Shape Factor Method Research Articles

Numerical infrared heating of semi transparent thermoplastic using ray tracing method

Thermoforming process include a heating stage of the thermoplastic specimen by infrared heaters. The knowledge of the temperature distribution on the surface and through the thickness of the preform is important to make good prediction of thickness and properties of the manufactured part. Currently in industry, the fitting of the process parameters is given by experience and it is expensive. Our objective is to provide tools that are able to simulate the heat transfers between the infrared heaters and the specimen in order to reduce the fitting cost and to control the qualities of the end product. We use the optical method called ” ray tracing ” (RTM) to simulate the radiative transfer. First, we compare the RTM with the shape factor method on a simple example: the heating of a square sheet by one infrared lamp. Then, we show the 3D heating stage of a rectangular specimen. In that case, we use 6 lamps to simulate an infrared oven. The RTM allows to compute a source term in the transient heat balance equation. We can use commercial codes to solve the heat balance equation.

Estimation of the earthing resistance by the shape factor method

Estimation of the earthing resistance by the shape factor method

Critical heat flux prediction for water boiling in vertical tubes of a steam generator

This paper presents a methodology for the prediction of the critical heat flux (CHF) for the boiling of water in vertical tubes operating under typical conditions found in steam generators. At the furnace, the water flows through long vertical tubes under an axially non-uniform heat flux and with relatively low mass fluxes. This fact causes that the recent theories and correlations, which have been developed for conditions typically found in nuclear reactors, cannot be directly applied for the prediction of the CHF in the furnace tubes. In this context, the mechanistic theories focused into the CHF prediction have proved their usefulness to predict CHF avoiding the use of correlations and experimental constants. Hence, in order to assist the CHF problem in steam generators, the sublayer dryout theory, initially formulated for CHF in vertical tubes uniformly heated, is extended by combining it with the shape factor method ( F-factor), to account for the effects of the axially non-uniform heat flux distribution. The critical wall temperature (CWT) of the tubes is calculated from CHF data. The reliability of the modified theory for the CHF prediction is tested by comparing CWT results against measured data from a steam generator of a power plant. Good consistency and approximation is found between predicted and measured data.

Graphite shape characterisation in cast iron—from visual estimation to fractal dimension

Thin wall iron castings are characterised by a much finer structure than that obtained in regular commercial castings. Existing microstructure standards do not cover this fine range of microstructures. Although computer aided image analysis may provide some answers, limitations exist. Graphite shape in spheroidal and compacted graphite iron is particularly sensitive to the measurement method. This paper offers a discussion on the various shape factors commonly used for evaluation of graphite shape. Selected shape factors are compared in terms of their ability to fully describe graphite shape across the whole spectrum of graphite morphologies in thin wall iron castings. While several shape factors can be used, it appears that sphericity is a better descriptor of spheroidal graphite shape than compactness. Compactness cannot distinguish well between exploded and spheroidal graphite, or poorly shaped and well-shaped spheroidal graphite. Our experimental data demonstrate that the shape factor method, otherwise intuitive, accurate and fast, cannot be used indiscriminately, as it is pixel size dependent. The posibility of using the fractal dimension method, which is pixel size independent, to quantify the morphological complexities of graphite shape was also investigated. Unfortunately, it was found that there is partial overlapping of the fractal dimension values for different graphite shapes (flake versus spheroidal graphite or compacted versus exploded graphite). Thus, it is recommended to use shape factors for graphite shape measurement in thin wall iron castings. The optimum pixel size for graphite shape evaluation in thin wall spheroidal and compacted graphite iron castings is 0.5 to 0.6 μm.

Extension of the shape‐factor method to highly polar systems

Extension of the shape‐factor method to highly polar systems

Movement of Entamoeba histolytica trophozoites in rat cecum and colon intact mucus blankets and harvested mucus gels.

Entamoeba histolytica trophozoites were centrifuged into mucus gels harvested from in vivo loops of rat cecum and proximal colon. Frank ameba movement was not detected in the colonic mucus, but attenuated motility was measured in the cecal mucus. The harvested rat cecal mucus had significantly lower apparent viscosity and neutral glycoprotein concentration values than the colonic mucus. A shape factor method was developed to assess the motility of amebae in mucus gels and intact mucus blankets. Shape factor data obtained from harvested mucus gel and intact mucus blanket experiments indicated that such mucus severely attenuated trophozoite movement with the attenuation being greater with colonic than with cecal mucus. Entamoeba trophozoites are known to be able to generate a pseudopod force of 3.3 x 10(-6) Newtons. Latex microspheres of the size range of Entamoeba trophozoites were forced through cecal and colonic mucus gels under gravity. Colonic mucus gels could withstand a force of 3.3 x 10(-6) Newtons while cecal mucus could not, suggesting that the ameba movement that was observed in cecal mucus involved mechanical penetration of the mucus by the ameba pseudopodia and did not require prior gel dissolution by Entamoeba enzymes.

Inversion methods for satellite studies of the Earth's Radiation Budget: Development of algorithms for the ERBE Mission

The Earth Radiation Budget Experiment carries a three‐channel scanning radiometer and a set of nadir‐looking wide and medium field‐of‐view instruments for measuring the radiation emitted from earth and the solar radiation reflected from earth. This paper describes the algorithms which are used to compute the radiant exitances at a reference level (“top of the atmosphere”) from these measurements. Methods used to analyze data from previous radiation budget experiments are reviewed, and the rationale for the present algorithms is developed. The scanner data are converted to radiances by use of spectral factors, which account for imperfect spectral response of the optics. These radiances are converted to radiant exitances at the reference level by use of directional models, which account for anisotropy of the radiation as it leaves the earth. The spectral factors and directional models are selected on the basis of the scene, which is identified on the basis of the location and the long‐wave and shortwave radiances. These individual results are averaged over 2.5° × 2.5° regions. Data from the wide and medium field‐of‐view instruments are analyzed by use of the traditional shape factor method and also by use of a numerical filter, which permits resolution enhancement along the orbit track.

The Principle of Corresponding States and Prediction of Gas-Liquid Separation Factors and Thermodynamic Properties: A Review

Abstract A review is made of the development of the principle of corresponding states and the utility of the molecular shape factor method for the description of properties of pure fluids and fluid mixtures. From consideration of angle averaging of the potential energy of nonspherical molecules, shape factors were devised to relate the state of an acentric fluid with that of a reference fluid. With the development of correlations for the correspondence of states, an accurate equation of state of the reference fluid is made to apply to many fluids. The method is extended to mixtures with the introduction of van der Waals' combining rules. Extensive calculations show that the use of methane as the reference fluid yields useful results for paraffin hydrocarbons up to about C7, cyclic hydrocarbons of even higher molecular weight, and nonassociating polar substances. Diverse properties are examined including volumetric properties, vapor pressures, K-values, enthalpies, excess properties of mixing, and transpor...