Experimental study for visualizing CO2-dissolved water plume migration under hydraulic gradient conditions and implication for field monitoring data.

Investigating the possible direction of a CO2-dissolved water plume migration near the potential CO2 leakage area is a significant task because it helps estimate the spatial and temporal monitoring scale to detect the signal of released CO2 from the storage. Accordingly, the Korea CO2 Storage Environmental Management (K-COSEM) research center tried to develop an intensive monitoring system and applied it to the artificial CO2 release test in the actual field. Monitoring data from the field tests depicted the horizontal movement of the CO2-dissolved water plume along the direction of the groundwater flow. However, it remains unclear how the CO2-dissolved water plume migrates vertically and how gas accumulation occurs near the capillary zone. The present study simulated the CO2 release test with a visual expression method utilizing a Hele-Shaw cell with hydraulic gradient conditions (i = 0, 0.1, and 0.01) and tried to estimate the significant influences on a diffusive-advective transport of the dissolved gas plume with the shallow aquifer condition. The visualization experiment results were intuitively verified to determine whether the theoretical principles of action related to plume flow applied in this context. The results suggest that a CO2-dissolved water plume is distributed by hydraulic gradients and density-driven CO2 convective flow. The plume shape, center, and area were analyzed using an image analyzer program; the results demonstrated that the plume characteristic evolved depending on the significant effects on the plume. When the plume was mainly affected by the hydraulic gradient, it rapidly moved from the injection point to the last boundary; in contrast, when it was influenced primarily by density-driven CO2 convective flow, it flowed diagonally downward in the shape of varied branches. The numerical model calculated the migration of the CO2-dissolved water plume affected by both factors. The laboratory experiment and numerical simulation results suggest that the migration of a CO2-dissolved water plume may be affected by the hydraulic gradient and density-driven CO2 convective transport. As such, these factors should be considered when designing and analyzing CO2 monitoring signals to detect CO2 leaks from shallow aquifer systems.

Detection of Gas Pipeline Leakage Using Distributed Optical Fiber Sensors: Multi-Physics Analysis of Leakage-Fiber Coupling Mechanism in Soil Environment.

Optical fiber sensors are newly established gas pipeline leakage monitoring technologies with advantages, including high detection sensitivity to weak leaks and suitability for harsh environments. This work presents a systematic numerical study on the multi-physics propagation and coupling process of the leakage-included stress wave to the fiber under test (FUT) through the soil layer. The results indicate that the transmitted pressure amplitude (hence the axial stress acted on FUT) and the frequency response of the transient strain signal strongly depends on the types of soil. Furthermore, it is found that soil with a higher viscous resistance is more favorable to the propagation of spherical stress waves, allowing FUT to be installed at a longer distance from the pipeline, given the sensor detection limit. By setting the detection limit of the distributed acoustic sensor to 1 nε, the feasible range between FUT and the pipeline for clay, loamy soil and silty sand is numerically determined. The gas-leakage-included temperature variation by the Joule-Thomson effect is also analyzed. Results provide a quantitative criterion on the installation condition of distributed fiber sensors buried in soil for the great-demanding gas pipeline leakage monitoring applications.

Experimental Study of Leakage Monitoring of Diaphragm Walls Based on Distributed Optical Fiber Temperature Measurement Technology.

In geotechnical engineering seepage of diaphragm walls is an important issue which may cause engineering disasters. It is therefore of great significance to develop reliable monitoring technology to monitor the leakage. The purpose of this study is to explore the application of a distributed optical fiber temperature measurement system in leakage monitoring of underground diaphragm walls using 1 g model tests. The principles of seepage monitoring based on distributed optical fiber temperature measurement technology are introduced. Fiber with heating cable was laid along the wall to control seepage flow at different speeds. The temperature rise of the fiber during seepage was also recorded under different heating power conditions. In particular the effect of single variables (seepage velocity and heating power) on the temperature rise of optical fibers was discussed. Test results indicated that the temperature difference between the seepage and non-seepage parts of diaphragm wall can be monitored well using fiber-optic external heating cable. Higher heating power also can improve the resolution of fiber-optic seepage. The seepage velocity had a linear relationship with the final stable temperature after heating, and the linear correlation coefficient increases with the increase of heating power. The stable temperature decreased with the increase of flow velocity. The findings provide a basis for quantitative measurement and precise location of seepage velocity of diaphragm walls.

An Effective Collaborative Mobile Weighted Clustering Schemes for Energy Balancing in Wireless Sensor Networks.

Collaborative strategies for mobile sensor nodes ensure the efficiency and the robustness of data processing, while limiting the required communication bandwidth. In order to solve the problem of pipeline inspection and oil leakage monitoring, a collaborative weighted mobile sensing scheme is proposed. By adopting a weighted mobile sensing scheme, the adaptive collaborative clustering protocol can realize an even distribution of energy load among the mobile sensor nodes in each round, and make the best use of battery energy. A detailed theoretical analysis and experimental results revealed that the proposed protocol is an energy efficient collaborative strategy such that the sensor nodes can communicate with a fusion center and produce high power gain.

Electronic Textiles Based on Highly Conducting Poly(vinyl alcohol)/Carbon Nanotube/Silver Nanobelt Hybrid Fibers.

Highly stable conducting fibers have attracted significant attention in electronic textile (e-textile) applications. Here, we fabricate highly conducting poly(vinyl alcohol) (PVA) nanocomposite fibers with high thermal and chemical stability based on silver nanobelt (AgNB)/multiwalled carbon nanotube (MWCNT) hybrid materials as conducting fillers. At 20 vol % AgNB/MWCNT, the electrical conductivity of the fiber dramatically increased (∼533 times) from 3 up to 1600 S/cm after thermal treatment at 300 °C for 5 min. Moreover, PVA/AgNB/MWCNT fiber resists the harsh conditions of good solvents for PVA as well as high temperatures over the melting point of PVA, whereas pure PVA fiber is unstable in these environments. The significantly enhanced electrical conductivity and chemical stability can be realized through the post-thermal curing process, which is attributed to the coalescence between adjacent AgNBs and additional intensive cross-linking of PVA. These remarkable characteristics make our conducting fibers suitable for applications in e-textiles such as water leakage detectors and wearable heaters. In particular, heating behavior of e-textiles by Joule heating can accelerate the desorption of physically trapped moisture from the fiber surface, resulting in the fully reversible operation of water leakage monitoring. This smart e-textile sensor based on highly stable and conductive composite fibers will pave the way for diverse e-textile applications.

Development of a leakage monitoring system in isolated limb perfusion with portable gamma camera. / Desarrollo de un protocolo de monitorización de fuga en perfusión de miembro aislado con gammacámara portátil.

Isolated limb perfusion (ILP) is a method for treating unresectable lesions of limbs in patients with melanoma or sarcoma by using high doses of tumor necrosis factor alpha and melphalan. These high doses can result in high systemic toxicity if there is a drug leak from the isolated circulation of the limb to the systemic. This makes it imperative to monitor the leakage rate (F[%]) during the infusion, currently performed with radiotracers. The objective of this work was to develop a leakage monitoring protocol as accurate as possible to ensure safe ILP. MATERIAL AND METHOD: We built a phantom with 3compartments (body, limb and precordial area) and a high sensitivity collimator fitted to a portable gammacamera. We simulate ILP with scheduled leaks every 10minutes from 1% to 9% (theorical F[%]). We mesured F(%) using 2equation: one is the proposed in the literature and another corrected by decay of the radioisotope. We test the optimal radiopharmaceutical doses to minimize the detector dead time error and compare F(%) mesured by both equations regarding the theoretical F(%). The leakage monitoring protocol was used in 17 ILP of 16 patients and an analysis of the recorded data was performed. RESULTS: We found significant differences between F(%) mesured using the first equation and theoretical F(%), obtaining results very adjusted to the theorical after applying the decay correction. CONCLUSIONS: The decay correction of the radioisotope is a simple manner to carry out the procedure more safely, reducing the error in the calculation of F(%).

Using stress wave technology for leakage detection in a landfill impervious layer.

This paper proposes a stress wave monitoring method for monitoring and locating leakage through the impervious layer at a landfill to resolve the "first pollution, then discovery" problem caused by the existing electrical monitoring method. The experimental results show that the linear distance to the geophones from the leak point should be less than 31.5 m to provide a well-defined rupture signal. The amplitudes of the stress wave signals generated during the yield and rupture stages of the high-density polyethylene (HDPE) film are more obvious and easily identified by the geophones; the rupture signal duration is approximately 100 ms, and the bandwidth is distributed within 0 kHz to 1 kHz. By studying the stress wave first arrival times calculated by the picking model, the average error of the picking model is approximately 0.35 ms, and the iteration of the model is ceased when the thresholds of the discriminating indices are 3.5 and 0.9. Experiments reveal that the positioning model should stop iterating when the absolute value of each element in the calibration vector is less than 140. The average positioning error is 0.248 m, and the maximum fiducial errors of the positioning model in the X-axis and Y-axis directions are 0.32% and 0.58%, respectively.