Lesson 4 - Principles of Fluid Mechanics 2
This lesson will extend our knowledge of fluid mechanics by considering two important laws: the conservation of both mass and energy. We will also examine the various flow regimes which are present within a pipe or duct carrying moving fluids.
Transitional Flow
As we have previously described laminar flow as the flow present up to a Re of 2,100, and turbulent flow beyond a Re of 4,000, it should come as no surprise that the Re region in-between has been left for some special albeit brief attention. And indeed, the flow 2,100 < Re < 4,000 is special as it cannot really make up its mind whether it is laminar or turbulent.
In flows with the same Re, in the range 2,100 < Re < 4,000, the flow could be laminar, or turbulent, or change from laminar to turbulent with time.
The transition from laminar to turbulent can be promoted through other flow disturbances, e.g. the starting of pumps or opening/closing of valves, changes in internal pipe roughness or the presence of pipe fittings etc. To this extent, transitional flow can be considered to be finely balanced and at times, unstable.
The study of transitional flow is very mathematical and complex. Fortunately, the presence of transitional flow is very uncommon in most practical brewery situations and will not be considered further here.