MODULE 3

Section 1:   

Boundary Layer and Turbulence

Section 2:   

Pressure Drop and Friction Factor

Section 4: 

Convection With Change of Phase

Flow Categorization

It is not always obvious to choose the best empirical correlation for a given problem but the following categorization is found in many textbooks:

External or Internal Flow

The differences between an external and an internal flow were already mentioned. Examples were given in figures 4 and 5.

Forced or Natural Convection

The flow is “forced” when an external device pushes the fluid past the solid body. In the case of an internal flow, the device that forces the flow is a pump or compressor.

In a “free or natural” convection, the fluid motion occurs without the assistance of an external device. The heating or cooling of the fluid close to the solid body generates density differences in the fluid creating the motion (buoyancy forces).

Laminar or Turbulent Flow Regime

The concept of turbulence was presented previously. In a forced convection flow the Reynolds number is used to establish the transition from the laminar to the turbulent regime. In natural convection flows the Grashof number is used.

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