Some well known instabilities

1. Falling film

This instability occurs when the Reynolds number is of the order of 1-10 and it is caused by inertial effects. This is the reason behind the ripples observed on the surface of the falling film. The mass/heat transfer rates we estimate can have significant errors.

2. Natural convection

If there are two plates close to each other, and one is cooled and the other is heated, circulation patterns are observed.  There is a density variation with variation in temperature.Patterns form starting from a uniform state. This is an example of “self-organization” where the system knows how it wants to evolve.

A point to note here is that this phenomenon is not observable for all values of . It is only at some critical value of that this pattern formation takes place. If were very small in magnitude, there would be no such phenomenon. In fact, in that case, pure conduction would be occurring. Another important point is that the process of evolution should not be confused with instability.