The chemical reactions of titanium in air include both TiO2 and TiN. The phenomena are quite complex, and the reaction mechanisms are still unclear. However, as titanium is in widespread use all over ...the world, it is important that the reaction mechanisms be thoroughly investigated. Therefore, in this study, the continuous variations in the electrical contact resistance and the friction coefficient are simultaneously measured to monitor the dynamics of self-mated titanium pairs in an air, O2 or N2 gas flow. When a large amount of TiO2 formed on the surface of the plate for Ti/Ti, the results showed the tribo-physical phenomena of higher electrical contact resistance, friction coefficient almost doubled and severe wear. When a large amount of TiN formed on the surface of the plate for Ti/Ti, the results showed the tribo-physical phenomena of lower electrical contact resistance, friction coefficient almost halved and mild wear with some lubrication. Therefore, variations in the electrical contact resistance can be applied to determine whether the chemical reaction on the surface was TiO2 or Ti with TiN. The unsymmetrical frictional models and wear mechanisms of the self-mated titanium pairs in the air, O2 or N2 gas flow were proposed.
This analysis has studied natural convection for the temperature-dependent viscosity of fluids inside porous media between two concentric spheres by numerically solving the Brinkman-Darcy-Forchheimer ...model, vorticity transport, and energy equations. Parameters included Rayleigh numbers (5.0 × 10
3
-8.0 × 10
4
) at radius ratios of 1.5, 2.0, and 3.5 with porosities of 0.4 and 0.9 for variable-viscosity fluids with Prandtl numbers (158, 405, and 720) when the Darcy number was changed at 0.1 and 0.001. The results showed that the mean Nusselt number varied with Rayleigh number, porosity, radius ratio, and variable viscosity but did not change with the Darcy number.
A Study of Solar Panel Chimney for House Ventilation Sheng, Chih; Chou, Huann Ming; Wang, Song Hao ...
Applied Mechanics and Materials,
09/2013, Volume:
422, Issue:
Information Engineering for Mechanics and Materials Research
Journal Article
Peer reviewed
A concept of solar chimney utilizing solar panels for building passive ventilation is proposed in this paper. First, CFD Numerical analyses were conducted to test the feasibility. Major dimensional ...parameters were considered in the simulation and meaningful air flow rates were observed under normal conditions. Experiments were conducted to confirm the concept and to understand the physical mechanism of the phenomenon by air buoyancy. Based on the results of the study, the proposed solar panel chimney and its advantages are worth of further investigation. Based on this innovative concept, the rooftop solar panel could be re-arranged, grouped and boxed to form an effective solar panel chimney, to serve as passive ventilation system without much cost and fully utilize the solar power.
Damage to mechanical components caused by wear is considered to be an important issue for mechanical engineers. For the purpose of wear resistance, it is necessary to improve the material properties ...of the mechanical elements. Furthermore, low friction plays an important role in saving energy. Hence, it is important to establish a key technology for wear resistance and low friction through appropriate materials science for related industries. In general, the tribological properties of aluminum alloys are very different from those of steels. Hence, aluminum alloys should be specially considered and clarified for their tribological properties before being applied industrially. This paper therefore aims to further investigate the effects of the content of doping elements on the friction and wear of the selected aluminum alloys. From the experimental results, it can be concluded that the higher the Si content, the smaller the friction coefficient, and the milder the variation. The higher the content of iron and copper, the more materials are removed, showing better machinability. Moreover, three frictional models and wear mechanisms that describe the effects of the content of doping elements on the friction and wear are proposed. The wear mechanisms change as the silicon content increases, from the junction growth to the wedge and the ploughing particles. As a result, better choices of aluminum alloys with regards to friction and wear can then be made. These results have great practical importance.
In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to simultaneously estimate the unknown boundary heat flux and convective heat ...transfer coefficient in a curved plate cooled by an impinging slot jet from the knowledge of temperature measurements taken within the plate. Subsequently, the distributions of temperature in the plate can be determined. It is assumed that no prior information is available on the functional forms of the heat flux and convective heat transfer coefficient; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors and locations in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the heat flux and convective heat transfer coefficient and temperature distributions can be obtained for the two test cases considered in this study.
The electrical industries have been fast developing over the past decades. Moreover, the trend of microelements and packed division multiplex is obviously for the electrical industry. Hence, the high ...heat dissipative and the electrical insulating device have been popular and necessary. The thermal conduct coefficient of aluminum nitride (i.e., AlN) is many times larger than the other materials. Moreover, the green technology of composite with phase change materials (i.e., PCMs) is worked as a constant temperature cooler. Therefore, PCMs have been used frequently for saving energy and the green environment. Based on the above statements, it does show great potential in heat dissipative for the AlN film compositing with PCM. Therefore, this paper is focused on the research of thermal contact resistance and heat transfer between the AlN/PCM pairs. According to the experimental results, the heat transfer decreases and the thermal contact resistance increases under the melting process of PCM. However, the suitable parameters such as contact pressures can be used to improve the above defects.
This paper investigates experimentally, the transient characteristics of a small methanol reformer using partial oxidation (POX) and auto-thermal reforming (ATR) for fuel cell applications. The ...parameters varied were heating temperature, methanol supply rate, steady mode shifting temperature, O
2/C (O
2/CH
3OH) and S/C (H
2O/CH
3OH) molar ratios with the main aim of promoting a rapid response and a high flow rate of hydrogen.
The experiments showed that a high steady mode shifting temperature resulted in a faster temperature rise at the catalyst outlet and vice versa and that a low steady mode shifting temperature resulted in a lower final hydrogen concentration. However, when the mode shifting temperature was too high, the hydrogen production response was not necessarily improved. It was subsequently shown that the optimum steady mode shifting temperature for this experimental set-up was approximately 75
°C. Further, the hydrogen concentration produced by the auto-thermal process was as high as 49.12% and the volume flow rate up to 23.0
L
min
−1 compared to 40.0% and 20.5
L
min
−1 produced by partial oxidation.
The subject was to design a fuel converter of CO2, focusing on parameters on thermal image observation of porous media-catalyst interface during excess enthalpy reforming process. The methodology was ...using auto-thermal reforming technique to provide the heat of oxidation reaction. The heat provided the needed high temperature during CO2 reduction processing. H2-rich syngas was produced by the assistance of surface reaction of catalyst. The experiments were performed by using visualization technique for thermal image observation during reforming process. The results could be applied to the understand the temperature distribution. This study covers two parts, including thermal image observation, and reactant conversion characteristics under various reforming parameters. The experimental results show that the hybrid reformer can achieve excess enthalpy condition under the tested parameters. Additionally, the optimal CH4 conversion efficiency can reach 93.28 %. CO2 conversion efficiency is reaching between 0.35 and 8.65 %. The thermal image observation technique to determine catalyst local high temperature of reforming process is important in academic and practical application. Moreover, it provided information for basic research during reforming process
The electrical technology has been a fast development over the past decades. Moreover, the tendency of microelements and dense division multiplex is significantly for the electrical industries. ...Therefore, the high thermal conductible and electrical insulating device will be popular and important. It is well known that AlN still maintains stablility in the high temperature. This is quite attractive for the research and development department. Moreover, the thermal conduct coefficient of AlN is several times larger than the others. Therefore, it has been thought to play an important role for the radiator of heat source in the future. Therefore, this paper is focused on the studies of heat conduction and thermal contact resistance between the AlN flake and the copper specimens. The heating temperatures and the contact pressures were selected as the experimental parameters. According to the experimental results, the materials are soft and the real contact areas between the interfaces significantly increase under higher temperatures. As a result, the thermal contact resistance significantly decreases and the heat transfer rate increases with increasing the heating temperature or the contact pressures.
This study is to investigate the characteristics of critical and neutral thicknesses of an insulated oval duct by using two-dimensional numerical analysis and the one-dimensional
PWTR model, coupled ...with accurate oval duct surfaces. Critical heat transfer occurs when the outer radius of an insulated circular duct is less than its critical insulation radius. The heat transfer rate increases with increasing the insulation thickness until the maximum value is reached at the critical insulated thickness, then it decreases until the point of neutral thickness, where the heat transfer rate is the same as that of a non-insulated duct. Thus, any insulation effort is meaningless if the insulation thickness is less than the neutral insulated thickness. These characteristics are very important for small size insulated duct, especially in conditions of low ambient air/gas convective coefficients. It shows in this study that the critical phenomena of an insulated oval duct is very similar to those of an insulated circular duct except it’s critical and neutral thicknesses are smaller for larger oval axes ratio.
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