This report investigated, both experimentally and numerically, the cooling process in water assisted injection moulded parts. Experiments were carried out on a laboratory developed water assisted injection moulding system, which included an injection moulding machine, a water pump, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The resin used was semi-crystalline polypropylene. The in-mould temperature of the polymeric materials during the cooling process was measured. A transient heat transfer finite element model was adopted to simulate and predict the temperature variation within water assisted injection moulded products. Simulated results matched well with the experimental data. Experimental investigation and numerical simulations of a water assisted injection moulding cooling process can provide an improved understanding of the influence of water related parameters on the cooling process of water assisted injection moulded parts.

The natural convection in a horizontal fluid layer heated from below has complex dynamic behaviour. For the Rayleigh-Bénard convection of low Prandtl number fluids, the calculated flow and temperature fields are very sensitive to the truncation error of numerical algorithms. Different kinds of finite-difference schemes might yield different numerical results. In the present work the error analysis of the upwind scheme and QUICK scheme for the Rayleigh-Bénard convection of low Prandtl number fluid was conducted. It shows that the upwind scheme will introduce numerical dispersion. This effect enlarges the viscosity term of the momentum equations and therefore no oscillation could be predicted. The QUICK scheme has higher calculation accuracy. However, it introduces an additional third-order differential term which might overestimate the oscillation effect.