The present study aims at monitoring the bulk and bubble-scale behaviour of anionic polyacrylamide-sodium dodecyl sulphate stabilized foam in the absence and presence of oil. Dynamic stability tests provided results indicating that polymer increases the foam dynamic stability and decreases the drainage. Oil slows down the drainage rate of polymer-surfactant foam. In the absence of oil, foam is drained gradually/smoothly whereas remarkable fluctuations are evident in drainage graphs when oil is present. The Hele-Shaw cell was employed to conduct bubble-scale as well as statistical analyses on how foam texture is influenced by a polymer-surfactant system and hydrocarbon. Bubble-scale analyses, taken right after foam generation in the absence of oil, revealed that foam bubble sizes and their standard deviation increase by polymer concentration. The coefficient of variation of foam bubble sizes drops with polymer concentration in the absence/presence of oil, meaning the growth of foam texture uniformity. Oil increases the bubble size diversity in the foam texture. Disproportionation/Ostwald ripening is hindered by increasing the foam bubble distribution uniformity by adding polymer to the foaming solution. At polymer concentrations higher than 13 Â 10 À4 g/g, a polymersurfactant mixture generates foam in the presence of oil as stable as foam in the absence of oil, while at the polymer concentrations lower than 7 Â 10 À4 g/g, bubbles are highly unstable when oil is present. Results of this study help to gain a better understanding about the extent to which polymer could enhance the foam stability in bulk/bubble-scale, which might be applicable for enhanced oil recovery operations.
Coupled free-flow–porous medium systems are of great importance in various natural and industrial applications. Modeling of such systems is always challenging, especially when droplets form at the interface between the two domains. We propose a new concept to take droplet formation, growth and detachment at the interface into account. In this concept, we use pore-network modeling to describe the porous medium and the Navier–Stokes equations for the free-flow domain. New coupling conditions are developed which include droplet interactions with the free flow and the porous medium. Impacts of using different descriptions of the forces acting on the triple contact line and contact angle hysteresis on the predicted onset of the droplet detachment are examined. In addition, we compare the new approach with another model built using ANSYS Fluent based on the volume of fluid method. The results show that the new model is able to describe the droplet formation, growth and then detachment by the free flow. The proposed model provides a base for further developments to handle formation of multiple droplets at the interface between a free flow and a porous medium as well as to include the evaporation in future works.
For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single-and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyse the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel.
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