The increasing demand for freshwater, alongside increasing microplastics and persistent microbiological contaminants, is degrading water quality and highlighting the need for advanced treatment processes with better retention performance. Low-pressure reverse osmosis (LPRO) presents a promising solution for producing drinking water from freshwater, offering an optimal balance between water quality and production costs. However, uncertainties remain regarding the long-term evolution of these performance metrics, which are primarily based on data from reverse osmosis membranes used in seawater desalination. This study investigates the impact of membrane aging on LPRO performance and the role of membrane heterogeneity within a spiral-wound module. New and long-term aged membranes were compared in terms of permeability, salt retention, and virus retention, with additional analysis of microplastic retention. Natural membrane aging led to increased permeability and decreased salt retention, without affecting virus and microplastic retention, for which retention remained total across the tested coupons. Performance heterogeneity was observed depending on the position of the coupons within the module, with a more significant degradation at the beginning of the module and winding, likely due to mechanical effects associated with higher pressure and deformation. In contrast, coupons located at the end of the module and winding showed minimal performance impact. No impact was observed on virus and microplastic retention, which remained complete, confirming that viruses do not pass through an intact membrane but rather through membrane defects and seals. Autopsy of the LPRO modules revealed membrane defects (glue patches, minor and major folds) that affected membrane performance. In particular, the presence of apparent major folds led to significant performance degradation, with lower permeability and salt retention. The folds also caused the passage of viruses into the permeate, while microplastic retention remained unaffected. The virus passing through the permeate of an LPRO pilot would therefore be due to defects in the membrane and Orings of the modules.
Gas/wall collision mechanisms play a key role in Knudsen diffusion process. In particular, the channel wall structure has a major influence in mass transfer. So, we investigate the influence of the wall roughness, anisotropy and porosity on the self-diffusion of helium and neon in nanochannels. Three materials are proposed: graphite and β-cristobalite and amorphous silica. The study makes it possible to analyze, in function of temperature, the correlation between 1/the ballistic/diffusion transition regime of the surface gas transfer, 2/the transition of the bouncing process to a linear increase of the bounce number with time and 3/the shape of the surface residence time distribution characterized by a Fréchet like distribution at short time and an exponential decay at long time. As concerns the amorphous SiO 2 , the bounce must be redefined owing to the transfer inside the material which is dominated by a cage effect. The anisotropy effect on collision process and Knudsen diffusion is analyzed by means of a tensorial computation of the tangential momentum accommodation coefficient and of the mean square displacement. Using the Langevin at the channel scale and the Arya model, the ballistic/diffusion transition time of the mean square displacement is related to the collision frequency and the collision number required for the velocity to be uncorrelated. A stochastic model confirms the molecular dynamics results with β-SiO 2 channel: The behavior of the Knudsen diffusion coefficient according to the Arrhenius law and the influence of collision frequency on transition time.
In numerical studies of quasi-2D problems, such as laminar flame propagation through a slit, the quasi-2D assumption is commonly applied to simplify the problem. However, the impact of the third dimension (in the thickness between walls) can be significant due to strong curvature. The intrinsic Darrieus-Landau instability, the Saffman-Taylor instability, and the thermodiffusive instability lead to curved flame fronts in both the transverse and normal directions and radically change the global flame speed. This study investigates the interaction of these instabilities and their impact on premixed flames freely propagating in narrow channels. Two lean fuel-air mixtures are considered: one with unity Lewis number Le = 1 and another with Le = 0.5. A single-step Arrhenius-type reaction is used for combustion modeling. Joulin Sivashinsky's model [1], termed the 2D+ model, is implemented to capture the confinement effect due to walls. By comparing 3D Direct Numerical Simulations (DNS) and 2D simulations at unity Le, we find that the 2D+ model accurately reproduces confinement effects for channel width h up to 3.6δ T (δ T : thermal flame thickness), extending the validity of Darcy's law.
However, for larger h, interactions between flame curvatures in two directions result in higher flame surface increment and consumption speed. Besides, for 3D cases with Le = 0.5, positive curvature regions on the flame front primarily contribute to the global reaction due to the Lewis effect. Statistical studies on flame dynamics between walls in 3D cases are also
Effective combustion modeling relies on the precise estimation of hydrogenair combustion characteristics. In this sense, Millán-Merino and Boivin [1] designed a single-step mechanism for hydrogen combustion that accurately recovers the adiabatic flame temperature using a variable stoichiometric coefficient formalism. The present study proposes a drastic simplification of this approach (further reducing computational cost and complexity) and formally clarifies the contribution of the variable stoichiometric coefficients and their evolution across the flame internal structure.
This chapter presents the activity conducted by the ITPA topical group (TG) on Diagnostics over about the last 15 years. Following a general introduction of the ITER Diagnostics led by their measurement roles, the document is organized in several subchapters detailing the design support, research and development activity conducted by each of the specialist working groups (WGs) of the TG. Please note that the magnetic diagnostics were supported at the TG without a specific WG. Their status is included in the general introduction. In the following some highlights of the subchapter's contents are provided. Recent advances in ITER first wall (FW) diagnostics for the measurements of plasma-metallic wall interaction in support of the ITER research plan are reported. An InfraRed imaging Video Bolometer for ITER has been developed and tested on several tokamaks to measure the radiated power loss. A laser-induced breakdown spectroscopy (LIBS) technique which utilizes a pulsed laser beam to ablate locally by Nucl. Fusion 65 (2025) 113001 Review inconsistencies. Physics-based modeling and parameter relationships provide additional information improving the treatment of ill-posed inversion problems. A coherent combination of all kind of available information within a probabilistic framework allows for improved data analysis results. The concept of integrated data analysis (IDA) in the framework of Bayesian probability theory is outlined and contrasted with conventional data analysis. Components of the probabilistic approach are summarized and specific ingredients beneficial for data analysis at fusion devices are discussed. This paper is part of the Special Issue: On the Path to Tokamak Burning Plasma Operation: A collection of papers prepared by the ITPA Topical Physics Groups reviewing progress in the development of the physics basis for burning plasma operation.
