Applications of the forced vortex.

I cannot think of an application of a forced vortex per se.

 

Steel pipes are cast by running molten steel into a mould that rotates on a horizontal axis. This seems to be a process that is much dependent on empirical methods for its design.

 

There are separators that depend on rotation to achieve their function. Oil, in an emulsion of oil and water, can be separated by rotating the emulsion in a cylindrical vessel that rotates about a vertical axis. If the emulsion were to be just left in a vessel for a long time the two fluids would separate under the action of gravity but rotation at high speed imposes a centripetal acceleration that is much greater that the acceleration due to gravity and the separation takes place in a much shorter time. As the centripetal acceleration at any point in a forced vortex is given by  where  is the angular velocity the separator will work with the emulsion occupying an annulus of the vessel and not full so that there is an inside radius to require a centripetal acceleration. A separator could also separate suspended solids from oil.

 

There are all sorts of cyclone separators. A wide range of solids can be carried in pipes in a flow of air. Typical examples are dust extractors and pneumatic conveying. In both cases particulate solids are entrained in the flow and must be separated at discharge. The cyclone has an upright conical shape with a cylindrical section at the top.  The air and particulates enter the cylindrical upper section tangentially. The solids slow down and follow a spiral path to the bottom of the cone and fall out into a collection system. The air is discharged to the atmosphere from the centre of the top at low speed. It is moot point whether this process depends on the forced vortex.

 

One might see the centrifugal pump as an application of the forced vortex. Certainly, when a centrifugal pump runs against a closed delivery valve there is a forced vortex in the pump and the net head on the valve can be calculated from the dimensions of the impeller and its speed but, as soon as the valve is opened, there is a flow and we need a better explanation for the action of the pump than the forced vortex.

 

It seems to me that an understanding of the mechanics of the forced vortex can lead to ideas for the design of devices to achieve some objective but mostly, once the ideas have come into existence, the realisation of a practical device in hardware results from trial.

 

A forced vortex appears to occur in nature at the centre of rotating storms.