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This study conducts a computational fluid dynamics (CFD) analysis to assess passive autocatalytic recombiners (PARs) for mitigating hydrogen risks in severe accidents. We modeled hydrogen-air mixtures' thermal-fluid dynamics and chemical reactions, comparing single-step reaction rate models with detailed chemical mechanisms on platinum-coated catalyst plates. Results indicate that the simplified single-step model accurately predicts hydrogen recombination on Pt surfaces. Incorporating radiative heat transfer was essential; neglecting it led to significant overestimations of catalyst plate temperatures and hydrogen removal rates. While CFD results aligned with experimental trends from the REKO-3 apparatus, discrepancies arose due to overestimated recombination rates. These findings highlight the importance of precise chemical and thermal modeling in optimizing PAR design, enhancing hydrogen reduction efficiency, and minimizing auto-ignition risks. The validated CFD model offers valuable guidance for improving hydrogen removal efficiency of PARs during severe accidents.

This paper investigates the application of Schlieren flow visualization for detecting leaks in pipelines carrying high-temperature fluids. Two experimental setups were constructed: one with a 25 mm PTFE tube featuring a 2 mm diameter perforation, and another with a 100 mm diameter pipe insulated with an aluminum jacket and featuring a 12 mm leak gap. A single-mirror-off-axis Schlieren system, employing a 150 mm diameter parabolic mirror, was used to visualize the leaks. The temperature of the leaking air varied between 20 and 100 °C, while the ambient temperature was maintained at 14 °C. To quantify the leaks, the coefficient of variation for pixel intensity within the leak region was calculated. Results showed that for the PTFE tube, leaks became detectable when the temperature difference exceeded 34 °C, with the coefficient of variation surpassing 0.1. However, in the insulated pipe, detecting clear leak patterns was challenging. This research demonstrates the potential of Schlieren visualization as a valuable tool in enhancing pipeline leak detection.

The mixing of fibrous additives in the polymer base is being widely investigated for improving the mechanical properties of printed parts using fused filament fabrication (FFF). In this study, flow visualisation experiments and computational fluid dynamics (CFD) analysis were conducted on the flow channel of a nozzle with an orifice for enhancing the through-layer physical properties of the printed parts. Flow visualisation experiments were conducted on the flow channels of nozzles installed with orifices of various shapes. Using ball-milled carbon fibre in high-viscosity polydimethylsiloxane (PDMS) that imitates filament flow in FFF, the fibre angles were measured for different internal and external locations of the nozzle. The distribution of the fibre angles inside the nozzle was compared with the gradient of the flow field calculated for the same shape by CFD analysis. It was found that the orifice structure inside the nozzle increases the vertical alignment of the fibre. An abrupt increase in the extension rate at the exit of the orifice is considered to be the reason behind the rotation and vertical orientation of fibres inside the nozzle channel. Results presented in this work provide the basis for achieving improved through-plane physical properties of FFF printed parts through fibre alignment.

Hydrogen has emerged as a promising carbon-neutral fuel source, spurring research and development efforts to facilitate its widespread adoption. However, the safe handling of hydrogen requires precise leak detection sensors due to its low activation energy and explosive potential. Various detection methods exist, with thermal conductivity measurement being a prominent technique for quantifying hydrogen concentrations. However, challenges remain in achieving high measurement sensitivity at low hydrogen concentrations below 1% for thermal-conductivity-based hydrogen sensors. Recent research explores the 3ω method’s application for measuring hydrogen concentrations in ambient air, offering high spatial and temporal resolutions. This study aims to enhance hydrogen leak detection sensitivity using the 3ω method by conducting thermal analyses on sensor design variables. Factors including substrate material, type, and sensor geometry significantly impact the measurement sensitivity. Comparative evaluations consider the minimum detectable hydrogen concentration while accounting for the uncertainty of the 3ω signal. The proposed suspended-type 3ω sensor is capable of detecting hydrogen leaks in ambient air and provides real-time measurements that are ideal for monitoring hydrogen diffusion. This research serves to bridge the gap between precision and real-time monitoring of hydrogen leak detection, promising significant advancements in the related safety applications.

Abstract Reinforced retaining walls are structures constructed horizontally to resist earth pressure by leveraging the frictional force imparted by the backfill. Reinforcements are employed because they exhibit excellent safety and economic efficiency. However, insufficient reinforcement can lead to collapse, and excessive reinforcement reduces economic efficiency. Therefore, it is important to select the appropriate type, length, and spacing of reinforcements. However, in actual sites, although the stress and fracture mechanisms in the straight and curved sections of reinforced soil retaining walls differ, the same amount of reinforcements are typically installed. Such an approach can lead to wall collapse or reduce economic feasibility. Therefore, in this study, the behaviours of straight and curved sections fortified with reinforcements of various lengths (1, 3, 5, and 7 m) are predicted through a three-dimensional numerical analysis. The retaining walls are of the same height, but the reinforcement variations in the aforementioned sections influence the wall behaviour differently. Based on the results, the optimum reinforcement lengths for the straight and curved parts were selected. By installing reinforcements of different lengths in these sections, the maximum reinforcing effect with minimum reinforcement was derived. This study further found that the curved section of the wall required more reinforcements, and the reinforcement lengths for the curved and straight sections should be separately optimized.

Tunneling, especially in urban areas, affects many structures on the ground, which directly influences the usability and stability of the structures. The settlement of and axial stress on the pile foundation are important factors that determine the behavioral characteristics of the pile foundation. Therefore, this study uses numerical analysis and machine learning to derive a prediction model of pile axial stress due to tunnel excavation adjacent to the piled raft. Numerical analysis data were utilized for machine learning purposes, and the effects of the input data on the prediction model were scrutinized. The numerical analysis revealed that the change in the pile axial stress resulting from tunnel excavation differed depending on the pile’s location, with the greatest axial stress reduction occurring in the center of the piled raft. Furthermore, the rate of reduction was higher in soils with lower relative densities. Several algorithms were employed to derive the prediction model, with tree-based algorithms displaying notable performance in predicting pile axial stress. Additionally, preprocessing the data with appropriate feature engineering techniques exhibited superior predictive power, and incorporating settlement data aided in enhancing the prediction model’s performance.

In this study, computational fluid dynamics (CFD) analysis was performed to investigate the cause of the thermal stratification in the channel and the temperature non-uniformity of the plate heat exchanger. The flow velocity maldistribution of the channel and the merging parts caused temperature non-uniformity in the channel width direction. The non-uniformity of flow velocity and temperature in the channel is shown in Section 1 > Section 3 > Section 2 from the heat exchanger. The non-uniform temperature distribution in the channel caused channel stratification and non-uniform outlet temperature. Stratification occurred at the channel near the merging due to the flow rate non-uniformity in the channel. In particular, as the mass flow rate increased from 0.03 to 0.12 kg/s and the effectiveness increased from 0.436 to 0.615, the cold-side stratified volume decreased from 4.06 to 3.7 cm3, and the temperature difference between the stratified area and the outlet decreased from 1.21 K to 0.61 K. The increase in mass flow and the decrease in temperature difference between the cold and hot sides alleviated the non-uniformity of the outlet temperature due to the increase in effectiveness. Besides, as the inlet temperature difference between the cold and the hot side increases, the temperature non-uniformity at the outlet port is poor due to the increase in the stratified region at the channel, and the distance to obtain a uniform temperature in the outlet pipe increases as the temperature at the hot side increases.

Vital underground structures such as sewers, power transmission lines, subways, and underpasses are potentially vulnerable to adverse effects from aboveground construction. In this study, the influence of pile installation on nearby existing tunnels was investigated. Both a laboratory model test and finite-element numerical analysis were conducted. Twelve different combinations of horizontal and vertical offsets between the pile and the tunnel were investigated. Different surcharge loads (allowable and ultimate) were also considered. In this way, the appropriate separation distance between the existing tunnel and the piles was established for sandy, medium-compaction soil. Although this study considers simple ground conditions, it facilitates safe construction by confirming the appropriate separation distance and comparing the areas that cannot be penetrated by the structures of each standard.

For tunneling in urban areas, understanding the interaction and behavior of tunnels and the foundation of adjacent structures is very important, and various studies have been conducted. Superstructures in urban areas are designed and constructed with piled rafts, which are more effective than the conventional piled foundation. However, the settlement of a piled raft induced by tunneling mostly focuses on raft settlement. In this study, therefore, raft and pile settlements were obtained through 3D numerical analysis, and the change rate of settlement along the pile length was calculated by linear assumption. Machine learning was utilized to develop prediction models for raft and pile settlement and change rate of settlement along the pile length due to tunneling. In addition, raft settlement in the laboratory model test was used for the verification of the prediction model of raft settlement, derived through machine learning. As a result, the change rate of settlement along the pile length was between 0.64 and −0.71. In addition, among features, horizontal offset pile tunnel had the greatest influence, and pile diameter and number had relatively little influence.

Recent studies have increasingly investigated construction methods for tunnel excavation because of growing underground space development. Although the New Austrian tunneling method (NATM)—a representative tunnel excavation method—can be applied to various ground conditions, as well as having good constructability and economic feasibility, it suffers from problems such as vibration and noise. By contrast, excavation using a tunnel boring machine (TBM)—a representative mechanized construction method—affords advantages such as stable excavation, minimized ground and environmental damage, noise, and vibration. However, it cannot be applied easily to various ground conditions, and it suffers from problems such as high construction costs and delays owing to equipment defects. Therefore, the simultaneous pilot tunnel excavation using the TBM—which affords advantages such as constructability, economic feasibility, and minimized noise and vibration—and rear enlargement blasting using NATM was investigated in this study. A protection shield was installed to minimize accidents occurring from equipment defects (a disadvantage of TBM) and analyze the decrease in the effect of NATM blasting, which depends on the use of the protection shield and the separation distance through 3D numerical analysis.

In this study, the 3ω method was used to determine the thermal conductivity of nanofluids (ethylene glycol containing multi-walled carbon nanotubes (MWCNTs)) with temperature gradients. The thermal modeling of the traditional 3ω method was modified to measure the spatial variation of thermal conductivity within a droplet of nanofluid. A direct current (DC) heater was used to generate a temperature gradient inside a sample fluid. A DC heating power of 14 mW was used to provide a temperature gradient of 5000 K/m inside the sample fluid. The thermal conductivity was monitored at hot- and cold-side 3ω heaters with a spacing of 0.3 mm. Regarding the measurement results for the hot and cold 3ω heaters, when the temperature gradient was applied, the maximum thermal conductivity difference was determined to be 3% of the original value. By assuming that the thermo-diffusion of MWCNTs was entirely responsible for this difference, the Soret coefficient of the MWCNTs in the ethylene glycol was calculated to be −0.749 K−1.

In this study. the measurement of thermal conductivity and interfacial thermal resistance between the microheater and polydimethylsiloxane (PDMS) with different surface roughness is measured by the bidirectional 3ω method. The PDMS samples with a different surface roughness of arithmetic average of roughness profile ranging from 0.29 to 2.58 µm are considered. Maximum pressure of 250 kPa between PDMS and 3ω sensor is applied to manipulate the interfacial thermal resistance between the sample and the 3ω sensor. Comparison of measured and theoretically calculated temperature amplitudes are made to fit the thermal conductivity of PDMS and interfacial thermal resistance at the heater-sample interface. The thermal conductivity of PDMS is found to agree well with the literature value. The interfacial thermal resistance between the PDMS and microheater ranged from 4.5 x 10-7 to 8.7 x 10-7 m²K/W. [ABSTRACT FROM AUTHOR]

The bidirectional 3ω method was used to measure the thermal conductivity of a mixture of polydimethylsiloxane (PDMS) and carbon fiber. A PDMS and carbon fiber mixture was printed using fused filament fabrication (FFF) with and without an orifice channel in the extrusion nozzle. Through-plane alignment of carbon fibers inside the PDMS medium can be promoted by embedding an orifice channel in the nozzle during FFE Thermal conductivity measurement of samples with carbon fiber content varying from 0 to 20 wt. % was performed. Compared with a pristine PDMS. the composite's thermal conductivity increased up to 50%. Additionally. through- and in-plane thermal conductivities were analyzed through the calculation of the anisotropy ratio. The sample fabricated with the orifice channel embedded nozzle showed up to a 12% higher anisotropy ratio compared to the non-orifice nozzle fabricated sample. In the FFF process, an orifice-embedded nozzle is found to enhance through-plane thermal conductivity by promoting the perpendicular alignment of carbon fibers. [ABSTRACT FROM AUTHOR]

Regenerative heat exchangers, which increase the temperature of newly supplied air using the waste heat of exhaust gas, are installed in large thermal systems, such as thermal power plants and industrial boilers, to improve their thermal efficiency. These devices are also known as air preheaters, and the rotary regenerative type has been widely used. The heat transfer performance of a rotary regenerator is enhanced as the heat capacity, which is the product of the density and specific heat, increases rather than the thermal conductivity of heat exchanging plates (HEPs). Studies to replace the existing metal materials with polymers, which are resistant to corrosion and inexpensive, have garnered attention. In this study, the heat transfer performance of HEPs fabricated using polytetrafluoroethylene, Mono Cast nylon, stainless steel, and aluminum is experimentally compared using a laboratory-scale experimental setup. It is confirmed that the polymer materials have similar or larger effectiveness compared to metals within the experimental error. [ABSTRACT FROM AUTHOR]

Nanofluids containing vanadium dioxide (VO2) are used in applications such as actuators, smart windows, and gastrointestinal tracts. Therefore, measuring the thermal conductivity of nanofluids with VO2 characteristics is important in various environmental industries. In this study, the bidirectional 3 omega (3ω) method was used to measure the thermal conductivity of nanofluids. Experimental equipment for measuring VO2 nanofluids in various environments was designed and fabricated. The effectiveness of the bidirectional 3ω equipment was verified by measuring the thermal conductivity of ethylene glycol, which has been extensively reported in the literature. The effects of elapsed time, specimen thickness, and operation temperature on the thermal conductivity are discussed in this paper. In addition, the measuring error was investigated with regard to the precipitation of particles in the suspension. [ABSTRACT FROM AUTHOR]

The 3ω method is widely used for measuring the thermal properties of a substrate or thin film on which a microheater is deposited. Recently, samples with non-formal shapes and has a thermal conductivity of 1 W/mK or below have been analyzed using the bidirectional 3w method. In measuring the thermal conductivity of such samples, the measurement sensitivity and accuracy can be increased using a 3ω sensor fabricated on a low thermal conductivity substrate such as glass or polyimide. In this study, thermal characterization is conducted on a microheater deposited on glass and polyimide substrates for a 3ω sensor. The effects of the microheater thickness and the interfacial thermal resistance between the substrate and microheater, on the temperature amplitude and phase lag are analyzed. Results from analytic solutions considering the microheater thickness and the interfacial thermal resistance are compared with results from numerical analysis of two-dimensional conduction heat transfer and experiment. [ABSTRACT FROM AUTHOR]

Thermoplastic polymer composites are considered as substitutes fur metallic materials because of their advantages in terms of huperior corrosion resistance, mass-productivity, lightness. etc. However, their applicalions are limited owing to their low melting temperature and electrically and thermally insulating characteristics. Numerous experiments are carried out to overcome these limitations and enhance physical properties by analyzing and controlling additive alignment. To achieve enhancement. it ix important to understand the rhcology of the additive in a polymer matrix and the resulting alignments inside the mc)ld during the molding process. In this study, a flow visualization experiment was carried out to simulate an injection molding process of polymer composites with carbon fiber as an additive. The alignment of carbon fiber is analyzed as it travels through the gate orifice of the mold channel. An experimental device consisting of a hall-milled-carbon-fiber and Polydimethylsiloxane mixture, syringe pump and tilbing. high speed camera with microscope. and lighting system is set up to visualize the additive alignment and orientation inside the mold channel. Two configurations of the gate orifice are used as mold channels. The location, length, and angle of additives were calculated by analyzing images acquired through flow visualization experiments. The orientation of fibers is observed to be determined by the relative amplitudes of velocity gradient components. In addition, it was observed that the position of the gate affects the average angle of the additives in the mold channel. [ABSTRACT FROM AUTHOR]

Purpose The current standard chemotherapy for advanced biliary tract cancer (BTC) has limited benefit, and novel therapies need to be investigated. Materials and Methods In this prospective cohort study, programmed death ligand-1 (PD-L1)--positive BTC patients who progressed on first-line gemcitabine plus cisplatin were enrolled. Pembrolizumab 200 mg was administered intravenously every 3 weeks. Results Between May 2018 and February 2019, 40 patients were enrolled. Pembrolizumab was given as second-line (47.5%) or ≤ third-line therapy (52.5%). The objective response rate was 10% and 12.5% by Response Evaluation Criteria in Solid Tumor (RECIST) v1.1 and immune-modified RECIST (imRECIST) and median duration of response was 6.3 months. Among patients with progressive disease as best response, one patient (1/20, 5.0%) achieved complete response subsequently. The median progression-free survival (PFS) and overall survival (OS) were 1.5 months (95% confidence interval [CI], 0.0 to 3.0) and 4.3 months (95% CI, 3.5 to 5.1), respectively, and objective response per imRECIST was significantly associated with PFS (p < 0.001) and OS (p=0.001). Tumor proportion score ≥ 50% was significantly associated with higher response rates including the response after pseudoprogression (vs. < 50%; 37.5% vs. 6.5%; p=0.049). Conclusion Pembrolizumab showed modest anti-tumor activity in heavily pretreated PD-L1--positive BTC patients. In patients who showed objective response, durable response could be achieved. [ABSTRACT FROM AUTHOR]