In seed separation, one may wonder why do we need aerodynamics? Mechanical separation can be done by size or by length. But by separating the seeds in this way, one looks only at one physical criterion. However, when we bring aerodynamics into the play, we can be much more accurate. Each kernel can be separated very precisely according to its sink speed.
With regards to aerodynamics, there are basically two major ways of separating the seeds: in an air channel or on gravity tables. The challenge with an air channel is that it needs a very homogenous air speed. If this is not the case, then good kernels will be eliminated and bad kernels might be selected in the good fraction. Often, we can see that in the middle of the air channel there is a peak in air speed, and towards the walls of the channels a much lower speed. This causes separation by accident, and not by precision. So, one of the first things to do before using an air channel to separate the seeds is to make sure the airspeed is as homogeneous as possible.
We should also not forget that the flight behaviour of each kernel is different. It is easy to imagine that round seeds, such as soybean seeds, have a different flight behavior than thin and elongated seeds such as wheat, grasses or carrots. We often see that with elongated kernels we need some extra assistance or instrument, for example vibration to make sure that the kernel enters the enter flow in the right way.
The sink speed is very much dependent on weight and as a result, the air speed can be very different per species, sometimes differing with a factor 15. In order to get a good picture of this, in our company we use simulation systems to simulate the air flow lines.
The biggest advantage of applying smart aerodynamics in seed separation is that it greatly helps to eliminate the middling fraction of your seeds, also called the ‘headache fraction’, because of the difficulty in making a good separation and getting rid of the middlings.
When installing our machines at seed processing plants, we provide a lot of advice to our clients, for example that simple things such as the weather can be of great influence on the separation result. In Northern European countries the air volume is different from Southern Europe, and there is a difference in air volume between summer and winter. So, a cleaning plant needs to take measures to keep the air volume as constant as possible. This will provide a great advantage to their seed processing.