Permeability correction factor for fractures with permeable walls

Enhanced Geothermal Systems (EGS) are based on the premise that heat can be extracted from hot dry rocks located at significant depths by circulating fluid through fracture networks in the system. Heated fluid is recovered through production wells and the energy is extracted in a heat exchange chamber. There is much published research on flow through fractures, and many models have been developed to describe an effective permeability of a fracture or a fracture network. In these cases however, the walls of the fracture were modelled as being impermeable. In this paper, we have extended our previous work on fractures with permeable walls, and we introduce a correction factor to the equation that governs fracture permeability. The solution shows that the effective fracture permeability for fractures with permeable walls depends not only on the height of the channel, but also on the wall permeability and the wall Reynolds number of the fluid. We show that our solution reduces to the established solution when the fracture walls become impermeable. We also extend the discussion to cover the effective permeability of a system of fractures with permeable walls.R. Mohais, C. Xu, P. A. Dowd, and M. Han

Earthquake classifying neural networks trained with random dynamic neighborhood PSOs

This paper investigates the use of Random Dynamic Neighborhoods in Particle Swarm Optimization (PSO) for the purpose of training fixed-architecture neural networks to classify a real-world data set of seismological data. Instead of the ring or fully-connected neighborhoods that are typically used with PSOs, or even more complex graph structures, this work uses directed graphs that are randomly generated using size and uniform out-degree as parameters. Furthermore, the graphs are subjected to dynamism during the course of a run, thereby allowing for varying information exchange patterns. Neighborhood re-structuring is applied with a linearly decreasing probability at each iteration. Several experimental configurations are tested on a training portion of the data set, and are ranked according to their abilities to generalize over the entire set. Comparisons are performed with standard PSOs as well as several static non-random neighborhoods.Arvind S. Mohais, Rosemarie Mohais, Christopher Ward and Christian Posthof

Temperature and heat transfer profiles of a fluid film squeezed between two permeable isothermal discs rotating within a magnetic field

We consider the case of an electrically conducting fluid squeezed between two permeable, parallel discs placed within a magnetic field. Each disc is maintained at a distinct isothermal temperature and is allowed to rotate independently. The upper disc is then set in motion towards the lower one. Using a similarity solution, analytical and numerical solutions are derived from which the effects of various flow parameters on the temperature and heat transfer profiles are studied. The Hartmann number has an effect on the temperature profiles when the discs are allowed to rotate in the same direction, but the effects are negligible during rotation in the opposite direction. The Prandtl number also affects the temperature and heat transfer profiles for small values of the Squeeze Reynolds number. The effect of permeability on the heat transfer profile varies depending on the speed of rotation of the discs relative to each other.B. Bhatt and R. Mohai

Fluid flow through branched channels in a fracture plane in an enhanced geothermal system

Fluid flow in Enhanced Geothermal Systems (EGS) occurs primarily through fractures which are embedded in an almost impermeable granite rock matrix. Experimental and numerical studies have shown that flow in fractures exhibits channeling effects; this means that flow occurs along preferred pathways, most likely the paths of least resistance. There has been evidence to date of dendritic and star-like patterns in granite and as a result, authors have used fractal theory in order to address flow phenomena in these patterns. The application of Bejan’s Constructal theory to this problem however has never been attempted. We base our model on dendritic patterns of flow paths in heterogeneous rock fractures. Flow enters into a main channel which bifurcates into daughter channels of unique dimensions of length and height. We study these parameters for consecutive channels in the flow path and show that for minimization of resistance to flow within a plane using area and volume constraints for a T-shaped channel, a simple relationship holds for the ratios of lengths and heights which will enable maximum flow for this configuration.R. Mohais, C. Xu, P. A. Dowdhttp://www.asmeconferences.org/congress2012

Connectivity analysis of the Habanero enhanced geothermal system

Chaoshui Xu, Peter Alan Dowd, Rosemarie Mohai

An analytical model of coupled fluid flow and heat transfer through a fracture with permeable walls in an EGS

R. Mohais, C. Xu and P.A. Dowdhttps://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=7302

CFD modelling of the velocity profile within a single horizontal fracture in an enhanced geothermal system

Accurate prediction of geothermal fluid velocity profiles in the fractures is essential in determining the mass flow rate and hence energy extraction in Enhanced Geothermal Systems (EGS) which embrace Hot Dry Rock (HDR) systems and Hot Sedimentary Aquifer (HAS) systems. Previous studies have addressed flows in fractures assuming fracture walls as impermeable boundaries. However this assumption is unrealistic since the channel walls may contain cracks and fissures arising from the initial hydraulic fracturing process. The channel walls thus exhibit permeable characteristics at the boundary which will affect the velocity profiles in the fracture. There has been recent development of mathematical models to predict velocity profiles for low Reynolds number flows in HDR fractures by considering the effects of slip boundary conditions at the walls. In this paper, computational fluid dynamics (CFD) model based on the Finite Volume approach is used to predict the fluid velocity profile in a single fracture in an EGS system. A fluid-porous interface model based on an analytical equation has been implemented in the commercial CFD code ANSYS/CFX. One advantage of this model is that it can take into consideration of different values of the slip coefficient, α, which is a dimensionless quantity characterising the structure of permeable material at the fluid-porous interface wall. This interface velocity model is used to investigate the effects of values of α on the channel flow. It is found when α increases from 0.1 to 4, there is an increase in pressure drop in the flow. The fluid-porous interface velocity decreases and the maximum velocity at the center line of the channel increases as α increases from 0.1 to 4.Zhao Feng Tian, Rosemarie Mohais, Chaoshui Xu and Xiongwei Zhuhttp://www.afms.org.au/conference/18%20AFMC%20TOC.ht

The television entrepreneurs: social change and public understanding of business [Boyle, R. & Kelly, L.]

Review of a book which seeks to understand the relationship between television representations of the world of business on UK television. The book is based on research funded by an Arts and Humanities Research Council grant. The review highlights a transition from a genuine documentary approach to business television programming, to its incorporation into the contemporary programme format known as 'reality television'. The review highlights the ways in which this kind of television programming has merged with a pervasive celebrity culture