Instability phenomena in a two-phase microchannel thermosyphon

The behavior of a two-phase thermosyphon, consisting of a microchannel evaporator plate and a condenser, is investigated to gain insight into the system limiting instability. A microchannel plate has been fabricated with 56 square channels that have a 1 × 1 mm cross section and a length of 115 mm. Experiments have been conducted for various condenser heights with the heat flux as the control variable. A step increase in heat flux is used to quantify the response of the system, including variations in mass flow rate, temperature, and pressure drop. Results show that small fluctuations about the steady state give rise to the instability for situations with a uniform heat load. A predictive model based on the momentum equation is introduced to estimate the onset of instability, and the threshold heat flux is predicted to within ±10% uncertainty.     

Synthesizing User Centered and Designer Centered IS Development Approaches Using General Systems Theory

This paper uses general systems theory to provide an expanded view of information systems in organizations. Three general viewpoints and corresponding approaches to information systems development are identified. The designer centered or American approach to information systems development is based on a functionalist perspective of information systems and a problem solving orientation. The user centered or European approach to information systems development takes an expanded view of information systems that specifically considers humans and recognizes their aspirations and goals and uses a democratic, participative approach to develop systems in an effort to produce an improved workplace and a better quality of worklife for users. A third viewpoint on information systems development, business process centering, is identified that further expands the components of the system to include the set of integrated tasks that provide value to the customer. We define a new development approach that combines the strengths of these approaches based on general systems theory, business process centering, and a measurement and control system.     

The nuclear option for US electrical generating capacity additionsutilizing boiling water reactor technology

The technology status of the advanced boiling water reactor (ABWR) and the simplified boiling water reactors (SBWR) is presented along with an analysis of the economic potential of advanced nuclear power generation systems based on BWR technology to meet the projected domestic electrical generating capacity need through 2005. The forecasted capacity needs are determined for each domestic North American Electric Reliability Council (NERC) region. Extensive data sets detailing each NERC region's specific generation and load characteristics, and capital and fuel cost parameters are utilized in the economic analysis, by means of an expansion planning model, of the optimal generation additions required to meet this need. In addition to a reference case, several sensitivity studies are performed with regard to capital costs and fuel price escalation     

Radial Alignment of Carbon Nanotubes via Dead-End Filtration

Dead-end filtration is a facile method to globally align single wall carbon nanotubes (SWCNTs) in large area films with a 2D order parameter, S_2D, approaching unity. Uniaxial alignment has been achieved using pristine and hot-embossed membranes but more sophisticated geometries have yet to be investigated. In this work, three different patterns with radial symmetry and an area of 3.8 cm² are created. Two of these patterns are replicated by the filtered SWCNTs and S_2D values of ≈0.85 are obtained. Each of the radially aligned SWCNT films is characterized by scanning cross-polarized microscopy in reflectance and laser imaging in transmittance with linear, radial, and azimuthal polarized light fields. The former is used to define a novel indicator akin to the 2D order parameter using Malu's law, yielding 0.82 for the respective film. The films are then transferred to a flexible printed circuit board and terminal two-probe electrical measurements are conducted to explore the potential of those new alignment geometries.