Luke Fullard

On the Initiation of a Hydrothermal Eruption Using the Shock-Tube Model

In this work, the authors introduce the shock-tube model for a hydrothermal eruption in a geothermal reservoir. The governing equations, based on the multiphase Euler equations and a Darcy-type law, are solved using a three-phase weighted sub-system numerical solver. Results are then presented which show the importance of the geometry of the geothermal reservoir in predicting the initiation of a hydrothermal eruption. In particular, the porosity, permeability, and cohesion of the reservoir are shown to significantly affect the pressure difference required to initiate an eruption. Finally, the authors show the importance of the initial liquid water/water vapour volume fractions in determining the size of an eruption, and further show boiling to be of major importance.

The Effect of Heaped and Sloped Powder Layers on Ejection Times and the Residence-Time Distribution of a Conical Mass-Flow Hopper

The flow of a hypothetical Coulomb material flowing under gravity from a conical mass-flow hopper is modelled using stress field theory. The assumptions inherent for a Coulomb material can be combined with the assumption of radial flow within the hopper to determine the velocity profile within the hopper. From the velocity profile, ejection times and residence time distributions may be calculated. Since, in a real granular system, the powder layer interface is generally not flat, but sloped at some angle, (nominally the angle of repose), the residence time distribution and ejection times will be dependent on the initial geometry of the powder layers. Residence time distributions and ejection times are calculated for a given granular material in a conical mass-flow hopper firstly for the case of flat layers, secondly for the case where the powder forms a conical heap at the angle of repose, and thirdly for the case when the powder is sloping against a wall. It is found that the shape of the powder layers greatly changes the residence time distribution and ejection times in the system, and needs to be considered when performing residence time measurements in the industrial setting.

A brief investigation into ejection times from a conical mass flow Hopper - Coulomb and conical model difference

A conical mass flow hopper system is modelled using stress field theory as found in [1]. The authors present the governing equations for the stress and velocity fields under the radial flow assumption for the Coulomb and conical yield functions. The ejection times for the two models are compared and are shown to be vastly different between the two models. The residence time distributions for the models are presented. We conclude that the choice of model has a large effect on the predicted mixing as a powder travels through the hopper system.

The Effect of Cracks and a Steam Cap on Hydrothermal Eruptions

The shock-tube model for a hydrothermal eruption in a geothermal reservoir (Fullard and Lynch, Trans Porous Med, 2011) is used to simulate eruptions that have a steam phase present near the surface in the form of a steam cap or a large crack. Simulations are performed with various steam cap/crack depths and it is shown that the presence of a steam phase greatly reduces the size of an eruption. We show that a steam cap type eruption is physically unlikely because of the large pressure differences required, but conclude that rock cracking is potentially a viable initiation mechanism for a hydrothermal eruption.