GENERAL CHARACTERISTICS OF PIPE FLOW

The general method of transporting fluid (liquid or gas) is the flow through a closed conduit. It is commonly called 'pipe' if it is of round cross-section and 'duct' if the cross-section is not round. The common examples include water pipes, hydraulic hoses, air distribution in a duct in an air conditioning plant etc. The main driving force for the flow to occur is the pressure differential at both ends of the pipe and the walls of the pipe which is designed to withstand this pressure difference without any undue distortion of the shape.

The basic governing equations such as mass, momentum and energy conservation can be applied for viscous, incompressible fluids in pipes and ducts. Following assumptions are made for present analysis;

• Cross-section of the duct is circular unless otherwise specified.

• The pipe is completely filled with fluid being transported otherwise the flow may be treated as open-channel flow where gravity alone is the driving force.
• The driving potential is the pressure difference across the pipe.

The flow of fluid in a pipe may be laminar, turbulent or transitional depending upon the flow rates. Such a flow in the pipe is characterized by a dimensionless number called "Reynolds number" and is defined as,
                                              (1)
where are the density and viscosity of the flowing fluid, is the diameter of the pipe and is the average velocity in the pipe.