Soil hydraulic parameters, particularly the soil hydraulic conductivity and soil water characteristic curve (SWCC), play a critical role in hydrogeological investigations and rainfall-induced hazard assessment. However, conventional measurements are often time-consuming and difficult to implement under field conditions. This study proposes a practical data assimilation framework for rapid estimation of soil hydraulic parameters, which integrates mini disk infiltrometer (MDI) tests, three-dimensional finite element (FE) seepage simulations, and a merging particle filter (MPF) approach. A sequential updating strategy is further incorporated to assimilate information from multiple measurements and improve estimation robustness. The proposed framework is validated through laboratory soil column experiments involving Toyoura sand, silica sand K-5, and Masado soil. Time-series infiltration measurements obtained from MDI tests are assimilated into transient seepage simulations based on the Richards’ equation, and the estimated parameters are compared with independently measured SWCCs and hydraulic conductivities. The results demonstrate that the framework can accurately estimate soil hydraulic parameters using only MDI infiltration measurements, while Monte Carlo simulations (MCS) successfully reproduce measured infiltration responses with all NRMSE values below 20%. Furthermore, sensitivity analyses indicate that the estimation results are relatively insensitive to assimilation sequence, whereas assimilation quantity and prior uncertainty exert greater influence on parameter identifiability and convergence. Overall, the proposed framework provides a rapid and reliable approach for probabilistic characterization of soil hydraulic parameters and shows promising potential for large-scale hydrogeological investigations.
The CO2 huff-n-puff process offers dual benefits by enhancing bitumen recovery while contributing to carbon capture, utilization, and storage. This study investigates the evolution and stability of CO2 gas bubbles during the puff stage and their contribution to the volumetric expansion of foamy bitumen under reservoir-relevant temperatures. Experiments were conducted in a high-pressure vessel, where pure CO2 was injected into bitumen samples and allowed to dissolve under controlled conditions during the huff stage. Upon reaching quasi-dynamic equilibrium, the system was rapidly depressurized to atmospheric pressure to initiate the puff stage. Bubble evolution was recorded and analyzed using image-based techniques. Four key parameters of bubbles: half-life, size, number, and circularity, that characterize bubble evolution and stability, were quantified and compared across all conditions. The results reveal two distinct temperature-dependent regimes: a low-temperature regime (25 and 35 °C) and a high-temperature regime (45 and 55 °C). Lower temperatures and higher pressures generally produced smaller, more uniform, and longer-lived bubbles, leading to enhanced foam stability and higher expansion factors. In contrast, higher temperatures produced larger, short-lived bubbles and reduced foam stability. Among all parameters, bubble half-life and bubble size (particularly median bubble size) emerge as the most reliable indicators of bubble stability and foam expansion, whereas bubble number and circularity provide supplementary information on bubble dynamics and morphology. These findings provide new insight into CO2–bitumen interactions during the puff stage and clarify the role of bubble stability in governing foamy bitumen behavior under non-thermal conditions.
The transition to non-platinum group metal (PGM) electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs) is central to achieving sustainable and cost-effective energy conversion. However, the continued widespread use of platinum counter electrodes in electrochemical testing introduces a critical artefact, namely, platinum dissolution, migration through the electrolyte and redeposition onto the working electrode. This potentially skews performance metrics and undermines claims of ‘platinum-free’ sustained ORR activity. This study systematically investigates this issue using a model nitrogen-doped carbon electrocatalyst with inherently low catalytic activity, allowing facile observation of small performance improvements that may be difficult to separate in high-performance catalysts. Platinum wire and graphite rod counter electrodes are compared under load cycling and start-stop conditions in both acidic and alkaline media over 60,000 potential cycles. We demonstrate that platinum contamination from the counter electrode significantly enhances ORR activity and slows performance degradation, effects which are absent when a graphite counter electrode is used. Transmission electron microscopy (TEM) confirms platinum electrodeposition on the working electrode. These findings challenge prevailing experimental protocols and establish the graphite counter electrode as essential for accurate benchmarking of non-PGM catalysts. The work delivers a clear methodological clarification with broad implications for electrocatalyst development and validation.
Hemi-wicking has been widely studied on engineered high-aspect-ratio and hierarchical micro/nanostructures, where well-defined geometries promote capillary transport. However, the mechanisms governing hemi-wicking on practical surfaces with weak, irregular nanoscale roughness remain poorly understood. Here, glass surfaces with nanoscale roughness were prepared by chemical etching, and wetting near an advancing water contact line was observed using Coherence Scanning Interferometry (CSI). The same area was measured before and during wetting. The wet-state measurements revealed a nanoscale-thick liquid film extending tens of micrometers ahead of the apparent contact line, even on a surface with a roughness factor of only 1.003, indicating an almost negligible increase in surface area. By aligning the wet and dry profiles, the film length was accurately quantified. Statistical analysis of the geometrical features extracted from the dry surface topography showed that longer films formed where depressions were more closely spaced and where deeper parts of the roughness were connected into continuous pathways extending farther ahead of the contact line. These geometries can enhance capillary driving pressure and effective permeability by shortening liquid-transfer distances and providing alternative in-plane pathways around local blockages. A Darcy-type interpretation indicates that film extension is governed by network-level liquid transport rather than isolated flow-path width alone. The liquid film also weakened structural pinning and reduced the local advancing contact angle. These findings show that weak nanoscale roughness, often regarded as a surface imperfection, can serve as a design parameter for controlling passive liquid transport and contact-line motion.
