Characterization of two-phase flow in a single rock joint

An experimental study using a triaxial apparatus was used to analyze the two-phase flow patterns in jointed rock specimens. Rock specimens having a single natural fracture were tested for two-phase flow of water and air. Triaxial tests were conducted to characterize the two-phase flow through fractured granite specimens at low confining pressures. It was found that for a relatively smooth joint (JRC<6), bubble flow pattern occurred within the rock joint when the gas velocity is below 15 m/s. The average velocity of water usually varied between 0.1 and 0.5 m/s for bubble flow patterns. In this velocity range, air bubbles were able to form along the joint walls or to be randomly displaced within the water phase. When the gas velocity inside the rock joint exceeded 22 m/s, the flow patterns took annular form for non-zero capillary pressures (i.e., injected gas pressure is not equal to injected water pressure). At elevated (>0.25 MPa) gas injection pressures, the gas occupied the main part of the fracture and the liquid was able to flow as an unstable film forming an annular flow along the joint. When the annular flow developed, the mixture flow pattern was independent of the air flow velocity. This was due to the fact that once the injected air velocity reached a critical value (i.e., 20 m/s), water velocity inside the joint was negligible for a given confining pressure and injected water pressure. Further increase in inlet air pressures developed a single-phase air flow with no water flow.     

An experimental evaluation of the effects of ripple current generated by the power conditioning stage on a proton exchange membrane fuel cell stack

In this article, an impedance model of the proton exchange membrane fuel cell stack (PEMFCS) is proposed. The proposed study employs an equivalent circuit of the PEMFCS derived by the frequency response analysis technique. An equivalent circuit for the PEMFCS is developed to evaluate the effects of ripple currents generated by the power-conditioning unit. The calculated results are then verified by means of experiments using a commercially available PEMFCS. The relationship between ripple current and fuel cell performance, such as power loss and fuel consumption, is investigated. Experimental results show that the ripple current can contribute up to a 6% reduction in the available output power. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.     

Low-energy ion beam treatment of α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>(0001) and improvement of photoluminescence of ZnO thin films

A low energy N₂ ^? ion beam impinged on a α-Al₂O₃(0001) single crystal surface in the range of fluence 5×10¹⁵/cm²?1×10¹⁸/cm² at room temperature. After ion bombardment, chemical bonding on the modified sapphire surface was investigated by x-ray photoelectron spectroscopy. Below a fluence of 1×10¹⁵/cm², only a non-bonded N1s peak at the binding energy 398.7 eV was found, but further irradiation up to 2×10¹⁷/cm² induced Al?O?N bonding at around 403 eV. The occurrence of Al?N bonding was identified at ion fluence higher than 5×10¹⁷/cm² at 396.6 eV. II–VI ZnO thin films were grown on an untreated/ion-beam-induced sapphire surface by pulsed laser deposition (PLD) for the investigation of the modified-substrate effect on photoluminescence. The ZnO films grown on modified sapphire containing Al?O?N bonding only, and both Al?O?N and Al?N bonding showed a significant reduction of the peak related to deep-level defects in photoluminescence. These results are explained in terms of the formation of Al?N?O and Al?O?N layers and relaxation of the interfacial strain between Al₂O₃ and ZnO.     

Optimization of casting conditions for heat and abrasion resistant large grey iron castings

Numerical simulation technology was applied for optimizing the casting design and conditions in large cast iron castings for marine engine. By the simulation of mold filling and solidification sequences the problems of the previous casting conditions were analyzed and marked improvements for large cylinder liner parts were derived from these results. Especially the amount and positions of chills were optimized to increase the mechanical properties and to minimize the shrinkage and microporosity in the castings. Ultrasonic testing, penetration testing and mechanical property testing were carried out for the parts with the modified casting conditions. It showed that no defects in the castings were found and the productivity could be distinctly increased. The mechanical properties satisfied also the specification demanded.     

Analysis of the Tubular Single Lap Joint with Nonlinear Adhesive Properties

The majority of the load transfer of an adhesively-bonded joint is accomplished by the nonlinear behavior of the adhesive. In this paper, the torque transmission capability and shear stress distribution of the tubular single lap joint were calculated by incorporating the nonlinear shear properties of the adhesive. The nonlinear shear properties were represented by three different mathematical models such as two-parameter exponential, linear perfectly-plastic and multilinear strain-softening approximations.

From the analyses and experiments, it was found that all the analyses with nonlinear approximations predicted the torque transmission capabilities accurately, but the two-parameter exponential approximation gave the best predictions with the simplest form for use in numerical calculation.     

Torque Transmission Capabilities of Bonded Polygonal Lap Joints for Carbon Fiber Epoxy Composites

Although carbon fiber epoxy composite materials have excellent properties for structures, the joint in composite materials often reduces the efficiency of the composite structure because the joint is often the weakest area in the composite structure.

In this paper, the effects of the adhesive thickness and the adherend surface roughness on the static and fatigue strengths of adhesively-bonded tubular polygonal lap joints have been investigated by experimental methods. The dependencies of the static and fatigue strengths on the stacking sequences of the composite adherends were observed.

From the experimental investigations, it was found that the fatigue strength of the circular adhesively-bounded joints was quite dependent on the surface roughness of the adherends and that polygonal adhesively-bonded joints had better fatigue strength characteristics than circular adhesively-bonded joints.     

Analysis of culture fluorescence by a fiber-optic sensor inNicotiana tabacum plant cell culture

The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight estimated by the structured kinetic model as well as by empirical correlation.     

Crack initiation and propagation behavior of zirconium cladding under an environment of iodine-induced stress corrosion

Tests of iodine-induced stress corrosion cracking (ISCC) were carried out to elucidate the initiation and propagation of cracks in the claddings of zirconium alloys. Zircaloy-4 cladding and Nb-contained zirconium cladding were pressurized with and without a pre-cracked state at 350°C in an iodine environment. The results show that pitting nucleation and growth play an important role in initiating ISCC. Pits preferentially grow and agglomerate around the grain boundary, where the number of pits increases with the iodine concentration and the hoop stress of the claddings. A model of grain-boundary pitting coalescence and a model of pitting-assisted slip cleavage, which were proposed to clearly elucidate the crack initiation and propagation process under ISCC, produce reasonable results. The Nb-contained zirconium cladding exhibits higher ISCC resistance than Zircaloy-4 from the standpoint of a higher threshold stress-intensity factor and a lower crack propagation rate.     

Reaction of TiO2-Al-C in the Combustion Synthesis of TiC-Al2O3 Composite

Reaction mechanisms and the thermal structure in the reaction zone during the combustion of TiO₂, Al, and C to form TiC-Al₂O₃ composite were studied. The reaction between each component was studied and the combustion wave structure and real-time temperature profile were analyzed. Titanium aluminide species, present in the aluminothermic reduction of TiO₂, did not occur in the presence of C, because of the high thermodynamic stability of TiC. The activation energies of the exothermic reaction in the 3TiO₂-4Al-3C system were determined by DSC analysis. This suggests that the combustion reaction is mainly controlled by carbon diffusion through solid TiC. The combustion wave was observed to propagate in an unstable mode. The temperature profiles in the reaction zone were of the sawtooth type and the products were of layered structure.     

The application of the artificial neural network and taguchi method to process sequence design in metal forming processes

This study shows the correlation between the design methodology of the artificial neural network (ANN) and the statistical design of experiments (DOE) approach and is demonstrated for process design in various metal forming processes. After investigating the effect of each parameter upon the characteristics by the Taguchi method which is one of the DOE, orthogonal array (OA) table and characteristics are applied to ANN as experimental data and then opiimal design parameters are established. Using the rigid plastic FEM, the simulations are performed and the results of ANN are confirmed. This technique requires smaller runs than the conventional method to find the optimal condition of design parameters for the design’s aim. This new technique can be used in a wide range of metal forming process designs.