Cass T. Miller

Transport during flow of generalized Newtonian fluids (GNFs) appears often in systems that can be treated in a simplified form as either cylindrical tubes or slit openings between parallel plates. Based on the pioneering work of Taylor, analytical solutions for transport in these simplified systems were derived generally. This includes analytical solutions for advection dominated transport, as well as a computation of the enhanced molecular diffusion coefficient in low Peclet number systems. These generally derived solutions were developed without assuming any specific fluid rheology and can predict transport when only a steady velocity field is known. The newly derived general solutions for species transport were applied to Cross and Carreau model fluids using a semi-analytical solution for velocity of these fluids. The semi-analytical solutions derived herein were compared to microscale simulations and showed agreement with the numerical error of those simulations. Because of the general nature of the transport solutions derived herein, these solutions can be applied to other non-Newtonian fluids, such as viscoelastic or viscoplastic fluids, as a straightforward extension of this work.

Dilute species transport in generalized Newtonian fluids (GNFs) is typically described using explanatory empirical approaches assuming a traditional Fickian form, which is an approach that lacks predictive ability for systems and conditions not specifically investigated. Dilute species transport was investigated for a wide range of Cross and Carreau fluids flowing through a set of monodisperse and polydisperse sphere pack porous media. Both microscale and macroscale simulations were performed to demonstrate that GNF fluid flow can be predicted based upon Newtonian characterization of the media and rheological characterization of the fluid. Dilute species transport was shown to have a Fickian limit with dispersivity dependent on the porous media, fluid properties, and the flow rate in a nonlinear fashion. Dimensionless analysis and symbolic regression was used to deduce an explanatory and predictive function to describe dispersivity in terms of relevant system properties, enabling prediction of dilute species transport for GNFs flowing through porous media that does not require any non‐Newtonian experiments or parameter estimation.

Molecular-scale simulations of pressure-driven transport through polyamide nanogaps (5–100 Å) were performed to investigate fundamental transport mechanisms. Results show that transport in nanogaps ≤ 10 Å is always subdiffusive, but superdiffusive transport was observed in nanogaps ≥ 20 Å. Near typical operating pressures for applications (Δp = 100 atm), only the 100 Å nanogap exhibited superdiffusive behavior. Since openings in common membrane materials are typically <20 Å, results indicate that subdiffusive to diffusive transport dominates for typical applications, such as reverse osmosis.

Porous medium researchers and practitioners usually rely on macroscale models to represent systems of concern. While macroscale models have often been formulated phenomenologically, the thermodynamically constrained averaging theory (TCAT) provides a means to rigorously derive closed macroscale models for a wide variety of systems. However, the TCAT approach can appear overwhelmingly complicated, the entry point for use unclear, and the advantages not self-evident. In response to these perceived shortcomings, we demonstrate several aspects of TCAT macroscale model formulations for single-fluid flow in a porous medium. Specifically, we illustrate an essentially exact macroscale model derived from a rigorous connection across scales, show how an entropy inequality can be used to derive an approximate macroscale form for the Stokes-flow regime, and examine models in the transition flow regime. A special emphasis is placed upon leveraging available results, and other application opportunities are summarized.

Carreau fluids occur routinely in porous medium systems for a range of applications, and the dependence of the viscosity for such fluids on the rate of strain tensor poses challenges to modeling at an averaged macroscale. Traditional approaches for macroscale modeling such flows have relied upon experimental observations of flows for generalized Newtonian fluids (GNFs) and a phenomenological approach referred to herein as the shift factor. A recently developed approach based upon averaging conservation and thermodynamic equations from the microscale for Cross model GNFs is extended to the case of Carreau fluids and shown to predict the flow through both isotropic and anisotropic media accurately without the need for GNF-flow experiments. The model is formulated in terms of rheological properties, a standard Newtonian resistance tensor, and a length-scale tensor, which does require estimation. An approach based upon measures of the morphology and topology of the pore space is developed to approximate this length-scale tensor. Thus, this work provides the missing components needed to predict Carreau GNF macroscale flow with only rheological information for the fluid and analysis of the pore morphology and topology independent of any fluid flow experiments. Accuracy of predictions based upon this approach is quantified, and extension to other GNFs is straightforward.

The authors assess the current status of scholarly publishing and reach the conclusion that the current situation is both in a state of flux and not sustainable. While such an assessment is becoming increasingly well understood, a solution to the problems seemingly does not exist. What even embodies an improvement to the current state of scholarly publishing depends on one’s perspective. The authors approach the problem from the perspective of the main producers and consumers of scholarly knowledge—academic and governmental research institutions. From this perspective, they define a set of objectives for scholarly publishing and dissemination of published works, and they assess the challenges with current approaches to meeting these objectives for commercial publishers, professional organization publishers, and academic press publishers. Based on this analysis, the authors propose a new model for academic publishing that might help achieve the stated objectives. The academic research community alliance model suggested is based on the scholarly community taking on the responsibilities of peer review, article production, and knowledge dissemination while acting in an altruistic way of doing so. The proposed approach is described in detail, and both challenges and potential solutions to the impediments to implementing this model are explored. Finally, the authors report on initial efforts to build support for the proposed model, which suggests that meaningful progress on this difficult problem is possible.