# Frictional Pressure Drop

Published: August 23, 2021 | Last updated: July 5, 2023

## What Does Frictional Pressure Drop Mean?

Frictional pressure drop is the main type of pressure drop in a fluid flow. It can be of two types: major frictional pressure drop and minor frictional pressure drop. Classification depends on factors such as pipe material and its roughness, shape and size, as well as the type of flow: laminar, turbulent or transitional. Pressure drop is a very important factor in fluid flow and should be kept at a minimum, as it increases operational cost. Frictional pressure drop is one of the three different types of pressure drops in a pipe, the other two being gravitational pressure drop and acceleration pressure drop.

## Trenchlesspedia Explains Frictional Pressure Drop

Frictional pressure drop can be calculated using different methods, as the same equation will not be applicable for differing flow rates, flow types and fluid types. Major frictional pressure drop occurs in straight lengths of pipes, while minor frictional drop occurs in pipe fittings and valves.

Major frictional pressure drop in a pipe can be calculated using the Darcy-Weisbach equation, which has the basic form:

Δp/L = fD • (ρ/2) • (‹v2/D)

Minor frictional pressure drop in pipe fittings and valves can be found using the:

• Equivalent length (leq) method
• Flow coefficient (Cv) method
• Resistance coefficient (K) method

It has been found that frictional pressure drop increases with increasing roughness of the pipe.

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