The Effect of surfactant on the drag and wall correction factor of a drop in a bounded medium

In the present article, the analytical solution for creeping motion of a drop/bubble characterized by insoluble surfactant is examined at the instant it passes the center of a spherical container filled with Newtonian fluid at low Reynolds number. The presence of surfactant characterizes the interfacial region by an axisymmetric interfacial tension gradient and coefficient of surface dilatational viscosity. Under the assumption of the small capillary number, the deformation of spherical phase interface is not taken into account. The computations not only yield information on drag force and wall correction factor, but also on interfacial velocity and flow field for different values of surface tension gradient and surface dilatational viscosity. In the limiting cases, the analytical solutions describing the drag force and wall correction factor for a drop in a bounded medium reduces to expressions previously stated by other authors in literature. The results reveal the strong influence of the surface dilatational viscosity and surface tension gradient on the motion of drop/bubble. Increasing the surface tension gradient and surface dilatational viscosity, results in linear variation of drag force. When the surface tension gradient increases, the drag force for unbounded medium increases more as compared to the bounded medium hence wall correction factor decreases with increase in surface tension gradient whereas it increases with increase in surface dilatational viscosity.

Solidification characteristics in a spherical capsule integrated with pin fins and rectangular fins - a comparative study

This study aims at investigating the solidification characteristics in a spherical capsule with pin fins and rectangular fins of same length and volume immersed in a constant temperature bath (-6°C, -9°C, -12°C). The fins are made of copper and are attached to the inner surface of the spherical capsule. The fin lengths correspond to the annulus fill volume margin of 75% taken on the inside wall of the spherical container. The findings showed that the overall solidification period of the capsules with rectangular fins was reduced. Also, the subcooling phenomena is completely eliminated at bath temperature of -6°C. Results also indicated that 50% PCM mass is reduced effectively with the provision of fins. Thus, with the employment of rectangular fins better potential energy savings can be attained when operated at partial charging mode at higher bath temperature.