V8.4: Laminar and Turbulent Mixing

(Related to Textbook Section 8.3.1—Transition from Laminar to Turbulent Flow)

A turbulent flow creates a much faster rate of mixing than a laminar flow.

The only mixing present in laminar flow takes place on the molecular scale, which provides small mass transfer rates, and hence a large time scale for mixing. Turbulent flow on the other hand also has mixing at the macroscopic scale due to the random, turbulent fluctuations in the flow. This is a very effective means of mass transfer in the flow, so the time scale for mixing is significantly reduced. This animation depicts the difference between laminar and turbulent mixing. Applications that focus on enhanced transport, such as mixing and heat transfer, benefit from turbulence in the flow due to the enhance mixing, though it should be noted that turbulent flow also increases the wall shear stress, which increases drag. Therefore, it is often a tradeoff between the advantaged and disadvantages of turbulent flow.