Creep and superplasticity were investigated by testing a fine-grained extruded Mg–Zn–Zr magnesium alloy under a wide range of applied stress in the temperature range between 100 and 300 ℃. Grain boundary sliding be...Creep and superplasticity were investigated by testing a fine-grained extruded Mg–Zn–Zr magnesium alloy under a wide range of applied stress in the temperature range between 100 and 300 ℃. Grain boundary sliding became the dominating mechanism at 200 ℃, leading to a true superplastic behaviour at 300 ℃, where superplasticity was attained even under relatively high strain rates （5×10-3 s-1 ）. By contrast, for lower temperatures, the straining process was controlled by dislocation climb. A comprehensive model, taking into account the simultaneous operation of the different mechanisms, was developed to describe the strain rate dependence on applied stress.展开更多
This work aims to design a cleaning system for the solar PV panels under Medina climatic conditions. This system powered by the PV module itself. Full cleaning system has been designed and tested utilizing a wiper and...This work aims to design a cleaning system for the solar PV panels under Medina climatic conditions. This system powered by the PV module itself. Full cleaning system has been designed and tested utilizing a wiper and water jet to remove the accumulated dust and other dirt from solar panels surface. The proposed cleaning system can be worked for long time efficiently. All the strength system components were examined and found to be stable and reliable. Also, the performance of cleaning system evaluated and comparison between the clean and dusty module performance has been conducted. The system performance has been evaluated for both clean and dusty panel at variable inputs of solar radiation. At input power of 805 W/m2, the efficiency found to be 13.78% for the cleaning panel and 9% for dusty panel, whereas at the input power of 460 W/m2, the estimated efficiency was 12.6% and 7.3% for clean and dusty panel respectively. Significant reduction in the efficiency has been reported as 35% and 42% for both cases. Therefore, the present work can be considering as a promising and efficient system to solve the problem of poor performance of the photovoltaic cells in areas that experience dusty environment and external pollutants. In addition, it is safe clean and economic system.展开更多
The major issues of Micro-Thermo-Photo-Voltaic(MTPV) micro-combustors are flame instabilities, which narrow the operational range, and non-uniform wall temperature, which lowers the overall efficiency. The purpose of ...The major issues of Micro-Thermo-Photo-Voltaic(MTPV) micro-combustors are flame instabilities, which narrow the operational range, and non-uniform wall temperature, which lowers the overall efficiency. The purpose of the present research is to propose a novel micro-combustor with combined baffle and cavity configuration to address these issues. For this aim, a numerical modeling approach is validated and used. The performance of the improved combustor is compared with another recent baffle-bluff configuration. It is shown that the novel design improves the average wall temperature by 36.4 K and mitigates its standard deviation by 13.4 K. Moreover, using the optimal baffle thickness, these enhancements can be augmented by 4% raise of average wall temperature, 62%increase of temperature uniformity, and 20% reduction in overall emission. The baffle length of 0.6 times the combustor length and thickness of 0.0625 times the baffle spacing result in the optimal operation due to the flame lift-off in the upstream direction. According to the sensitivity analysis, the most effective geometrical parameters are the baffle length and thickness. It is expected that using this novel micro-combustor with optimized design parameters improves the overall efficiency of MTPV systems.展开更多
In this study,the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition und...In this study,the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition.The criticality conditions for a slab,an infinite cylinder,and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system.Exact solution for a Semenov model with convection heat loss was also presented.The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared.The critical parameterδis calculated and compared with those of Frank-Kamenetskii solution values.The validation of the calculated ignition temperatures with other exact solution and experimental results were offered.The relation between critical parameters form Semenov and F.K.models solution was introduced.展开更多
Globalization is a reality resulting in many changes in the refractory industry. In this paper some of the threats and opportunities, which are influencing the future prosperity of the refractory industry on a worldwi...Globalization is a reality resulting in many changes in the refractory industry. In this paper some of the threats and opportunities, which are influencing the future prosperity of the refractory industry on a worldwide basis, are being evoked. Some key technical and management issues are underlined, in terms of adjusting the productivity-quality-cost to the customers requirements ; producing unshapes versus shapes; innovations supported by research; international profile for the import-export game; training and education. Consequences for China, who does play a dominant role due to the size of its internal market （ customers demand） and the magnitude of its production capability （including raw materials availability）, are being drawn.展开更多
Modeled grain structures of normalized carbon steels using voronoi tessellation is reported in this work. Three stages of programming were used in modeling the microstructures. The first stage was iteration of the vor...Modeled grain structures of normalized carbon steels using voronoi tessellation is reported in this work. Three stages of programming were used in modeling the microstructures. The first stage was iteration of the voronoi cells in order to obtain equivalent grain size with experimental specimens. In the second stage, the pearlite phase was introduced using the lever rule represented by a plot of random points. The third layer was modeled to reveal the grain boundaries of the carbon steels. The values of the grain sizes of modeled microstructures showed good agreement with experimental values. The study has shown that the microstructures can be modeled fairly accurately thus enabling a fairly quick export of geometric models on to some other finite element packages for analysis of stress-strain effect on microstructure and generally a stressmicrostructure response could be determined.展开更多
Abstract： The most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enh...Abstract： The most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enhanced thermo-hydraulic performance. Thermo-hydraulic design of CHEs （Compact heat exchangers） is strongly dependent upon the predicted/measured dimensionless performance （Colburnj factor and Fanning friction vs. Reynolds number） of heat transfer surfaces. This paper describes the numerical analysis to study the heat transfer coefficient and friction factor of Serrated fins in water medium. CFD （Computational fluid dynamics） methodology has been used to develop the single phase water heat transfer coefficient and friction factor correlations for serrated fins using ANSYS Fluent 14.5. The results are compared with previous air-cooled models and experimental results of water. The water cooled CFD analysis results shows that the Prandtl number has a large effect on the Nusselt number of the serrated fin geometry. Finally, the generalized correlations are developed for serrated fins taking all geometrical parameters into account. This numerical estimation can reduce the number of tests/experiments to a minimum for similar applications.展开更多
Solar energy is the most available, clean and inexpensive source of energy among the other renewable sources of energy. This work deals with experimental steady to determent the performance of solar tower steam produc...Solar energy is the most available, clean and inexpensive source of energy among the other renewable sources of energy. This work deals with experimental steady to determent the performance of solar tower steam production for power generation. Designed and fabricated of a solar tower, consist of a central receiver tank （0.4 m × 0.6 m × 1.0 m） and 150 heliostat mirrors arranged around it. The central tank was made of galvanized steel. Each heliostat consisted of two （0.5 m × 0.5 m） mirrors. The results of this work produce steam at temperature 110 ℃. Large steam quantity could be obtained when using large scale experimental. The results of the work give good indication for application of solar energy to produce power in Iraq.展开更多
Traffic sector presents a major contributor to air pollution in Palestine. This has been maximized as Israeli closure of major roads resulted in major congestion in most of Palestinian cities in West Bank, which cause...Traffic sector presents a major contributor to air pollution in Palestine. This has been maximized as Israeli closure of major roads resulted in major congestion in most of Palestinian cities in West Bank, which causes high emissions of exhaust gases, such as carbon monoxide （CO）. nitrogen oxides （NOx）. particulate matters （PM）, volatile organic compounds （VOCs） and sulphur dioxide （SO2）. In order that traffic induced pollution can be assessed in Palestine. in this paper, an approach is presented by which the traffic emissions can be estimated relying on the emission factors as input together with vehicle types, annual traveled distance, etc.. The outcomes cover the emission from the various types of vehicles in West Bank.展开更多
This work demonstrates the processing,modeling,and characterization of nanocrystalline refractory metal tantalum(Ta)as a new structural material for microelectromechanical system(MEMS)thermal actuators(TAs).Nanocrysta...This work demonstrates the processing,modeling,and characterization of nanocrystalline refractory metal tantalum(Ta)as a new structural material for microelectromechanical system(MEMS)thermal actuators(TAs).Nanocrystalline Ta films have a coefficient of thermal expansion(CTE)and Young’s modulus comparable to bulk Ta but an approximately ten times greater yield strength.The mechanical properties and grain size remain stable after annealing at temperatures as high as 1000°C.Ta has a high melting temperature(Tm=3017℃)and a low resistivity(ρ=20µΩcm).Compared to TAs made from the dominant MEMS material,polycrystalline silicon(polysilicon,Tm=1414℃,ρ=2000µΩcm),Ta TAs theoretically require less than half the power input for the same force and displacement,and their temperature change is half that of polysilicon.Ta TAs operate at a voltage 16 times lower than that of other TAs,making them compatible with complementary metal oxide semiconductors(CMOS).We selectα-phase Ta and etch 2.5-μm-thick sputterdeposited films with a 1μm width while maintaining a vertical sidewall profile to ensure in-plane movement of TA legs.This is 25 times thicker than the thickest reactive-ion-etchedα-Ta reported in the technical literature.Residual stress sensitivities to sputter parameters and to hydrogen incorporation are investigated and controlled.Subsequently,a V-shaped TA is fabricated and tested in air.Both conventional actuation by Joule heating and passive self-actuation are as predicted by models.展开更多
This article has been retracted at the request of the Editor-in-chief,since substantial parts of this article were previously published in Tribology in Industry:A.Belhocine,N.M.Ghazali,O.I.Abdullah.Structural and Cont...This article has been retracted at the request of the Editor-in-chief,since substantial parts of this article were previously published in Tribology in Industry:A.Belhocine,N.M.Ghazali,O.I.Abdullah.Structural and Contact Analysis of a 3-Dimensional Disc-Pad Model with and without Thermal Effects.2014.Tribology in Industry 36(4):406-418(2014).展开更多
基金partly financially supported by Ort Braude College of Engineering, Israel
文摘Creep and superplasticity were investigated by testing a fine-grained extruded Mg–Zn–Zr magnesium alloy under a wide range of applied stress in the temperature range between 100 and 300 ℃. Grain boundary sliding became the dominating mechanism at 200 ℃, leading to a true superplastic behaviour at 300 ℃, where superplasticity was attained even under relatively high strain rates （5×10-3 s-1 ）. By contrast, for lower temperatures, the straining process was controlled by dislocation climb. A comprehensive model, taking into account the simultaneous operation of the different mechanisms, was developed to describe the strain rate dependence on applied stress.
文摘This work aims to design a cleaning system for the solar PV panels under Medina climatic conditions. This system powered by the PV module itself. Full cleaning system has been designed and tested utilizing a wiper and water jet to remove the accumulated dust and other dirt from solar panels surface. The proposed cleaning system can be worked for long time efficiently. All the strength system components were examined and found to be stable and reliable. Also, the performance of cleaning system evaluated and comparison between the clean and dusty module performance has been conducted. The system performance has been evaluated for both clean and dusty panel at variable inputs of solar radiation. At input power of 805 W/m2, the efficiency found to be 13.78% for the cleaning panel and 9% for dusty panel, whereas at the input power of 460 W/m2, the estimated efficiency was 12.6% and 7.3% for clean and dusty panel respectively. Significant reduction in the efficiency has been reported as 35% and 42% for both cases. Therefore, the present work can be considering as a promising and efficient system to solve the problem of poor performance of the photovoltaic cells in areas that experience dusty environment and external pollutants. In addition, it is safe clean and economic system.
文摘The major issues of Micro-Thermo-Photo-Voltaic(MTPV) micro-combustors are flame instabilities, which narrow the operational range, and non-uniform wall temperature, which lowers the overall efficiency. The purpose of the present research is to propose a novel micro-combustor with combined baffle and cavity configuration to address these issues. For this aim, a numerical modeling approach is validated and used. The performance of the improved combustor is compared with another recent baffle-bluff configuration. It is shown that the novel design improves the average wall temperature by 36.4 K and mitigates its standard deviation by 13.4 K. Moreover, using the optimal baffle thickness, these enhancements can be augmented by 4% raise of average wall temperature, 62%increase of temperature uniformity, and 20% reduction in overall emission. The baffle length of 0.6 times the combustor length and thickness of 0.0625 times the baffle spacing result in the optimal operation due to the flame lift-off in the upstream direction. According to the sensitivity analysis, the most effective geometrical parameters are the baffle length and thickness. It is expected that using this novel micro-combustor with optimized design parameters improves the overall efficiency of MTPV systems.
文摘In this study,the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition.The criticality conditions for a slab,an infinite cylinder,and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system.Exact solution for a Semenov model with convection heat loss was also presented.The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared.The critical parameterδis calculated and compared with those of Frank-Kamenetskii solution values.The validation of the calculated ignition temperatures with other exact solution and experimental results were offered.The relation between critical parameters form Semenov and F.K.models solution was introduced.
文摘Globalization is a reality resulting in many changes in the refractory industry. In this paper some of the threats and opportunities, which are influencing the future prosperity of the refractory industry on a worldwide basis, are being evoked. Some key technical and management issues are underlined, in terms of adjusting the productivity-quality-cost to the customers requirements ; producing unshapes versus shapes; innovations supported by research; international profile for the import-export game; training and education. Consequences for China, who does play a dominant role due to the size of its internal market （ customers demand） and the magnitude of its production capability （including raw materials availability）, are being drawn.
文摘Modeled grain structures of normalized carbon steels using voronoi tessellation is reported in this work. Three stages of programming were used in modeling the microstructures. The first stage was iteration of the voronoi cells in order to obtain equivalent grain size with experimental specimens. In the second stage, the pearlite phase was introduced using the lever rule represented by a plot of random points. The third layer was modeled to reveal the grain boundaries of the carbon steels. The values of the grain sizes of modeled microstructures showed good agreement with experimental values. The study has shown that the microstructures can be modeled fairly accurately thus enabling a fairly quick export of geometric models on to some other finite element packages for analysis of stress-strain effect on microstructure and generally a stressmicrostructure response could be determined.
文摘Abstract： The most popularly used fin types in compact heat exchangers are the serrated fins, wavy fins, louvered fins and plain fins. Amongst these fin types the serrated fins assume lot of importance due to its enhanced thermo-hydraulic performance. Thermo-hydraulic design of CHEs （Compact heat exchangers） is strongly dependent upon the predicted/measured dimensionless performance （Colburnj factor and Fanning friction vs. Reynolds number） of heat transfer surfaces. This paper describes the numerical analysis to study the heat transfer coefficient and friction factor of Serrated fins in water medium. CFD （Computational fluid dynamics） methodology has been used to develop the single phase water heat transfer coefficient and friction factor correlations for serrated fins using ANSYS Fluent 14.5. The results are compared with previous air-cooled models and experimental results of water. The water cooled CFD analysis results shows that the Prandtl number has a large effect on the Nusselt number of the serrated fin geometry. Finally, the generalized correlations are developed for serrated fins taking all geometrical parameters into account. This numerical estimation can reduce the number of tests/experiments to a minimum for similar applications.
文摘Solar energy is the most available, clean and inexpensive source of energy among the other renewable sources of energy. This work deals with experimental steady to determent the performance of solar tower steam production for power generation. Designed and fabricated of a solar tower, consist of a central receiver tank （0.4 m × 0.6 m × 1.0 m） and 150 heliostat mirrors arranged around it. The central tank was made of galvanized steel. Each heliostat consisted of two （0.5 m × 0.5 m） mirrors. The results of this work produce steam at temperature 110 ℃. Large steam quantity could be obtained when using large scale experimental. The results of the work give good indication for application of solar energy to produce power in Iraq.
文摘Traffic sector presents a major contributor to air pollution in Palestine. This has been maximized as Israeli closure of major roads resulted in major congestion in most of Palestinian cities in West Bank, which causes high emissions of exhaust gases, such as carbon monoxide （CO）. nitrogen oxides （NOx）. particulate matters （PM）, volatile organic compounds （VOCs） and sulphur dioxide （SO2）. In order that traffic induced pollution can be assessed in Palestine. in this paper, an approach is presented by which the traffic emissions can be estimated relying on the emission factors as input together with vehicle types, annual traveled distance, etc.. The outcomes cover the emission from the various types of vehicles in West Bank.
基金supported by the US National Science Foundation(NSF)grant number CMMI-1635332the Kavcic-Moura Endowment Fund for the support.
文摘This work demonstrates the processing,modeling,and characterization of nanocrystalline refractory metal tantalum(Ta)as a new structural material for microelectromechanical system(MEMS)thermal actuators(TAs).Nanocrystalline Ta films have a coefficient of thermal expansion(CTE)and Young’s modulus comparable to bulk Ta but an approximately ten times greater yield strength.The mechanical properties and grain size remain stable after annealing at temperatures as high as 1000°C.Ta has a high melting temperature(Tm=3017℃)and a low resistivity(ρ=20µΩcm).Compared to TAs made from the dominant MEMS material,polycrystalline silicon(polysilicon,Tm=1414℃,ρ=2000µΩcm),Ta TAs theoretically require less than half the power input for the same force and displacement,and their temperature change is half that of polysilicon.Ta TAs operate at a voltage 16 times lower than that of other TAs,making them compatible with complementary metal oxide semiconductors(CMOS).We selectα-phase Ta and etch 2.5-μm-thick sputterdeposited films with a 1μm width while maintaining a vertical sidewall profile to ensure in-plane movement of TA legs.This is 25 times thicker than the thickest reactive-ion-etchedα-Ta reported in the technical literature.Residual stress sensitivities to sputter parameters and to hydrogen incorporation are investigated and controlled.Subsequently,a V-shaped TA is fabricated and tested in air.Both conventional actuation by Joule heating and passive self-actuation are as predicted by models.
文摘This article has been retracted at the request of the Editor-in-chief,since substantial parts of this article were previously published in Tribology in Industry:A.Belhocine,N.M.Ghazali,O.I.Abdullah.Structural and Contact Analysis of a 3-Dimensional Disc-Pad Model with and without Thermal Effects.2014.Tribology in Industry 36(4):406-418(2014).
