Porosity is one of the defects most frequently encountered in aluminium die castings. Porosity formation causes costly scrap loss and limits the use of die-cast parts in critical high-strength applications. The amount of porosity is closely related to die casting process parameters. A considerable reduction in porosity formation can be obtained using the Taguchi approach in the die casting process. An example of the off-line technique used in the Greek die casting industry is given, with the aim of illustrating practicality and ease of use by industry engineers and managers. In the thick-walled sample casting studied, the final intensification pressure contributed 69 per cent towards the reduction in porosity. Among the other parameters considered, melt and die temperatures have a smaller effect (about 10 per cent), followed by the plunger velocities in the second and first stages which have only a slight effect on porosity formation. In addition, the expected quality improvement and the cost savings under optimum parameter settings were evaluated. The expected improvement in reduction in porosity formation was found to be 48.6 per cent, while the expected cost savings for multiple casting parts under optimum conditions was calculated to be 71.4 per cent/$1 loss before the experiment.

No abstract

The relationship between size and intensity of laser light scattered from coal particles, glass beads and calibration pinholes in the size ranges 10–140 m̈m, 17–240 m̈m and 5–200 m̈m respectively has been measured. The purposes were to determine the effect of shape of non‐spherical particles and beads by varying three parameters in the collection optics. These were: the angle, θc, between the axis of the collection optics and that of the incident laser beam; the aperture of the f/3.66 collection lens; and the diameter of the spatial filter on the photodetector. A spatial filter diameter of 0.5 mm was used on the detector as a compromise between image vignetting and reducing the size of the effective measuring volume of the instrument. Due to refraction, and particularly for diameters larger than about 80 m̈m, the beads scattered more light than the pinholes or the coal particles. A mask, introduced to limit the collection lens aperture to angles less than 5.3°, reduced the intensity collected from the beads, while the response curves for the pinholes and coal particles were unaffected. Non‐spherical beads larger than about 60 m̈m with aspect ratios up to 1.8 resulted in departure from the response curve, established from the calibration pinholes, by up to a factor of two. The aspect ratio was defined by the maximum and minimum projected lengths of the image of the scatterer. The response curves for beads and coal particles approached that of the pinholes as θc was changed from 2.5° to 1.4° and as the angular position of the mask limiting the aperture of the collection lens nearest to the incident beam axis, θi, was reduced from 2.9° to 0.9°. The best results were obtained for θi and θc equal to 0.9° and 1.4° respectively, for which the precision and accuracy were 9 m̈m and + 5 m̈m for nominally spherical glass beads and 5 m̈m and −1 m̈m for the coal particles for diameters up to 60 m̈m and aspect ratio up to 2.5.

This article presents gas velocity and temperature measurements obtained in a versatile multi-fuel swirl-stabilized laboratory burner of 100 kW total thermal input, which was designed as a scale model of a 110 MW coal burner operating in a cement rotary kiln. The laboratory burner is able to produce flames with different aerodynamic characteristics, namely, the independent adjustment of swirl to axial air and to burn a combination of gaseous, liquid, and pulverized solid fuels; only gaseous fuel, i.e. methane, was used in the present investigation. Experimental measurements were obtained in the near-burner region, with and without combustion, under varying operating conditions. The present investigation was mainly focused on the effect of swirl and its interaction with the combustion process.

The development of a detailed mathematical modelling approach for phosphoric acid fuel cells (PAFCs) is described and typical results are presented, discussed, and compared with experimental data found in the literature. A three-dimensional, integrated electrochemical computational-fluid dynamic analysis of a steady-state operation was attempted. The developed model was applied for validation purposes to a specific electrochemical system found in the literature; however, it can be applied to a variety of fuel cell systems. The model has been applied to investigate the effects of various parameters on system performance, justifying the claim that such studies can be very useful tools for optimizing the operation of a PAFC unit or stack. The predictions obtained of the average cell and stack voltage as well as of the generated power show good agreement with the limited experimental data found in the literature.