# Friction Coefficient with Laminar Flow

## Laminar flow and friction coefficient

The friction coefficient - or factor - of a fluid flow at **laminar** conditions can be calculated as

λ = 64 / Re

= 64 μ / (d_{h}u ρ)

= 64 ν / (d_{h}u) (1)

where

λ = friction coefficient (non-dimensional)

Re = Reynolds Number (non-dimensional)

μ = absolute (dynamic) viscosity(Ns/m^{2}, lb_{m}/s ft)

d_{h}=hydraulic diameter(mm, ft)

u = mean velocity in flow (m/s, ft/s)

ρ =density of fluid (kg/m^{3}, lb_{m}/ft^{3}^{ })

ν=μ/ρ= kinematic viscosity (m^{2}/s, ft^{2}/s)

Equation *(1)* is only valid at laminar conditions where Reynolds Number is less than *2300*. For turbulent conditions where Reynolds Number exceeds* 4000* the Colebrook equation should be used to calculate the friction coefficient.

In practice laminar flow is only actual for viscous fluids - like crude oil, fuel oil and other oils.

The friction coefficient for laminar flow indicated in the Moody diagram (SI based):