Depending on the flow regime, the pressure losses vary, because the behavior of the fluid is changing

So far no equation does fully evaluate the energy losses regardless of the type of flow

it is therefore necessary to determine what is the flow regime , to select the appropriate equation for calculating the coefficient of pressure losses .

• in a duct:

The flow rates vary versus:

speeds , viscosity , Diameters,roughness , density.

They are determined by the Reynolds number .

If Re <2000 the flow is laminar.

we use the formula Poiseuille laminar flow to find the coefficient of pressure losses ,

if 2000 <Re <3000 the regime is transitional.

(he can switch from one state to another it is good to do the calculation in the two states to assess the possible behavior of the fluid)

if 2000 <R e <10 5 l ' flow is Smooth turbulent

we use the formula Blasius flowing Smooth turbulent to find the coefficient of pressure losses ,

if 2000 <R e l ' flow is turbulent

to find the coefficient of pressure losses , Colebrook is used in all cases turbulent flow

These values are orders of magnitude, the transitions are gradual

• flat surface or plate , Frictional forces also depend on the flow regime, this regime varies from laminar to turbulent depending on the distance to edge.

It distinguishes a critical distance at which the transition between laminar and turbulent done.

the boundary layer thickness depends on the flow regime and distance from the edge