Fluid Flow Head Loss Darcy - Weisback Equation

Fluid Flow Table of Contents
Hydraulic and Pneumatic Knowledge

Head loss is the reduction in the total head or pressure (sum of elevation head, velocity head and pressure head) of the fluid as it moves through a fluid system. Head loss is unavoidable in real fluids. It is present because of: the friction between the fluid and the walls of the pipe; the friction between adjacent fluid particles as they move relative to one another; and the turbulence caused whenever the flow is redirected or affected in any way by such components as piping entrances and exits, pumps, valves, flow reducers, and fittings. Frictional loss is that part of the total head loss that occurs as the fluid flows through straight pipes.

The head loss for fluid flow is directly proportional to the length of pipe, the square of the fluid velocity, and a term accounting for fluid friction called the friction factor. The head loss is inversely proportional to the diameter of the pipe.

Head loss General Equation:
hL = f L v2 / D


hL = Head Loss (Change of pressure)
L = Length of pipe
v = Average fluid velocity
f = Fluid friction factor
D = Diameter of pipe

Head loss in a Pipe (Darcy - Weisback Equation):

Open: Head loss in a Pipe (Darcy - Weisback Equation) Calculator

hL = Head Loss (Change of pressure)
L = Length of the pipe;
D = Hydraulic diameter of the pipe (for a pipe of circular section, this equals the internal diameter of the pipe);
V = Average velocity of the fluid flow, equal to the volumetric flow rate per unit cross-sectional wetted area;
g = Local acceleration due to gravity;
f = Dimensionless coefficient called the Darcy friction factor. It can be found from a Moody diagram or more precisely by solving Colebrook equation.