http://hdl.handle.net/2440/299 2013-06-19T16:05:03Z 2013-06-19T16:05:03Z Varney, Josephine Judith Bean, Nigel Geoffrey http://hdl.handle.net/2440/78365 2013-06-17T04:30:14Z 2011-12-31T13:30:00Z

Title: Building a model to investigate the effect of varying ambient air temperature on air-cooled organic Rankine cycle plant performance Author: Varney, Josephine Judith; Bean, Nigel Geoffrey Abstract: Air-cooling is necessary for geothermal plays in dry areas and ambient air temperature significantly affects the power output of air-cooled thermal power plants. Hence, a method for determining the effect of ambient air temperature on subcritical and supercritical, air-cooled binary Rankine cycles using moderate temperature geothermal fluid and various working fluids is presented. Part of this method, includes a method for maximizing working fluid flow from a supercritical heat exchanger. In the example presented isobutane is used as the working fluid, while the geothermal fluid temperature and flowrate are set at 150°C and 126kg/s. Results of this analysis show that for every 14°C increase in ambient air temperature, above the ambient temperature used for design purposes, there is ~20% loss in brine efficiency; while conversely, there is no gain in brine efficiency for any drop in ambient air temperature below the ambient air temperature used for design purposes. Using the ambient air temperature distribution from Leigh Creek, Australia, this analysis shows that an optimally designed plant produces 6% more energy annually than a plant designed using the mean ambient temperature.

2011-12-31T13:30:00Z Varney, Josephine Judith Bean, Nigel Geoffrey http://hdl.handle.net/2440/78364 2013-06-17T04:30:10Z 2011-12-31T13:30:00Z

Title: Performance of air-cooled organic Rankine cycle plants using temperature distributions from arid parts of South Australia Author: Varney, Josephine Judith; Bean, Nigel Geoffrey Abstract: Air-cooling is necessary for geothermal plays in dry areas and ambient air temperature significantly affects the power output of air-cooled thermal power plants. Hence, a method for determining the effect of ambient air temperature on subcritical and supercritical, air-cooled binary Rankine cycles using moderate temperature geothermal fluid and various working fluids is presented. Part of this method, includes a method for maximizing working fluid flow from a supercritical heat exchanger. In the example presented isobutane is used as the working fluid, while the geothermal fluid temperature and flowrate are set at 150°C and 126kg/s. Results of this analysis show that for every 14°C increase in ambient air temperature, above the ambient temperature used for design purposes, there is ~20% loss in brine efficiency; while conversely, there is no gain in brine efficiency for any drop in ambient air temperature below the ambient air temperature used for design purposes. Using the ambient air temperature distribution from Leigh Creek, Australia, this analysis shows that an optimally designed plant produces 6% more energy annually than a plant designed using the mean ambient temperature.

2011-12-31T13:30:00Z Bean, Nigel Geoffrey O'Reilly, Malgorzata Marzena http://hdl.handle.net/2440/78345 2013-06-17T02:30:20Z 2012-12-31T13:30:00Z

Title: A stochastic two-dimensional fluid model Author: Bean, Nigel Geoffrey; O'Reilly, Malgorzata Marzena Abstract: We introduce a Stochastic Two-Dimensional Fluid Model that consists of two stochastic fluid flows driven by the same underlying Markov chain, where one of the fluids is unconstrained. We develop the theoretical and numerical framework for the transient analysis of the model. We derive the important generator matrix of a particular Laplace-Stieltjes transform of the model, which is the foundation of our analysis. We use it to develop expressions for the Laplace-Stieltjes transforms of various performance measures for the transient analysis of the model and construct powerful algorithms for their numerical evaluation. An example of an application in a queueing environment is given.

2012-12-31T13:30:00Z Green, John Edward Bassom, Andrew Peter Friedman, Avner http://hdl.handle.net/2440/78317 2013-06-16T23:30:06Z 2012-12-31T13:30:00Z

Title: A mathematical model for cell-induced gel compaction in vitro Author: Green, John Edward; Bassom, Andrew Peter; Friedman, Avner Abstract: We present a mathematical model for cell-induced gel contraction in vitro. The core of the model consists of conservation equations for the mass of the gel and the number of cells, coupled to a force balance on the gel. On the basis of previously reported experimental findings for collagen gels, which are frequently used experimentally, the gel is treated as a compressible viscous fluid while inertial effects are neglected. The flow is assumed to be isothermal, and a linear pressure–density relation is adopted. The force exerted on the gel by cells is assumed to depend upon the local environment surrounding the cell: influences can include the cell and extracellular matrix density, and the concentration of a diffusible chemical produced by the cells. We consider the simple, but experimentally relevant, case of spherically symmetric gels. For cell-free gels, we show how simple experiments might be used to determine the parameters in the model. When the cell-derived forces are given by a prescribed function of position, we are able to obtain the early time and steady-state behavior of the solution analytically. We perform numerical simulations which generate predictions of how the gel density evolves during compaction under differing assumptions concerning the factors influencing the force exerted by the cells. These results are compared with some previous observations reported in the literature.

2012-12-31T13:30:00Z