In the present work,multi walled carbon nanotubes(MWCNT)reinforced magnesium(Mg)matrix composite was fabricated by friction stir processing(FSP)with an aim to explore its mechanical and electrochemical behavior.Micros...In the present work,multi walled carbon nanotubes(MWCNT)reinforced magnesium(Mg)matrix composite was fabricated by friction stir processing(FSP)with an aim to explore its mechanical and electrochemical behavior.Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500μm.FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface.Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites.Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg,implying the significance of secondary phase(MWCNT)in decreasing the corrosion resistance of the composite.展开更多
Determination of turbulent mixing rate of two phase flow between neighboring subchannels is an important aspect of sub channel analysis in reactor rod bundles. Various models have been developed for two phase turbulen...Determination of turbulent mixing rate of two phase flow between neighboring subchannels is an important aspect of sub channel analysis in reactor rod bundles. Various models have been developed for two phase turbulent mixing rate between subchannels. These models show that turbulent mixing rate is strongly dependent on flow regimes;their validity was examined against specific or limited experiments. It is vital to evaluate these models by comparing the predicted two phase turbulent mixing rate with available experimental data conducted for various subchannel geometries and operating conditions. This paper describes evaluation of different models for two phase turbulent mixing rate for both gas and liquid phase against large range of experimental data which are obtained from various subchannel geometries. The results indicate that there is large discrepancy between the predicted and experimental data for turbulent mixing rate. This paper provides important shortcoming of the previous work and need for the development of a new model. In the view of this, a two phase flow model is presented, which predicts both liquid and gas phase turbulent mixing rate between adjacent sub channels of reactor rod bundles. The model presented here is for slug churn flow regime, which is dominant as compared to the other regimes like bubbly flow and annular flow regimes, since turbulent mixing rate is the highest in slug churn flow regime. The present model has been tested against low pressure and temperature air-water and high pressure and temperature steam-water experimental data found that it shows good agreement with available experimental data.展开更多
Steam explosion is one of the crucial and poorly understood phenomena which may occur during severe accident scenario and may lead to containment failure. In spite of several experimental and analytical studies, the r...Steam explosion is one of the crucial and poorly understood phenomena which may occur during severe accident scenario and may lead to containment failure. In spite of several experimental and analytical studies, the root cause of steam explosion has not been understood. Recent claims in the literature suggest that the presence of fine fragmentation during steam explosion causes its occurrence. In order to investigate this and understand the root cause of steam explosion, series of experiments were performed with 50 g to 2500 g of CaO-B<sub>2</sub>O<sub>3</sub>, a corium simulant in 4.5 litre of water. It was observed that steam explosion may occur even in the absence of fine fragments, which is contrary to the claims in the literature. To investigate further, conversion efficiency analysis was performed. This suggested that the amount of thermal energy converted to mechanical energy is more important deciding factor in explaining the occurrence of steam explosion. The present study discusses the importance of conversion efficiency in deciding steam explosion and also gives a new perspective to look at steam explosion phenomenology.展开更多
Nuclear industries have faced the unfavorable circumstance such as components obsolescence and aging of instrumentation and control system, therefore, nuclear society is striving to resolve this issue fundamentally. V...Nuclear industries have faced the unfavorable circumstance such as components obsolescence and aging of instrumentation and control system, therefore, nuclear society is striving to resolve this issue fundamentally. Various studies have been conducted to address components obsolescence of instrumentation and control system. Intuitively FPGA （field programmable gate arrays） technology is replacing the high level of micro-processor type equipped with various software and hardware which causes acceleration of the aging and obsolescence in I ＆ C （instrumentation and control） system in nuclear power plants. FPGAs are highlighted as an alternative means for obsolete control systems. When engineers design the control system of NPPs （nuclear power plants） with FPGAs, it is important to meet the system development life cycles and conduct the verification and validation activities regarding to FPGA-based applications for use in NPPs. Because the verification and validation process is more important than the design process, engineer should consider the characteristics of FPGA, HDL （hardware description language） programming, faults mode, and optimization technique. And also these characteristics should be reflected in verification and validation activities. As a minimum requirement, system designers require that HDL-programmed applications should be developed in accordance with system development life cycle and HPD design process. In the verification and validation processes, a review, test, and analysis activities should be properly conducted.展开更多
The film thickness should be known for extrazting the intrinsic surface resistance from the effective surface resistance as measured by using the dielectric resonator method. Thicknesses of 70 nm to 360 nm are measure...The film thickness should be known for extrazting the intrinsic surface resistance from the effective surface resistance as measured by using the dielectric resonator method. Thicknesses of 70 nm to 360 nm are measured for YBa2 Cu3 O7-δ films in a non-invasive way by using the two-resonant-mode dielectric resonator （TDR） method. A futile resonator with the respective resonant frequencies of 15.25-15.61 GHz and 15.10-15.37 GHz for the TE021 and the TE012 modes is used for this purpose. Differences between the values as measured by using the TDR technique and those measured by using a step profilometer appear to be less than 3%, which is smaller than the previous value of 5% as measured by using a 8. 6 GHz single-resonance mode futile resonator [Lee et al. J. Korean Phys. Soc. 54（2009）1619]. Merits of using the TDR method are discussed.展开更多
Statistical analysis of pressure fluctuations in spouted beds has been used as a well-established diagnostic tool to determine bed and flow characteristics because of its smooth operation. However, in many recent and ...Statistical analysis of pressure fluctuations in spouted beds has been used as a well-established diagnostic tool to determine bed and flow characteristics because of its smooth operation. However, in many recent and conventional applications of spouted beds such as drying, coal gasification, catalytic conversion, biomass treatment, and chemical vapor deposition, direct estimation of the heat transfer rate from the solid bed to the gas or vice versa has proven to be difficult. A variance and spectral analysis of pressure fluctuation is extended here to characterize the heat transfer phenomena in a spouted bed. In the present study, zirconia and alumina were used as the bed materials, and argon and nitrogen were used as the spouting gases. Experiments were conducted at various heating rates for different superficial gas velocities for a range of temperatures up to 300 °C. Significant changes in the gas density and viscosity with different extents of heat transfer were observed to affect the momentum diffusivity and gas–particle interaction, which in turn led to local pressure fluctuations, causing the bed to behave differently. In the present work, a novel approach is proposed to establish a link between local pressure fluctuation and the extent of heat transfer in the bed. This method shows potential for correlation of the statistics of pressure fluctuation with the thermal properties of individual solids and gases. Thus, the technique can be extended to many industrial applications for the indirect estimation of the extent of heat transfer and prediction of unknown thermal properties of products in solids or gases.展开更多
文摘In the present work,multi walled carbon nanotubes(MWCNT)reinforced magnesium(Mg)matrix composite was fabricated by friction stir processing(FSP)with an aim to explore its mechanical and electrochemical behavior.Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500μm.FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface.Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites.Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg,implying the significance of secondary phase(MWCNT)in decreasing the corrosion resistance of the composite.
文摘Determination of turbulent mixing rate of two phase flow between neighboring subchannels is an important aspect of sub channel analysis in reactor rod bundles. Various models have been developed for two phase turbulent mixing rate between subchannels. These models show that turbulent mixing rate is strongly dependent on flow regimes;their validity was examined against specific or limited experiments. It is vital to evaluate these models by comparing the predicted two phase turbulent mixing rate with available experimental data conducted for various subchannel geometries and operating conditions. This paper describes evaluation of different models for two phase turbulent mixing rate for both gas and liquid phase against large range of experimental data which are obtained from various subchannel geometries. The results indicate that there is large discrepancy between the predicted and experimental data for turbulent mixing rate. This paper provides important shortcoming of the previous work and need for the development of a new model. In the view of this, a two phase flow model is presented, which predicts both liquid and gas phase turbulent mixing rate between adjacent sub channels of reactor rod bundles. The model presented here is for slug churn flow regime, which is dominant as compared to the other regimes like bubbly flow and annular flow regimes, since turbulent mixing rate is the highest in slug churn flow regime. The present model has been tested against low pressure and temperature air-water and high pressure and temperature steam-water experimental data found that it shows good agreement with available experimental data.
文摘Steam explosion is one of the crucial and poorly understood phenomena which may occur during severe accident scenario and may lead to containment failure. In spite of several experimental and analytical studies, the root cause of steam explosion has not been understood. Recent claims in the literature suggest that the presence of fine fragmentation during steam explosion causes its occurrence. In order to investigate this and understand the root cause of steam explosion, series of experiments were performed with 50 g to 2500 g of CaO-B<sub>2</sub>O<sub>3</sub>, a corium simulant in 4.5 litre of water. It was observed that steam explosion may occur even in the absence of fine fragments, which is contrary to the claims in the literature. To investigate further, conversion efficiency analysis was performed. This suggested that the amount of thermal energy converted to mechanical energy is more important deciding factor in explaining the occurrence of steam explosion. The present study discusses the importance of conversion efficiency in deciding steam explosion and also gives a new perspective to look at steam explosion phenomenology.
文摘Nuclear industries have faced the unfavorable circumstance such as components obsolescence and aging of instrumentation and control system, therefore, nuclear society is striving to resolve this issue fundamentally. Various studies have been conducted to address components obsolescence of instrumentation and control system. Intuitively FPGA （field programmable gate arrays） technology is replacing the high level of micro-processor type equipped with various software and hardware which causes acceleration of the aging and obsolescence in I ＆ C （instrumentation and control） system in nuclear power plants. FPGAs are highlighted as an alternative means for obsolete control systems. When engineers design the control system of NPPs （nuclear power plants） with FPGAs, it is important to meet the system development life cycles and conduct the verification and validation activities regarding to FPGA-based applications for use in NPPs. Because the verification and validation process is more important than the design process, engineer should consider the characteristics of FPGA, HDL （hardware description language） programming, faults mode, and optimization technique. And also these characteristics should be reflected in verification and validation activities. As a minimum requirement, system designers require that HDL-programmed applications should be developed in accordance with system development life cycle and HPD design process. In the verification and validation processes, a review, test, and analysis activities should be properly conducted.
文摘The film thickness should be known for extrazting the intrinsic surface resistance from the effective surface resistance as measured by using the dielectric resonator method. Thicknesses of 70 nm to 360 nm are measured for YBa2 Cu3 O7-δ films in a non-invasive way by using the two-resonant-mode dielectric resonator （TDR） method. A futile resonator with the respective resonant frequencies of 15.25-15.61 GHz and 15.10-15.37 GHz for the TE021 and the TE012 modes is used for this purpose. Differences between the values as measured by using the TDR technique and those measured by using a step profilometer appear to be less than 3%, which is smaller than the previous value of 5% as measured by using a 8. 6 GHz single-resonance mode futile resonator [Lee et al. J. Korean Phys. Soc. 54（2009）1619]. Merits of using the TDR method are discussed.
文摘Statistical analysis of pressure fluctuations in spouted beds has been used as a well-established diagnostic tool to determine bed and flow characteristics because of its smooth operation. However, in many recent and conventional applications of spouted beds such as drying, coal gasification, catalytic conversion, biomass treatment, and chemical vapor deposition, direct estimation of the heat transfer rate from the solid bed to the gas or vice versa has proven to be difficult. A variance and spectral analysis of pressure fluctuation is extended here to characterize the heat transfer phenomena in a spouted bed. In the present study, zirconia and alumina were used as the bed materials, and argon and nitrogen were used as the spouting gases. Experiments were conducted at various heating rates for different superficial gas velocities for a range of temperatures up to 300 °C. Significant changes in the gas density and viscosity with different extents of heat transfer were observed to affect the momentum diffusivity and gas–particle interaction, which in turn led to local pressure fluctuations, causing the bed to behave differently. In the present work, a novel approach is proposed to establish a link between local pressure fluctuation and the extent of heat transfer in the bed. This method shows potential for correlation of the statistics of pressure fluctuation with the thermal properties of individual solids and gases. Thus, the technique can be extended to many industrial applications for the indirect estimation of the extent of heat transfer and prediction of unknown thermal properties of products in solids or gases.
