commercial Anter Flashline 3000 thermal diffusivity measurement system is used to measure the thermal diffusivitiy and heat capacity of bulk materials at high temperatures. With regards to the specific experiments, I examine the thermal conductivity and interface thermal conductance of two different types of nanocrystalline metallic alloys of nickel-iron and cobalt-phosphorus. I find that the thermal conductivity of the nanocrystalline alloys is reduced by a factor of approximately two from the thermal conductivity measured on metallic alloys with larger grain sizes. With subsequent molecular dynamics simulations performed by a collaborator, and my own electrical conductivity measurements, we determine that this strong reduction in thermal conductivity is the result of increased electron scattering at the grain boundaries, and that the phonon component of the thermal conductivity is largely unchanged by the grain boundaries. We also examine four complex bulk metallic glass (BMG) materials with compositions of Zr₅₀Cu₄₀Al₁₀, Cu_46.25Zr_44.25Al_7.5Er₂, Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂, and Ti_41.5Zr_2.5Hf₅Cu_42.5Ni_7.5Si₁. From these measurements, I find that the addition of even a small percentage of heavy atoms (i.e. Hf and Er) into complex disordered BMG structures can create a significant reduction in the phonon thermal conductivity of these materials. This work also indicates that the addition of these heavy atoms does not disrupt electron transport to the degree with which thermal transport is reduced. / Ph. D.

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