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This study proposed a simple side-incident TE11 mode microwave probe for the rapid and long-range inspection of cracks in metallic pipes. The probe feeds the microwaves to a metallic pipe, which works as a waveguide; the reflection signal provoked by a defect is measured for detection and localization. The probe enables the detection of both circumferentially and axially oriented cracks, unlike those reported in earlier studies. To achieve better performance, numerical simulations were conducted to evaluate the conversion efficiency and optimize the insertion length of the coaxial cable and the exposed length of the cable core wire. The simulation results suggest that the optimized probe configuration is feasible for pipes with various diameters by proportionally changing the current probe configuration. Although injected microwaves propagated in two directions, the ratio of microwaves to one direction could be controlled by adjusting the inclination angle and the exposed length of the cable core wire. Subsequently, three TE11 probes fabricated according to the simulation results were used to detect circumferential and axial slits in a brass pipe. The results showed that circumferential slits in the vertical positions (parallel to the nontilted coaxial cable) and axial slits in the horizontal positions (perpendicular to the nontilted coaxial cable) caused large reflections, consistent with the electromagnetic field distribution of the TE11 mode microwaves in a circular waveguide. Further experiments verified the feasibility of the designed probe for pipes with different diameters and for directional pipe inspection. [ABSTRACT FROM AUTHOR]

This study explores the applicability of microwave nondestructive testing to detect a metal pipe's inner crack. Three-dimensional finite element simulations were conducted to study the inspectability of cracks using microwaves in different modes and the dependency of the reflection characteristics of microwaves on crack size. The simulation results showed that microwaves in the TM01 and TE01 modes can detect circumferential and axial cracks, respectively. The positive relationship between crack size and intensity corresponding to the reflected microwaves was obtained in simulations and then verified by experiments. In both simulations and experiments, the axial crack length showed a small influence on the results, especially for shallow crack detection. In the experiments, circumferential and axial cracks with a width of 0.3 mm were detected using microwaves. The experimental results revealed that signal amplitudes decreased when a slit penetrated a pipe wall, probably due to a microwave leakage. [ABSTRACT FROM AUTHOR]

This study investigated the applicability of microwave non-destructive testing, which has been proved effective in quickly detecting the defect location in a long pipe, to the size evaluation of wall thinning defects. Artificial wall thinning defects with different sizes (depths and lengths) and edge profiles were introduced to a flanged brass pipe with a total length of 15 m, and reflected microwave signals were measured in experiments. A signal processing method combining windowing and dispersion compensation was proposed to extract the defect-related reflection signals in the frequency domain. Resonant frequencies, at which the amplitude of extracted signals dropped significantly, decreased with the increase of either wall thinning depth or length. In addition, the results demonstrate that wall thinning location and pipe end conditions have little influence on resonant frequencies after signal processing. A back propagation neural network was trained by simulation data, using resonant frequencies as the input, to simultaneously evaluate defect depth and length, and the performance was validated by experiments. Maximum prediction errors of depth and length of wall thinning were 0.06 mm and 0.57 mm, respectively, which indicated the feasibility of the proposed method to evaluate the wall thinning defect sizes. [ABSTRACT FROM AUTHOR]

A multi-elbow piping system is adopted for the Japan sodium-cooled fast reactor (JSFR) cold-legs. Flow-induced vibration (FIV) is considered to appear due to complex turbulent flow with very high Reynolds number in the piping. In this study, pressure measurement for a single elbow flow is conducted to elucidate pressure fluctuation characteristics originated from turbulent motion in the elbow, which lead potentially to the FIV. Two different scale models, 1/7- and 1/14-scale simulating the JSFR cold-leg piping, are tested experimentally to confirm whether a scale effect in pressure fluctuation characteristics exists. A distinguishing peak can be seen in each power spectrum density (PSD) profile of pressure fluctuation obtained in and downstream of the flow separation region for both scaled models. When nondimensionalized, the PSD profiles show good correspondence regardless of scale model and even of Reynolds number simulated in this study. [DOI: 10.1115/1.4002813] Keywords: fast reactor, cold-leg piping, elbow flow, flow-induced vibration, flow separation, pressure fluctuation

T-junction is one of the familiar components in the cooling system of power plants with enormous capability of high-cycle thermal fatigue. This research investigates the structure and mixing mechanism of turbulent flow in a T-junction area with a 90 deg bend upstream. According to the wide distribution of turbulent jets in the T-junction, a reattached jet was selected previously as the best representative condition with the highest velocity fluctuation and the most complex structure. For considering the mixing mechanism of re-attached jet, T-junction is subdivided into few lateral and longitudinal sections, and each section is visualized separately by particle image velocimetry technique. Corresponding to the experimental data, the branch flow acts as a finite turbulent jet, develops the alternative type of eddies, and causes the high velocity fluctuation near the main pipe wall. Three regions are mainly subject to maximum velocity fluctuation: the region close to the jet boundaries (fluctuation mostly is caused by Kelvin--Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex), and the re-attached area (fluctuation mostly is caused by changing the pressure gradient in the wake area above the jet). Finally, the re-attached area (near the downstream of wake area above the jet) is introduced as a region with strongest possibility to high-cycle thermal fatigue with most effective velocity fluctuation on the main pipe wall above the branch nozzle. [DOI: 10.1115/1.3112383] Keywords: fluid mixing structure and interaction, mixing tee, PIV, piping system, turbulent flow

This study experimentally investigates the efficacy of TE11 mode microwaves in detecting bend-region cracks. Three types of bends with different dimensions were deployed in a 3 m piping system and then tested, with an axial or circumferential slit machined at different angular positions to simulate a crack. The TE11 mode microwaves were excited using self-designed TE11 mode microwave probes and utilised for crack detection. The experimental results show clear reflection peaks at the bend position, demonstrating the feasibility of applying TE11 mode microwaves in the detection of bend-region cracks. Furthermore, the peak location of reflection is in accordance with the angular position of the slit. The findings also indicate that the peak amplitude of reflection is affected by the factors of mode conversion of microwaves at a bend. In addition, the experimental results also manifest an excellent signal-to-noise ratio to both two types of slits, suggesting that the microwave NDT is a powerful tool for bend-region inspection. [ABSTRACT FROM AUTHOR]

A new scheme is proposed, which can treat electromagnetic field of the type-II superconductor under transient temperature field. In the analysis, one of the critical state models, the Bean model was employed to determine the current distribution in the superconductors and effect of magnetic flux flow was also taken into account. We chose both low and high Tc superconducting materials. Numerical results indicate that the flux flow strongly affects the stability against the quench in both materials. Index terms - High-temperature superconductors, Superconducting filaments/wires, Eddy currents

This paper describes a new method to calculate electromagnetic force acting between high [T.sub.c] superconducting material and permanent magnet, where the effect of grain boundary in the high [T.sub.c] superconductor is taken into account. The results show that hysteresis of the electromagnetic force is strongly affected by existence of the grain boundary.

A new method to calculate three dimensional current distributions in twisted superconductors is proposed in this paper by introducing the twisted coordinates together with periodic boundary conditions. Numerical analysis is performed based on the critical state model, by which the current distributions in type-II superconductors can be calculated. Numerical results indicate that the longitudinal currents are induced in the normal conductor region when the relatively large longitudinal magnetic flux is applied.

In this study, fluid flow of liquid metal with free surface and melting of metal under electromagnetic force was investigated numerically. The computational code was developed by the authors based upon a finite difference method to simulate the free surface flow and the eddy current simultaneously. The VOF method was introduced to treat the free surface, and magnetic vector potential was used for eddy current analysis. The free surface shape predicted by the code agreed with that obtained experimentally. Furthermore, the code was improved to calculate the phase change (melting) of solid metal by Joule heating due to eddy current. Numerical results of melting of metal were also demonstrated.

By introducing twisted coordinates, a quasi three-dimensional formulation is performed to evaluate A.C. losses such as hysteresis and coupling losses in type-II superconductors when both transport currents and magnetic field paralle to the currents exist. The numerical results indicate that the hysteresis loss induced in the superconductors increases when the transport current exists, while the coupling loss is not affected by its existence.

A quench detection method using a low-temperature superconducting quench detector (QD) has been proposed to protect rare-earth barium copper oxide (REBCO) coils at temperatures below 20 K in magnetic fields. In this study, we first conducted an experiment at 4.2 K in 0–9 T using a locally- degraded REBCO tape and Nb–Ti QDs (Nb–Ti/Cu, Nb–Ti/Cu–Ni). Quick quench detection before thermal runaway of the REBCO tape was demonstrated by the Nb–Ti/Cu–Ni QD in 0–9 T, whereas Nb–Ti/Cu QD exhibited quick quench detection only at 9 T. Furthermore, we numerically evaluated the quench detection time of Nb–Ti QDs attached to a REBCO tape with local degradation at 4.2 K in 0–9 T. The simulation reproduced the experimental results. Moreover, the contact resistance between the REBCO tape and QD should be lower than 1.0 × 10−3 m2K/W for quick quench detection. [ABSTRACT FROM AUTHOR]

Rare-earth barium copper oxide (REBCO) tape is used for resistive type superconducting fault current limiters (RSFCLs) owing to its quick response and simple structure. To shorten the recovery time, film boiling on the REBCO tape should be suppressed as it exhibits poor heat transfer performance. To address the aforementioned issue, this study utilized low thermal conductivity materials as the thermal/electrical interface material for porous-stabilized REBCO tape. The experimental results showed that the cooling and recovery performances were dramatically improved by utilizing an insulating epoxy, which has a thermal conductivity of 0.6 W/mK. Based on the visualization of the boiling behavior, the liquid-solid contact between liquid nitrogen and the REBCO tape was promoted by the insulating epoxy, in which the film boiling was easily broken. [ABSTRACT FROM AUTHOR]