Subject
Fluid flow in a pipe varies across its diameter and along its length dependent upon the properties of the fluid, the pipe and the nature of the flow (laminar or turbulent).
Liquids are [theoretically] incompressible so the inlet and outlet velocities and flowrates must be [almost] identical. Differences occur in head and pressure, which are generated by friction in the liquid and between it and the pipe.
Inlet pressure and head are always greater than outlet pressure and head, i.e. there will be a positive pressure drop over the length of the pipe.
Gases are compressible so whilst mass flow rates and velocities must be [almost] identical, volumetric and linear velocities will vary with viscosity. There will be a positive pressure drop over the length of the pipe.
Calculator
The pipe flow calculator determines the properties of a fluid flowing through a circular enclosed pipe of a specified length at any point across its diameter according to classical theory.
The instantaneous velocity of a fluid varies across the diameter of the pipe with volumetric flow rate and pipe surface quality. Pipe Flow applies the fanning friction factor to the fluid velocity.
For help using this calculator see Technical Help
Pipe Flow Calculator  Options
Liquid
This calculation option is for a flowing liquid, the conditions for which are similar at the inlet and the outlet ends of the pipe as liquids are assumed to be incompressible.
You enter 
and the pipe flow calculator will provide: 


Liquid specific weight

Local velocity (@ r)

Average velocity

Maximum velocity

Radius @ ave. velocity

Mass velocity

Mass flow rate

Reynolds No.

Fanning friction factor

Pressure coefficient

Pipe outlet head

Pressure drop

Total loss

Gas
This calculation option is for a flowing gas, the conditions for which are different at the inlet and the outlet ends of the pipe as gases are compressible.
You enter: 
and the pipe flow calculator will provide: 


Average inlet density

Local inlet velocity (@ r)

Average inlet density

Maximum inlet velocity

Average inlet velocity

Maximum inlet velocity

Average outlet density

Local outlet velocity (@ r)

Average outlet velocity

Maximum outlet velocity

Radius @ average velocities

Mass velocity

Quantity flow rate

Reynolds No.

Fanning friction factor

Pressure coefficient

Check minimum system requirements