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Analysis of Rarefied Effects of a Nano-scale Magnetic Head/Disk

Chinese Journal of Mechanical Engineering 2009年第3期22卷 336-340页

作者： WANG Yazhen gyimah glenn kwabena HUANG Ping School of Mechanical andAutomobile Engineering South China University of Technology Guangzhou 510640 China Guangdong College of Industry and Commerce Guangzhou 510640 China

When the decrease in the space between magnetic head and disk arrived at 10 nm or less, which is much lower than the mean free path of gas molecules, the gas flow presents distinctive features against the macro features because of the rarefied effects. The modified Reynolds equation considering rarefied gas effect is used to calculate the rarefied region of a negative pressure magnetic head working in the distance of 10 nm. Inverse Knudsen number was adopted to calculating the ratio of the rarefied area. According to the numerical resuks, discussions and analyses are then presented to reveal the rarefied effect on the working performances of a magnetic head. The results show that the magnetic head works in the slip-flow and transition regions and moves to the transition region with the increase in velocity. Furthermore, the maximum rarefied effects occur at the side edges where the flying height is thinner and pressure is lower, rather than in the minimum flying height on the rear. The results also show that with considering the rarefied effects, the load-carrying capacity of the magnetic head and the maximum pressure decrease significantly, but the minimum pressure slightly changes.

关键词： rarefied region rarefied effect magnetic head/disk

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Study of Wear in a Novel Cu-Based Sintered Alloy for Train Brakes (Influence of Sintered Temperature)

Study of Wear in a Novel Cu-Based Sintered Alloy for Train B...

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作者： glenn kwabena gyimah 华南理工大学

学位级别：硕士

A novel Cu-based composite frictional train brake material composed of several elements such as Al, SiO2, Fe, graphite, Sn, Mn and MoS2 re-enforced with other elements was treated under Powder Metallurgy （P/M） route. Well prepared powders were hydraulically compacted at 650MPa. The materials were sintered at three different temperatures （850oC, 900oC and 950oC） at a constant pressure. The dry sliding friction and wear characteristics of three different sintering treatment temperatures were investigated and the results were remarkable. The tribological behavior of these materials was analyzed by pad-on-disk tests without lubrication and the coefficient of friction, wear rate and wear number were studied in order to identify the effects of the sintering temperature on the base materials composition. The porosities were found to be very high but were adequate to give the right self lubrication properties and to reduce seizure. It was found that the porosity varies inversely proportional to the increase in sintering temperature. The pores in the sintered material were mainly solid lubricants such as graphite and other low melting elements. This also resulted in poor hardness and mechanical properties, which were compensated by its ability to reduce seizure. Much lower wear frictional coefficient, k and the highest coefficient friction,μwith a high wear number, Wn were obtained, indicating a good wear resistance property of the friction material. Three forms of wear mechanisms were observed during the dry sliding process, namely;delamination wear, plowing wear and abrasive wear. The abrasive wear results in flake or break-away debris. These wear mechanisms were found to be responsible for high wear rates on samples sintered at 850oC and 900oC. Generally, the materials demonstrated excellent brake performance and wear resistance. The average values of friction coefficient under excessive pressure （3.13MPa） dry conditions were 0.336, 0.343, and 0.404, at 850oC, 9

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Towards Climate Responsive Building Design: Bio-Climatic Design Features of Residential Building Typologies in the Warm-Humid Climate of Ghana

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Journal of Building Construction and Planning Research 2021年第2期9卷 170-187页

作者： Samuel Amos-Abanyie kwabena Abrokwa gyimah Eunice Akyereko Adjei Department of Architecture Kwame Nkrumah University of Science and Technology Kumasi Ghana Department of Mechanical Engineering Kwame Nkrumah University of Science and Technology Kumasi Ghana

Climatic considerations in the architectural design of most contemporary buildings have not been strictly adhered to by building design and construction professionals in the last few decades in the developing world, with users being denied the inevitable interactions with the natural surroundings offered by climate. The situation leads to utilization of energy-based equipment such as air conditioner that is environmentally unsustainable. The study aimed to evaluate the bioclimatic design features of residential building typologies and to identify features that can enhance the environmental responsiveness of buildings. This study adopted the Mahoney Tables to undertake a climatic analysis to develop appropriate design guidelines for the climate context. The developed design guidelines were then used to evaluate the bio-climatic design features of a sampled number of residential building types. The study revealed that features of the buildings reflect the recommended design guidelines, but to varied extents among the building typologies that were studied. Occupants generally find their spaces unsatisfactory primarily as a result of the experience of hot discomfort. The findings are expected to engender a renewed interest in the design of buildings in response to prevailing climatic conditions to reduce reliance on energy use and to serve as a useful reference for contemporary architectural design practice and education.

关键词： Bio-Climatic Design Sustainability Mahoney Tables Climate Responsive Design Architectural Design

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