Description

p₁ - inlet pressure

Absolute pressure at the pipe start

p₂ - outlet pressure

Absolute pressure at the pipe end

Δp - pressure drop

Pressure difference between pipe start and pipe end

q - volume flow rate

Fluid flow rate in terms of units of volume per unit of time

ṁ - mass flow rate

Fluid flow rate in terms of units of mass per unit of time

L - pipe length

Length of a pipe in which pressure drop is calculated

D - pipe diameter

Internal circular pipe diameter

H - channel height

The height of channel for rectangle shaped pipe

W - channel width

The width of channel for rectangle shape pipe

k_r - pipe roughness

Pipe internal surface roughness

V - velocity

Flow velocity in terms of units of distance per unit of time

A - area

Internal pipe cross section area

f - friction coefficient

Coefficient of friction for pressure drop due to friction calculation

Re - Reynolds number

Dimensionless number representing viscous versus inertial forces ratio

δ - boundary layer

Thickness of laminar layer formed in turbulent flow connected to pipe wall surface

ρ - fluid density

Mass per unit of volume

ν - kinematic viscosity

Result of fluid particles colliding to each other and moving at different velocities in terms of area per square unit of time

μ - dynamic viscosity

Result of fluid particles colliding to each other and moving at different velocities in terms of mass per square unit of distance and time

K - resistance

Coefficient used for calculation of minor losses due to local resistances in pipe line like bends, tees, reducers, valves, etc.

Calculation setup

Select value to calculate. You should enter not selected one.

Δp

pressure drop

q / ṁ

volume/mass flow rate

D

internal pipe diameter

Select value to input. You should enter selected one. The other one will be calculated

p₁

pressure on the pipe start

p₂

pressure on the pipe end

Select value to input. You should enter selected one. The other one will be calculated

q

volumetric flow rate

ṁ

mass flow rate

Select value to input. You should enter selected one. The other one will be calculated

ν

kinematic viscosity

μ

dynamic viscosity

Select pipe shape

round pipe

full cross section fluid flow

rectangle pipe

for rectangle channels and full cross section flow

When is this calculator applicable?

You can use pressure drop in pipe calculator for pressure drop and flow rate calculation for all Newtonian fluids (gases and liquids) with constant density (incompressible flow) in closed, round or rectangle pipe.

If the flowing fluid is gas, pressure change due to friction, local resistances or height change has to be low (less than 5-10%) to be sure that this calculator is applicable and that it gives correct results. If the pressure change is higher than 10%, you should use the calculator for compressible gas flow.

If you select gas as flowing fluid, the calculator assumes that gas has perfect (ideal) gas properties, i.e., the ideal gas law is applied to calculate any of the unknown gas state values - pressure, temperature or density.

Pressure drop calculator is suitable for laminar and turbulent flow regime.

Also, when it is not applicable?

You can't use this calculator for compressible gas flow where the pressure of the gas is changing more than 5-10%. For that purpose, you can use one of available gas pressure drop calculators.

You can't use this calculator if the fluid is non-Newtonian, i.e., its viscosity is changing with the shear rate or due to some other changed condition.

Pressure drop calculator is not applicable if the flowing fluid contains solid particles or if the flowing fluid is the mixture of liquid and gas, i.e., multiphase flow.

If the flowing fluid is gas but not a perfect (ideal) gas, i.e., if it's pressure, temperature and density are not related according to ideal gas law, this calculator is not applicable, also.

If the viscosity of flowing fluid is changing due to flow temperature change, this calculator is not applicable as it takes viscosity as a constant value.