A two-dimensional numerical investigation of the oscillatory flow behaviour in rectangular fire compartments with a single horizontal ceiling vent

This paper presents a comparison of fire field model predictions with experiment for the case of a fire within a compartment which is vented (buoyancydriven) to the outside by a single horizontal ceiling vent. Unlike previous work, the mathematical model does not employ a mixing ratio to represent vent temperatures but allows the model to predict vent temperatures a priori. The experiment suggests that the flow through the vent produces oscillatory behaviour in vent temperatures with puffs of smoke emerging from the fire compartment. This type of flow is also predicted by the fire field model. While the numerical predictions are in good qualitative agreement with observations, they overpredict the amplitudes of the temperature oscillations within the vent and also the compartment temperatures. The discrepancies are thought to be due to three-dimensional effects not accounted for in this model as well as using standard ‘practices’ normally used by the community with regards to discretization and turbulence models. Furthermore, it is important to note that the use of the k–ε turbulence model in a transient mode, as is used here, may have a significant effect on the results. The numerical results also suggest that a linear relationship exists between the frequency of vent temperature oscillation (n) and the heat release rate (Q0) of the type n∝Q0.290, similar to that observed for compartments with two horizontal vents. This relationship is predicted to occur only for heat release rates below a critical value. Furthermore, the vent discharge coefficient is found to vary in an oscillatory fashion with a mean value of 0.58. Below the critical heat release rate the mean discharge coefficient is found to be insensitive to fire size.

Buoyancy driven flow and its stability in a horizontal rectangular channel with an arbitrary oriented transversal magnetic field

An MHD flow is considered which is relevant to horizontal Bridgman technique for crystal growth from a melt. In the unidirectional parallel flow approximation an analytical solution is found accounting for the finite rectangular cross section of the channel in the case of a vertical magnetic field. Numerical pseudo-spectral solutions are used in the cases of arbitrary magnetic field and gravity vector orientations. The vertical magnetic field (parallel to the gravity) is found to be he most effective to damp the flow, however, complicated flow profiles with "overvelocities" in the comers are typical in the case of a finite cross-section channel. The temperature distribution is shown to be dependent on the flow profile. The linear stability of the flow is investigated by use of the Chebyshev pseudospectral method. For the case of an infinite width channel the transversal rolls instability is investigated, and for the finite cross-section channel the longitudinal rolls instability is considered. The critical Gr number values are computed in the dependence of the Ha number and the wave number or the aspect ratio in the case of finite section.

Slicing issues in CAD translation to STL in rapid prototyping

The rapid prototyping (RP) process is being used widely with great potential for rapid manufacturing of functional parts. The RP process involves translation of the CAD file to STL format followed by slicing of the model into multiple horizontal layers, each of which is reproduced physically in making the prototype. The thickness of the resulting slices has a profound effect on the surface finish and build time of the prototype. The purpose of this paper is to show the effects of slice thickness on the surface finish, layering error, and build time of a prototype, as well as to show how an efficient STL file can be developed. Three objects were modeled and STL files were generated. One STL file for each object was sliced using different slice thicknesses, and the build times were obtained. Screenshots were used to show the slicing effect on layering error and surface finish and to demonstrate the means to a more efficient STL file. From the results, it is clear that the surface finish and build time are important factors that are affected by slice thickness

Reflection is alive and well, but not what you think

More and more, Business and Management students (and those in other disciplines) are being asked to undertake written reflection upon their learning as part of assessed course-work. This paper examines this trend and explores the thinking behind it: why lecturers see reflection as valuable to students, whether they undertake reflection themselves, what theoretical underpinning they perceive as justifying and explaining their views. The results of a survey undertaken among Business and Management lecturers are reported, which appear to show that the most influential writer on the subject of reflection in learning – the one most frequently cited by the respondents – is David A. Kolb, author of the well-known Experiential Learning Theory (1984), and one of the moving forces behind experiential learning in general. His ideas have attracted a good deal of criticism, but are still current, having been suitably updated and defended, (2005). The paper critically re-examines Kolb’s Experiential Learning Theory, challenging its relevance to most of Higher Education, as characterised by Peter Jarvis in his useful table of learning situations as “formal and intended” (2004; 108). Other criticisms of Kolb’s Experiential Learning Theory are advanced that are entirely new. Returning to the survey, the papers discusses the reasons lecturers believe reflection is valuable to students and concludes that Kolb’s model, and others such as Schön’s (1987), fail to adequately explain or even identify them.