Heat transfer of permeable discs rotating in a magnetic field

Print OnlyAn electrically conducting Newtonian fluid is squeezed between two parallel infinite axisymmetric discs placed in an orthogonal magnetic field. Both discs are permeable. The upper disc is allowed to rotate in its own plane while moving freely along the z-axis. The lower disc is fixed with respect to the z-axis, but is allowed to rotate within its own plane. This paper addresses two cases, the first where each disc is set at a constant uniform temperature, the temperature of the upper disc being higher than the temperature of the lower disc. Using a similarity solation for small Reynolds numbers, analytical and numerical solutions are derived through which the effects of the permeability on the temperature and heat transfer profiles of the fluid film are studied. In the first case, the heat transfer profile is affected by the disc permeability up to the limiting where the discs rotate at the same speed. The temperature profile however is unaffected. In the second case considered, the lower disc is subjected to a heat flux whilst keeping the upper disc at a uniform constant temperature. In the second case, analytical and numerical solutions show that although the temperature and heat transfer profiles are influenced by the temperature ratio of the disc, they however remain unaffected by disc rotation and disc permeability.Rosemarie Mohais and Balswaroop Bhat

On the effect of permeable magmatic foam on heat transfer in channelized lava flow

Rosemarie Mohais, Balswaroop Bhat

Comparing predicted and observed ground motions from subduction earthquakes in the Lesser Antilles

This brief article presents a quantitative analysis of the ability of eight published empirical ground-motion prediction equations (GMPEs) for subduction earthquakes (interface and intraslab) to estimate observed earthquake ground motions on the islands of the Lesser Antilles (specifically Guadeloupe, Martinique, Trinidad, and Dominica). In total, over 300 records from 22 earthquakes from various seismic networks are used within the analysis. It is found that most of the GMPEs tested perform poorly, which is mainly due to a larger variability in the observed ground motions than predicted by the GMPEs, although two recent GMPEs derived using Japanese strong-motion data provide reasonably good predictions. Analyzing separately the interface and intraslab events does not significant modify the results. Therefore, it is concluded that seismic hazard assessments for this region should use a variety of GMPEs in order to capture this large epistemic uncertainty in earthquake ground-motion prediction for the Lesser Antilles.

Fluid flow and heat transfer within a single horizontal fracture in an enhanced geothermal system

We present an analysis of fluid flow and heat transfer through a single horizontal channel with permeable walls which are at different temperatures. The problem is set in the context of hot dry rock geothermal energy extraction where water, introduced through an injection well, passes through a horizontal fracture by which transfer of heat is facilitated through advection of the fluid flowing toward the recovery well. We consider the walls of the fracture to have properties of a permeable medium and we study the effect of slip boundary conditions on velocity and temperature profiles for low Reynolds number (< 7) based on a similarity solution and perturbation expansion. We show that the velocity and heat transfer profiles are altered with the channel width, the permeability and a slip coefficient α, which is a dimensionless constant related to the inherent properties of the channel.Rosemarie Mohais, Chaoshui Xu, Peter Dow

Heat transfer of coupled fluid flow within a channel with a permeable base

We examine the heat transfer in a Newtonian fluid confined within a channel with a lower permeable wall. The upper wall of the channel is impermeable and driven by an accelerating surface velocity. Through a similarity solution, the Navier–Stokes equations are reduced to a fourth-order differential equation; the analytical solutions of which determined for small Reynolds numbers show dependence of the temperature and heat transfer profiles on the slip parameter based on the properties of the porous channel base. For larger Reynolds numbers, numerical solutions for three main groups of solutions show that the Reynolds number strongly influences the heat transfer profile. However, the slip conditions associated with the porous base of the channel can be used to alter these heat transfer profiles for large Reynolds numbers. The presence of a porous base in a channel can thus serve as an effective means of reducing or enhancing heat transfer performance in model systems.Rosemarie Mohais, Balswaroop Bhat

Comparing predicted and observed ground motions from subduction earthquakes in the Lesser Antilles

This brief article presents a quantitative analysis of the ability of eight published empirical ground-motion prediction equations (GMPEs) for subduction earthquakes (interface and intraslab) to estimate observed earthquake ground motions on the islands of the Lesser Antilles (specifically Guadeloupe, Martinique, Trinidad, and Dominica). In total, over 300 records from 22 earthquakes from various seismic networks are used within the analysis. It is found that most of the GMPEs tested perform poorly, which is mainly due to a larger variability in the observed ground motions than predicted by the GMPEs, although two recent GMPEs derived using Japanese strong-motion data provide reasonably good predictions. Analyzing separately the interface and intraslab events does not significant modify the results. Therefore, it is concluded that seismic hazard assessments for this region should use a variety of GMPEs in order to capture this large epistemic uncertainty in earthquake ground-motion prediction for the Lesser Antilles.John Douglas, Rosemarie Mohai