Browsing by Author "Griffiths, W.D."

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Heat transfer at the metal-sand interface was investigated for the case of solidification of cast iron in (1) cylindrical sand moulds and (2) ceramic cylindrical moulds with sand blocks at the bottom. An inverse method of solving the one-dimensional heat conduction equation was used to determine the metal-sand interfacial heat flux transients and heat transfer coefficients with the heat conduction equation modified to take into account the packed bed nature of the sand mould, the effect of convection of the mould gases and the evolution and absorption of heat due to mould reactions. However, temperature measurements in the moulds during the experiments revealed that the heat transfer in the cylindrical sand moulds was not truly radial and could therefore not be used to obtain accurate interfacial heat transfer results. In the case of solidification of cast iron against sand blocks, mean values of the heat flux of about 50 kWm-2 were measured for green and dry clay-bonded silica sands, with and without additions of seacoal. The corresponding heat transfer coefficients were about 625 Wm-2K-1. Within the scatter of results obtained there was no discernible difference in the heat flux or the heat transfer coefficients with the different sand formulations. The heat transfer mechanisms through the sand-casting interface were interpreted from an examination of the nature of the sand and casting surfaces. Heat transfer through the interface is proposed to occur by conduction through the gas forming the atmosphere of the interface and by radiation, in approximately equal amounts.
(Maney Publishing michael.wagreich@univie.ac.at, Metal/mould interfacial heat transfer during solidification of cast iron in sand moulds) Prabhu, K.; Griffiths, W.D.
2001
Metal-mould interfacial heat transfer during solidification of cast iron against cast iron chills
(2000) Prabhu, K.N.; Griffiths, W.D.
Heat transfer during the unidirectional solidification of a cast iron alloy against cast iron chills was investigated using an inverse modelling approach. Chills of thickness 100 mm and 10 mm were used, to simulate gravity die casting conditions and the use of chills in sand moulds. In both cases transient heat transfer, measured by the interfacial heat flux and heat transfer coefficient, declined from initially high values in the first few seconds of solidification, to values about an order of magnitude lower which persisted for the remainder of the experiments. In the case of the thin chill it became saturated with heat until it was no longer in a position to extract further heat from the casting. These results were interpreted by studying the resistance to heat transfer from the casting offered by the casting-chill interface and the chill itself. For example, the thermal resistance of the casting-chill interface can be influenced by the deformation of their respective surfaces and their subsequent relationship.
Metal-mould interfacial heat transfer during solidification of cast iron against cast iron chills
(2000) Prabhu, K.N.; Griffiths, W.D.
Heat transfer during the unidirectional solidification of a cast iron alloy against cast iron chills was investigated using an inverse modelling approach. Chills of thickness 100 mm and 10 mm were used, to simulate gravity die casting conditions and the use of chills in sand moulds. In both cases transient heat transfer, measured by the interfacial heat flux and heat transfer coefficient, declined from initially high values in the first few seconds of solidification, to values about an order of magnitude lower which persisted for the remainder of the experiments. In the case of the thin chill it became saturated with heat until it was no longer in a position to extract further heat from the casting. These results were interpreted by studying the resistance to heat transfer from the casting offered by the casting-chill interface and the chill itself. For example, the thermal resistance of the casting-chill interface can be influenced by the deformation of their respective surfaces and their subsequent relationship.
One-dimensional predictive model for estimation of interfacial heat transfer coefficient during solidification of cast iron in sand mould
(2002) Narayan, Prabhu, K.; Griffiths, W.D.
A one-dimensional predictive model is proposed to estimate the interfacial heat transfer coefficients during unidirectional solidification of a cast iron alloy, vertically upwards, against a sand block. The model is based on the surface roughness characteristics of the casting and sand surfaces and the concave deformation of the initial solidified casting skin towards the sand surface. The modelled interfacial heat transfer coefficients and predicted temperatures inside the casting and the sand block showed an approximate agreement with experimentally determined values. The model showed that radiation was a significant mode of casting/sand interfacial heat transfer with the predicted contribution of radiation to the overall heat transfer being nearly 50%. The evaluation of the model in comparison to the interfacial heat transfer models proposed by Zeng and Pehlke suggested that the interfacial conditions considered in this model, namely, the mean peak to valley heights of the casting/sand mould surfaces and the gap width calculated from the deformation of the initial solid skin, gave a more accurate prediction. This predictive heat transfer model has an advantage over the inverse modelling technique as the matching of experimentally measured temperatures to determine the boundary conditions is avoided and the heat transfer coefficients can be estimated as an integral part of the casting simulation.
One-dimensional predictive model for estimation of interfacial heat transfer coefficient during solidification of cast iron in sand mould
(2002) Prabhu, K.N.; Griffiths, W.D.
A one-dimensional predictive model is proposed to estimate the interfacial heat transfer coefficients during unidirectional solidification of a cast iron alloy, vertically upwards, against a sand block. The model is based on the surface roughness characteristics of the casting and sand surfaces and the concave deformation of the initial solidified casting skin towards the sand surface. The modelled interfacial heat transfer coefficients and predicted temperatures inside the casting and the sand block showed an approximate agreement with experimentally determined values. The model showed that radiation was a significant mode of casting/sand interfacial heat transfer with the predicted contribution of radiation to the overall heat transfer being nearly 50%. The evaluation of the model in comparison to the interfacial heat transfer models proposed by Zeng and Pehlke suggested that the interfacial conditions considered in this model, namely, the mean peak to valley heights of the casting/sand mould surfaces and the gap width calculated from the deformation of the initial solid skin, gave a more accurate prediction. This predictive heat transfer model has an advantage over the inverse modelling technique as the matching of experimentally measured temperatures to determine the boundary conditions is avoided and the heat transfer coefficients can be estimated as an integral part of the casting simulation.