Xiaobing Huang

Squeeze film testing of ceramic pastes

Abstract Equipment is described in which pastes are squeezed out from the region between two parallel circular discs. The force on the upper disc is measured for different fixed approach speeds of the discs. Two disc diameters are used, in conjunction with two ceramic pastes and one model paste. Different surface finishes are used on the discs and the effects of adding glass fibre and alumina fibre to the pastes are examined. Industrial squeezing flows are found in such processes as filtration, pressing, rolling, and injection moulding. A theory for squeezing flow is given which shows that, under certain conditions, a plot of squeezing force against the reciprocal of gap will be a straight line. The conditions are that the shear stress is constant and that the flow is dominated by shear forces. This is shown to occur in many real cases, although the biaxial extension of the bulk material also affects the load. It is shown that, for ceramic pastes, plate velocity has little effect on the force. For all pastes, rougher surfaces increase, and lubrication reduces, the force required to squeeze the paste. Wall slip is shown to occur in some non-lubricated situations. Fibre addition usually increases the stiffness of the pastes, especially for longer, thinner, fibres. In one case, a paste is found to flow more easily when thick, short fibres are used. Rings of coloured paste are used to show that several deformation profiles are possible: bell shaped, triangular, and near parabolic. Tests are shown to be simple to perform and the shear stresses obtained in this geometry found to be higher than those for flow in dies.

Study on force relaxation of ceramic paste

Abstract A theory is given for the relationship between the applied force and time for ceramic pastes during relaxation. The theory provides a simple expression based on the fundamental parameters of the system. Experimental work has been carried by means of squeeze film flow tests. In this investigation, it is found that a three element model can be used to describe the relaxation response of the ceramic paste used in the present work. This model indicates that ceramic pastes are viscoelastic fluids with highly viscous properties. The particle packing in the material may affect the relaxation response. The addition of fibre can enhance the elastic property of ceramic paste. The experimental data have demonstrated that using fibre to replace powder can make the pastes more solid-like. The surface condition can influence the relaxation parameters, which is evident when the material is highly elastic.

CFD Modelling of Cadmium Telluride (CdTe) Thin Film Coating with Inline AP-MOCVD

A CFD numerical model has been established to study the growth of cadmium telluride (CdTe) on substrate using metalorganic chemical vapour deposition technique in atmospheric pressure (AP-MOCVD) and hydrodynamics in an inline MOCVD reactor. The numerical simulations have been conducted using the CFD code – ANSYS Fluent. Dimethylcadmium (DMCd) and diisopropyltelluride (DIPTe) have been employed as precursors while H2 is acting as the carrier gas. In order to assess the effect of various conditions on CdTe film growth and uniformity, heat transfer and mass transport behaviours of the chemical species in the reactor have been fully investigated. In addition, material utilization and fluid dynamics in the reactor are also discussed.

Approximate flow analysis of paste forming process for simplified ceramic dome

Abstract The types of flow obtained during the formation of hemispherical domes are difficult to analyse. The aim in the present paper is to model ceramic paste flows in a press moulded ceramic dome with a simplified ‘top hat’ shape. The simplified process can be separated into a number of flows, each of which can be analysed easily. The rheological behaviour of ceramic paste in these flows is usually difficult to determine, since the materials are neither homogenous nor simple fluids. Models are presented to characterise the flows and validate them experimentally. Theoretical predictions are in good agreement with the experimental data.

Micro-bubble dispersion in a two-dimensional mixing layer

Dispersion of microbubbles (db < 100 ?m) in a turbulent mixing layer was investigated numerically using a Discrete Vortex Modelling (DVM) while two-way interaction between the dilute dispersed cloud of microbubbles and free-shear layer was taken into consideration. The emphasis of this study is to examine the instantaneous dispersion features of microbubbles entrained by large-scale vortex structures embedded in the free-shear layer, and the effect of interphase momentum coupling on the evolution of the large-scale vortex structures due to the presence of the microbubbles. It was found that the laterally local void fraction profiles achieve similarity conditions downstream of the mixing layer. The simulation revealed that the growth rate of the lateral void fractions is similar to those of the velocity thickness but the lateral void fractions spread greater than the velocity thickness. The correlations between the local void fractions and local vorticity indicated that there is not prominent enhancement of the local void fraction in the centre of the large-scale vortices. In the numerical modelling, two important parameters, drag and lift coefficients in the equation of motion, were also assessed.