One way to calculate the pressure drop of fluid through a pipe is using the Reynolds number, which is equal to the velocity of the liquid's flow multiplied by the diameter of the pipe and then divided by the kinematic viscosity of the fluid. It is denoted as "Re."
Factors that cause a pressure drop in pipes include friction, changes in kinetic energy and elevation of the pipes. If the Reynolds number falls below 2320, there is a laminar flow. In laminar flows, circular layers of the fluid glide past one another in an organized manner. The fluid is at maximum velocity at the pipe axis, and the roughness of the pipe doesn't determine the pressure drop.
If the Reynolds number is greater than 2320, there is a turbulent flow. In turbulent flows, the fluid particles move in a non-uniform manner contrary to the direction of the main flow. The roughness of the pipe determines the pressure drop caused by turbulent flows.
To determine the pressure drop in circular pipes, first multiply the pipe friction coefficient by the length of the pipe, the diameter of the pipe and the velocity of flow squared. Next, divide the result by twice the diameter of the pipe.