Numerical simulations of two-dimensional curtain coating were performed using VOF method in order to find operational conditions of coating processes. The curtain shape was dependent on the flow rate of liquid, the viscosity of liquid, and the moving speed of a substrate. The results reproduced the previously obtained coating window which represented five regimes of coatable, uncoatable, heel formation, air entrainment, and heal formation with air entrainment. Formation of the curtain and its shape were discussed using the numerically visualized flow fields.
Three quantities were measured to provide a database for validation of computations with a CFD (computational fluid dynamics) code. The quantities were the radial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm), the temperature gradients in the pipe wall (thickness, 5.5 mm) and the radial temperature distributions of the cooling water in the annulus gap (8.25 mm) outside the pipe. From these temperature distributions, three kinds of condensation heat fluxes were obtained from the enthalpy decreasing rate of the steam-air mixture based on the assumption of saturated conditions, the temperature gradient in the pipe wall, and the enthalpy increasing rate of the cooling water. These three heat fluxes were different especially in the downstream region, where the heat flux was low, so that the average of the three heat fluxes was used to evaluate factors affecting the condensation heat transfer. This average was expressed by a function of the steam density difference between the main flow of the mixture and the mixture on the wall surface, the average steam velocity and the thermal boundary layer thickness. The suction effect due to condensation was also discussed.
The development of the molten core cooling system without the electric power based on a lesson of Fukushima daiichi nuclear power plant accident is carried out over the world. Many researchers reported that the nano-fluid had the capability of critical heat flux enhancement and the nano-fluid could be applied to cool the molten core in combination with natural circulation flow. The purpose of this study is to obtain the better understanding of the flow characteristics of multiphase flow, which mix air and nano-fluid (water and TiO2 nano particle) under natural circulation condition. Experiments were carried out at atmospheric pressure and room temperature. Seven kinds of vertical test section are used; three circular tubes, two rectangular channels and two tapered tubes. The following conclusions can be obtained. (1) As the two-phase flow, the multiphase fluid was found to have stable natural circulation without problems. (2) There was approximately no great difference between the flow characteristics (void fraction, flow rate and pressure drop) of the natural circulation of multiphase flow and the air-water two phase flow.