Rayleigh–Bénard Instability of an Ellis Fluid Saturated Porous Channel with an Isoflux Boundary

The onset of the thermal instability is investigated in a porous channel with plane parallel boundaries saturated by a non–Newtonian shear–thinning fluid and subject to a horizontal throughflow. The Ellis model is adopted to describe the fluid rheology. Both horizontal boundaries are assumed to be impermeable. A uniform heat flux is supplied through the lower boundary, while the upper boundary is kept at a uniform temperature. Such an asymmetric setup of the thermal boundary conditions is analysed via a numerical solution of the linear stability eigenvalue problem. The linear stability analysis is developed for three–dimensional normal modes of perturbation showing that the transverse modes are the most unstable. The destabilising effect of the non–Newtonian shear–thinning character of the fluid is also demonstrated as compared to the behaviour displayed, for the same flow configuration, by a Newtonian fluid.

Rayleigh–Bénard Instability of an Ellis Fluid Saturated Porous Channel with an Isoflux Boundary

The onset of the thermal instability is investigated in a porous channel with plane parallel boundaries saturated by a non–Newtonian shear–thinning fluid and subject to a horizontal throughflow. The Ellis model is adopted to describe the fluid rheology. Both horizontal boundaries are assumed to be impermeable. A uniform heat flux is supplied through the lower boundary, while the upper boundary is kept at a uniform temperature. Such an asymmetric setup of the thermal boundary conditions is analysed via a numerical solution of the linear stability eigenvalue problem. The linear stability analysis is developed for three–dimensional normal modes of perturbation showing that the transverse modes are the most unstable. The destabilising effect of the non-Newtonian shear–thinning character of the fluid is also demonstrated as compared to the behaviour displayed, for the same flow configuration, by a Newtonian fluid.

Rayleigh–Bénard Instability of an Ellis Fluid Saturating a Porous Medium

The Ellis model describes the apparent viscosity of a shear–thinning fluid with no singularity in the limit of a vanishingly small shear stress. In particular, this model matches the Newtonian behaviour when the shear stresses are very small. The emergence of the Rayleigh–Bénard instability is studied when a horizontal pressure gradient, yielding a basic throughflow, is prescribed in a horizontal porous layer. The threshold conditions for the linear instability of this system are obtained both analytically and numerically. In the case of a negligible flow rate, the onset of the instability occurs for the same parametric conditions reported in the literature for a Newtonian fluid saturating a porous medium. On the other hand, when high flow rates are considered, a negligibly small temperature difference imposed across the horizontal boundaries is sufficient to trigger the convective instability.

An efficient lubrication-based code for solving non-Newtonian flow in geological rough fractures

<p>The study of the flow in a single fracture is the starting point to understand the complex hydraulic behaviour of geological formations and fractured reservoirs, whose comprehension is of interest in many natural phenomena (e.g., magma intrusion) and the optimization of numerous industrial activities in fractured reservoirs (e.g., Enhanced Oil Recovery, drilling engineering, geothermal energy exploitation). Despite the considerable technical prospects of this topic, the associated mathematical complexity and computational burden have so far mostly discouraged investigations of the combined effects of fracture heterogeneity and of the complex rheology of relevant fluids. Indeed, magmas, foams, muds, and suspensions of natural colloids such as clay particles in water are complex fluids and often present in subsurface applications and natural processes. These fluids are characterized by a shear-thinning behavior, which can be well described by the Ellis model, a continuous three-parameter model that behaves as a power-law fluid at high shear rates and as a Newtonian fluid at low shear rates. The Ellis model parameters are: <em>n</em> the power law exponent, <em>μ</em><sub>0</sub> the low shear rates viscosity, and <em>τ</em><sub>1/2</sub> the shear rate such that <em>μ<sub>app</sub></em>(<em>τ</em><sub>1/2</sub>)=<em>μ</em><sub>0</sub>/2. We use this rheological description in combination with the lubrication theory, which is a depth-averaged formalism permitting us to reduce the full 3-D problem to a 2-D plane formulation. It has been applied to study Newtonian flow in a single fracture for decades and, as far as the aperture gradient remains small (∇<em>d</em>«1), the approximation error introduced by this model is limited. We present here a lubrication-based numerical code aiming at simulating the flow of an Ellis fluid in rough-walled fractures. The code is composed of two modules: a 2D FFT-based fracture aperture field generator and a lubrication-based non-Newtonian flow solver. The former module generates a random aperture field <em>d</em>(<em>x</em>,<em>y</em>) with isotropic spatial correlations, given a mean aperture ⟨<em>d</em>⟩, a coefficient of variation <em>σ<sub>d</sub></em>/⟨<em>d</em>⟩, a Hurst exponent (<em>H</em>) and a correlation length (<em>l<sub>c</sub></em>), reproducing realistic geometries of geological fractures. In the latter module, a 2-D finite volume scheme is adopted to solve the non-linear lubrication equation describing the flow of an Ellis fluid. The equation is discretized on a staggered grid, so that <em>d</em>(<em>x</em>,<em>y</em>) and the pressure field <em>p</em>(<em>x</em>,<em>y</em>) are defined at different locations. Computational efficiency is achieved by means of the inexact Newton algorithm, with the linearized symmetric system of equations solved via variable-fill-in Incomplete Cholesky Preconditioned Conjugate Gradient method (ICPCG), and a parameter-continuation strategy for the cases with strong nonlinearities. The code proves to be stable and robust when solving flow within strongly heterogeneous fractures (e.g., <em>σ<sub>d</sub></em>/⟨<em>d</em>⟩=1), even on very fine and coarse meshes (e.g., 2<sup>14</sup>×2<sup>14</sup>) and considering a wide range of power-law exponents (e.g., 0.1≤<em>n</em>≤1). The code is validated by comparing the results against analytical solutions (e.g., parallel plates model, sinusoidal profile) and full 3-D CFD simulations, considering different closures.</p>

Model Pencarian Informasi Pada Generasi Milenial Mahasiswa IPI Pascasarjana UIN Sunan Kalijaga Yogyakarta Angkatan 2018

ABSTRACT Introduction. nformation is a medium that has high use value. For everyone, the need for information is everything for the sake of carrying out daily activities. The purpose of this study in general is to find out the information seeking model for IPI Postgraduate students of UIN Sunan Kalijaga Yogyakarta class of 2018, these students are included in the millennial generation. Specific or more specific objectives in this research are; (a) to determine the variety of generations, (b) to find out the information needs of students, (c) to find out the origins of information seeking sources, (d) to find out information seeking models, (e) and to find out barriers to information seeking Data Collection Method. This research is a descriptive qualitative research, using a case study model. The determination of the research subjects was carried out by using purposive sampling technique. This research uses information theory. The informants in this study were 13 students of postgraduate IPI concentration class 2018. The data collection techniques in this study used interview techniques and documentation study. Results and Discussions. Based on the results of interviews and data analysis conducted, the results indicate the need for information on IPI postgraduate class 2018 students in the form of; books, internet journals, videos, recordings, and literature related to IPI concentration. Sources of information used by students are; books, reading rooms in libraries, internet, seminars, and human resources. Information seeking model by students in the form of; Ellis' model: starting, chaining, browsing, differentianting, mentoring, extracting. Conclusions. Using methods or models to obtain information, and obstacles in obtaining information cannot be avoided because of the limited skills students have. The Ellis model is a model or search for the right information to be implemented by IPI postgraduate students of class 2018

The Ellis Model of Information Seeking Behavior and the Peripheral Scientific Community

This chapter explores the relationship between the Ellis Model of Information Seeking Behavior and the scientific community of Venezuela. The research employs a qualitative method to investigate the main information seeking activities of a scientific community in the periphery in the context of dependency theory. The following elements of the Ellis model are supported by the data gathered and analysis: starting, browsing, chaining, filtering, extracting, and information management.

The Ellis Model of Information Seeking Behavior and the Peripheral Scientific Community

This chapter explores the relationship between the Ellis Model of Information Seeking Behavior and the scientific community of Venezuela. The research employs a qualitative method to investigate the main information seeking activities of a scientific community in the periphery in the context of dependency theory. The following elements of the Ellis model are supported by the data gathered and analysis: starting, browsing, chaining, filtering, extracting, and information management.