Pressure-drop reduction and heat-transfer deterioration of slush nitrogen in horizontal pipe flow

Cryogenic slush fluids such as slush hydrogen and slush nitrogen are two-phase, single-component fluids containing solid particles in a liquid. Since their density and refrigerant capacity are greater than those of liquid-state fluid alone, there are high expectations for the use of slush fluids in various applications such as clean-energy fuels, spacecraft fuels for improved efficiency in transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental tests were performed using slush nitrogen to obtain the flow and heat-transfer characteristics in two different types of horizontal circular pipes with inner diameters of 10 and 15 mm. One of the primary objectives for the study was to investigate the effect of pipe diameter on the pressure-drop reduction and heat-transfer deterioration of slush nitrogen according to changes in the pipe flow velocity, solid fraction and heat flux. In the case of an inner diameter of 15 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 3.6 m/s. On the other hand, in the case of an inner diameter of 10 mm, pressure drop was reduced and heat-transfer characteristics deteriorated when the pipe flow velocity was higher than 2.0 m/s. From these results, it can be seen that a larger pipe diameter produces a higher onset velocity for reducing pressure drop and deteriorating heat-transfer characteristics. Furthermore, based on observations using a high-speed video camera, it was confirmed that pressure drop was reduced and heat-transfer characteristics deteriorated when the solid particles migrated to the center of the pipe and the flow pattern of the solid particles inside the pipe was pseudo-homogeneous.     

Experimental and numerical analysis of channel-length-dependent electrical properties in bottom-gate,bottom-contact organic thin-film transistors with Schottky contact

Channel length dependence of field-effect mobility and source/drain parasitic resistance in pentacene thin-film transistors with a bottom-gate, bottom-contact configuration was investigated. Schottky barrier effect such as nonlinear behaviors in transistor output characteristics appeared and became more prominent for shorter channel length less than 10 μm, raising some concerns for a simple utilization of conventional parameter extraction methods. Therefore the gate-voltage-dependent hole mobility and the source/drain parasitic resistance in the pentacene transistors were evaluated with the aid of device simulation accounting for Schottky contact with a thermionic field emission model. The hole mobility in the channel region shows smaller values with shorter channel length even after removing the influence of Schottky barrier, suggesting that some disordered semiconductor layers with low carrier mobility exist near the contact electrode. This experimental data analysis with the simulation enables us to discuss and understand in detail the operation mechanism of bottom-gate, bottom-contact transistors by considering properly each process of charge carrier injection, carrier flow near the contact region, and actual channel transport.     

Thermodynamics of antimony,arsenic, and tin in CaO—CaF2 melts

In view of the importance of tramp element contamination of steel products through a large volume of scrap consumption in the near future, the thermodynamic behaviour of Sb, As, Sn and Cu in CaO—CaF₂ melts under reducing conditions was studied by examining the dependences of distribution of each element between Cu, Ag or Sn alloys and CaO—CaF₂ melts on the CaO activity, oxygen partial pressure and temperature around 1 500°C. As a result, the reaction products on treatment by Ca compounds were demonstrated to be Ca₃Sb₂, Ca₃As₂, Ca₂Sn and CaCu. Experimentally obtained distributions were extrapolated to lower oxygen partial pressures less than 10^?18 atm to estimate the feasibility of removing those tramp elements from molten iron. It is thermodynamically indicated that if the prevailing oxygen partial pressure of the environment is below 10^?23 atm, these impurities, except Cu, would be substantially removed from molten steel.     

Aseismic evaluation for aging degradation of nuclear power plant components

The commercial operation of light water reactor plants in Japan already has a history of nearly 30 years. Since the beginning of the 1990s, studies have been conducted on aging degradation of nuclear power plants in Japan and abroad and, earlier in 1999, the domestic program of plant life management (PLM) was settled on. The program is based on the results of the PLM Study, which started in 1997. The purpose of the study was to develop the preventive maintenance program with an evaluation of aging degradation for maintaining the functions of plant component equipment. Taking account of the need for proper management of aging degradation, meanwhile, the technical evaluation of aseismic capability of aged plants is also considered to be important. Based on this concept, we evaluated the impact of assumed aging degradation on the aseismic capability of the plant facilities and structures covered by the PLM Study. In the aseismic evaluation, aging degradation modes selected in the PLM Study were divided into two categories—the one is including some degradation modes which impact on the aseismic capability of the facilities and structures should be taken into account, the other is including those whose impact might be ignored. Then the aging degradation modes composing the former one were quantitatively evaluated primarily based on the Technical Guidelines for Aseismic Design of Nuclear Power Plants (JEAG-4601) (NUREG/CR-6241, 1987). The result of the evaluation indicated that no aging degradation mode to be reflected in the maintenance program was extracted from the viewpoint of securing the aseismic capability of the plant components. However, establishment of rational evaluation methods for aging degradation, e.g. aseismic capability evaluation of thinned piping systems, was made a future technical subject.     

A decentralized control system for stabilizing multimachine power systems

A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system.     

Usefulness and limitations of ultrasonography in the initial evaluation of blunt abdominal trauma

BACKGROUND: In the assessment of blunt abdominal trauma, the reliability of ultrasonography (US) in identifying individual organ injuries remains uncertain, in spite of its usefulness in detecting hemoperitoneum. This study was designed to evaluate the overall diagnostic value of US, including identification of individual organ injuries. METHODS: The accuracy of US in the detection of intra-abdominal injuries and the identification of individual organ injuries was evaluated in 1,239 patients seen during a 15-year period. Accuracy was based on detection of intraperitoneal fluid, free air, or irregular parenchymal lesions. RESULTS: For the detection of injuries, US was 94.6% sensitive, 95.1% specific, and 94.9% accurate. Individual organ injuries were identified with sensitivities of 92.4, 90.0, 92.2, 71.4, and 34.7% for the liver, spleen, kidneys, pancreas, and intestine, respectively. CONCLUSION: US is reliable for the detection of injuries and the identification of solid-organ injuries despite its poor sensitivity for intestinal injuries.     

Hyperparathyroidism--comparison of flash imaging with spin echo MR imaging

MR images of the neck were prospectively studied in 19 patients with hyperparathyroidism. Fast low angle shot (FLASH) sequence was performed in addition to T1- and T2-weighted spin echo (SE) sequences. FLASH images were obtained with 320/12/20 degrees (TR/TE/flip angle) using presaturation technique. TE of 12 ms was chosen to eliminate high signal of fat tissue. In the evaluation of detectability, a combination of T1-weighted SE and FLASH images (T1WI + FLASH) was compared with a combination of T1- and T2-weighted SE images (T1WI + T2WI). MR imaging correctly depicted 20 of 30 abnormal glands on both T1WI + FLASH and T1WI + T2WI. FLASH imaging effectively eliminated high signal of fat tissue. Nineteen abnormal glands demonstrated higher signal than surrounding tissues on FLASH images, whereas 12 glands were high-intense on T2-weighted SE images. We conclude that FLASH imaging provides improved tissue contrast and anatomic delineation and, thus, may replace T2-weighted SE imaging in the neck.     

Unusual effects of catechol upon the hydroliquefaction of coal

The effect of catechol on coal hydrogenolysis was studied using tetralin as a solvent vehicle. A constant high liquefaction yield was observed when the amount of catechol added was reduced from 10 to 0.1 % based on the weight of coal. Under the same hydrogenolysis conditions, identical conversion yields were observed even when no catechol was added. Separate experiments were carried out, using a new internal vessel and the original stirrer, to examine the effect of the stirrer on liquefaction yield. Improved liquefaction yields were achieved in these experiments (an increase from 31 to 64% at 400 °C and from 46 to 78% at 420 °C for Miike coal; from 26 to 48% at 400 °C and from 36 to 73% at 420 °C for Wandowan coal; and from 16 to 34% at 400 °C and 21 to 55% at 420 °C for Lithgow coal). This suggests that an active catalytic species is formed on the surface of the stirrer and the internal surface of the autocalve.